Chevrolet C60s - Front Wheel "shimmy"

[cordenj]

I'd welcome any thoughts on why this is happening and suggestions for curing it.

Tyres: 10 x 20 Bar grips (good secondhand)

Wheels: standard splitrims. I have had the two front wheels professionally balanced in an attempt to cure this. One wheel required significant number of lead weights to be pronounced suitably balanced. Had hoped that would cure it, but sadly not.

Tyre Pressure: 43psi in each side

Symptoms: At any speed above 20 mph the front wheels can suddenly start to violently "shimmy", usually triggered by a pot-hole (of which we have many in UK!). Slowing down causes the "shimmy" to slow and stop and the truck can then be driven on without coming to a complete halt. I say it is violent because the steering comes "alive" and when viewed from outside the cab appears to shake.

Checks I've carried out so far:
1. Checked tyre pressures to be 43psi

2. Checked wheel balance weight still on rims

3. Checked toe-in by stretching thin cord across face of fitted tyres and aligned to rears as I would for the Jeep. Very slightly "toed-in" - about 3/8 in . Manual say should be zero.

4. Camber: With wheels jacked off the ground, measured camber with spirit level. Found LHS wheel to lean out 1 1/4 in across the diameter of the tyre.
RHS wheel lean out just 1/4 in.

I probably should I check these again with the wheels on the ground, but is this a significant difference on these trucks?

5. Steering: With wheels jacked off the ground, about 2 inches movement in steering wheel rim before wheels start to move. Is this within reasonable limits for a CMP C60? My Jeep has similar play but does not shimmy.

6. Wheel bearings: with wheels jacked up, wheels rotate freely and there is no obvious play when the top of each wheel is pulled in and out.

7. Steering tie-rod: levered rod to see if any excessive play or movement. None visible.


Any thoughts or ideas based on experiences with these trucks are very welcome as the truck isn't driveable for any distance like this.

Many thanks

[Mike K]

I have seen that type of thing before .

It can be caused by badly adjusted or incorrectly fitted king pin / swivel bearings . Does your vehicle have tapered roller bearings on both the upper and lower sides ? The pre load on the swivel bearings needs to be set according to the manual . Some of these older 4X4's used a bronze cone on one side, Dodges I think . Mike

[Ron King]

Yes king pin bearings worn or not enough bearing preload.
Check caster too and add caster spring wedges if nessary.

[rob love]

The jeeps have always been especially susceptible to that and it is common enough to have the nickname "death wobble". First time I have heard of it on a CMP, but the reason will be the same: worn and out of spec steering components. It won't necessarily be one thing, but more likely a combination of several.

The kingpin bearings on the CMPs are a chronic problem, and hard to find. But you can add to that the general wear through the system. It is usually only two of them that take the load (can't remember if it is the uppers or the lowers, but if you disassemble them that far you will know soon enough). You can be a bit inventive and repack them, although they are not meant to do so. Some here have replaced them with standard tapered bearings along with some adapters. Likely a better choice, although you will be cutting some shims to get the preload right.

I would suggest biting the bullet and taking it to a truck service center who can properly do an alignment. They very likely won't be able to do the alignment, but will give you a list of things wrong that need fixing first.

A bandaid solution to the death wobble is to give it a bit more toe in. Mind you, if you truly have 3/8 of an inch, that would seem to me to be quite a lot already. More toe in will of course cause more wear to the tires, but how many miles do you put on your truck anyway? Another solution is the installation of a steering damper, but that is of course un-original.

I don't like to suggest bandaid solutions to things like brake or steering, as the end results can be bad.

[chris vickery]

Another place often overlooked on MVs is the pitman arm ball as well as any other components like drag link etc.
The pitman arm ball end is often worn with flat spots and the bearings wear. Sometimes these are overly loose as well.
As Rob stated, things like steering and brakes are the most important.
Loss of control can mean loss of your life.
Do it right.

[Hanno Spoelstra]

John,

The RNLA CGT suffers from the same problem: severe shimmy above 25 mph. In between The Final Push liberation tours I checked for any visible play in the steering components. We found play on the drag link and adjusted it, which helped. The shimmy was not gone, but played up at higher speeds and a lot less severe.

Like the others have said, check for play and make sure the axle and steering alignment - wheel camber, axle caster and wheel toe-in - are up to spec. Do you have a maintenance manual? If not let me know, I will scan the relevant pages for you.

If it turns out the pivot pin bearings are worn out: they are available (contrary to popular belief).

HTH,
Hanno

[cordenj]

Thanks everyone for thoughts.

I've looked at my manual to get suggested solutions and specs,

One thing I am going to go through, and follow the sequence in the manual, is the steering box adjustment.

The truck has done relatively few miles in the 9 years since it was completely rebuilt, so doubt the bearings are worn out IF they were replaced or fully checked during the rebuild.

[Phil Waterman]

Hi

In 30 years of driving CMPs I've had this problem with all three of my trucks. In each case I've done as suggested check setting, looked for play installed heavy-duty steering damper. All good things to do any way, some improvement but no complete fix, but each time changing the tires solved the problem or moved the speed that it starts at well above normal driving speed.

My C60S is the happiest highway truck of the three, even with the radio box the 261 engine and 11:00x20 tires it is smooth at 50-60 MPH ( with 11:00 tires the truck thinks it is doing 50 ) All three of my trucks have recent manufacture new tires. My C60L has a little shimmy as you get to 45-50 MPH which I suspect is from no front shocks which is letting little wheel hop feed in to steering. I suspect that the steering geometry of the pitman arm steering connector link is not perfect that allows the up down motion to be converted to lateral motion in the steering. Will see if this goes away once the shocks are bolted in.

Given my experience would try the following with the wheels jacked up take large block position so it just doesn't touch the tire hold something on the block and slowly turn the wheels to mark a line down the center of the tire. Then look at your line is it staying centered on the tread and did then your marker try to move in and out as you turned the wheel. Assuming the tires are running true an are not egg shaped, then would try moving your tires around front to rear side to side, does the shimmy change?

Cheers Phil

[cordenj]

Originally Posted by Phil Waterman

Given my experience would try the following with the wheels jacked up take large block position so it just doesn't touch the tire hold something on the block and slowly turn the wheels to mark a line down the center of the tire. Then look at your line is it staying centered on the tread and did then your marker try to move in and out as you turned the wheel. Assuming the tires are running true an are not egg shaped, then would try moving your tires around front to rear side to side, does the shimmy change?

Thanks Phil,
I did wonder if changing the tyres was partly the cause. The ones on it when I bought the truck last autumn were very badly cracked - so I sourced some good secondhand 11x20s from a Bedford RL. But didn't get to drive it very fast with the old tyres, so I don't know if the shimmer was there.

I'd have hoped that the professional balancing of the front wheels/tyres would have highlit any defects, but I'll try your recommendation.
I might also take up a offer to try some other wheels with 12x20s fitted to see if that cures it.

[lynx42]

Check the caster. My C60S was more than terrible and I found that the front springs had sagged a bit and the caster was way out.

I machined up a pair of wedges to, from memory, 9degrees and fitted them from the rear. Shimmy gone straight away even with old tyres.

Regards Rick.

[Lynn Eades]

Many types of 4 wheel drives can suffer from this. To eliminate the problem requires that all aspects of the front end are up to spec.after an initial general check, I would check the king pin preload (as previously suggested) Every thing helps to either eliminate or compound the problem. Things like lateral float at spring shackles, spring set (loss of castor) a slightly grabbing brake. Tyre, wheel, brake drum balance, out of round, wheel bearing play, any aspect of a tyre (off set in mold?)that is not perfect is detrimental. (some tyres will go out of round when parked with a load on them, and will not come right until they are once again warm from driving)

If the truck has Timken taper rollers as king pin bearings (Dodge used bronze upper cones in a Timken cup (I suspect they had condensation problems rusting the upper cones) they wear in one place becoming loose in the straight ahead position. Correct preload causes a somewhat alarming distortion of the housing but they then drive well (assuming everything else is good as mentioned previous posts)
Another possibility is the state of the universal joint in the front half shafts, and also the centering of the joint on the king pin axis line (shimmed in a jeep, depending on axle joint type)

Any one of these things can help to set off this shimmy.
Hope this is food for thought.

[David Dunlop]

John.

I had the same problem with an M38. After a wheel balance failed to cure it, I started checking everything from the steering knuckles inward and up to the steering box, replacing every suspect bearing, pin and tie rod end. The problem gradually improved as each suspect part disappeared from the system, but still showed up whenever I hit a serious pothole or bad railway crossing. At that point i noticed the front spring assemblies had a noticible lack if arch to them. put new springs, shackes and pins on the front end and problem finally solved. Never came back either.

As others said, it is an area where a number of smaller problems seem to add up and have a very alarming effect. Definitely an area where it pays to take your time sorting it out.

David

[motto]

Mention has been made of wheel balancing but what type of balance was done, static or dynamic?
Static balancing has definite limitations in that the location of the 'heavy spot' is not defined axially i.e. it may be toward the inside or outside of the wheel. When weights are added to 'balance ' the wheel they can be just as easily be put on the opposite side of the wheel to the heavy spot and make the dynamic imbalance worse.
Dynamic, on vehicle balancing is a far better option if you can find someone with the equipment to do it as this removes the unknown and also takes the hub and drum into account.

David

[Lynn Eades]

Wheel balance would generally be less of a problem with big old M.Vs. than the likes of modern vehicles with smaller dia. wheels traveling at higher speeds.

In saying that, I do not disagree with any of the above.

John If you have measured correctly then something is definately wrong (1" difference in camber??) were you on level ground to start with?

Jack it up and see if you have any play in the vertical plane (grab the tyre top and bottom and try to wobble the wheel)
If there is any movement get someone else to apply the brakes and try it again
If the movement has gone, it is wheel bearing adjustment. If it is still there, it is in the king pins.
You also need to deal with the toe in as well. 3/8" will be scrubbing the hell out of your tyres with each wheel trying to go in different directions.

If you disconnect the drag link (steering arm end)and then swing the wheel asemblies through their steering arc (left and right) you may be able to pick up any roughness in the king pins.

If you do have to do king pins, keep in mind that king pin bearing preload is normally set without the knuckle seals fitted.

[rob love]

Originally Posted by Lynn Eades

If you disconnect the drag link (steering arm end)and then swing the wheel assemblies through their steering arc (left and right) you may be able to pick up any roughness in the king pins.

Not sure one can swing a pair of 20" tires with the wheels still on the ground unless you have a pair of alignment plates underneath. If the axle is jacked up and the wheels are in the air, then the problem may not be evident as you have transferred the weight away from the kingpin normally under load to the kingpin that normally does not carry a load.

[cordenj]

Originally Posted by lynx42

Check the caster. My C60S was more than terrible and I found that the front springs had sagged a bit and the caster was way out.

I machined up a pair of wedges to, from memory, 9degrees and fitted them from the rear. Shimmy gone straight away even with old tyres.

Regards Rick.

Thanks Rick,
I'd not measured the castor as have never needed to consider that on other vehicles I've had . I see the manual says 1 1/2 - 2 inches, so will check

[cordenj]

Originally Posted by David Dunlop

John.

I had the same problem with an M38. After a wheel balance failed to cure it, I started checking everything from the steering knuckles inward and up to the steering box, replacing every suspect bearing, pin and tie rod end. The problem gradually improved as each suspect part disappeared from the system, but still showed up whenever I hit a serious pothole or bad railway crossing. At that point i noticed the front spring assemblies had a noticible lack if arch to them. put new springs, shackes and pins on the front end and problem finally solved. Never came back either.

As others said, it is an area where a number of smaller problems seem to add up and have a very alarming effect. Definitely an area where it pays to take your time sorting it out.

David

Thanks David.
Yes I think it is a case of slowly working through the possible causes. That is why everyone's thoughts here are very useful

[cordenj]

Originally Posted by motto

Mention has been made of wheel balancing but what type of balance was done, static or dynamic?
Static balancing has definite limitations in that the location of the 'heavy spot' is not defined axially i.e. it may be toward the inside or outside of the wheel. When weights are added to 'balance ' the wheel they can be just as easily be put on the opposite side of the wheel to the heavy spot and make the dynamic imbalance worse.
Dynamic, on vehicle balancing is a far better option if you can find someone with the equipment to do it as this removes the unknown and also takes the hub and drum into account.

David

Hi David,

They were static balanced (on a large machine but off the vehicle) at a specialist truck tyre company. The wheels ended up with weights on both inner and outer faces. Before I changed the tyres, the wheels had large amounts of weight added so clearly been balanced before; so thought that might be the shimmy cause.

[cordenj]

Originally Posted by Lynn Eades

Wheel balance would generally be less of a problem with big old M.Vs. than the likes of modern vehicles with smaller dia. wheels traveling at higher speeds.

In saying that, I do not disagree with any of the above.

John If you have measured correctly then something is definately wrong (1" difference in camber??) were you on level ground to start with?

Jack it up and see if you have any play in the vertical plane (grab the tyre top and bottom and try to wobble the wheel)
If there is any movement get someone else to apply the brakes and try it again
If the movement has gone, it is wheel bearing adjustment. If it is still there, it is in the king pins.
You also need to deal with the toe in as well. 3/8" will be scrubbing the hell out of your tyres with each wheel trying to go in different directions.

If you disconnect the drag link (steering arm end)and then swing the wheel asemblies through their steering arc (left and right) you may be able to pick up any roughness in the king pins.

If you do have to do king pins, keep in mind that king pin bearing preload is normally set without the knuckle seals fitted.

Hi Lynn,
I rechecked the camber with wheels on level ground, the figures decreased slightly on both side with the weight of the truck on them, but still a difference between left and right hand side.
With the wheels jacked up, I tried shaking wheels to see if any play. There was no perceptible movement, even with a lever under the wheel, so that implies to me that the bearings are not too loose. The wheels rotate freely too, so no reason for possible "grabbing" being the cause.

[Dave Mills]

I am certainly no expert on the CMP and have watched with interest the conversation. I am delving into the unknown here but may I suggest that you check your shock absorbers. If you have checked everything else it seems like you may need to check these, if they are faulty they can cause a shimmy once you increase speed and hit any form of undulation in the road surface.

Dave.

[jake neville]

our marmon herrington gun tractor had this same problem when we first put it on the road. the entire front axle had been overhauled and the wheels balanced. when it got around 20mph it started shaking so violently it was dangerous and uncontrolable. we fitted castor wedges to the front which made a big difference. it now only comes in mildly when you hit a bump around 50mph.

robin mawson had similar problems with his white scout car. he played around with his for quite some time. tried a number of things and still had problems. eventually he tried ajusting the toe in more than what it said to in the book. no shimmy at all from zero to flat out.

we are planning to try the same on the marmon when we get time. this obviously increases tyre ware but for the amount we drive these old trucks waring out tyres is highly unlikely.

give it a try?

[Mike K]

Originally Posted by jake neville

we fitted castor wedges to the front which made a big difference. it now only comes in mildly when you hit a bump around 50mph.

50 mph in a M-H - YOUR KIDDING So what brand of turbo have you fitted on that flathead

[cordenj]

Thanks for advice everyone.
Now off to celebrate 70th Anniversary of the liberation of the Channel Islands (well Guernsey) for a week.

Sadly not in the Chev as planned until this wheel issue is resolved, so having to take the Jeep and one of my trailers.

I'll investigate the shimmy more on my return.

[Bob Carriere]

Based on all the work that has been done already .....

Start with the tie rod ends....... they can be disassembled to visually verify wear...... not unusual to see oval wear spots. Look at the tapered hole where the tie rod connects to the eggcup..... in some case the tapered hole has gone oval...... they can be machined larger and a new tapered insert manufactured.

Then move on the steering arms..... take them apart...again not unusual to find some round pins with significant wear spots..... then move on to tighten the steering box..... which you may need to remove and look at the innards .

If none of that improves the shimmy look at totally disassembling the front axle egg cups...... there are NO cone bearing in the CMP like the Dodge axle. You will be looking at the New Departure 928 bearings mounted on solid pins... they should be hard to remove as they are a tight fit..... any looseness or wear patterns should be visible to the naked eye...... when removing the end caps you will find small circular shims.... save them and keep track of how many which side.....when you reassemble you need to preload the bearing as per the manual. Dirk as the New Departure bearings and use to have spare shims..... other wise start buying front axles for spare parts. I have taken CMP front axles apart that the New Departure bearings where literally worn out and fell apart in my hands. Old bearing if good are usually a tight fit and and need to be pulled out and pressed back in place.

From my experience you need to start at the wheel bearings which has been addressed then move on to the next connection point one step at a time.

I know you can ruin the front axle of a Dodge M series in one Winter of driving with wheel chains..... the solution was to have the oval holes of the front axle flange drilled out and new tapered inserts pinned in place..... it would have been cheaper to buy a scrap M37 for parts. The tie rod ends were also replaced at the same time.

Good luck.

Bob C

[cordenj]

Back from the Guernsey 70th Anniversary trip (in the Jeep) and now back to trying to resolve the Chev's Wheel Shimmy.

As two heads are better than one, I asked good friend, expert mechanic and fellow CMP owner, Andy to give me a hand to investigate further.

We spent all day yesterday working through the front axle.

Started by checking and slightly tightening the steering box. A test drive showed some improvement but a dose of major shimmy meant more investigation was required.

As some have said here, we think this is a combination of different factors that cumulatively cause the issue.

So logically it is a case of going through each possible cause and trying to eliminate it ,apart from what I've already listed earlier in the thread:

1. Steering Gear - checked, adjusted and ok
2. Front Axle tie rod - checked and in good condition
3. Wheel bearings - both sides are correctly set and in good condition
4. Pivot Pin bearings:
Near-side_steering knuckle binding slightly in the the chromed housing. Checked shimming and reset to avoid binding. Both bearings in good condition.
Off-side_steering knuckle binding in the the chromed housing. We think this side was overshimmed and had placed great pressure on the Pivot Bearings....unfortunately both need to be replaced....so will be trying to contact Dirk or Stefan on Monday for replacements.
We suspect that this wheel shimmy is not a new issue on this vehicle and that the bearings had been very tightly shimmed in an attempt to stop it.

5. Front springs - The photos below show the front springs, which have clearly sagged over the last 70 years......and as several posters on this thread have suggested, this is probably the a major contributor to the shimmy issue and the caster will be way out.
Close examination of the photos show some small wedges have been fitted in the past. My plan now is to try to get a pair of larger wedges machined a at a local engineering shop.

Once new Pivot bearings hopefully sourced and are fitted and the new wedges are placed between the spring and axle....and we'll see what happens.

Can't help feeling the real solution is a replacement set of good front C60S springs which can restore the correct caster. Anybody know of any in UK, Belgium or Netherlands?

[rob love]

You could take the springs to a good spring shop for re-arcing. Springs are "bull-work" and I have always generally found having this done to be very reasonably priced. The shop will dis-assemble the complete springs, re-arc each leaf, install slip pads and rebound clips as necessary, reassemble them, and you can do the spring bushings at the same time.

Just make sure they don't over do it. We used to have empty trucks leaving the shop looking like they were carrying tons of weight becaue the front ends would sit higher than the back.

[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