Transmission / axle wind up !!! Cmp

[Mark Towers]

Hi,

I was driving my 1944 CMP LAAT home this afternoon from a bank holiday show in rather muddy water logged field. It had rained none stop all weekend.

I fired the old girl up and selected 4 wheel drive. I drove across the boggy fields no problem taking it real easy.

When I was out and clear from the mire and onto the hard Tarmac road , I tried to select 2 wheel drive for normal road use..... But the lever was really hard to select 2 wheel drive ..... I shunted forward slowly in first gear then tried again.... With a little less resistance I finally got her into 2 wheel drive and set off home.

As I got up to 20 mph the Cab started bouncing. I pulled over to check if I had a flat tire , but all tyres were fine....... I set off sgain and the bouncing had eased off this time when I got to 20 mph but I noticed that my engine was working harder than usual and it was taking longer to reach cruising speed (35-40mph)

It felt like I was towing a trailer!........ I pulled over again to check if my hand break was released properly or if I had a sticking break drum on one of the wheels ?....... The hand break was free and the wheel hubs cool.

I then tried pushing my lorry on the flat road but I could feel more resistance than normal ..... I tried to select 4 wheel drive again as I suspected that the transmission was to blame.

The selector moved into 4 wheel drive but wanted to spring back hard into 2 wheel drive ..... After selecting 4 wheel drive I reversed back a couple of foot and forward a couple of foot.

I then set off again in 2 wheel drive . It still felt like I was under powered and towing somthing ? I continued on and after a mile or so there was a loud bang and the lorry felt like she hopped or skipped

Suddenly my power came back and I was up to crusing speed and all felt and sounded healthy again...... I got the lorry home safely.

Can anyone one kindly tell me if this was a bad case of Transmission Wind up? ..... Has that loud bang caused any damage ? ..... And what can I do different next time to avoid axle/transmission wind up ?

I really hope I haven't damaged the old girl !!!! I've only just got her back on her feet .

Kind regards,

Mark Towers

[Richard Farrant]

Mark,
As you observed, the box was under pressure from the axles and would not slip out of 4wd. What I normally do with my Bedford is ease it out before leaving the soft stuff, or failing that, run the wheels on one side on to a grass verge, or similar, this will take the pressure off the gears and allow it to slide out of 4wd.

[rob love]

To avoid the windup, you have to make sure your tires are the same diameters front and rear, and the tire pressures are adjusted so as to provide the proper deflection front and rear. End of the day you wi9ll still have some level of windup.

I have always just backed up a foot or two, and let off the gas. The shifter will usually move freely as the gas pedal is released.

The same thing happens to everything from jeeps to deuces. Some vehicles (full time 4x4 chevrolets for example) had differentials in the transfer case, but would still experience windup when placed in hi-loc or lo-loc.

[Phil Waterman]

Hi Mark

Both of my C60 trucks have done this at one time or another. Has Rob points out the problem is less pronounced if the tires are all the same actual diameter.

Another thing to check is that the linkages are actually adjusted correctly so that the lever movement actually matches the detent location. Too check this put the truck on a flat floor and jack up one front wheel to be sure you unload the front wheel drive.

You don't mention if you had the truck down in low range, I've had the loading problem and the difficulty in shift out of low range as well. In that case you need to jack up one front and one rear to get rid of the loading then adjust the linkages per the manual.

The other thing I have found is that the shifting tower if it is not well lubricated and used and get very stiff all by itself, this will add to the problem. I suspect that the detent ball and springs get stiff from lack of use. So as part of my spring check on the when I have the truck up on jack stands I just work the high-high 4x4- and low in and out until the lever is moving smoothly.

As I think you said your truck has the winch be sure you have the winch brake on full when you play this game for obvious reasons. The winch needs the same checking to be sure that the lever position and the actual detent on the power take off of the winch are matching. Have you used the winch yet?

Be careful the winch it is much more powerful then anything I've encountered on US trucks of the same size. Do you have the winch scotches?

Cheers Phil

[motto]

In my (non Blitz) experience it's not unusual to find that when you try to disconnect the front axle (Jeep, GMC, Studebaker, Dodge) it is not possible whilst stopped or driving forward. Disconnect is easily achieved in every case by reversing the vehicle a short distance, sometimes only a few feet.
Recently at an event a long time HMV owner asked me if I could help him as he couldn't get his '42 Jeep out of four wheel drive. Once again, a few feet in reverse did the trick.
I think the wind up in soft conditions is due to the load and/or traction differences between axles. On hard going simply going around a corner will do it as will any variation in tyre circumference.
In answer to the question about the loud bang being associated with any damage, I would say most likely not. If the vehicle ran fine after that it would have been the dog clutch disengaging and they are very robust.
Just as an aside, White scout cars were permanent four wheel drive, no disconnect, no power divider. The vehicle weighed around four ton and the drive line coped with it so a bit of windup is no big deal.

David

[Ganmain Tony]

Originally Posted by Mark Towers

I really hope I haven't damaged the old girl !!!! I've only just got her back on her feet .

Kind regards,

Mark Towers

Mark,

If it's giving you sleepless nights, prehaps a check of all items that hold oil (Diffs, gearbox, trans case) to make sure no broken metal bits are at the bottom of them.??

[Mark Towers]

Hi Phil,

Thank you for your reply :-)

In answer to your question about the winch.... Yes I have used her only twice ! The first occasion was whilst towing my Bofors around a field. It had bee rating here in the West Country for weeks...... The ground clearance on the Bofors is fairly poor and the jack stabiliser discs dug into the the ground and started to plough up the field... Eventually the all four wheels on my LAAT were spinning. I slipped tow of the gun and drove the old girl out no problem. I had never used the winch before and decided to try it out !
I ran the cable out and hooked it up the the gun.... The winch pulled it out effortlessly !
I was rather impressed ..... It destroyed the field though lol.

Yes I have the winch scotches but didn't need to use them in the end as the hand break seemed to hold the LAAT ?

The second time I used the winch was to see how long the cable was. I over cooked it and ran the complete cable off the drum . Very long indeed. I hooked up to my VW Polo and rewound the cable back in under weight.

I took the old girl for a road run yesterday evening (20 mile round trip) she ran fine ... But I will still carry out further checks that other forum members have kindly instructed !

Thanks again.

Kind regards,

Mark

1944 CMP F60 LAAT
1942 Canadian 40mm Bofors Gun
1940 BSA M20
1944 Military Cycle Bike

[Mark Towers]

Hi fellow members.

Thank you very much for all your helpful pointers.

I will further investigate the transmission with the sound advice that you have kindly instructed :

Although a 20 mile road test without any issues was carried out yesterday evening.

I will report back to this thread if I find any thing wrong

Kind regards,

Mark Towers

1944 CMP f60 LAAT
1942 Canadian 40mm Bofors gun
1940 BSA M20
1944 Military Cycle Bike

[John Hackett]

As a quick extra note on the wind up. Sometimes it helps if you zig zag a bit when reversing, as it changes the rolling distance of front and rear wheels and can release quicker and easier.
Cheers.