Front End Wobble

[luke000]

I just took my 86 on the highway for the first time ever and there was a very pronounced wobble in my front end to the point where I would not let go, I could control it but not let go. I have brand new tires on the bike and properly inflated. I did notice that my front fork seemed soft, could this have possibly reduced my head tube angle resulting in the twitch? The wobble was about 3 times/second give or take. And it was much more pronounced the faster I went above what I would guess was 70 (my spedo cable fell out as I left my driveway). I still have my original steering bearings (did not SEEM loose when I had the bike apart) and stock fork brace and stock air springs. I might just be a hypochondriac but tell me what you think.

[Peder_y2k]

Did you install the new tires yourself? Is the front wheel properly balanced? Is there proper air pressure in the forks?

-Pete, in Tacoma WA USA

'83,88

[ChurchBuilder]

Are you sure the tires are balanced? I had a similar but less severe vibration after I put on new tires. I used Ride-On and all vibrations went away.

Also, you might check your fork brace for hairline cracks.

[luke000]

I did not mount the tires my self, I had a guy (usually does very good work and have not heard a single complaint about him from myself or anyone) mount them and he told me he balanced them.

[Brown Angel]

I used to get the trembling on the curves at a higher rate of speed, I got a nice super brace from Bongo Bob and it cured it loved it.. But do check for balance being on.

[Snaggletooth]

I did not mount the tires my self, I had a guy (usually does very good work and have not heard a single complaint about him from myself or anyone) mount them and he told me he balanced them.

 

Just to check, eyeball where the bead meets the rim to assure yourself the tire is seated completley and evenly all around the rim. I've run into a few where the tire didn't seat properly, but held air and they would shake like a dog.

 

Check for any miss weights.

 

A bad fork can affect that also. Very low oil level on one side with stock springs would add to the feel.

 

Steering head bearings adjusted and lubed?

[MiCarl]

Some things are pretty easy to check on a 1st gen....

 

Put it on the center stand and load someone into the passenger seat to lift the front wheel off. Then the following:

 

Spin the front tire. Look for any radial or lateral run out. If there is more than 2mm you've got a tire or mounting problem. Any roughness could be a wheel bearing problem or just brakes dragging a bit.

 

Turn the bars lock to lock. Feel for any binding or roughness. Resistance should be steady across the range of movement without any slight catching. Problems here are head bearings.

 

Grab the bottom of the fork legs. Pull/push forward/backward. You should feel no looseness. If you feel motion you've got a problem with the forks or head bearings.

 

Grab the wheel and push/pull forward/backward feeling for any play. There should be none. If you found some play here and not in the earlier steps you've got a wheel bearing problem.

 

Unload your passenger assistant. Check the rear tire and wheel bearings as you did the front. Feel for any play in the swing arm.

 

Report your results back here.

[bongobobny]

There are several things that cause front end wobble on a 1st gen. Tire balance, steering head bearings, shocks, and as Angel mentioned the flimsy stock fork brace. Question, did you notice oscillation before mounting the new tire?? Do you have one tire a radial and the other a bias ply?? Questions, questions...

 

Edit*** Make sure the tire is not mounted backwards!! There is a directional arrow for proper mounting on the tire...

[luke000]

Some things are pretty easy to check on a 1st gen....

 

Put it on the center stand and load someone into the passenger seat to lift the front wheel off. Then the following:

 

Spin the front tire. Look for any radial or lateral run out. If there is more than 2mm you've got a tire or mounting problem. Any roughness could be a wheel bearing problem or just brakes dragging a bit. No runout at all, tire seated properly, and only slight caliper drag (I took them off and the drag went away)

 

Turn the bars lock to lock. Feel for any binding or roughness. Resistance should be steady across the range of movement without any slight catching. Problems here are head bearings. Only binding I found I THINK is the cables no indexing like I usually find in headsets

 

Grab the bottom of the fork legs. Pull/push forward/backward. You should feel no looseness. If you feel motion you've got a problem with the forks or head bearings. No play found

 

Grab the wheel and push/pull forward/backward feeling for any play. There should be none. If you found some play here and not in the earlier steps you've got a wheel bearing problem. No play found

 

Unload your passenger assistant. Check the rear tire and wheel bearings as you did the front. Feel for any play in the swing arm. Rear seems to check out as well

 

Report your results back here.

 

I am stuck It might just be wind that day or something else. I never took the bike on the road what so ever before the new tires. And I think I mentioned before anything under Highway speeds is sooth as a Swiss watch.

[Peder_y2k]

Maybe the new tire just needs to be 'broken in', or, maybe it was the road causing the symptom.

-Pete, in Tacoma WA USA

'83,88

[MiCarl]

My 89 has the flimsy fork brace. Never had a situation like you describe, even in heavy wind.

 

Something isn't right.

 

Another thought is to make sure the forks are tight in the tree and same height.

 

These can be tricky. I had a friend/customer claimed her RSTC had severe head shake. Her husband had no problem and it rode like a dream for me. Passed all the tests I had you do.

 

I repacked the head bearings using moly grease and she says it's fine now.

[luke000]

My 89 has the flimsy fork brace. Never had a situation like you describe, even in heavy wind.

 

Something isn't right.

 

Another thought is to make sure the forks are tight in the tree and same height.

 

These can be tricky. I had a friend/customer claimed her RSTC had severe head shake. Her husband had no problem and it rode like a dream for me. Passed all the tests I had you do.

 

I repacked the head bearings using moly grease and she says it's fine now.

 

Ok I think I will grease my steering bearings and re-torque everything and see if that does anything. I am also very tempted to do a progressive spring set. How hard is it to do the springs? Keep in mind I am a mountain bike mechanic and I am used to working on some of the most advanced suspension on 2 wheels. I am just wondering how much of the bike needs to come apart and is it a matter of just dropping in the springs or do I have to gut the system of some sort of air spring cartage?

[Snaggletooth]

If all you want to do is change to the Progressives it's quite simple. Loosen the top pinch bolts on the upper tree and remove the top caps from the forks, slowly to bleed off any air pressure.

 

Fish out the OEM spring spacers and springs. Drop in the new Progressives, set the preload with the new spacers, set the fork oil level and cap it back up. Tighten the pinch bolts back up and you're done.

 

Of course you might want to bleed out the old oil and pump up the new but it's a pretty simple operation for a straight change out.

[MiCarl]

If you're going to do the steering bearings I suggest you go ahead and pop new ones in. You're already doing most of the labor so you might as well have new ones.

 

As Snaggletooth explained, replacing the springs is a pretty minor job. Since you'll be tearing the front apart anyhow it'll add just minutes to the overall job. I'd replace the fork oil while at it, let them bleed out while you do the rest of the job.