Topic: Incurable front end shimmy

[fatmatt650]

I purchased a 1977 Cb750F several years ago from the original owner. She said she'd dropped it pretty hard in traffic once and never really rode it much thereafter. I did the standard fluff and buff on a bike that's been garaged for 30 years and have since put many miles on it but I'm considering getting rid of it due to a persistent front end wiggle. I've been through several sets of tires and have had them balanced once by a professional. It got slightly better after the balancing but was still there. I use it mainly for loaded touring and that is when the wiggle is worst. If I let go of the handlebars it begins a terminal shimmy that is very disconcerting when you just want to stretch your back for a sec. I've rebuilt the headset several times and it appears to be in perfect condition and adjusted perfectly but have not replaced the front wheel or tried Allballz tapered roller bearings yet. I'm wondering if I should try both of these remedies before ditching the bike or if it's pointless. Anyone have any experience w/ this issue?

[flybox1]

Ever pay any attention to the rear?
Swingarm bushings, Bearings, etc....

[fatmatt650]

I've inspected everything for play and found nothing. The bike had less than 3,000 miles on it when I got it so I doubt it's from excessive wear in other areas. It currently has about 17k on it and the issue hasn't changed much since I first got the bike.

[robvangulik]

No defect is incurable!
When you find the cause, it can be fixed.
Is the frame straight, are the wheels in line, wheel bearings okay, fork legs straight, tyres front AND rear round, enough tread, balanced and enough pressure, is the engine firmly bolted in the frame....all possible causes for shimmy.

[oldhatt45]

fatmatt650,

One thing to look at is the side to side position of the Front Wheel.
From the one picture, I'm not sure if your bike has spokes or Comstars.
If it has spoked wheels, One of the things that often went unnoticed on (at least the CB's) is the fact the front wheel is likely offset (side to side) by 3 or 4 mm.  You should give that a look if your bike has spoked wheels.

Hope this helps,

Charlie

[70CB750]

Ever pay any attention to the rear?
Swingarm bushings, Bearings, etc....

That!

[chewbacca5000]

I would wonder about frame straightness, but should be ok if it was just a drop and not an accident.

Just becuase the bike only has 3,000 miles does not mean all your bearings are good.  I have taken apart 3 full sets of wheels lately and found maybe one good bearing out of the 6.

That 30+ year storage can cause grease to dry out and there is a good chance there is rust in there.  Doing wheel bearings is easy with the right tools.  ie. bearing remover from pit possie, and the right size drill bit 3mm.

Drill out the old peen, be sure to go deep enough and the old retainers come out fairly easily.

The tappered bearing are what people get for that shaky head.  I had one could not take hands off the bars at all.

[calj737]

Have you greased the swing arm? Mileage isn't the issue, age is. Tire pressure too is paramount when diagnosing wobbles.

A bike that's been dropped wouldn't usually bend forks, but it certainly can bend the steering stem, damage swing arm bushings, or taco a wheel. Has the wheel been re-trued (spokes)?

[Don R]

My thought was wheel trueness. Is that a word? I'd go for some tapered bearings too. I have a K0 that had the wobblies, it was the neck bearings, made worse by lowering blocks. When I opened up the neck it already had tapered bearings in it but they were dinged.
 Due to age the wheel bearing grease can be dried up too.

[DH]

Have you greased the swing arm? Mileage isn't the issue, age is. Tire pressure too is paramount when diagnosing wobbles.

A bike that's been dropped wouldn't usually bend forks, but it certainly can bend the steering stem, damage swing arm bushings, or taco a wheel. Has the wheel been re-trued (spokes)?

+1...............And check if the steering stops and plate on the frame are bent, and to what degree. It can sometimes be an indicator of how severe the lay down.

[przjohn]

Don't take your hands off the bars.  KTM990ADV bikes are notorious for this and the best guess so far from the Peanut Gallery is the Pirelli front tires. Changed mine to Contis and the dreaded head shake after letting go of the bars disappeared.

[Jerry Rxman Griffin aka MuthaF'er]

Tapered bearings and bronze bushings in the rear. Process of elimination if something isn't obvious.

Nice looking pair of F's!

When it was dropped there is a possibility the fork tubes and the triples twisted a little. Make sure that's all aligned correctly.

[evanphi]

Make sure your your wheels/tires are balanced AND trued.

Bent swingarm?

[madmtnmotors]

Heavily loaded will amplify any issues. I would grease the swingarm and switch to tapered neck bearings up front. While the forks are off, go ahead and disassemble them, new fluid and seals, and check the tubes for straightness. My money is on bent fork tube and or bent rim. You mentioned having the tire balanced, but did they check the runout (in/out and up/down) for trueness of the rim?

"Dropped it pretty hard in traffic" makes me suspect fork tubes. They are susceptible to damage and I believe the weakest link.

[Retro Rocket]

Try loosening the forks in the triple clamps and realign them, have a real good look at your front tire, I've seen some pretty bad wobbles caused by poor tires, poor fitment and worn tires. +1 to checking every thing else mentioned here...

[toobad]

I have a 73 CB500 that had a bad "vibration" problem at 45 mph.  Solved it by replacing the ball bearings with quality tapered bearings.  I also have spoke wheels with an extended fork.  I would try the tapered bearings.  Funny thing was the guy at the bearings parts outlet nailed it after he heard my bike was a CB500.  Said he gets calls all the time and the tapered bearings always solve the vibration.  If your is hard core wobbles then this might not work for you.  Good luck!

[SOHC4 Cafe Racer Fan]

Have you eliminated the possibility of a bent frame?

[jdubb1977]

My '76 750F had some serious wobble when I bought it. Turns out one of the fork springs was broken in half. Just another place to look.

[MCRider]

Speaking of tiires... even good looking, low mileage ones will produce a shimmy if they are 5+ years old or more and subsequently hardened with age.

That has been the fix (new soft rubber) for a few of members with this problem.

[Tim2005]

You didn't buy that in the Boston area, did you? I had a very similar looking bike with a very very similar sounding shimmy- which would particularly happen when braking into downhill corners. Quite scary indeed, I've never ridden another bike that behaved like that. The bike had several things that were a little wrong but I could never find anything that was the underlying cause... I only had it for a few weeks when I was out in the US for a trip, and so "Old Shakey" is out there somewhere still...