P38A Drivetrain Whine on acceleration & deceleration

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pwood999

pwood999

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Been chasing down the cause of my drivetrain whine (and new rumble) today, so started with front propshaft. The UJ at the transfer box definitely needs replacing, so will do them all as it doiesn't cost much.

There also seems to be slight play on the transfer front output bearing. (probably much less than 1mm by feel). Can this be replaced without removing the TB ?

There's definitely some slack on both differential pinions, gonna look at them as well.
 
pwood999 said:
Been chasing down the cause of my drivetrain whine (and new rumble) today, so started with front propshaft. The UJ at the transfer box definitely needs replacing, so will do them all as it doiesn't cost much.

There also seems to be slight play on the transfer front output bearing. (probably much less than 1mm by feel). Can this be replaced without removing the TB ?

There's definitely some slack on both differential pinions, gonna look at them as well.
Click to expand...
My transfer box was the same on rear output. I did the bearing in situ, removed the cross member as well... Put it all back together.... It was still same 🤷 that was 5yr ago and it's still the same and no worse 🤯
 
[update] Took it for short drive round the block with front prop removed & see if the whine is still there. Can't hear it up to 30mph, so I'm thinking of taking front diff out the check it while it's accessible.
(Yes I did put nuts & washers back on the TB output flange non-removable bolts so they couldn't rattle around or mash up the TB housing !!)

RAVE links around the sections a bit, but for rear bearing it says Rear Flange, Differential & Output Shaft, so the back cover & chain has to come off ? Front bearing seem relatively easy ?
 
Last edited:
BTW, I'm assuming with front prop removed there's nothing to strain the VCU because the output flange just spins ? Therefore I should be able to safely check for rear diff whine at higher speeds ?

Rear prop off & driving with front prop only puts all the torque through the VCU hence why it's a bad idea ?
 
pwood999 said:
BTW, I'm assuming with front prop removed there's nothing to strain the VCU because the output flange just spins ? Therefore I should be able to safely check for rear diff whine at higher speeds ?

Rear prop off & driving with front prop only puts all the torque through the VCU hence why it's a bad idea ?
Click to expand...
Sorry, wrong on both counts. Front prop removed, VCU locks the centre diff to provide drive to the rear.
Rear prop removed, VCU locks the centre diff to provide drive to the front. At no time does the VCU pass drive torque, it's a diff lock.
Centre diff001.jpg
 
ok thanks Keith. Do you think I would be ok for a short drive up to 40-50mph, or is that gonna kill the VCU ? Only need 1 mile round trip to get out of the 30 zone.
 
Another question about the slight play in the front flange bearing. Looking at the exploded diagrams, it seem the centre diff has two bearings, but the flange relies on one bearing & whatever tolerances exits between it and the diff splines ? Could this be the reason for the play rather than failing bearing ?

It should be more obvious if I take the VCU out, but what experience have others had ?
 
Front prop UJ's replaced & greased today. VCU bearing also arrived, so next dry day will do that, and then pop the prop back on.

If those don't help, will try EP90 in the diff !!
 
Started to take the VCU cover off to do the front bearing today, and got a fair bit of ATF coming out. Is there a seal behind the VCU ? If so I presume it's transfer box off time ?
 
Now drained the TB amd after a cupful or so, it stopped dripping from the VCU housing. Cannot for the life of me figure out how to get the VCU &front cover out with crossmember in place, so taking that off next..
 
Looking at RAVE, it appears the spline above is also the sun gear, so the wobble probably depends on play in the planet gears, which are meshed with the diff outer driven casing. So when not engaged with the VCU it's only supported at one end ?

1716581449598.png
 
VCU Bearing & seal replaced & VCU re-installed. Slight play in front flange but seems better than before. I suspect rear output bearing might need doing as well. Front prop vibration at speed now gone after changing the UJ's.

Put 80W90 in front diff instead of the 75W90 I used a few weeks back. Acceleration whine is almost inaudible, and decelaration whine is definitely less than before. Will get 80W90 for rear diff next week.

Still need to measure the spare diffs in garage, and if they look good, will try them when I get time.
 
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