wobble starting at 85 mph

1980 750 LTD 4 cylinder. bone stock, new tires, new fork oil, no air pressure added afterwards.

I have noticed when I hit 85 on my bike it starts to wobble. I realize the girl is 30 yrs old and I don't go 85 hardly ever, but I am concerned this might be the start of a problem. Aside from steering stem bearings, could old/bad shocks or shock springs (in the front) cause this? What about an uneven amount of fork oil in the forks? I had trouble using the measuring procedure outlined in my manual so I used my wifes measuring cup to get very close to the amount of oil the manual called for. (yes, she was pissed).

Any ideas?

Thanks,
Andy

Did it have the wobble before the new tires? If not, check that the tires are seated evenly all the way around.

If you had the tires professionally mounted and balanced at a shop, I'd go tell them about the wobble. If they're a reputable shop they'll recheck their mounting and balance for free. If you didn't have them professionally balanced go do so, it's well worth the few bucks if you're going to exceed 60mph.

Get the proper air in those shocks, they weren't designed to run without it, and they dive harder and ride lower in the stroke when they don't have the proper air.

Check or recheck the alignment of your rear wheel while your at it. You really, really, don't want to land in a high speed wobble. They aren't fun by any meaning of the word.

I never went that fast on the old tires...they were that bad, so I don't know. The bike rides straight at cruising speeds, but if I take both hands off the bars, it ALWAYS drifts to the right. It did that even before I put new tires on.

A buddy and myself mounted the tires, no balancing....I'll get that done. I figured if I didn't feel a vibration that they would be ok.

See, I had air in them, but I've heard from people on a different forum and a local guy not to put air in them... I have a pump used for a full suspension bicycle that I will put the right amount of air in with.

The rear tire should be ok, but I'll have to recheck it anyway since I have to get my tires balanced.

If you find the tires are fine, and if the wobble continues after the fork oil / air pressure is corrected, you may want to check the swing arm bushings/bearings and the steering stem bearings. Both of these checks are fairly easy to perform, and a problem in either of these areas can cause a wobble. Ed

also check for correct tire pressure.Do u have a fairing on the bike? Fairings have a tendancy to cause speed wobble as well.bj

If it pulls to the right, check your rear axle allignment. Mine did the same thing, and mine was off by one marker.

My bike had a little vibration after my restoration. I thought the tires were seated correctly all the way around but one spot on the rear was a hair off.

Check the runout to make sure it's not the tire or rim. Put the bike up on the center stand and place some sort of block (I used a one foot section of a 4x4 post) centered directly behind the tire about 1/8" clearance and spin the wheel. I think mine was off like 1/8" in one spot but it felt like it was off an inch going faster than 50. just pull the valve stem and keep trying to reseat the tire. No need to remove the wheel or anything.

Don't know whether you want to try it but it sounds like wheel balance to me. Get back up to speed and then keep accelerating, if its wheel balance you should be able to ride out of the wobble in about 10 to 15 mph, personally I'd whip the wheel out and get it balanced again at the shop, quickest way to eliminate that aspect of the problem.

Joe Fabulous wrote:

Don't know whether you want to try it but it sounds like wheel balance to me. Get back up to speed and then keep accelerating, if its wheel balance you should be able to ride out of the wobble in about 10 to 15 mph, personally I'd whip the wheel out and get it balanced again at the shop, quickest way to eliminate that aspect of the problem.

Joe, are you trying to kill this guy too? Keep accelerating through the wobble??? "SHOULD be able to ride out of the wobble?" And what if he doesn't and instead goes into an irrecoverable tankk slapper and breaks his neck?? Even if that doesn't kill him, what good will it do?? Please be more responsible with your crappy advice!!! Ed

Ed, you obviously don't like my advice, thats fine. Take your car or bike or whatever to a garage and you will find a mechanic, all trained and qualified like me! A standard road test and a way of diagnosing a wheel balance problem on a car or bike is to drive through it, once it starts it only continues through a small speed range and then disappears, if it doesn't disappear then it usually isn't a balance issue. You will see however one point which you fail to comment on is my actual advice was to take the wheel out and just get it balanced, quite sensible I thought!

these bikes will take a bit of set up...chances are guys are right about the tires having some defect or some mis aligned /wrong install glitch...but also the fact that you now are pushing it farther is a thing to consider...

When i got my kz900 3 yrs back i knew some tricks to set up old kz's...even so it took 3 months and money to fix the wobbles and shakes..i would get better shocks and then notice something else up front..i'd fix that and then notice the tires were steering into corners slow...change tires and notice the chain was slapping now and the rear lever was sloppy...all of this whilke doing faster and faster runs....in the end the bike would do 125 with no wobble...but now it get jumpy and light in the front..only now that it is tracking and handling it is not ever that i take it up past 110...problems worked through...keep pushing...keep upgrading....good luck...