Front end dive on /5

[rider1d]

I didn't run the 750 for over a year, and never realized how bad the front-end dive was. In addition the brakes are grabbing, making for a dangerous combination.
Taking off the fork caps, it turns out there were no spacers, and no preload whatsoever. The springs are at least 20, 000 miles old. In draining the oil completely (doing a rebuild) it was quite gunky, and there were only 2 wiper rings on each shock absorber (damper rods), when there should have been three. What is the most likely cause of the front-end dive - the springs, the dampers, the used oil (also at least 20K), or the lack of preload?

 

[PGlaves]

Those long-travel forks dive. They just do. Even when new. My advice: clean everything up, Install all the correct parts. Then add the correct volume of fork oil. That bike takes 3 weight I think. Some folks have used transmission fluid. I would use 5 wt fork oil. It will still dive some. Then add 15cc or so of additional fork oil. This will reduce the volume of the air column above the oil, which will compress to higher pressure sooner and limit dive.

 

[melville]

Also be sure the caps at the tops of the forks are sealing. BMW provide a crush washer but it's hard getting a proper crush with the pin wrench that tightens those alloy caps. I've had good luck with an O-ring from the hardware store.

If it's not sealed on top, then changing the fluid level will have no effect on dive as the air space will always be at atmospheric pressure.

 

[dduelin]

I remember reading a magazine review of the R100 of the early 80s and one thing that stuck in my mind all these years was "the forks collapse like a pole axed mule when braking." I had a 1981 R100 and that's the way BMW made forks back then. Soft springs, soft damping, and long travel.