I just posted a new web page on rebuilding and refinishing the fork tubes. You can see this entry on the right hand column and can access it by clicking the 31 BMW R75/5 Fork Rebuild link.
I’m labeling the web pages for this project with the number BMW uses to identify major sub-systems of the R75/5 so you can easily correlate procedures with parts. You can see the numbers on Hucky’s /5 parts page.
Here are some before and after pictures.
Starting Out with Wheel and Fender Removed
Grungy Fork Slider Removed
Final Product, Rebuilt and Refinished
Great blog and informative fork rebuild article. The photos and descriptions help understand the scope of the project. I am rebuilding 78 R100/7 forks. There were no internal bumpers and there is a lower rebound spring (Heavy wind about 6 inches long). The closest approximation to my fork is the one Clymer identifies as Type 1 – however there is no lower rebound spring shown in this diagram. Several questions – are you aware of any other articles on this fork model? Does the main fork spring get replaced with the closer wound coils facing down? Should the gaps on the three wiper rings be aligned or staggered? A million thanks!
Hi John,
I’m curious if the internals of your forks look anything like the ones in my 1983 R100RS?
31 BMW 1983 R100RS Replace Fork Seals, Install Slider Dust Covers
The springs are after market ones with adjustable rates for the initial and close to fully compressed spring rates.
I believe folks made modifications to the fork internals to improve the forks. Common changes were smaller springs at the bottom to increase the spring rate when the forks were almost fully compressed. Other changes were PVC or metal plugs used to reduce sag with a front fairing.
The larger rubber bumper that fits into the bottom of the lower fork slider and even the smaller one at the top often dissolves and there is nothing left of them.
The “piston rings” on the top of the internal damper act like the piston rings in the engine. I would off-set the gaps to improve sealing.
The conventional wisdom on orientation of the fork spring inside the fork has the tighter wound coils at the top “to reduce unsprung weight”. That said, the action of the spring–getting stiffer as it compresses a lot which is what progressive rate springs are designed to do–does not change if the tighter wound coils are at the top or the bottom.
There are some articles Bob Fleischer has posted that maybe of interest.
http://bmwmotorcycletech.info/frontforks.htm
http://bmwmotorcycletech.info/section8stdampers.htm
http://bmwmotorcycletech.info/front-fork-oils-amounts.htm
I hope this helps.
Best.
Brook.
Sir,
Although it has already been said by many others, I will take my turn.
Your blog is beautiful and provides invaluable information to the Airhead community.
I am about to embark on rebuilding the forks on my R75/5 and am curious about the damper ring compressor tool which you borrowed from BMW. Do you have any other photos of the tool itself that might illustrate its shape/configuration?
It looks like it might be a simple enough lathe project if I could gain some insight into the cross section.
Any help you can offer would be greatly appreciated.
Thanks again for all of your generous work.
Jonathan
Hi Jonathan,
Thank you for the kind words. I sent you a separate email with information about the BMW tool. BTW you can purchase this tool from MAX BMW, or any BMW shop for $36.30 if you wish, part# 83 30 0 401 938.
Best.
Brook Reams.
Hi. I thought I might get away with just replacing the cracked fork gaiters, until all this oil gushed down the tube when I opened one of the lower gaiter clamps. I didn’t see any mention of fork oil in your repair (what type, how much, where to fill etc). Thank you. Chris
Hi Christopher, For that year bike and fork I typically use 7.5 weight Bel-Rey fork oil. It goes in the top of each fork tube before tightening the top fork spring nuts. On later models, that bolt has a smaller tapped hole in the center of the nut so you can add fork oil and not have to remove the top fork spring nuts. I hope that helps.
Best.
Brook.