Topic: Front suspension

[Tom H]

I have a Cb 750 and have drained the oil fork oil and replaced it with ATF as was recommended and now the front end has a constant bounce to it. I'm wondering if there is a step that I missed during the oil change or if I might need to disassemble the front end for inspection. 

[gkw120649]

Have you tried using "fork" oil instead of ATF.

[eldar]

Atf is supposedly usable, but I would go with regular fork oil.  If you still have the bounce though, you may not have added enough or assembled something wrong.

[cjackel]

Does it really have a "constant" bounce? Or does it bounce at 35-50 mph?

I have a 78 also, and I changed the fork oil and used ATF per the service manual. I get
a bounce at 35-50 mph, but I think my wheel is out of round.

Did you have a bounce prior to the fork oil change?

[Jonesy]

My front wheel did the hippity-hop around 40-45 MPH. After getting the wheel balanced it was fine.

What year 750 do you have? I read somewhere that the forks on the early bikes used 10W-30 oil, which is much thicker than ATF. I think it was partway through the 1973 model year when they switched over to a different design which used ATF. I found this out the hard way when I changed the oil in the front forks of my uncle's bike. He complained that the ride was awful harsh after the oil change. When I got a real Honda manual, I learned I put the wrong stuff in. Draining and refilling with ATF solved the problem. Stupid Haynes manuals.....

[nomadwarmachine]

Rule One is that these forks are stone age equipment compared to the forks in modern motorcycles.  That being said, I have managed to reduce the Buick-like bounce by filling the forks with the equivalent of road tar and using progressively wound springs.  If you can find some 20W fork oil, try that, or the 10W-30 mentioned above.  It improves the feel tremendously.  If that still doesn't work, you should prolly disassemble them and make sure that nothing is blocking the valve mechanism.  While the wheel is off, you should also put it on a test stand and give it a spin to check the round.  Any major bulges will be obvious.

[Tom H]

What started this problem was that I bought a new front tire and it was not perfectly round and the front suspension was bouncing so I changed the fork oil to see if this would help and it did not. Then I took the tire back to the dealer and they replaced the tire with a new one but the front suspension is still bouncing. The front suspension was not bouncing before the tire change but the fork oil was really dirty and needed to be changed anyway. My clymer repair manual said to use a good SAE 10w30 and I tried that first but the ride was the same And yes it does seem to be worse at 40 to 50 mph. Also the second tire is not perfect either but much better than the first.

[eldar]

If you have gone through 2 tires and both were bad, you may want to get the rim checked.