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1977 R100 RS front shock question  

Mike McQuillen
New Member Expired Membership

I have one of my front shocks apart and it seems to have an extra, non OEM, spring on the lower portion instead of the white rubber bumper. There was no rubber bumper on disassembly. Any one know why the extra spring in place of the bumper? How should I reassemble? Note; the picture shows the new rubber bumper I purchased prior to disassembly, it was missing altogether.

Thanks, I will appreciate any input.

Topic starter Posted : 11/14/2020 16:32
Richard Whatley
Member Moderator

I can't answer the detailed question, but the thing to do is disassemble the other fork. Which ever way you go on rebuild, you definitely want the same exact parts on both sides.

Hope this helps.

[color=blue]Don't hide 'em, Ride 'em !!

Posted : 11/15/2020 08:03
James Strickland
Honorable Member Expired Membership

Those are examples of bottoming springs. They are/were aftermarket accessories that were available in the 70's and early 80's. If I found them in a bike that was new to me, I would remove them and replace with original equipment rubber bottom bumpers.


Also, the original rubber type bumpers (black) turn into mush after several years. The parts currently supplied in re-build kits appear to be a whitish, soft nylon of some sort.  I have a pair of those bottoming springs in an un-opened package in my parts bins if anyone wants them.

Posted : 11/21/2020 08:55
Mike McQuillen
New Member Expired Membership

Hi James, thanks for your reply. I suspected they were an aftermarket addition because the bike has a bunch of aftermarket stuff from that time period. I have seen the bumper turned to mush on other bikes and there is usually a bunch of mushy residue left in there. These shocks were fairly clean so I suspect someone removed them and used the springs instead.  I had planned to remove the spring and install new bumpers if no one replied. Your reply confirms my thoughts.

Topic starter Posted : 11/21/2020 11:40
David M Swan
Active Member Expired Membership

Yes it is a bottoming spring (allows shock compliance with heavy braking weight shift or hard cornering).  It results in a more gradual rising spring rate as the forks tended toward bottoming.  Keep it, it is much better than rubber bumper & about the same volume (so no need to worry about fork oil volume).  Done several, usually; the # -017 stock RS spring, 1/2-5/8" spacer at the top ('81 and later get rid of original spring and spiral spacers), mix up 7 1/2 to 8 1/2 viscosity (most people call weight) depending on your ride preferences.  BMW seems to prefer almost no compression damping so you blend to be a bit high for rebound, low for compression damping or visa-versa or sacrificing a bit of each.  We are not talking a lot.  This should give you a good working fork for street riding (assuming good seals & alignment, etc) but maybe not the ultimate you could get with complete inner replacement.  Over stiff springs, sudden hydraulic lock up (what honda used to like) or hard bumper stop, I believe, are poor solutions for telescopic fork dive.

Posted : 12/28/2020 12:14


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