As I’m doing a rebuild, I disassembled the handlebars, controls and steering stem along with removing the forks. As the steering is “notchy”, I’m planning on replacing the steering stem bearings and races and I’ll document that in a separate post.
I found a fork rebuild kit at Hucky’s in Section 31 Fork, Shocks, Parts, and picked that up along with some new fork springs. At 97,500 miles and 40 years, the springs have likely given their all. Here’s a list of the parts I used.
|07 31 R kit 005||Front Fork Rebuild Kit|
|31 99 0 000 001||Front Fork Spring, progressive, pair|
Remove Handlebars and Controls
Refer to the General Teardown document (see the link below) and your Haynes manual for more details about how to remove the handle bars.
Since I am stripping the bike down to the frame, I had removed the electrics from the frame and the wiring harness earlier so when I removed the headlight and the steering stem, I’d keep the harness attached to it.
Remove Fork Sliders
First, I removed the fork sliders. Remove the rubber plug on the bottom of the slider to expose the 8 mm attached to the plunger. I use the following tool to loosen the nut from the damper, a vice grip holding a 13 mm socket.
As shown below, place the socket on the nut and then insert an Allen key into the socket in the bottom of the damper rod. Turn the socket to loosen the nut and remove it.
Next, remove the circular steel bands holding the rubber gaiters to the fork slider and pull the slider off the fork tube. In the top of the fork tube you will see the fork seals. You can remove these with a seal puller. I find that heating the tubes with a heat gun until it’s hot to the touch makes it easy to pop the seals out of the fork sliders. Be careful not to score the inside surface around the seal.
Below is a picture of the disassembled fork sliders with seals (green), sliders, steel rings for the fork gaiters, the ring under the large fork retaining nut, cap on bottom of fork slider, 8 mm nuts and wave washer.
Disassemble Fork Slider
At the bottom of the fork slider is a large cap nut that seals the bottom of the fork tube. I removed that next by putting the slider in my vice with rubber jaws and using a breaker bar to loosen the nut. Remove the rubber o-ring inside the slider. Here are the parts at the lower end of the fork slider, in order from left to right.
At this point, the fork tubes and internal damper rods are exposed.
Remove Fork Tubes from Steering Stem
To remove the fork tubes, loosen the Allan head pinch bolt on the bottom of the steering stem. I like to insert a large screw driver into the slot and with moderate pressure, spread the clamp a little bit to loosen it, and then twist the fork tube while pulling down on it to slide it out of the steering stem.
Remove Handlebars and Controls
Since I’m going to powder coat the controls, I removed them, but it all you want to do is rebuild the forks, then skip the control removal and just remove the handlebars so you can get access to the chrome covers on top of the fork spring nuts.
I removed the left and right hand control levers. The front brake lever has a switch for the stop light, so remove the rubber boot and then unscrew the wires from the switch. Then unscrew the switch from the control
Then I removed throttle cables and the right side control and disassembled it.
On the left side, I removed the clutch cable from the transmission so I had slack in the cable. I slide the inner cable out of the ferrel as it has a slot cut through one side, and then removed the left side control and disassembled it.
At this point I removed the steering damper rod and the lower friction assembly from the bottom of the lower fork clamp.
This bike had handlebar pull backs. I removed them and the handlebars exposing the chrome forks screw caps.
Now, at the top of the fork tube, remove the chrome cover using the pin wrench in the tool kit. Underneath them you will find a large nut holding the fork springs in the fork tube.
Then, carefully remove the fork spring retaining nuts using the wrench in the tool kit. Since this has fork spring pressure on it, keep your face away from the large nut as it may suddenly get launched if you aren’t careful. Remove the fork springs.
I removed the headlight and then the headlight ears from the steering head. Here is the headlight ears disassembled.
Removing Damper Rod
Turn the fork tube upside down and you will see the snap ring at the bottom of the tube. Use snap ring pliers to remove the clip.
There are two kinds of retaining rings, the one I have and another style that has holes in it that will fit the pin wrench in the tool kit.
Folks have used needle nose pliers spread open to seat the outside of the jaws into the 1/2 circle cut-outs to twist the ring out. I tried that and had no success. My son made a crude tool out of a scrap steel bar with a slot in the middle. I used 3 mm bolts, nuts and washers to create a pin wrench that would fit into the 1/2 circle cut-outs.
And before I got this from my son, I was visiting BMW of Denver and Clem loaned me his tool. This is very clever IMHO.
I removed the top retaining ring using my “scrap steel with 3mm screws” tool.
NOTE: My use of “top” and “bottom” here is from the perspective of looking at the bottom of the fork tube which is the end of the tube facing you as you remove the retaining rings. Of course, when the tubes are mounted in the triple clamps, what I call top and bottom are reversed from the actual top and bottom of the fork tube.
There is a metal ring and then a second retaining ring after that. Rather than adjust the depth of the 3 mm screws in my tool, I used Clem’s on the second retaining ring and it came out immediately. At this point, I pulled the damper rod out the bottom of the fork tube. Below are the parts from outside to inside shown left to right.
Rebuild Damper Rod
Here is the fork rebuild kit I got from Hucky’s. There are new fork tube seals, the white bumper at the bottom of the fork damper, the small metal sealing ring at the top of the fork tube, the big copper ring goes under the large retaining nut at the bottom of the fork slider and the small copper ring goes on the 8 mm threaded stud on the bottom of the damper rod, the six metal rings are piston rings that go in the top of the damper assembly. The large rubber bumper goes in the bottom of the fork slider. Sometimes this has dissolved but in my case it was intact. The plastic bag has small springs that hold a check valve ball bearing in the bottom of the damper rod. I didn’t use them as I left the ball valve alone.
Fork Damper Details
I decided to leave the springs the hold the metering ball in place and just replace the piston rings on the top of the damper.
When I was talking to Clem at BMW of Denver, he loaned me this nifty tool to keep the rings compressed when I reinserted the damper rod into the fork tube. I’ve read that another trick is so use two feeler gauges and then insert the damper rod. The feeler gauges compress the rings so they can slide past the threads in the bottom of the fork tube.
Here’s the tool.
The larger diameter end is conical on the inside so it can be slide up the damper rod from the bottom and will compress the rings as shown below. Note in this picture, the compressor is shown upside down (I always do things backwards at first 🙂 ). The larger diameter part of the compressor should be at the top.
Here is the damper rod with the compressor inserted into the fork tube. You just slide the damper rod through the compressor into the fork tube.
After inserting the damper rod into the fork tube, put the white bumper into the bottom of the fork tube and push it past the threads on the inside of the fork tube.
The two steel threaded rings are identical. The bottom ring has the edge point up so it can hold the metal spacer.
I spun the ring in using a finger and then tightened it using needle nose pliers.
Now, place the metal spacer ring on top of the bottom retaining ring.
Now insert the other retaining ring with the edge pointing downward. I spun it in with my finger and used the needle nose pliers to tighten it so it was below the snap ring groove in the inside of the fork tube.
Finally, I used the snap ring pliers to put the snap ring back into its groove in the bottom of the fork tube.
The small copper washer will go on the threaded portion of the damper shaft when I insert the fork slider onto the fork tube.
Rebuild Fork Slider
But first, it’s time to insert the new fork seals in the fork slider. I heat them up with a heat gun until they are hot to the touch and then pound them in with either a socket or a fork seal tool I use but failed to get a picture of.
I take the large threaded plug that screws into the bottom of the fork slider and insert the black bumper stop so the curved side goes in the bottom of the threaded plug.
Then, I put some Hylomar on the land of the threaded plug and the put the large copper washer on the land.
I mounted the fork tube back in the triple clamp and tightened the Allan bolt. Then I torqued the bottom plug to specifications. Next, I put the wave washer and 10 mm nut on the threaded portion of the damper rod and torqued it to specifications..
Here are the rebuilt and refinished fork tubes.
To refinish the fork sliders, I use Scotch Bite pads (green) and AutoSol aluminum cleaner to get minor scrapes and dirt removed. Next, I use “00” steel wool with AutoSol aluminum cleaner to get the surface clean and starting to shine. I like to use blue paper shop towels to clean off the black residue between applications of AutoSol. This can take a couple of applications to get all the grime out of the crevices in the rough casting. Then, I use AutoSol aluminum polish to get a shine applying it with a blue paper shop towel and finished up with AutoSol Aluminum protective spray and lightly buff it with a clean cloth. These look good as new and I hope work as well.
2017-03-24 Update table of contents; change some picture captions; minor edits.
2020-12-31 Correct size of nut on damper rod: it’s 8 mm and uses a 13 mm socket.
2021-10-11 Correct typos.
Pingback: 1972 R75/5 Rebuild: Fork Rebuild and Refinish | Motorcycles & Other Musings
Mr. Reams, I have been searching for a proceedure with quality pictures prior to starting rebuilding my ’73 R60/5 forks. Thank you for your efforts, QUALITY JOB!
Thanks for stopping by and looking around. I hope this helps you out. If you have questions along the way, let me know.
With this great guide, I bet I could do this. Steve
Beautiful site! I’ve been going through essentially the entire same rebuild on my ’73 R75/5 which I’ve owned since ’76. Finding your site is like opening the lid on a treasure chest of knowledge. Well organized, great pics. Immensely useful and practical information. Thank you for the time and effort you’ve taken to record it.
Well, thanks for stopping by and for the very kind words. I was hoping this material would be helpful to fellow airheads and it’s gratifying to hear that it is.
BTW, as my next adventure, I’m toying with investing in another project with a similar level of documentation and focusing on rebuilding a R100RS. I’m looking for a suitable bike as I don’t have one in my small stable. Please keep your eyes open and ping me if you see anything interesting.
Have a Merry Christmas.
Great write up! I am in the market for a similar project and I will visit this several times, I’m sure. Craigslist had a 100 gs for a descent price.
Thanks for the compliment. BTW, if you run across an R100-RS in your searches that might be a good candidate for a rebuild, send me the link. I’m starting to look around for the next project and I lust for an R100-RS bike 🙂
https://denver.craigslist.org/mcd/4266115465.html here is a RS. The dumbest thing I have ever done is sell my 1150 gs, to a dealership!!! I replaced it with an 1150 r. They are pretty much the same bike but i miss the gs. https://denver.craigslist.org/mcy/4306020610.html here is gs. I would think either of these bikes could be talked down in price but might not be rough enough to spend the time and money in a rebuild. The project I was looking at was sold so keep me in mind if you run across a project r 60 or 70
Cool beans. I’ll keep my eyes open for GS and let you know if I spot one. Are you in Denver metro area?
Brook, thanks again for saving the day for me with a fantastic pictorial documentation. these few pictures told me what clymer’s and haynes manuals could not get through my thick skull.
One thing that is confusing though: the top and bottom threaded retaining rings… you refer to them opposite to how my I visualize them. Looking at the fork assembly as it would be on the bike, what you call the bottom ring is really the top, or am I reading wrong?
At any rate, a minor quibble. Your site has proved invaluable to me in the course of several projects. thanks!
Ah, yes you raise a good point. I am using “top” and “bottom” when veiwing the fork tube from the bottom. That seemed a natural way to refer to the rings as the “top” one is the first one you see followed by the “bottom” one when the tubes are in this orientation. As you point out, when the tubes are mounted in the triple clamps, the the top and bottom reverse themselves.
I added a note to the writeup to call attention to my useage. Thank you for pointing this out so I can reduce the opportunity for confusion. 🙂
It is heartening to know that some 1300 pictures I’ve taken on this project have provided valuable. Digital photograhpy and blogs are essentially free tools, so previous limits on what you can show don’t apply anymore. This is one of the good things from digital technology that offsets the numerous bad things.
Best of success on your project.
I’ll just add my own thanks, once again, for your fantastic visual documentation! I anticipate doing this same project on my ’71 R75/5 in the near future … first I have to spend some time with the clutch!
Questions: Did you look at other spring options (e.g. Ikon) before choosing the set from Hucky? And if you would have had to replace the rear shocks, what might you have used as replacements? I know everyone has differing opinions.
Thanks again and best wishes!
I’m pleased this documentation is helpful for you. And best of success with the clutch work.
Your question about front fork springs:
No, I just went with stock replacement springs. With the Windjammer fairing adding weight to the front forks, I’ll likely add some PVC pipe as spacers on the top of the springs to set the preload when I get that far.
Your question about rear shocks:
I debated replacing them at some length, but in the end, I was interested in “original” look for the time being. However, there are much better modern shocks that look very much like the stock BMW shocks. I would likely go with YSS shocks. I suggest you drop a note to Tom Cutter at Rubber Chicken Racing Garage. Tom is very knowledgeable about suspension options and resells YSS and other brands. His advice when I was debating shock choices was well informed. You can contact him at
tpcutter2 (at) aol (dot) com
or use his website,
I hope this is helpful.
Hi Brook I have a 1974 R75/6 I am bringing ba ck to life. I love your site, so helpful. But….in rebuilding the front forks, I came to the …getting the ringss on the damper into the fork tube….. Having Clem give you a tool from the shop, is one thing, but I was totally blindsided as to how difficult this can be….without Clem’s tool. I thought and looked around for something that might work. A couple feeler gauges did me no good. I really had to put on my thinking cap. I ended up cutting 3 pieces of copper house wire (12 guage) stripping it, bending a loop to fit over the edge of the tube , just long enough to hit the raised area after the threads. Then I had to file the wire down so it was the thickness of the lip, then insert the damper, the wire compressed the rings, and the rings slipped into the tube.
Anyway, it worked, and it is a difficult little thing to pull off without the proper tools, or a BMW shop next door. THE SECOND FORK WASN’T SO SMOOTH, BUT I will attack it tomorrow.
Thanks again for the time you have taken
I’ve heard of the idea to use feeler gauges to compress the rings on the damper rod so you can insert the rod into the tube, but I haven’t tried it. It sounds like “easier said than done”. Nonetheless, you came up with a low cost tool that worked. Awesome.
And thanks for the kind words about the content of the site. I hope to add to it this winter.
A much belated note on a technique I just read about to help get the “piston rings” on the fork damper rod retracted enough to slide the rod into the fork tube. The idea is to use three (3) 3×5 index cards and trim the cards so they wrap around the inside of the fork tube with a bit of a gap at the end of the the “tube” created by the cards. Then, pull them out and wrap them around the piston rings on the damper rod and squeeze the cards tight so you can slip the damper rod and piston rings wrapped by the index cards into the fork tube. I imagine you could use some tap to help keep the tube of 3×5 cards compressed as you slide the damper rod into the fork tube.
I’ve not tried this yet, but it sounds like a better way to do this than feeler gauges since there is more of the piston rings wrapped inside the 3×5 card “tube”, so the rings ought stay compressed better.
I hope this idea helps someone else. IF so, post a note about how well this worked.
I am about ready to re-assemble the forks. My question is about the fork oil. It says 280cc per fork. My question is application. How is the best way to put it in?
I measured it and poured it into the top of the fork tube before tightening the top nut.
Thank you for an excellent write up on this procedure. I’ve just taken the forks apart on a 1971 R60/5 and this will greatly aid in the reassembly.
This is an interesting project for me. It was my dad’s motorcycle before he died, and my brother inherited it and later took it apart. It’s been sitting for 9 years in pieces, and now I’m reassembling. Of course easier said than done. 🙂
It turns out the right-hand fork was seized from sitting so long. It took quite a pounding (and lots of heat) to get it apart. The information I’m looking for now is what the allowable clearances are in terms of damage to the fork slider. I expect I’ll need to get it machined but haven’t figured that out yet.
Anyway, thanks again and keep up the good work. I intend to start posting about my project on ADVRider.com soon.
Gerry in Victoria, BC
I’m glad this write-up has helped you on your project. It’s much harder to work on a project that is in pieces than one that you took apart yourself.
You don’t specify what damage or level of corrosion occurred in the right side fork tube (inner) or the slider. But, the inner fork tube takes a lot of stress and for that reason, it may be safer to consider replacing the inner fork tube entirely and perhaps the outer slider. These can be found in the used market (Beemer Boneyard, Re-psycle, for example) and inner tubes are also available from third party manufacturer’s (Forking by Frank, for example) at less cost than BMW stock tubes.
I hope to hear about another airhead back on the road when you finish your project.
I have a 74 R90/6 (had for a NUMBER of years) I didn’t find any rubber caps on the bottom of the sliders, no ‘holes’ in the caps, so I unscrewed them (unscrewed them ALL the threads) and I can’t get the caps OFF to get inside (want to put new rubber boots ON) How will I get the caps off? If you have never been into an OLD slider, you can’t BELIEVE how black, and THICK the stuff that leaks out of them can be, (Has NEVER been into, and lacks about 800 miles having 300,000 on it.) I am also going to have to replace the boot covering the universel joint. I REALLY don’t look forward to THAT) I think your article may be of some help before I get finished…thanks for the work involved in producing it!
Yes, I can believe the sludge in the bottom of forks that have not been serviced. There is a rubber bumper at the bottom that eventually disintegrates over time. Quite a mess 🙂
I’m not exactly clear about what you are having problems with on the fork slider. Can you tell me the part number(s) on the following diagram that you are trying to remove?
To remove the lower fork sliders, you have to remove the nut (13) that threads onto the insert on the end of the damper rod which is (21) on this diagram.
I show how I did that in the write-up using a socket, vice grips and Allan wrench.
If you then slacken the metal straps holding the fork boot to the lower fork slider, the slider will come off the fork tube. Be careful it doesn’t bang on the floor or your foot. You can now replace the fork boot. BTW, ordering the original BMW part is a good idea. I’ve acquired some inexpensive Chinese reproductions and they disintegrated in 18 months. I found out these are made from recycled rubber and do not last. I believe BMW is still sourcing these from suppliers that use new rubber.
That’s all that’s necessary to replace the fork boots.
I hope this helps.
Scrolling up 11 and 12 photo’s (from the bottom of story) you depict inserting the white rubber bumper into the fork leg prior to the threaded retainer(s)
Isn’t the rubber part supposed to be inserted between the fork spring and the top of the damper rod? It serves no purpose sliding on the damper rod?
Or does it?
Thanks for looking at the write-ups. I believe the damper rod can bottom or top out inside the fork tube, so there are two rubber bumpers, the black one at the bottom of the fork tube to protect it from bottoming out and the white one on the top to protect against topping out. The spring is compressed between the top threaded fork nut and the metal ring that threads inside the fork tube.
Said another way, if you look at MAX BMW parts fiche for an R75/5:
and select “31 Front Suspension” then click the picture for the fork assembly:
it looks like the parts go inside the fork tube in this order”
(7) which is the white bushing, then
(8) the metal threaded ring, then
(9) the solid metal ring, then
(8) the other metal threaded ring, and finally
(11) the circlip.
I believe that’s the order I show in my write-up.
I hope this helps.
Ahhh…now its starting to make sense. Thanks for your reply!
Another method to compress the damper rod piston rings and get them beyond the threads in the fork tube:
Cut a square of aluminum beer can about 3″ by enough to wrap around the compressed rings
Form it into a cylinder and insert it into the fork tube so the end is just beyond the threads
Spread the outer end a bit and insert the damper rod; hold on to the aluminum and the rod will slide into the tube easily.
Thanks for the write up, made this project much less daunting!
You describe a ” small metal sealing ring that goes on top of the fork tube” with the pic of the parts you got in the rebuild kit; left ring in the top row. Where exactly does that go? Thanks again.
Thanks for the tip. The metal ring (part# 07 11 9 963 384) in that picture fits on the bottom of the chrome caps (part# 31 42 1 234 399) that screw into the fork cap nuts (part# 31 42 1 238 904).
I hope this helps.
thanks for all the information! I’m planning on customizing my r75 and was wondering if it is possible to leave out the black headlight ears sins i want to put on clip ons. also is it possible to leave the rubber protector out? or would that cause a lot of dust to enter the tubes?
Thanks for stopping by.
Yes, you can remove the headlight ears and the rubber “gaiters” on the fork tubes. But, you need something to protect the fork seals from dirt, water and debris. There is an external dust cover with a felt wiper that is used on the R90S and R100RS bikes to protect the fork seal from dirt. The felt wiper is part number (31 42 1 237 213) and the dust cover is part number (31 42 1 237 205). You need two of each. Note, one value of using the gaiters is they protect the fork tubes from nicks due to rocks and gravel impacting them. If the tube is nicked, then the fork seal is damaged and leaks, repeatedly. For this reason, many people replace the external dust cover and wiper with the gaiters.
You may also want to investigate a stronger top plate than the stock one used on this bike. See (http://www.pbase.com/toastertan/top_braces) for some well regarded items that improve handling and keep the fork tubes aligned.
I hope this helps.
Brook, Your site is a wealth of knowledge, as usual. I’m deep in the forks of my 72 75/5 replacing the buffers and wiper rings, when I came across something on Max’s Fiche – to reference your list above:
“it looks like the parts go inside the fork tube in this order”
(7) which is the white bushing, then
(8) the metal threaded ring, then
(9) the solid metal ring, then
(8) the other metal threaded ring, and finally
(11) the circlip.”
Max shows two different (9) solid metal rings. One is listed as “HD” and has a .2 smaller ID. Part #10 here: https://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51885&rnd=07012015
Any thoughts? Since I have to pay the freight for just the wiper rings (I already had the rest from previous parts-runs) I’m wondering what the application for these are. Any thoughts appreciated!
I have used the standard parts. The HD one has a note at the bottom calling our the R90S VIN after which the HD part was used.
“FG* R90S 4 081 154,R90S(USA) 4 980 521 :”
The FG* means AFTER, so the note means “AFTER R90S VIN 4081154, R90S USA 4980521”. So for USA model R90S, bikes starting with 4980522 had this part.
I hope this helps.
Awesome, Thanks for the info!
Thanks for your effort sir. I’m about to open mine, and was actually just checking in to see if there were any “flying” parts to look out for, and so it was. Great pictures and a very detailed description. Thank you!
I’m pleased this material is helpful to you. Best of success in your project.
just about to start in, on my friends R90 s great effort! feel able to start in and get it right first time thanks again see you didnt attempt the check valve springs! any reason or they must have been perfect ?”regards Jim
Thank you for the kind words. Yes, I opted to not worry about the check valve springs on the R75/5. On the R75/6 I did replace them (didn’t write that work up as it’s essentially the same as the R75/5), but I suspect unless they are damaged, they likely to last a long time. The harder part is removing the plug on the damper rod. It’s really on there. I used a propane torch to heat it in the event it had locktite, and that melted the spring.
Thanks Brook, Have a great New Year! thanks again for your great work Jim
Great write up. I used the feeler gauge method to install the rings. Took a couple of tries, and in the end a couple of .085 feeler gauges did the trick.
the flash card method did not work.
Cool beans, at least one of the techniques worked for you. 🙂
Hello Mr. Reams,
I am using your process to rebuild the forks of my R75/5. The large cap nuts at the bottom of the fork sliders (what max bmw lists as a screw cap) are stuck. I don’t have rubber jaws but I used a couple of pieces of wood to clamp the slider and I was unable to break the nuts free using a large wrench. I don’t want to damage the slider by clamping it too tightly or by applying too much force. Can you tell me a little more about your method to loosen them? Would you recommend heat? Penetrating oil?
Thank you very much for sharing your experience.
Yes, I would heat them as someone may have used loctite on the threads. Also, the aluminum slider will expand faster than the steel “cap screw”, so heating the slider near the cap screw will help They go on tight. I have had to use a cheater on the end of the socket handle to break them loose. I use an old fork tube which you may not have access to. But you can get some steel conduit from your local hardware store that will fit over the socket handle so you can get more leverage.
I hope this helps.
The heat worked like a charm. Thanks.
I don’t want to be a nuisance, but I have one more question. My goal in rebuilding my forks is to replace all of the rubber and plastic parts since my bike has seen little use but has been stored indoors for a long time. Twenty years actually. Anyway, there is a washer, shown on fiche, towards the top of the damper rod, between the coil spring and the guide support which holds the rings. From the picture at Max BMW, it appears to be plastic. It is item 15 on the diagram, part number 31 42 1 232 763. It is not visible in assembly, I do not know its function, and I don’t want to disassemble anything unecessarily. Did you inspect this or consider replacing it? Thank you, Max
I’d leave it as is and not bother replacing it.
So grateful for your site and the detailed descriptions on the different projects. I am starting to gently recondition an R75/5, and finding your site the most helpful out there.
One question I had, the Autosol cleaner that you mention, would this product also work to clean the engine housing, air cleaner covers, transmission housing as well? I’m trying to find a method that restores a natural shine without looking too polished/over polished. Finally, did you notice any fine scratch marks when using the scotch bite pads?
Many thanks for any feedback.
I’m pleased these write-ups have been helpful on your R75/5 project.
Yes, the cleaner and metal polish can be used to restore the finish of the engine cases, air cleaner and transmission.
Here is a procedure I have used.
1. Engine cleaner and then water from a spray bottle to remove it catching the run off in a rectangular oil drain pan.
2. Scotch brite pad with engine cleaner to get the baked on stubborn grunge out of the crevices.
3. If badly corroded, use a second clean scotch brite pad to remove the corrosion as best you can. This can take awhile and you can spray on some aluminum cleaner as well to help remove the corrosion.
4. Aluminum cleaner with “000” steel wool to deep clean the fine crevices in the aluminum.
5, Shop towel with aluminum cleaner to thoroughly remove any steel wool bits.
[I have even used a propane torch on the surface to incinerate any steel bits converting them to rust. Then I wipe down again with aluminum cleaner to completely remove any steel wool traces.]
6. Another trick I have used is to then apply brake cleaner to a shop towel and wipe down the aluminum. It seems to get the last traces of aluminum oxide (black color) off the aluminum.
7. AutoSol metal polish and/or aluminum polish. You can control the shine by how many times you polish the surface.
I hope this helps.
Thank you for an excellent outline of the steps needed for a rebuild; very enlightening. My situation is a bit different, as the forks and front suspension on my recently purchased ’71 R60/5 are in great working order, having been rebuilt in the last few months. The previous owner was an experienced BMW Technician, however he was going for a “Cafe style” look, so he did not install the fork boots (gaiters). My question is, does one need to remove the forks from the bike to install new gaiters and clamps, or can they be installed by simple removing the front wheel, brake assembly an fender brace? I’ve been told by a friend that the new gaiters should slip over the fork legs (w/stud the mounts) by simply stretching them a small amount. Does this seem correct to you, our must I disassemble the forks from the bike?
My sincere thanks in advance for your advice,
I always remove the lower fork slider to install the gators. You can’t get them on any other way AFAIK.
I hope this helps.
Hi, having studied the relevant diagrams of the forks supposedly fitted to my 1971 R75/5 I’ve come to the conclusion that mine don’t contain a number of parts I.e. there is only one threaded ring at the bottom of each fork tube, yours show 2 with spacers, there was no white bottoming bush at bottom of the fork tube and there are minor differences in the damper piston (nothing significant). My query is should I fit a white bush at bottom of the fork tube to act as a buffer? I have the relevant parts for the bottom of the sliders. As you say the rubber buffers disintegrate with time as I only had black debris at the bottom of my sliders. Without your excellent site life would have been extremely difficult for me, many thanks.
I’m glad my content helped you get the fork internal parts sorted out. It sounds like a previous owner rebuild did not pay proper attention to the required parts and age led to deterioration of the bottom damper. YES, you should have the bottom damper that fits into the slider.
Pigging back on this. My 1971 r60/5 did not have the white ring at all.
It has the same one piece screw in the fork bottom that the above writer references. (ie no bottom ring space and top ring, just a one piece screw in with the circlip holding it in place. From the looks o fit this was original.
I did have the black spacer in the bottom cap. In addition there is a spacer , metal /aluminum that is on the pipe part 18 (damper tube) on the 307 diagram mechanism? This slides fully and easily the entire length of pipe 18. Could this be a preload spacer? and is it needed?
That metal piece and the black ring are the same height when stacked as the newer white cap bumper and the white ring. These new parts are BMW parts from Bobs BMW kit. I can send a pic if needed. This bike sat for at least 10 years.
Since this is a fairly large job I don’t want to do it two times. None of the web pictures of fork innards look like what I have. Mine is a very early 1971.
I can send a pic if needed. Thank you for the work in posting and maintaining all of this.
I sent you an Email.
Thanks but my query is about the white nylon looking damper that is shown in the diagrams as being in the bottom of the fork tube which wasn’t in either of my tubes. I have the black rubber looking damper that fits into the bottom of the slider.
Both are required. One provides bottoming out protection and the other, over extension protection.
Many thanks, both now fitted.
Hi again Brook! I posted a note on the airhead list
about which fork oil on my R60/6. I was dumb enough not to note what I used, but there was a perfect ride. Perhaps I was too eager to get back on it!
I vacillate between 5wt and 7.5wt Bel-ray. But, this is an individual call based on what you want when you ride. I have learned that each manufacturer does not have the same viscosity for 5wt or 7.5wt, etc. Bob Fleischer, aka “Snowbum” has an article with the measured viscosity for various manufacture’s fork oil and also states what the original “red” BMW fork oil viscosity is. IIRC, Bel-ray viscosity is very close to the original red BMW oil viscosity, so I have been using that.
In your first picture under “fork damper details,” just above your finger/thumb there is the lighter colored metal spacer with a spring under it. What exactly is this design? To be more specific, what is the spring allowing to move? Is it the lighter colored ring above the spring, or the ring below it?
Sorry, I know it’s a dumb question but if those parts are supposed to move that’s something I cannot directly observe as mine is 100% seized up solid at the moment and I’m hoping a night in the parts washer alleviates this condition.
If you go to MAX BMW Parts Fiche for the R75/5:
Then select “31-Front Suspension” among the choices at the top of the page.
Next, in that section, select diagram “31_0307”.
Part# (17) is the spring you mention. The damper rod is part# (18) and you see that the metal collar under the spring is part of the damper rod, so that collar is rigid. Part# (9) (see diagram “31_0306” for details) is what the spring is pushing to the bottom of part#(14) and is the part on top of my fingers in that picture. Part# (9) can move.
I hope that helps.
Thanks so much for your writeup, it’ll be hugely helpful as I tackle the forks on my ’71 R75/5 this winter. One question – you mention using Hylomar at one point, but they make a number of products. Which Hylomar product will I want here?
I believe it’s “Universal Blue”
I hope that helps.
Best of success on your project. 🙂
Even in The Netherlands your site and Youtube posts are followed. I am rebuilding a R60/6 from 1974 and have a question. Why is it necessary to install the damper rod from the bottom side and not from the top of the fork tube? When I turned my fork tube upside down, the complete damper rod fell out. The piston had only 2 rings and they were totally worn.
The special tool screws into the threads on the bottom of the fork tube. It compresses the rings on the top of the damper rod when you insert the rod. This prevents damage to the rings. So, I insert the damper rod from the bottom, not the top.
If you try to push the damper rod out of the bottom of the tube, the rings will interfere with the screw threads and may damage the rings and/or prevent the rod from coming out.
I hope this helps.
Thanks for your reply. And it helps. What is confusing for me is that the official BMW repair manual and two other BMW books all say that the damper rod shall absolutely be pulled out from the bottom side of the tube and that is just opposite of what I understand from you.
My next challenge is to find the special tool to compress the rings.
One further question. My pistons look similar as the one on your Pictures, but when I measure the diameter it is below the minimum value that is in the repair manual. leave them or try to find new ones, if they are available at all.
I apologize for my original response to your question. I originally wrote “top” when I meant to say “bottom” I was thinking of the newer version of the forks instead of the ones used on the /5 models. I edited my earlier response to correct my mistake. 🙁
The piston rings that fit on the top of the damper rod are available from any BMW dealer (part# 31 42 2 333 753) and the tool is also available (part# 83 30 0 401 938).
This site in the US, MAX BMW, has a very useful on-line parts catalog that you can look at to find out if parts are available and what the part number is. This is the R75/5 parts fiche:
I hope this helps.
Thanks again for the update. When the piston itself is below the minimum dimension that is in the repair manual, would you then also replace the pistion or leave it with the new rings?
Well, you did mention ring problems. If a ring was broken, or one was missing, I suppose it’s possible the piston could wear against the inside of the fork tube. I’ve not seen that problem on my bike.
You can order the piston (part# 31 42 1 232 054) too if you wish. If you have the money to buy two pistons (assuming both are below minimum specifications), then you would have the comfort of knowing they are in specifications and not have to go back into the fork dampers at a later time.
Hi Brook –
Thanks for the great website with helpful pics and descriptions. I’m just starting a rebuild of my ’72 R75/5. Starting now with the front fork rebuild and I have some questions/comments.
Under paragraph “Remove Fork Sliders”, it notes to remove the 10mm nut at the end of the damper rod, and a few pics reference a 10mm nut. Should that be a 13mm nut? (it was on my mc anyway). Gripping the socket with vise grips didn’t work for me as the socket spun in the jaws even with considerable vise force. I found a 13mm offset wrench worked fine, along with a 4mm allen key. Glad I put an oil pan under the forks to catch the disgusting black ooze as I lowered the sliders! And as expected – ‘what bottom bumpers?’ – they were disintegrated.
Thanks again for the great documentation, I’m sure I’ll be using it extensively going forward.
– Dave W.
Thank you for your question. In fact the nut is 8 mm which requires a 13 mm wrench. I edited the text to correct that mistake.
All the best on your rebuild and investing in keeping another classic airhead on the road. 🙂
Your website is an amazing tool. Question in regards to removing the tubes; is it necessary to remove the center nut, headlight and ears? To my untrained eye it looks like that would be a bit of a shortcut, but I can’t seem to get my tubes out. I’m trying to figure out whether the ears are somehow impeding my progress or I just haven’t spread the pinch clamps out enough. Any thoughts?
Thanks so much for your time!
First off, thank you for your kind words about the content on my website.
I use a large blade screwdriver and put it vertically into the slot in the pinch clamp. Then a couple gentle taps with a mallet and the clamp opens enough to let the tube slide out. You don’t want to hit it too hard as the clamp is aluminum. A couple light taps should be enough.
You must remove the top fork nuts as they secure the tubes to the top brace.
As to the headlight ears, since they slide over the fork tube, when you remove the tubes, they will flop free along with the headlight. I think you are ahead to remove the headlight from the ears and support it.
I hope this helps.