High speed wobble


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wingingit2
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High speed wobble

Post by wingingit2 » Sun Mar 11, 2018 4:17 pm



I am looking for the less obvious reasons for a high speed wobble on my '75 GL1000.
I have done a swingarm bearing upgrade using needle thrust bearings and seals I got from Randakk. I also have upgraded the forks & brakes using modified GL1200 triple trees & CBR600 F2 cartridge forks & brakes, along with tapered roller bearing steering head bearings. I also have Lester wheels. I need to triple the bearing preloads but am sure they are ok.
Any Ideas or advice would be appreciated.


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Re: High speed wobble

Post by SnoBrdr » Sun Mar 11, 2018 7:24 pm

wingingit2 wrote:
Sun Mar 11, 2018 4:17 pm
I am looking for the less obvious reasons for a high speed wobble on my '75 GL1000.
I have done a swingarm bearing upgrade using needle thrust bearings and seals I got from Randakk. I also have upgraded the forks & brakes using modified GL1200 triple trees & CBR600 F2 cartridge forks & brakes, along with tapered roller bearing steering head bearings. I also have Lester wheels. I need to triple the bearing preloads but am sure they are ok.
Any Ideas or advice would be appreciated.
Is the front wheel balanced.

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Re: High speed wobble

Post by wingingit2 » Sun Mar 11, 2018 7:37 pm

Yes, had it mounted and balanced at my local dealer.
I tightened up the bearing preloads a bit and it made a small difference, but not much. This is happening at 95 to 100 MPH.
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Re: High speed wobble

Post by fatalbert » Sun Mar 11, 2018 9:00 pm

You have kind of a Frankenstein front end where some of the components may not be completly compatible. It is difficult to diagnose the cause since there has been a significant deviation from stock. The solution may be to stay well below 95 mph unless you have intentions of racing your bike. I am not sure but I thought the early GL1000's did have a tendency towards high speed wobble.

The only way to isolate the cause would be to remove all the modifications and add them back one at a time until the anomaly returns.

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Re: High speed wobble

Post by ekvh » Sun Mar 11, 2018 11:10 pm

Check fork lengths from triple tree to axle on both sides? Unequal lengths can pull the front wheel out of plane with the rear wheel.

There is a lengthy procedure for checking front and rear wheel planes using string lines that can tell you things the eyes can’t see. http://www.motorcycle.com/how-to/chassi ... -3444.html

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Re: High speed wobble

Post by kndw » Mon Mar 12, 2018 3:23 am

My '76 GL did that too. Now I just don't try such speeds anymore, which has completely eliminated the problem.

But seriously, I have heard numerous times that the old GL's have spaghetti frames and that they do not hold up well at high speeds or hard cornering. A friend of the family who worked at a motorcycle dealership during the time GL's first came out said that customers even returned the bikes; finding the frame's 'flexibility' unacceptable. I therefore wonder if the front end is where your problem comes from.

That being said, in my experience wobbles are most often due to either the steering stem bearings or the tires not being mounted/balanced properly. I would check it again. Is the guide line on the side of the tire evenly far from the rim all around? You can also try using dyna beads. These dynamically balance the wheel while riding. Never tried them, but it is an intriguing product.

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Re: High speed wobble

Post by wingingit2 » Mon Mar 12, 2018 9:57 am

fatalbert wrote:
Sun Mar 11, 2018 9:00 pm
You have kind of a Frankenstein front end where some of the components may not be completly compatible. It is difficult to diagnose the cause since there has been a significant deviation from stock. The solution may be to stay well below 95 mph unless you have intentions of racing your bike. I am not sure but I thought the early GL1000's did have a tendency towards high speed wobble.

The only way to isolate the cause would be to remove all the modifications and add them back one at a time until the anomaly returns.
I understand what you are saying, i say the same thing when people come to me with poorly modified intake/exhaust/igition with problems.
The modification was done because of this problem. And was done with skilled precision, as far as the machining goes. Also the fork lengths re the same as a stock front end.
This bike, when stock with new seals & bushings, and my '77, which is stock with new tubes & bushings, have the same problem at the same speeds.
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Re: High speed wobble

Post by wingingit2 » Mon Mar 12, 2018 9:58 am

ekvh wrote:
Sun Mar 11, 2018 11:10 pm
Check fork lengths from triple tree to axle on both sides? Unequal lengths can pull the front wheel out of plane with the rear wheel.

There is a lengthy procedure for checking front and rear wheel planes using string lines that can tell you things the eyes can’t see. http://www.motorcycle.com/how-to/chassi ... -3444.html
I will go thru this and make any adjustments I can, but it will have to wait until next Sunday.
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Re: High speed wobble

Post by wingingit2 » Mon Mar 12, 2018 10:00 am

kndw wrote:
Mon Mar 12, 2018 3:23 am
My '76 GL did that too. Now I just don't try such speeds anymore, which has completely eliminated the problem.

But seriously, I have heard numerous times that the old GL's have spaghetti frames and that they do not hold up well at high speeds or hard cornering. A friend of the family who worked at a motorcycle dealership during the time GL's first came out said that customers even returned the bikes; finding the frame's 'flexibility' unacceptable. I therefore wonder if the front end is where your problem comes from.

That being said, in my experience wobbles are most often due to either the steering stem bearings or the tires not being mounted/balanced properly. I would check it again. Is the guide line on the side of the tire evenly far from the rim all around? You can also try using dyna beads. These dynamically balance the wheel while riding. Never tried them, but it is an intriguing product.
I will go thru the above procedure but will not use Dyna Beads for 2 reasons. !) Every time you stop the wheel is out of balance, drastically. What happens when you hit a pothole or speed bump at speed? 2) Not only are you wearing the tire on the out side you are wearing the tire from the inside. Do you really thing a tire was meant to have things rolling around inside? I don't.

---------------------------------------------------------PLEASE DON'T TURN THIS INTO A DYNA BEADS THREAD----------------------------------------------------------------------------
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Re: High speed wobble

Post by kndw » Tue Mar 13, 2018 3:39 pm

wingingit2 wrote:
Mon Mar 12, 2018 10:00 am

---------------------------------------------------------PLEASE DON'T TURN THIS INTO A DYNA BEADS THREAD----------------------------------------------------------------------------
Why not? Do you not like them?

:mrgreen:

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Re: High speed wobble

Post by WingAdmin » Tue Mar 13, 2018 5:28 pm

wingingit2 wrote:
Mon Mar 12, 2018 10:00 am
I will go thru the above procedure but will not use Dyna Beads for 2 reasons. !) Every time you stop the wheel is out of balance, drastically. What happens when you hit a pothole or speed bump at speed? 2) Not only are you wearing the tire on the out side you are wearing the tire from the inside. Do you really thing a tire was meant to have things rolling around inside? I don't.

---------------------------------------------------------PLEASE DON'T TURN THIS INTO A DYNA BEADS THREAD----------------------------------------------------------------------------
Not to make this a Dyna Beads thread, but they are a simple way to eliminate wheel balance as a potential cause of the wobble issue.

Your two reasons: 1) You are correct, but I'm, not sure about you, but I don't notice much in the way of wheel balance issues when my wheel is stopped. By the time you are at a speed where wheel balance could become an issue, the beads have already redistributed themselves around the tire and it is balanced.

What happens when you hit a pothole? Nothing. You might bump the beads out of place for an instant, but they redistribute themselves back in place instantly as well - you don't notice a thing.

2) as for wear, the wear on the inside of the tire is absolutely negligible, as I have shown here in pictures I took when changing tires. I have gone through multiple sets of tires that wore out completely (on the outside) and the wear on the inside from the beads was barely any. The beads are not continuously rolling around in there, when you are riding, the beads are stuck to the inside of the tire and do not move.

Essentially, in my experience, Dyna Beads work, they do not wear your tire, and your tires stay balanced 100%, 100% of the time. I've used them on multiple motorcycles, and also on my truck - which I was completely unable to balance using lead weights.

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Re: High speed wobble

Post by eklimek » Tue Mar 13, 2018 6:06 pm

Wingit

Some idle thoughts

Has the trail changed?

Is the whobble in the handle bars with the frame stable or is the frame involved?

You addressed the swing arm. If you stiffen the rear shock, does the resonance disappear?

Ed

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Re: High speed wobble

Post by wingingit2 » Tue Mar 13, 2018 6:35 pm

I'm not sure if the trail changed, but it corners so much better.
The wobble is in the frame. Same thing my Ninja 600 did years ago.
I have new Progressive 412's on the back. I will adjust and see what happens. They are pretty stiff now.
I also have Race Tech Fork springs up front. I want to go to 7 1/2 weight fork oil because hitting freeze cracks is jarring.
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Re: High speed wobble

Post by ekvh » Tue Mar 13, 2018 8:26 pm

I hate to ask, but have you checked the tightness and integrity of the engine mounts and the frame pieces? I ask because you say it’s a frame wobble. The removable frame piece has a large 10-12mm? stud that protrudes through the frame piece that can get corroded and fail, at first being a little wobbly in the frame. It’s the one the left foot peg attaches to.

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Re: High speed wobble

Post by wingingit2 » Wed Mar 14, 2018 1:03 am

Good thought, I will check over the weekend when I get time.
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Re: High speed wobble

Post by eklimek » Wed Mar 14, 2018 7:50 am

wingit

If trail is decreased by fork height or rake change there is better turn in and more likely a handle bar whobble. (Like the front wheel caster on a shopping cart.) A tank slapper is the most common presentation. The opposite is true as well. The resonant frequency is adjusted with a steering damper.

Frame whobble is flexing at the steering head originating at the back.. You have probably had this is on a cruiser on a long sweeping turn and a slight bump giving a bucking riding feeling. With the bike leaning the flex point is at the steering head.

Frame flex is induce able with any impulse. Frame flex can be built in. Steady high speed is unlikely to cause this.

Not sure this helps.

Ed

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Re: High speed wobble

Post by wingingit2 » Wed Mar 14, 2018 9:30 am

I found out that the rear wheel is a 16" instead of a 17" which is stock. Wheels are Lester's and tires are 1 size wider than stock.
Also looked up Frame Spec's:
Gl1000 Caster angle is 62 Degrees, trail 4.7"
Gl1200 Caster angle is 60 Degrees Trail 4.6"
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Re: High speed wobble

Post by eklimek » Wed Mar 14, 2018 10:51 am

Wingit

Unless there is more going on you should not have adversely affected the trail.

The rear wheel is smaller and the front is taller (and wider) . This effectively tips the bike, (back down and the front up). It also makes the bike foot print slightly longer.

Picture the steering bearing axis extrapolated to the ground. It is always slightly ahead of the front tire contact patch so that the tire castor (trail) tends to restore straight line travel.


You have lifted and pushed the axis forward by the changes. The contact patch of the tires remain fixed. The trail is increased.

The front wheel should be harder turn in at corners and will tend to return to the straight ahead position as touring bikes prefer.

However, this is not the more sporty ride you described. Not trying to see problems where there are none; are the front forks fully extended in the triple tree?

Ed

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Re: High speed wobble

Post by WingAdmin » Wed Mar 14, 2018 11:03 am

I'm going to assume that you did, but are the new swingarm pivot bearings fully seated and correctly torqued? My 1100 developed a high speed wobble after I put new tires on it, and I ended up tracking it down to the swingarm pivot - a previous owner had installed them backwards (left one on right side and vice versa), allowing the swingarm about 1/4" lateral free play measured at the back end. The old, flat-worn tire was stable enough to prevent the wobble, but the new tire with its more rounded profile (and subsequent smaller contact patch) allowed the wobble to make itself known. Fixing and torquing the pivots removed the swingarm free play as well as eliminated the wobble.

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Re: High speed wobble

Post by wingingit2 » Wed Mar 14, 2018 3:42 pm

Left and right bearings on a 1000 are the same. They are needle bearings, unlike the others which use tapered roller bearings. Mine is also an upgrade to use needle thrust bearings instead of the composite washer the OEM used.
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Re: High speed wobble

Post by wingingit2 » Fri Mar 16, 2018 11:07 am

eklimek wrote:
Wed Mar 14, 2018 10:51 am
Wingit

Unless there is more going on you should not have adversely affected the trail.

The rear wheel is smaller and the front is taller (and wider) . This effectively tips the bike, (back down and the front up). It also makes the bike foot print slightly longer.

Picture the steering bearing axis extrapolated to the ground. It is always slightly ahead of the front tire contact patch so that the tire castor (trail) tends to restore straight line travel.

trail.jpg

You have lifted and pushed the axis forward by the changes. The contact patch of the tires remain fixed. The trail is increased.

The front wheel should be harder turn in at corners and will tend to return to the straight ahead position as touring bikes prefer.

However, this is not the more sporty ride you described. Not trying to see problems where there are none; are the front forks fully extended in the triple tree?

Ed
Yes forks are fully extended. It handles better because it tracks better. With no lower bushing in the original forks the slider tube was worn and sloppy. Also bigger fork tubes are stiffer.
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Re: High speed wobble

Post by Fred Camper » Sat Mar 17, 2018 5:00 pm

You may consider taller rear shocks from the cb750 to reset the frame to near stock geometry with the 16 inch Lester rear wheel. Bet progressive can update your shocks.

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Re: High speed wobble

Post by wingingit2 » Sat Mar 17, 2018 7:03 pm

I'm inseam challenged, kinda like the seat height. Don't race it, so it's not a problem.


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