Still Fighting Head Shake

[GlassBottle]

Hi all,

I bought my 1977 GS750 two years ago. Last season I noticed the front end started to feel "bouncy". Once I got up to around 40mph if I took my hands off the bars they would shake pretty violently. This past winter I went through the bike pretty well. Brand new steering head bearings and wheel bearings front and rear. New tires front and rear. I went for my first ride this season and the shake is still there. Which direction should I head in now?
Thanks for the help.

 

[bonanzadave]

Id probably rebuild the forks. Springs, bushings, seals & oil.

Were the old head bearings bad ? and were you able to "set" the friction on the new ones ?

 

[posplayr]

Forks should be in good shape but I would adjust the stem nut till there is some drag on turning the forks. On the GSXR the use a fish scale. On my stock ED fully restored there was a handlebar wobble at 20-30 mph

 

[GlassBottle]

Yea the old head bearings were real bad. I want to say original. They were the loose ball type. I was able to set the friction on the new ones. Maybe a didn't go tight enough? There is a little drag but not very much.

 

[steve murdoch]

A sketchy rear end can also transfer to the front.
Check for any slop in the swingarm bushings and the alignment of the wheels.

 

[silverhelme]

It might be a long shot but I bought a new GT550 in 1972 that after about a week of riding started to have the same symptoms. Took it back to the dealer and everything in the front end was redone but did not help. Being new the front tire only had about 300 miles on it but it was rebalanced ( actually removed from the rim remounted and rebalanced ) and the problem still existed. I finally had them replace the front tire ( which they tried to charge me for ) and it turned out that it was the problem. They never figured out what caused it but it might be worth checking.

 

[GlassBottle]

It might be a long shot but I bought a new GT550 in 1972 that after about a week of riding started to have the same symptoms. Took it back to the dealer and everything in the front end was redone but did not help. Being new the front tire only had about 300 miles on it but it was rebalanced ( actually removed from the rim remounted and rebalanced ) and the problem still existed. I finally had them replace the front tire ( which they tried to charge me for ) and it turned out that it was the problem. They never figured out what caused it but it might be worth checking.

Thanks for the reply. This has occurred with the old tire as well as with the new one. Maybe I'll try having the wheel rebalanced. Now that I think of it I should make sure the wheel is true as well.

 

[wymple]

Tires that don't work well with each other from front to rear can also be a problem.

 

[GlassBottle]

So today I tightened up the head bearings a little more but the shake persisted. I discovered that the rear brake is dragging a bit. I tried taking the pads out and going for a ride but the shake persisted. I had the front wheel checked for balance and trueness and it was good. I've noticed that this shake only happens between 40-45 mph. Anything under or over is okay.

 

[bonanzadave]

So today I tightened up the head bearings a little more but the shake persisted.

Did you loosen a set (top or bottom) of fork tree pinch bolts ? Tightening the stem nut is actually pulling the top and bottom of the tree together. Without loosening a set of pinch bolts you may not be doing anything.

I had the front wheel checked for balance and trueness and it was good. I've noticed that this shake only happens between 40-45 mph. Anything under or over is okay.

Kinda how mine was. Although I believe my front tire was older and you said "new tires" but I would not count out a defective front tire.

 

[posplayr]

+1 for Dave. The objective is handlebar drag not a tight nut.

 

[GlassBottle]

Yes sir I loosened up the top pinch bolts before tightening the stem nut. Yes new tires. They were bought about a month ago. It's very feasible it could be defective I suppose though.

 

[Guest]

A sketchy rear end can also transfer to the front.
Check for any slop in the swingarm bushings and the alignment of the wheels.

This......

 

[GlassBottle]

This......

I'm going to have to start playing around with the rear end.

 

[posplayr]

Realize there is a difference between "weave" and "wobble"

 

[bobgroger]

Finally....an advantage to being fat!

 

[GlassBottle]

Haha I'm definitely getting wobble. I guess I'm "daft" enough to take my hands off the bars!

 

[GlassBottle]

This is killing me! It's got a slight "bounce" to it now too. Only between 40-45mph. I snugged the head bearings until I felt the bike start to wander while on a test ride and then backed them off a little. I trued and rebalanced the front and rear tires. I double checked the swingarm bearings. I changed the fork oil with 10w. I tried different tire pressures. I even tried putting on an old set of shocks I had. Nothing seems to make it better or worse. At this point I may just have to ride it as is.

 

[posplayr]

This is killing me! It's got a slight "bounce" to it now too. Only between 40-45mph. I snugged the head bearings until I felt the bike start to wander while on a test ride and then backed them off a little. I trued and rebalanced the front and rear tires. I double checked the swingarm bearings. I changed the fork oil with 10w. I tried different tire pressures. I even tried putting on an old set of shocks I had. Nothing seems to make it better or worse. At this point I may just have to ride it as is.

How much handlebar force is required to turn the bar? You have to lift the front of the bike off the groudn and there should be some definite drag.

Here is a pages from a 1st gen GSXR 750 on using a scale. The initial force to move is between 200-500 grams at the end of the bar. You shoudl probably be at least at the lower end. 200 gram is about 6 oz.

 

[GlassBottle]

How much handlebar force is required to turn the bar? You have to lift the front of the bike off the groudn and there should be some definite drag.

Here is a pages from a 1st gen GSXR 750 on using a scale. The initial force to move is between 200-500 grams at the end of the bar. You shoudl probably be at least at the lower end. 200 gram is about 6 oz.

View attachment 50626

There is definite drag but I currently don't have a scale to use. I'd have to pick one up.