MLU FORUM  

Go Back   MLU FORUM > MILITARY VEHICLES > The Softskin Forum

Notices

Reply
 
Thread Tools Display Modes
  #1  
Old 03-05-15, 14:03
cordenj's Avatar
cordenj cordenj is offline
Registered User
 
Join Date: Mar 2009
Location: Surrey UK
Posts: 162
Default Chevrolet C60s - Front Wheel "shimmy"

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
__________________
John.
1943 Chevrolet C60s Wrecker;
1944 Chevrolet C8a HUP ZL-2
1944 Willys MB (British Guards Armoured Div);
1944 BSA Folding Bicycle (Best "Para Bike" at War&Peace Show 2011, 2012, 2014 and 2015);
Trailer, 10cwt, Water Lightweight, 100gallon;
Trailer, 10cwt, Cargo Lightweight 10cwt No1 MkII;
Trailer, 10cwt, Electrical Repair Mk.2; Ex-Airborne REME;
Trailer, 10cwt, Lightweight, Electric Welding Mk 2
Reply With Quote
  #2  
Old 03-05-15, 14:32
Mike Kelly's Avatar
Mike Kelly Mike Kelly is offline
Fan of Lord Nuffield
 
Join Date: Feb 2003
Location: Victoria Australia
Posts: 4,069
Default king bearings

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
__________________
1940 cab 11 C8
1940 Morris-Commercial PU
1941 Morris-Commercial CS8
1940 Chev. 15cwt GS Van ( Aust.)
1950 Land Rover signals replica
Reply With Quote
  #3  
Old 03-05-15, 15:08
Ron King Ron King is offline
Registered User
 
Join Date: Apr 2011
Location: Nowra NSW Australia
Posts: 78
Default

Yes king pin bearings worn or not enough bearing preload.
Check caster too and add caster spring wedges if nessary.
Reply With Quote
  #4  
Old 03-05-15, 15:13
rob love rob love is offline
carrier mech
 
Join Date: Feb 2003
Location: Shilo MB, the armpit of Canada
Posts: 6,545
Default

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.
Reply With Quote
  #5  
Old 03-05-15, 16:11
chris vickery's Avatar
chris vickery chris vickery is offline
3RD ECHELON WKSP
 
Join Date: Feb 2003
Location: Nipissing Ontario Canada
Posts: 2,778
Default

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.
__________________
3RD Echelon Wksp

1968 M274A5 Mule Baifield USMC
1958 M274 Mule 2cyl (4cyl engine waiting for transplant!)
1970 M38A1 CDN3 70-08715 1 CSR
1981 MANAC 3/4T CDN trailer
1983 M1009 CUCV
1971 M35A2
1956 M135 56-54921

RT-524, PRC-77s,
and trucks and stuff and more stuff and and.......

MLU, MVPA, G503, Steel Soldiers
Reply With Quote
  #6  
Old 03-05-15, 17:28
Hanno Spoelstra's Avatar
Hanno Spoelstra Hanno Spoelstra is offline
MLU Administrator
 
Join Date: Feb 2003
Location: The Netherlands
Posts: 11,998
Default

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
Reply With Quote
  #7  
Old 03-05-15, 18:43
cordenj's Avatar
cordenj cordenj is offline
Registered User
 
Join Date: Mar 2009
Location: Surrey UK
Posts: 162
Default

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.

.
__________________
John.
1943 Chevrolet C60s Wrecker;
1944 Chevrolet C8a HUP ZL-2
1944 Willys MB (British Guards Armoured Div);
1944 BSA Folding Bicycle (Best "Para Bike" at War&Peace Show 2011, 2012, 2014 and 2015);
Trailer, 10cwt, Water Lightweight, 100gallon;
Trailer, 10cwt, Cargo Lightweight 10cwt No1 MkII;
Trailer, 10cwt, Electrical Repair Mk.2; Ex-Airborne REME;
Trailer, 10cwt, Lightweight, Electric Welding Mk 2
Reply With Quote
  #8  
Old 03-05-15, 20:36
Phil Waterman's Avatar
Phil Waterman Phil Waterman is offline
Super Moderator
 
Join Date: Feb 2003
Location: Temple, New Hampshire, USA
Posts: 3,829
Default May be tires

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
__________________
Phil Waterman
`41 C60L Pattern 12
`42 C60S Radio Pattern 13
`45 HUP
http://canadianmilitarypattern.com/
New e-mail Philip@canadianmilitarypattern.com
Reply With Quote
  #9  
Old 03-05-15, 21:01
cordenj's Avatar
cordenj cordenj is offline
Registered User
 
Join Date: Mar 2009
Location: Surrey UK
Posts: 162
Default

Quote:
Originally Posted by Phil Waterman View Post
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.
__________________
John.
1943 Chevrolet C60s Wrecker;
1944 Chevrolet C8a HUP ZL-2
1944 Willys MB (British Guards Armoured Div);
1944 BSA Folding Bicycle (Best "Para Bike" at War&Peace Show 2011, 2012, 2014 and 2015);
Trailer, 10cwt, Water Lightweight, 100gallon;
Trailer, 10cwt, Cargo Lightweight 10cwt No1 MkII;
Trailer, 10cwt, Electrical Repair Mk.2; Ex-Airborne REME;
Trailer, 10cwt, Lightweight, Electric Welding Mk 2
Reply With Quote
  #10  
Old 04-05-15, 00:24
lynx42 lynx42 is offline
Rick Cove
 
Join Date: Jan 2007
Location: Paynesville, AUSTRALIA
Posts: 1,827
Default

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.
__________________
1916 Albion A10
1942 White Scoutcar
1940 Chev Staff Car
1940 F30S Cab11
1940 Chev WA LRDG "Te Hai"
1941 F60L Cab12
1943 Ford Lynx
1942 Bren Gun Carrier VR no.2250
Humber FV1601A
Saracen Mk1(?)
25pdr. 1940 Weir No.266
25pdr. Australian Short No.185 (?)
KVE Member.
Reply With Quote
  #11  
Old 04-05-15, 00:31
Lynn Eades's Avatar
Lynn Eades Lynn Eades is offline
Bluebell
 
Join Date: May 2003
Location: Tauranga, New Zealand
Posts: 5,069
Default

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.
__________________
Bluebell

Carrier Armoured O.P. No1 Mk3 W. T84991
Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6.
Dodge WC55. 37mm Gun Motor Carriage M6
Jeep Mb #135668
So many questions....
Reply With Quote
  #12  
Old 06-11-17, 02:00
Phil Waterman's Avatar
Phil Waterman Phil Waterman is offline
Super Moderator
 
Join Date: Feb 2003
Location: Temple, New Hampshire, USA
Posts: 3,829
Default Little Video of C60L Shimmy

Hi All

Been working on this for awhile takes almost as much time to upload as to shoot the video. This is my 1941 Pattern 12 C60L road test video shimmy between 35 & 40 MPH. Since then I've reduced the shimmy and raised its threshold to 45+ MPH. Comments please.

Screen Shot 2017-11-05 at 8.02.54 PM.jpg

Click here for video I can't get the embed to work correctly

https://youtu.be/vTPqSBq9klA

Cheers Phil
__________________
Phil Waterman
`41 C60L Pattern 12
`42 C60S Radio Pattern 13
`45 HUP
http://canadianmilitarypattern.com/
New e-mail Philip@canadianmilitarypattern.com

Last edited by Phil Waterman; 06-11-17 at 02:06. Reason: Could not get Youtube link to work
Reply With Quote
  #13  
Old 06-11-17, 08:49
cordenj's Avatar
cordenj cordenj is offline
Registered User
 
Join Date: Mar 2009
Location: Surrey UK
Posts: 162
Default

Excellent video Phil.

All seems very familiar to me!

I jacked up each axle and set up a pointer and ran each axle static. I had found one of my wheels to have a significant variation at the rim edge. changed that wheel with a spare I managed to obtain.

In the first two years of ownership, I had these split rims apart and together more times than I like to think about (good exercise I suppose). I made sure the mating faces of the two halves were clean and that they were bolting together correctly as I appreciate that a small error here will cause the rim movement we are seeing.

All 4 wheels are now reasonably straight in that there is only slightly movement at the rim on each one, certainly less than on you truck.

Tyres do have some "out of round" movement when run static, but am not sure how much of that is from sitting for a month between giving them some exercise.

Still, As I said at 25mph the truck runs well, and that is not a problem in the areas in tend to use it.
__________________
John.
1943 Chevrolet C60s Wrecker;
1944 Chevrolet C8a HUP ZL-2
1944 Willys MB (British Guards Armoured Div);
1944 BSA Folding Bicycle (Best "Para Bike" at War&Peace Show 2011, 2012, 2014 and 2015);
Trailer, 10cwt, Water Lightweight, 100gallon;
Trailer, 10cwt, Cargo Lightweight 10cwt No1 MkII;
Trailer, 10cwt, Electrical Repair Mk.2; Ex-Airborne REME;
Trailer, 10cwt, Lightweight, Electric Welding Mk 2
Reply With Quote
  #14  
Old 06-11-17, 10:22
Lynn Eades's Avatar
Lynn Eades Lynn Eades is offline
Bluebell
 
Join Date: May 2003
Location: Tauranga, New Zealand
Posts: 5,069
Default

Phil, the wheels are forged and I think that "eccentric" extra bit, is commonplace. The military Dodge rim was factory balanced. (welded on steel weight) I assume CMP wheels were as well.
I noticed the brake drum is not running exactly true. An out of round drum can be a culprit.
__________________
Bluebell

Carrier Armoured O.P. No1 Mk3 W. T84991
Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6.
Dodge WC55. 37mm Gun Motor Carriage M6
Jeep Mb #135668
So many questions....
Reply With Quote
  #15  
Old 06-11-17, 22:41
Andy Beevers Andy Beevers is offline
Registered User
 
Join Date: May 2011
Location: Kent, UK
Posts: 43
Default

John,
such a small world at times.
Somebody else reccomended Jones, called them this morning, in the post now, should be here tomorrow.
I have already got a bush puller and replacer so good on that thank you.
I have ordered an H10 adjustable reamer which should allow for what I need.

Phil, excellent video, however once you start on you tube difficult to stop, liked the HUP going out in the snow too.
Once those wheels start to go shimmy, it takes everything with it.
I did notice a little movement on the pitman arm draglink, (tighten screw all the way in, then back off half turn, fill with grease, sorry sucking eggs etc.) but from that view the temptation is to say the wheels start the shimmy and it just gets bigger till centrifugal force wins and pulls the shimmy back out like a gyroscope.

I will still follow the engineering principal of 1 item at a time, then I will know.
So, will get the springs done, then balance the wheels, and try to post a video like you have done, might take longer for me to do that than strip the truck!

Should be out for a roadtest this coming weekend, if all goes as promised.
__________________
Andy
C15A
Bsa parabike
Landrover 86"
TX1 London Taxi
Bonneville
Monkey bike
1943 GPW Australian
Reply With Quote
  #16  
Old 06-11-17, 23:03
Andy Beevers Andy Beevers is offline
Registered User
 
Join Date: May 2011
Location: Kent, UK
Posts: 43
Default

Phil,
Some other points,
truck sounds real good, accelerates well, gear changes, wow, so smooth and quiet.

The following are random thoughts that may get me somewhere, or not.
I am tempted to try something a bit different.
What if a weight was placed, of a significant size, on the wheel and then run again. If the shimmy was worse or better, then wheel/drum imbalance is the cause. It is a theory, if it can be made worse, then the opposite should make it better.

I have a box of stick on weights, will try, 100g strips, a couple should do something.
Then using the logic of the on car balancer, using the tyre valve as a starting point, should be able to do on road balancing. Problem though, is one wheel at a time is the best way, some more thought perhaps.
Not overly keen on testing one wheel at a time on axle stands, the way it shakes could be a bit more excitement than I need.
__________________
Andy
C15A
Bsa parabike
Landrover 86"
TX1 London Taxi
Bonneville
Monkey bike
1943 GPW Australian
Reply With Quote
  #17  
Old 07-11-17, 01:15
motto motto is offline
Registered User
 
Join Date: Apr 2010
Location: Woodend,Victoria,Australia
Posts: 1,045
Default

Quote:
Originally Posted by Lynn Eades View Post
Phil, the wheels are forged and I think that "eccentric" extra bit, is commonplace. The military Dodge rim was factory balanced. (welded on steel weight) I assume CMP wheels were as well.
The welded steel weights on the 3/4 ton Dodge wheels (I think supplied by Budd) seem to be a standard weight in a standard position to compensate for the valve stem cutout. I suspect they were not individually balanced though I have not compared wheels to confirm this. It would be an oddity if they were as I don't know of ex factory weights on Jeep or GMC/Stude wheels etc.

David
__________________
Hell no! I'm not that old!
Reply With Quote
  #18  
Old 07-11-17, 01:40
Lang Lang is offline
Registered User
 
Join Date: Jan 2004
Location: Brisbane Australia
Posts: 1,460
Default

These balance beads work absolutely wonderfully. They take into account any unbalance caused by bearings, drum weight, wheel weight and tyre weight and even slightly out of round.

The physics behind them is very complex but they are very widely used, even on 200mph race cars. They are relatively cheap and many brands.
Attached Images
File Type: jpg Balance.jpg (55.1 KB, 108 views)
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Motor Oil: "Riding the Film" 1937 Chevrolet Engine Lubrication Hanno Spoelstra The Softskin Forum 2 21-01-14 10:27
"2 friends in front of 3 Jeeps" Harry Moon The Softskin Forum 6 14-08-12 16:19
Chev and Ford 15cwt front "D" differences Keith Webb The Softskin Forum 13 29-10-11 12:29
New Book: "Amazing Airmen": "Canadian Flyers In The Second World War" RAF21 WW2 Military History & Equipment 1 27-11-09 03:30


All times are GMT +2. The time now is 03:59.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright © Maple Leaf Up, 2003-2016