Rear Diff...Is this normal?

[Steve-O]

Whilst replacing the rear wheels yesterday I noticed that my drivers side rear wheel would happily turn on the axle even though all the other wheels were still and touching the ground. I could see the centre prop shaft turn slightly then stop but the rear wheel could still turn albeit with some resistance. I am hoping that this is normal and has something to do with the diff lock arrangements but I confess I was surprised.
Any helpful thoughts answers gratefully appreciated

Steve

 

[adrianr]

Sounds ok to me.

This video might help with understanding what is happening...

viewtopic.php?f=43&t=12799

 

[Jon Wildsmith]

That should only be happening if either the driveline to the other wheel or the prop shaft are free to rotate.

 

[Beau]

If all the other wheels were on the ground, then there should be some moement but not enough to turn it around fully. It would just be a little play.

The only way it would turn around freely is if another one of the 3 wheels were off the ground, either front or rear.

 

[Chris]

Doesn't some of this rely on the handbrake not being on - not being in Park etc etc?

We've had this discussion only a couple of weeks ago. I jacked one wheel up on mine and I could turn it, it was stiff due to the VC but I could turn it definitely. With no lockers in or anything else clever in there, it is possible to lose drive to three wheels if one has no grip at all - but given the presence of the VC some drive get sent elsewhere.

Jon - please tell me this is right. I had just about convinced my self that I understood the drive line on these things. if the one wheel spun very freely, it would indicate that the VC was pooched. But getting resistance shows it's working. If it only rocked a little then wouldn't you have to be locked up on the diffs?

Chris

 

[Jon Wildsmith]

Doesn't some of this rely on the handbrake not being on - not being in Park etc etc?

Yes, if the transfer box is in neutral or the gearbox is not in park then the wheel should turn, with resistance from the VC in your case. If the prop isn't free to turn and the other wheels are on the ground then other than taking up backlash it shouldn't turn.

 

[Steve-O]

Doesn't some of this rely on the handbrake not being on - not being in Park etc etc?

Yes, if the transfer box is in neutral or the gearbox is not in park then the wheel should turn, with resistance from the VC in your case. If the prop isn't free to turn and the other wheels are on the ground then other than taking up backlash it shouldn't turn.

Oh dear, then I may have a problem.....scenario....one side of the rear diff locked because the wheel/tyre touching the ground, lever set to Park, centre prop just tacking up play, drivers side wheel in the air and turning completely with just a little resistance. Could it be a LS coupling? I'm not entirely sure mine even has a LSD fitted. Strange thing is there are no unusual noises and the thing drives on tarmac ok

 

[Jon Wildsmith]

I haven't fiddled inside an LSD Steve so if you have one of those I'm not sure if that could explain it. I was under the impression that they were like an open diff in terms of gearing but had various types of mechanism to transfer torque from side gear to side gear but maybe that's not the whole story. Assuming you're not having to drive round with the centre diff locked then it must be something like that because if it was a broken drive shaft for example then it just wouldn't go without intervention.

 

[AndyCook]

is there a sticker on the rear of the diff housing saying "LSD oil only" or similar?
what is the axle code on VIN plate on firewall in enging, that might give a clue as to if the diff is LSD or not

 

[adrianr]

I haven't fiddled inside an LSD Steve so if you have one of those I'm not sure if that could explain it. I was under the impression that they were like an open diff in terms of gearing but had various types of mechanism to transfer torque from side gear to side gear but maybe that's not the whole story. Assuming you're not having to drive round with the centre diff locked then it must be something like that because if it was a broken drive shaft for example then it just wouldn't go without intervention.

I am not 100% certain but pretty confident that it is a similar sort of deal to the VC in centre diff. Fails over time (read a few threads on MX5's and similar). Rear diff should be marked / labelled accordingly since it needs different type of oil.

 

[Steve-O]

Thanks all I will go and check when there's a bit more light tomorrow, my guess is that any sticker that was there may long since have parted company with the diff, I will still look though. The VIN indicates an "A04A" as the code, which I'm lead to believe is 7.5" ring gear with ratio of 4.3 or 4.55 and 2 pinion no mention of LS diff, should be "C" as last letter here perhaps. I'll have a crawl underneath and have a look

Steve

 

[Jon Wildsmith]

It's a 9.5" ring gear and 4.3 ratio. I'm assuming you don't have a rear locker knob as you haven't mentioned it?

 

[Steve-O]

It's a 9.5" ring gear and 4.3 ratio. I'm assuming you don't have a rear locker knob as you haven't mentioned it?

Sorry Jon, I do have a rear locker and a centre locker too. It seems there are various ways of interpreting those blasted confusing axle codes...I've spent nearly an hour trawling the net and got it wrong then!!!

 

[Jon Wildsmith]

If you have a rear locker then it's not LS, you only get one or the other not both at the same time

 

[Steve-O]

I can confirm that I do not have a limited slip diff. I have checked the rear diff locker warning light and it lights on bulb check and goes out promptly after. I presume therefore that the rear diff lock is not engaged. If my rear diff behaved as a normal, I would have expected that any one wheel off the ground would not be able to rotate beyond a few degrees at most, and this would be the normal allowance for wear and slack in the transmission. I think that what I have now discovered is that my rear diff will need a closer look. The symptoms I described could be the result of the drive shaft not engaging with the drive from the ring gear for whatever reason. I haven't found any info on the web of a known cause...ie. failing splines, pinions or ring gear. What is odd is that there are no unusual noises from the diff. When I get a moment I will pop the rear up on stands and see if there are any other symptoms, perhaps the shaft engages here and there. I do occasionally get the thunk from engaging reverse and on take up which I initially put down to the prop shaft. The mystery continues.

 

[Jon Wildsmith]

Did you do the wheel turning thing just that once or have you repeated it? If once then you should try repeating it in case things weren't how you think they were e.g. trans not in park. The combination of the wheel going round like that but you having a truck that drives normally doesn't compute

 

[Steve-O]

Right, I've just been out and raised the drivers rear wheel and tried to repeat the scenario......blow me the wheel turned.....about 4" at the tread and that was all I know for sure that I could continually rotate the wheel before, I even looked carefully at the prop and other wheels in disbelief at the time honest, the other three wheels were all touching the ground and I had a clear view of the rear prop. I'm going to put the rear axle up on stands and see if there could have been a point where one of the shafts could have lost drive.