Weaving Problem

[Anonymous]

Ok I have a problem with my motorcycle, It wants to wander or weave from about 30 to 50 mph, once you hit 60 it seems fine. It is a 1979 GS750e, I bought a little over a year ago. When I bought it it had old cheng shin tires on it and I rode it that way for the summer. The handlebars wobbled, pretty much at all speeds, it was worse at lower speeds. So this year I replaced the tires, the front is the same size, but the rear is a 120/90 when it was a 110/90. After replaced the tires the handlebars still wobbled. Then I noticed that the front wheel was bent in one spot, so i replaced with one from another 750 an 82, i think, the wheel was the exact same except it had slotted rotors. Wobble was still present, so i replaced the steering head bearings with tapered ones from dennis kirk. this fixed the wobble, but ever since then i've noticed the weave. Since then I replaced the wheel bearings front and rear, but the weave is still present. I've also installed progressive springs in the forks and filled them with equal amounts of 15w fork oil. I have new swingarm bearings, but i did not install them because the old ones seemed alright. I took off the rear tire and disconnected the suspension and the swingarm does not seem to have excessive play left to right and it moves smoothly up and down. I don't know if this has anything to do with it, but I put new brake pads (for a '79) in the front calipers.

at this point i really don't know what it could be and i would appreciate any help. I do know that if i set my rear springs on the firmest setting it makes the weave worse. I'm also not %100 sure that the front steering head nut is tightened to the correct torque specs. I used vise grips to tighten it up. I have tried loosening and tightening it up, but it didn't help the weaving problem. Could someone tell me where i could get a tool to tighten that up? I aksed at the dealers and they said they couldn't get one for me. Thanks

[KGB]

If you used the marks on the swingarm to align the chain...well they're know to be mis aligned.
Wobble is usually the front end, weave the rear.

Use the string method to check rear alignment, or a known straight 2X4.

Ask a riding buddy to ride behind you and take a good, not too close, look at the bike. Or you swap with him/her and look.

Put it on the center stand, weight the front and run it in gear, see if you notice anything also.
This can be very dangerous if not done correctly!

[Anonymous]

weave

Pull The rear shocks and take the springs off and check the damping on each as well as are they the same , also do the springs seem to have the same tension at say about 3" of compression? be sure and set the pre-load on the head bearings right, if it gets worse when you adjust up the rear shocks, kind of tells me you need to be looking at the rear of the bike such as mentioned the wheel alignment or a bent swingarm, or frame rear section bent ,does the bike look to have been down??

[Anonymous]

for the wheel alignment I used the marks on the swingarm. I know they're not perfect, but shouldn't it be pretty close? I don't know the total history of the bike, but I believe that it has never been in a wreck, but it has been dropped before, and the frame and swingarm don't look bent. how do i check the damping and the spring tension?

[Anonymous]

weaver

since Iam sure you dont have the tools to measure tension and damping it will have to be by your own personal feel and judgement ( should have quite a bit of resistance both ways up and down about equal on 50/50 shocks), check that you have damping in both directions and that the springs at least measure out the same in length,and that the tighter wind on the springs are facing down at the shock base, the chain adjuster marks on any brand of bike suck at best, and you need to take the advise of the other two guys that posted I use a set of home made vener calipers that I made, Iam betting that you have a bad shock, also check the shocks for rust on the travel part of the shock shaft and for oil leaks around the shaft and on the shock body, a bad rear shock will feel like a kind of dipping and weaveing feeling in corners and if your heavy enough while just going straight, if the bike is loaded down with a rack and bags this will also make it worse. check it out before you start buying things!!!