31 BMW 1973 R75/5 Rebuild Front Forks

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.

Parts Used

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 disassemble section 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.

Wiring Harness Removed

Forks with Wiring Harness Removed

Remove Fork Sliders

First, I removed the fork sliders. Remove the rubber plug on the bottom of the slider to expose the 10 mm attached to the plunger.  I use the following tool to loosen the nut from the damper, a vice grip holding a 10 mm socket.

.10mm socket and vice grip

Vice Grip and 10 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 lossen the nut and remove it.

Removing bottom nut from fork pipe

Removing 10 mm Nut on Damper Rod

Next, remove the circular steel bands holding the rubber gators 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 insider surface around the seal.

Here is the disassembled fork sliders with seals (green), sliders, steel rings for the fork gators, the ring under the large fork retaining nut, cap on bottom of fork slider, 10 mm nuts and wave washer.

Fork slider Parts and Fork Tube Top Retaining Caps

Fork slider Parts and Fork Tube Top Retaining Caps

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.

Fork Stanchion Parts-Outside to Inside

Bottom of Fork Slider, rubber cover, wave washer, 10 mm nut, fork plug, large copper ring, inner rubber bumper

At this point, the fork tubes and internal damper rods are exposed.

Forks with sliders off
Fork Tubes with Internal Damper Rods

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

Right Control Brake Light Switch

Right Side Control Front Brake Switch

Then I removed throttle cables and the right side control and disassembled it.

Right Control Disassembled

Disassembled Right Side Control

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.

Left Control Disassembled

Disassembled Left Side Control

At this point I removed the steering damper rod and the lower friction assembly from the bottom of the lower fork clamp.

Steering Damper Disassembled

Steering Damper Disassembly

This bike had handlebar pull backs. I removed them and the handlebars exposing the chrome forks screw caps.

Handle Bar Bracket & Pull Backs

Handlebar Pullbacks and Original Handlebar Mounts

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.

Handlebars Removed

Handlebars Removed Showing Chrome Covers Over Fork Spring Nuts

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.

Headlight ear and top clamp

Headlight Ears and Top Clamp Assembly

Headlight ear details

Headlight Ear Headlight Mount Detail

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.

Fork tube c-clip

Snap Ring at Bottom of Fork Tube with Damper Rod in Center

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.

Fork tube ring

One Style of Retaining Ring-You Can’t use Tool Kit Pin Wrench

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.

Quick&Dirty Threaded Ring Pin Wrench

Quick & Dirty Adjustable Pin Wrench

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.

Threaded Ring Pin Wrench Notches

Clem’s Simple Pin Wrench Tool

Threaded Ring Pin Wrench Tool

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.

Lower Fork Tube Parts-Outside to Inside

Snap Ring, Top Retainer, Metal Ring, Bottom Retainer, Rubber Stop, Damper Rod Assembly.

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 10 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.

Hucky's Fork Rebuild Kit (x2)

Hucky’s Fork Rebuild Kit

 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.

Rings on Top of Damper Rod

Damper Rod Piston Rings

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.

Ring Compressor

Damper Rod Ring Compressor

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.

Ring Compressor Installed

Ring Compressor (upside down) Covering Piston Rings on Damper Rod

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.

Inserting Damper Rod Thru Ring Compressor

Damper Rod with Compressor Inserted into 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.

Adding Lower Bumper Stop

Inserting White Bumper into the Bottom of the Fork Tube

Inserted Lower Bumper Stop

Bumper Stop Just Past Internal Threads

The two steel threaded rings are identical. The bottom ring has the edge point up so it can hold the metal spacer.

Bottom Threaded Ring-Ridge on Top

Retaining Ring Orientation for Bottom Ring

I spun the ring in using a finger and then tightened it using needle nose pliers.

Installing Bottom Threaded Ring

Tightening Bottom Retaining Ring

Now, place the metal spacer ring on top of the bottom retaining ring.

Spacer on Top of Bottom Threaded Ring

Metal Spacer Ring Inserted

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.

Adding top Ring-Ridge on Bottom

Putting Top Retaining Ring In

Finally, I used the snap ring pliers to put the snap ring back into its groove in the bottom of the fork tube.

Inserting C-clip

Inserting bottom snap ring

The small copper washer will go on the threaded portion of the damper shaft when I insert the fork slider onto the fork tube.

Copper ring on Damper Rod

Small Copper Ring on Threaded End of Damper Rod

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.

Heating Tube for Fork Seal Install

Using Heat Gun To Heat Top of Fork Slider Before Inserting Fork Seal

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.

Bumper, Curved Side Down

Inserting Lower Bumper Stop into Large Threaded Plug

Then, I put some Hylomar on the land of the threaded plug and the put the large copper washer on the land.

Washer on Plug

Large Copper Gasket on Bottom of Threaded Plug

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.

After Rebuild & Polishing

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.

Revisions

  • 2017-03-24   Update table of contents; change some picture captions; minor edits.

45 thoughts on “31 BMW 1973 R75/5 Rebuild Front Forks

  1. Pingback: 1972 R75/5 Rebuild: Fork Rebuild and Refinish | Motorcycles & Other Musings

  2. 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!

    • Hi Scott,

      Thanks for stopping by and looking around. I hope this helps you out. If you have questions along the way, let me know.

      Best.
      Brook.

  3. 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.

    • Hi Al,

      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.

      Best.
      Brook.

  4. 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.

    • Hi Tyler,

      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 🙂

      Best.
      Brook.

  5. 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

    • Tyler,

      Cool beans. I’ll keep my eyes open for GS and let you know if I spot one. Are you in Denver metro area?

      Best.
      Brook.

  6. 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!

    -eric

    • Eric,

      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.

      Best.
      Brook.

  7. 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!

    • Hi John,

      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,
      http://rubberchickenracinggarage.com/

      I hope this is helpful.

      Best.
      Brook.

  8. 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
    Jim

    • James,

      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.

      Best.
      Brook.

    • James,

      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.

      Best.
      Brook.

  9. Brook,
    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?

  10. Hi Brook,
    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

    • Hi Gerry,

      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.

      Best.
      Brook.

  11. 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!

    • Hi George,

      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?
      http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000582.png?v=07012015

      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.
      http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000580.png?v=07012015

      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.

      Best.
      Brook.

  12. 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?

    • Hi John,

      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:
      http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51885&rnd=07012015

      and select “31 Front Suspension” then click the picture for the fork assembly:
      http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000580.png?v=07012015

      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.

      Best.
      Brook.

  13. 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.

    • Hi Richard,

      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.

      Best.
      Brook.

  14. Hello,

    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!

    Jeroen

    • Hi Jeroen,

      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.

      Best.
      Brook.

  15. 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!

    Thanks,
    Jim

    • Hi Jim,

      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.

      Best.
      Brook.

  16. 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!

  17. 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

    • Hi 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.

      Best.
      Brook.

  18. 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.

  19. 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.

    • Hi Max,

      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.

      Best.
      Brook.

  20. 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

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