Front-end-wobble under hard braking

[Gearhead]

Folks,

 

There's been lots of dialog about front-end wobble, but I have a peculiar variant which happens under very hard braking. As in "I think I'm going to hit this car and die" hard braking. It happened to me in November on the Interstate when traffic came screeching to a halt and I obviously wasn't looking ahead very attentively, and then last night at maybe 60 mph somebody pulled out RIGHT in front of me. Thanks to God that I didn't hit anything either time, or fall over with the wobble. In both cases, while on the brakes hard, I think I felt the front tire partially lock, and the front wheel and handlebars went into a violent wobble that was very difficult to control despite my death-grip on the bars. Last night, being the second time, it occured to me as I was braking that the front end would go crazy. I want to be clear that this is NOT a whole-bike weave, but a front-end wobble; I've felt both in the past.

 

A little history if you're interested. I got my 87 with 45,000 miles on it and a lot of deferred maintenance. It exhibited a strong tendency toward the wobble at mid-speeds (30-45), but ONLY if I removed my hands from the bars. Light hand pressure always damped it out. It also had a touch of the high-speed whole-bike weave. Over the last 1.5 years I've done the following:

 

-New tires - 38psi F, 40psi R

-Progressive fork springs and rear shock unit

-Greased and checked rear swingarm and linkage

-Inspected, cleaned, packed and adjusted steering head bearings. I've tried a couple different preloads from the factory light setting to something a little tighter - no difference.

-Checked wheel bearings.

-Installed Superbrace

 

Through all this the whole-bike-weave has diminished; what remains is minimal, self-damping and I'm convinced it's normal in a full-dress bike. The wobble is mostly gone, with the single biggest factor being the new front tire (which has been the case in the past for me on other bikes). I can remove my hands at mid-speeds and it doesn't automatically start wobbling as before. However, even now it only takes the slightest provocation to start one. If I hit a little rock with the front wheel, or tap one of the grips with my hand, it will start.

 

The braking wobble feels like the regular front-end wobble, but the big difference is that it wobbles with my hands tight on the bars which it normally won't do.

 

The wobble has one other manifestation. When doing u-turn excercises (from the MSF experienced class), at low speed with the wheel at or near lock, I feel a bit of that wobble even though my hands are firmly on the bars.

 

I am sure these are all related; different manifestations of the same condition:

 

1) Mid speeds in a straight line, hands off bars, slight bump in road or tap on handlebars.

2) Higher speeds, hard on brakes, straight line, death grip on bars.

3) Low-speeds, tight u-turn, hands firmly on bars.

 

Anybody else had these experiences? How'd ya fix it?

 

Jeremy

[Eck]

Sounds like you already inspected and changed out the main culprits of possible causes..

 

A suggestion only here, but this MIGHT help..but not sure in your case.

 

http://www.tcbbrakesystems.com/

 

 

One more thing is you might want to check your wheel alignment (front to rear alignment)

[GeorgeS]

Have you Re-Torqued the Engine Mount Bolts?

 

A long shot, but worth checking.

[cmiles3]

Bent rim? Warped rotors? Wheel hop from threshold braking (tires slip, then grab, then slip... repeat cycle until stopped)? Brake cylinders/master cylinders need rebuilt? New brake lines needed?

 

I'm just guessing, but some or all of the above can lead to similar problems. Haven't experienced what you describe, but if your brakes are locking then releasing you might feel your bike rocking from the suspension reacting.

[Guest KitCarson]

I have read a lot of posts on this site about low speed wobble on these bikes. I have seen all the simple solutions discussed such as tires.....balance.....and other simple things. Generally out of line front to back will simply make the bike pull to one side or the other......used to be a common situation with chain driven bikes....used to check this with string. I do believe what you are describing......as you seem to have checked all the simple things, is you have some out of line forks. Forks out of alignment will certainly create a wobble.....just as much as .002 to .006 out of line will do it.....I honestly think this is what is going on. The fact that you can initiate the wobble by hitting the bars....sounds just like out of alignment forks. This is a pain to fix too!!

Some of the shops have laser tools to work on this with now......it is well worth it to have them do this. Kit

[Squeeze]

Hi,

 

i never expierenced something like that, nor do i know a specific Answer to cure it. Some Folks i know, have had similar Problems and got them fixed, but they did several Things at one Time and so there is no single Answer to this.

 

What i would do, is ...

 

1st

open al Pinch Bolts on the Fork Legs and retighten them from the lower to the upper End with the Wheel off the Ground

 

2nd

recheck the Fluid Level in the Legs and ensure they are equal and a 10 Weight Oil

 

3rd

dismount the Bearings, grind the Seats wider to give the new Races a loose fit, buy good new Bearings and glue them in with Loctite648

 

Of Course, a Test ride would be in Order between the Steps.

[Squeeze]

The Out of Alignment Theory ...

 

Yamaha stated here in Germany, that the Offset between front and rear Wheel of a Vmax within 9mm would be OK. 9 mm, that's 0.35 Inches ...

 

I don't think that would be the Way i like it, but even will not cause a Wobble. The Bike is just pulling to one Side.

[CrazyHorse]

Do both front brakes work are the disks straight? Frame cracked somewhere? Equal oil in both forks and both fork dampers working? Rims ok? Axles ok? Is your front wheel about to lock up sometimes you get a side to side motion before it skids?

 

Heres a somewhat interesting article. http://www.essortment.com/hobbies/streetbikemain_seuf.htm

[Eck]

I would think that Redneck and I both agree it's time for a 2nd gen

[Big Daddy]

I take it there is no cupping or flat spots on the front tire? My 83 did something similar at low speed. I put on a new front skin and problem solved.

[Marcarl]

From what you posted I don't think all your problems may relate to this, but then again they might, for if you don't have the steering head tight enough, you have no firm ground on which to decipher the rest. It doesn't take whole lot for the bearings to be loose. I like to tighten them up so that I know that they're too tight on a short easy test run, and then back them off a wee bit so that they will work as they should.

[Guest KitCarson]

JimBob and the link he put up is right......a bad rim is sometimes the cause of a lot of problems. You can put on ten new tires.....but if the rim is bad, it will wobble and at speed sometimes.....no way to know when and if......with the right harmonics....will go into a tank slapper.......get the front end off the ground....rig up a stationary reference point......use whatever you have, like heavy vise sitting on a concrete block...with a pencil or something in the vise up against the rim........slowly spin the rim and see if it is out of round.....both to the side and vertically out of round..........yes an out of round rim can do what you have described also.

 

Actually you seem to have more than one problem.....you get the wobble out of the front first........then worry about if the brakes are uneven or grabbing.

[Dano]

I would do what Kit suggested, but also do it on both front rotors. A bent rotor would not have to be out much to cause a wobble. The harder you're on the brakes, the more pronounced the wobble. Or, take a test ride, then try applying the front brake only (right handlebar lever), then the combo front/rear brake. This could help eliminate which rotor. The left rotor is the handlebar activated caliper, the right rotor is hooked up to the rear.

This holds true in your car, also. It usually happens when hot brake rotors hit cold water.

Also, pull your pads and "S" sand them on 400 grit sandpaper to dull the glaze on them.

 

Just a couple more suggestions, and good luck,

 

Dan

 

PS- a warped rotor will also cause the "hit & skip" braking sensation, as if the tire is losing grip with the road.

[Neil86]

Pretty sure the front left caliper is linked with the rear caliper, right front runs from handlebar lever.

[Dano]

[quote=Neil86;164910]Pretty sure the front left caliper is linked with the rear caliper, right front runs from handlebar lever.

 

Yep, my dyslexia kicked in again! Hope it doesn't happen when I need to pull in the clutch!!!!! Thanks Neil.

 

Dan

[Gearhead]

Thanks guys, for your suggestions. Some thoughts:

 

The TCB brake thingy is interesting. Many bikers are using SS brake lines and other means to firm up the brake feel, and this thing intentionally puts some "squish" in the lever - don't quite know what to make of that.

 

Engine bolts - haven't checked, will do so.

 

Brakes binding - Interesting theory, but I don't think this is a brake problem because it shows up in other circumstances. I could be wrong. I do have a VERY SLIGHT pulsing when on the foot brake - not sure which rotor is the problem, but it's SO slight; I've had worse before.

 

Bent rim - will inspect closely.

 

Forks out of alignment - this one makes no sense to me, but I've read about it happening on BMW's. Mine appear to be parallel and the wheel travels smoothly with the springs removed, 2 to 6 thou isn't much...

 

Squeeze, I did tighten the pinch bolts progressively with the wheel off the ground. I have replaced the fork oil with 10W, and it is equal, 50CC below spec with Prog springs. Head bearings and races looked OK but maybe there is a problem there.

 

Frame crack - could be I guess. Axles OK. Front wheel lockup doesn't happen often, and it's hard to say; the wobble and partial wheel lockup occurred essentially together, although if I had to guess I'd say the partial lockup came slightly before. And the lockup wasn't sudden, like a problem with the brakes or gravel on the road, it was partial, gradual and controllable, simply a result of really clamping on the brakes.

 

2nd gen - nice bikes, really pretty, not in budget, like VR anyway! :-)

 

New front tire really reduced the mid-speed version of the front wobble, but didn't totally cure it, and the tire is not that old or worn now.

 

Head bearings could be tighter. My past experience has always been that they were best with low preload - just remove the slop and no tighter. So, it goes against my grain to crank down on ther. I have tried a couple different preloads with this bike, but could try tighter.

 

Thanks again, will check these things out. Throw any more ideas at me!

 

Jeremy

[Squeeze]

...Head bearings and races looked OK but maybe there is a problem there.

 

Frame crack - could be I guess. ...

 

Jeremy,

 

Bearing Problem might not be the Look(worn or flat Spots) but the unround Seat of the Races in the Frame. I've written about this a Year ago.

 

See, when they fabricate the Frames, the Seats are welded to the Tube in the Frame. As you know, welding always makes Things a Bit contorted, but they do nothing about that. They just press the Races in their Seats while further Production.

 

This projects the Unroundness of the contorted Seats to the inside of the Races, where the Rollers should have a consistent Contact to the Race. and this is what make Things worse. Under Pressure the Rollers get a sharp contact on one Point and loose fit on the Point 1 Degree turned left or right.

 

You can feel this while trying to adjust the Head Bearings. On one Point it will feel very tight, almost locked up, when you turn the Steering a bit to left or right you feel like you should tighten it more for the Size of the Locknut Gap. You do nothing, you move the Handlebars one more Time from left to right and it feels god to go, next Movement brings back the first Impression and so on.

 

This is why Emil Schwarz invented the glueing of the Races into the Steering Head. The Races come in a proven round Shape and because they are not forced while the Loctite 648 gets hard, they stay it that Position after the Process.

 

This results in the fine Experience that you can really ADJUST the Bearing as you think it should go, turn them tighter and the Handlebars move harder.

 

First Time, i did this to my Max, not because i have had a Problem with it, but while i was mounting my new Upside Down Forks, i needed new Bearings and Races anyway. The Result was really amazing, almost unbelievable. I did know about the Change before, and expected a Progress, but even under those Circumstances, i was very pleased with the Outcome.

 

Please don't get me wrong, i won't say that is the Solution or the holy Grail of Chassis and Suspension Works, but since i did this, i've done it on several Bikes and, together with other work related opened Nuts and Bolts, it always cured these Issues. I know, i'm talking about a hundred USD in Parts and, depending on the Tools you can utilize, between 4 and 8 Hours Work time, but can you take your Hands of the Bars at 140 mph without the Fear of another beginning Wobble Expierence ??

 

 

And, from my Expierence, even while i'm swabian and very cheap on Parts, i will never ever buy or mount cheap Aftermarket Bearings on Steering Heads or Swingarms anymore. The Material is weak, way softer than any Yammi or SKF, Timken Steel.

 

 

Cracked or broken Frame ??? I won't put one single Buck on this. But you never know. One of my often used Phrases ... "don't assume anything, check it"

[Guest KitCarson]

Darn Squeeze....now I know why German engineered stuff is so good.....that is a good post.......I have noticed that about the bearings catching in one spot....Okay I will buy German from now on:rotfl::rotfl:

[Squeeze]

Darn Squeeze....now I know why German engineered stuff is so good.....that is a good post.......I have noticed that about the bearings catching in one spot....Okay I will buy German from now on:rotfl::rotfl:

 

 

Well, buy german !!!

 

 

german Beer !!!! :cool10::cool10:

 

 

 

 

 

 

 

Sorry for my long winded "Speech".

 

I just want to have that explained with my best "Kraut-English".

 

As the Captain in Hunt for red October said to Alec Baldwin ....

"It was a long Time ago, I don't know if i'm not sure about morsing the Measurements of the Playmate of the Month or anything else" :rotf::rotf:

[CrazyHorse]

Well, buy german !!!

 

 

german Beer !!!! :cool10::cool10:

 

 

 

 

 

 

 

Sorry for my long winded "Speech".

 

I just want to have that explained with my best "Kraut-English".

 

As the Captain in Hunt for red October said to Alec Baldwin ....

"It was a long Time ago, I don't know if i'm not sure about morsing the Measurements of the Playmate of the Month or anything else" :rotf::rotf:

 

I love your guys beer and it makes you feel real good quickly.

[wild hair 39]

i cleaned the rotors with a good degreaser,pulled the calipers let them set till a little rust showed,now braking is pretty smooth,also wheel bearing,mine felt good,put new ones on,wobble is gone