Chevrolet C60s - Front Wheel "shimmy"

[cordenj]

Thought I'd update on the continued frustrations of the wheel shimmy.

The parts arrived from Dirk very efficiently and we fitted the pivot bearings on the side where they had been over shimmed and damaged in the past.

I made up the special tool from the "Sept 43 Service Information Bulletin", to enable me to put tension on the Pivot Pin to correctly set the bearing tension.

While this was going on I had a pair of 3 degree and 6 degree wedges made at a local engineering shop

[cordenj]

I dropped the front axle and found that a previous owner had installed very small wedges....so clearly the castor angle has been a problem before.

I fitted the 3 degree wedges and then had to wait a month while a had the master cylinder rebuilt and brake hoses remade.

I've put up photos here, as while there is a lot of talk about wedges on the forum, I'd not found any photos of the job in progress.

So tonight was the first test drive with 3 degree wedges fitted.....and?

Made no difference at all! Bit disappointing, hit a small bump in road and got violent shimmy.

All I can do now is drop the axle again and try to 6 degree wedges to see if that works over the weekend.

It feels like I should be getting somewhere with this, especially as very small wedges had been fitted before

[Bob Carriere]

There has to be some looseness somewhere......

Reading back on previous postings......

There seemed to have been some improvements when the steering box was adjusted..... would it be worth while revisiting....or even doing a total disassembly of the gear box for a visual inspection of parts for unusual wear patterns.

Were the steering linkage taken appart for inspection.... I know I have taken some apart that had eggshape wear pattern on the round pivot balls or weak/collapsed springs.

Same could be said of the tie rods.... not sure if they are all meant to be taken apart but some I did and found some were good some were worn oval over the years of service.

Did you rotate the tires before your last road test. would it be possible to borrow a full set of wheels from a cooerative friend and do the road test again????
A bad set of already cupped tires could be a nasty composition to overcome.

Wishing you luck and will eagerly follow your trials and eventual tribulations in my search of knowledge.

Cheers

[Richard Farrant]

John,
Have you physically checked the shock absorbers for correct functioning? Not sure I have seen mention of them. I would borrow a pair of good known tyres and wheels to eliminate them also the road springs do look a bit flat. What is the condition of the spring shackle pins and bushes?

regards, Richard

[cordenj]

Thanks Bob/Richard,

I had suspected the replacement secondhand bar grips from the start, as I didn't get shimmy on the previous tyres that had a much "squarer" shoulder (but only did few miles on them before changing.

I can try to borrow a pair of wheels/tyres, but also have a pair of new modern 11x20s bar grips being delivered to W&P, so perhaps will fit them to see what happens.

The springs are definitely past their best and when the weight is on them, sit flat. Am trying to find a leaf spring refurbisher in south-east.

Will keep you posted on the 6-degree wedge test!

[Richard Farrant]

Originally Posted by cordenj

Thanks Bob/Richard,

I had suspected the replacement secondhand bar grips from the start, as I didn't get shimmy on the previous tyres that had a much "squarer" shoulder (but only did few miles on them before changing.

I can try to borrow a pair of wheels/tyres, but also have a pair of new modern 11x20s bar grips being delivered to W&P, so perhaps will fit them to see what happens.

The springs are definitely past their best and when the weight is on them, sit flat. Am trying to find a leaf spring refurbisher in south-east.

Will keep you posted on the 6-degree wedge test!

OK John.
Hope the tyres correct the problem. See you at the show.

regards, Richard

[Private_collector]

I get the same shimmy on my F15. It usually happens immediately after bounding out of a moderate pothole, of which we have MANY around my area. Have not had a chance to crack open the steering box yet, just learnt to tolerate the problem for now. I find the shimmy worsens quickly if I don't make a correction immediately. If a little steering force is applied L or R, then the wobble can be stopped in it's tracks. The first time it happened, I nearly pooped myself, because it was VERY violent. I hadn't learnt how to stop it at that stage, and because it was an isolated country road, I went for the brakes! It sure stopped the wobbles, because the truck literally came to a screeching halt. The silver lining was that I discovered the braking system is extremely good.

Curiously, I have not had this problem at a reasonable speed! In fact, once I go over 40-50km/h I can relax. Perhaps centrifugal force stops the problem occuring at higher speeds?!?! I do know the springs are good, so they shouldn't be an issue. Can't speak for the steering linkages, except they have no play which can be induced, or which is observable with movements of steering wheel back and forth. In fact even minor movements result in that movement being visible right through to the wheels. Can't feel any play in steering box at all, so the almost continual but very minor corrections needed to keep on course has me intrigued. For now, I am trying to resist the urge to disassemble the steering box, because I know it will become a full rebuild that I can't really spare the cash for just yet. Besides, I wouldn't be able to enjoy the challenge of driving a CMP.

The tyres I have on, are almost new. They are, however, Indian imports. If left sitting for some time (>1-2 days), they develop a flat spot that takes a couple of km driving to disappear. Once tyres are warmed up, they are fine. I think they have a bit of road noise, but can not really tell. The diesel engine is too noisy for me to be certain.

In near future I will be swapping the current tyres for a set of new NDBT ones. I will be curious to see if that change makes much, if any, difference to the wobbles. I will get the new ensemble professionally balanced before they are put into service. The current tyres/wheels had been balanced too, so I assume that isn't contributing (how's that for optomism!).

I am following this thread very closely. While certainly no comfort to know others are suffering same scenario, the suggestions are very, very, valuable to me, and if the tyre change doesn't fix the issue, the suggestions will assist me to know where to look next.

Thanks, to all contributors here

[gordon]

One thing I don't see specifically addressed is wheel straightness.

It's fairly easy to bend one of these rims, and you may have had the front wheels balanced but I'll bet they weren't turning very fast while they did it.

If it was OK before the replacement tyres, and isn't now, it may just be that one of the wheels is slightly bent, was on the rear, and you have put it on the front.

[Bob Carriere]

Hi John

As suggested by Richard, when you do the springs have a close look at the spring pins and bushing they can really wear off to a loose oval and I beleive Dirk still has them in stock...... that may be the last weak/loose link.

My worst shimmy experience was witrh a DOdge M37 thast had worn out tapered holes where the tapered tie rod fitted into...... had to replace the whole lower unit of the eggcup. The front suspension got worn that way after one Winter of driving with chains on the front axle. It shook so bad we had to come to a stop whenever we drove across a level rail road track crossing.

Good luck.