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Foreign Rebound Fork Spring and Damping Rod Clean Out

The place to discuss the R 90 S as well as the R90S Worldnet archives!
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jrsbike
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Joined: Tue Sep 16, 2014 1:49 pm

Foreign Rebound Fork Spring and Damping Rod Clean Out

Post by jrsbike »

Well I finally got to the front end of my long long 1974 90S rebuild project. I got a fork rebuild kit from Hucky's which included a white plastic rebound stop. What was odd in the disassembly was the presence of a one inch long rebound spring. I searched all the documents I could find and as far as I can tell, that unlike almost every fork I have disassembled, BMW did not employ a rebound spring and relied and oil rebound compression and a stop of some kind. Is this correct? Also, at the last minute I decided to disassemble the damping rods and glad I did! The interior was full of prehistoric muck. I used some Remington bore cleaner and a 9MM bristle bore brush on a Hopp's rod and the tubes are good as new. The spring and ball bearing were likewise caked in mud.
1974 BMW R90S
2015 BMW R1200R


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schrader7032
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Likely what that spring was

Post by schrader7032 »

Likely what that spring was is an after market anti-dive spring. They were somewhat popular in the day. The spring rate of this small spring was designed to deal with the dive of the front end under braking. I guess if you're not comfortable with the way the BMW front end works, you have to do something. One way is to have stiff fork springs, but then the ride is rough. The anti-dive spring lets you have a supple suspension for normal riding but have the anti-dive spring kick in when needed. Other ways to deal with this is to use thicker oil and/or adjust the amount of air in the fork.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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skychs
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Forks

Post by skychs »

Now I have to question my front forks. The spring that came inside my forks was easily 5-6" long. I tried it first without the spring but like you said it was too mushy. I then tried two different wt oils. Right now Im running the anti-dive springs and 10 wt oil and it seems to be ok but still a little stiff. I have a photo of mine but it will not let me post a photo anymore. Grrrrrrrr
1966 R60/2, 1967 R69S, 1975 R90S, 2020 R1250GSA

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