'90 K75S Bounce/Fork Seals

I replaced the front springs (Progressive) and put the recommended amount of 5W oil in. Replaced the rear shock with a Progressive 412. It's much better than it was.

I still have a problem where the front end bounces slightly up and down at 35-45 MPH. I tried the rear at all preloads, but I think it's front fork stiction. At any speed, the lower forks don't move when encountering the small irregularities in the road. They do respond over moderate bumps or when braking. When stopped, it takes some force to get the forks sliding. This is the "S" suspension.

Since this is my first K75, I don't know how much stiction is normal for the "sport" suspension. Any recommendations on fork seals? BMW or All Balls Racing? Others?

I did a quick alignment and torqued all the fasteners, which improved fork action somewhat. Nothing appears bent or racked, and the BMW mechanic who rode it several times didn't mention anything. I'll have to wait to clear out the garage (I have 4 bikes in it now) and tear down the front end to do a proper measurement and alignment.

jkbales said:

I replaced the front springs (Progressive) and put the recommended amount of 5W oil in.

Click to expand...

280-290cc. Correct?

I prefer 7W.

What preload spacer did you use?

98lee said:

280-290cc. Correct?

I prefer 7W.

What preload spacer did you use?

Click to expand...

Yes, 9.5 oz (281cc) with a 2.75 spacer.

Try doing a top-down fork alignment. It's easiest to do with the springs out of the forks, but if you have a really heavy strong friend, you can do it with him.

The goal is to get the fork legs aligned at maximum compression, the assures they run parallel to each other. Imagine how they would stick if slightly splayed at the bottom or pinched at the top.

First - loosen the clamp bolt on the bottom of the (from memory) right fork slider. Don't remove it - simply loosen it.

Then slightly loosen the bolts holding the fork bridge in place (it's part of the fender support)

Then slightly loosen the bottom triple tree bolts for the clamp that holds the fork tubes.

Get'cher large buddy on the bike, or if you've removed the springs, allow the fork to fully compress.

1 - If you have removed the springs - you want to lift the fork sliders as high as they will go - with the wheel on - and then start tightening the bolts from the top-down. First tighten the triple-tree clamps, and torque them correctly. Next tighten the fork brace bolts - and torque them. Finally tighten the fork slider/axle clamp, and torque it. Reinstall the springs, go for a ride and see how it feels.

2. If you're doing the large-friend technique, have him seated on the bike, off both center and side-stands, holding the bike upright with his tippie-toes. Have him hold the front brake on and bounce the front end down as far as he can. Repeat this several times, and then have him stop and stay still. Tighten the triple-tree clamps. Repeat the bounce/hold - tighten the fork brace bolts. Repeat bounce-hold and tighten the clamp bolt on the fork slider for the axle. Go for a ride and see how it feels.

The front forks can get misaligned, splayed (bottom not the same distance apart as the top) or twisted. This can happen with just a tire change. Realigning them should be SOP for any shop that works on the bike. It's easy and quick to do if you have a weighty friend, and it can make a big difference in how compliant the front end feels.

Also - polish the fork tubes with some high quality wax.. you'd be surprised how much easier the seals will slide on the tubes.

Don (in NJ who doesn't have to do this anymore since he has telelever and it's pretty much not needed..

That's the quick alignment I did, top down, like you said. Took the fenders off to get better access to the fork brace bolts. There was some improvement, but not as much as I'd like. I'll try the wax next. Thanks.