P38A Diff preload/whine

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Joss155

Joss155

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Rather than hijack the other thread. Let's start a new one. So as said I have a noisy diff. Well actually I think I have 2 as I can't pin point the whine. This is on acceleration only and at higher speeds of 60 plus. On a side note there is also some very slight vibration when accelerating too but only after longer periods of driving so when everything's become hot. I haven't inspected the propshafts myself but they have been inspected and I've been told the UJ's are absolutely fine. Off the throttle the truck is quiet and vibration free and tbh it's not all the time when driving long distances either. So back to the first issue. The whine. I assume they need either attention or replacement parts but some helpful pointers would be good. Are there known issues with pinion bearings etc. Also don't know how to check what diff it is. Something about it being a 3 pin or 4 pin diff.
It's a 1995 2.5 DSE absolutely basic spec(was)
 
I think you can remove one prop at a time for a short run to work out which is making the noise.

Vibration at speed but only after a while to warm up sounds like tyres.
 
It's two pin diffs or four pin diffs. Yours has two pin diffs front and rear. Only way to check props is to lift a front and rear wheel to unload them. Chock the car if you lift a rear one. You will never find play with the wheels on the ground.
 
I remember years ago, I had a rover 213 and it whined and vibrated terribly until one day, I swapped the front wheels to the back as part of the standard wheel rotation. The difference was chalk and cheese.
Now, looking at your profile, it would appear your wheels are far from standard.
If it were me, I'd try to borrow a set of standard wheels and see if the problem stops.
 
Cheers for the reply's guys.

The tyres on the truck are standard p scorpions in the correct size so not sure if the tyres are the problem but as I've got some BF's to put on the car Saturday I'll find out. I'll get the truck off the ground and check for play in the props myself. Any thoughts on the whine in the diff?
 
Joss155 said:
Cheers for the reply's guys.

The tyres on the truck are standard p scorpions in the correct size so not sure if the tyres are the problem but as I've got some BF's to put on the car Saturday I'll find out. I'll get the truck off the ground and check for play in the props myself. Any thoughts on the whine in the diff?
Click to expand...

Check the VCU. If the whine was on overrun it would be pinion bearings if it's constant, carrier bearings or a wheel bearing.
 
Its neither mate. Only on acceleration. Wouldn't say its a wheel bearing as it isn't that kind of noise. Will check the VCU. Is there a procedure to do the VCU?

Don't worry. I've looked it up.
 
Joss155 said:
Its neither mate. Only on acceleration. Wouldn't say its a wheel bearing as it isn't that kind of noise. Will check the VCU. Is there a procedure to do the VCU?

Don't worry. I've looked it up.
Click to expand...

Lift a front wheel put a socket and bar on a wheel nut and apply steady pressure, wheel should turn slowly.
 
Fitting new bearings and setting preload on them is pretty simple providing you use good quality bearings Timken, SKF Etc. And the crown wheel and pinion are in good condition. Preload and intrusion on pinion should not change overly providing you note any shims and replace them in the same position they came from. For checking preload you would need a piece of string and spring balance. Wrap string around pinion flange and attache to spring balance, then a steady pull, pinion should rotate at around 9 lbs pull. For setting pre load on carrier bearings you will need a DTI. Fit and preload pinion first. Then for carrier bearings with carrier bolts barely nipped, you adjust crown wheel towards pinion until there is no backlash on DTI. Then adjust up opposite side until you get 7 thou backlash on DTI. Then torque and lock up.
 
Last edited:
Grrrrrr said:
Does it?! :)

That had the look of easy if done before to me. 9 lb pull? Well, I've got a 32 lb long bow so that's mebbe 1/3 of that minus a bit.

still, never learn unless you try. I'd have a go. Worse case is grab another off a scrapper.
Click to expand...

Pre load on the pinons is set by shims. So if you need new bearings as long as you use good quality ones and replace any shims where they came from it should not be far out. It's when pre load is set with a crush spacer that it can become a bit of a long drawn out pig of thing to get right.
 
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