p38 rear diff

hi guys not been on for a while, once again after some of your good advise. when i first got my p38 it had a slight whine from a diff wasnt sure which one as it was real quite i didnt look into it, a few weeks ago i got a puncture on the n/s rear (im curruntly running 22" wheels) so i put my spare on which is a 16" wheel run it like that for about 2 weeks and it seemed to get rid of the slight whine i had, anyway put my whel back on with new tyre now the diff whine is alot louder now alot more than it was before, is this my diff giving up or is it due to different size wheels i was runnning??

lee 2110 said:

hi guys not been on for a while, once again after some of your good advise. when i first got my p38 it had a slight whine from a diff wasnt sure which one as it was real quite i didnt look into it, a few weeks ago i got a puncture on the n/s rear (im curruntly running 22" wheels) so i put my spare on which is a 16" wheel run it like that for about 2 weeks and it seemed to get rid of the slight whine i had, anyway put my whel back on with new tyre now the diff whine is alot louder now alot more than it was before, is this my diff giving up or is it due to different size wheels i was runnning??

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You run two different sized wheels with different rolling radius and ask why the diff is whining. It should be pretty obvious.:doh:

Your Diff is about to expire. Running two different size wheels will cause the Diff to work hard and wear out even more.

yeah thats what i thought i know daft question but wanted to make sure, any one got a diff lol

P38-Ireland was breaking a P38 try him

thanx mate pm'd him

wammers said:

You run two different sized wheels with different rolling radius and ask why the diff is whining. It should be pretty obvious.:doh:

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That's not as daft as it might first appear and in any 4x4 other than a RR (with its VC) would make SFA difference to the Diff. Even in the RR I don't think it would do any real harm to the VC.

A 255-65-16 has a radius of 332mm with a rolling circumference of 2251mm. A 275-45-20 has a radius of 351mm with a RC of 2304mm. For a 10km journey one wheel will turn 4442 revs and the other 4340. So the diff pinnions will have to make 102 revs over the course of that journey. Thats one diff rev for every 44 wheel revs in 100m driven.

To put that in context, drive one circle at full lock and the diff pinions will rotate 5 times.

The effect on the VC will be half of that, 1 rev for every 88 wheel revs, factored by the crown wheel ratio so I believe it is insignificant in the short term.

So IMHO, I wouldn't do it long term, but for 2 weeks it wouldn't bother me.

SpudH said:

That's not as daft as it might first appear and in any 4x4 other than a RR (with its VC) would make SFA difference to the Diff. Even in the RR I don't think it would do any real harm to the VC.

A 255-65-16 has a radius of 332mm with a rolling circumference of 2251mm. A 275-45-20 has a radius of 351mm with a RC of 2304mm. For a 10km journey one wheel will turn 4442 revs and the other 4340. So the diff pinnions will have to make 102 revs over the course of that journey. Thats one diff rev for every 44 wheel revs in 100m driven.

To put that in context, drive one circle at full lock and the diff pinions will rotate 5 times.

The effect on the VC will be half of that, 1 rev for every 88 wheel revs, factored by the crown wheel ratio so I believe it is insignificant in the short term.

So IMHO, I wouldn't do it long term, but for 2 weeks it wouldn't bother me.

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........................... op2: :der: :wtf: :deadhorse: :deadhorse:


wow did you get fresh batteries in the calculator there cormac? lol

SpudH said:

That's not as daft as it might first appear and in any 4x4 other than a RR (with its VC) would make SFA difference to the Diff. Even in the RR I don't think it would do any real harm to the VC.

A 255-65-16 has a radius of 332mm with a rolling circumference of 2251mm. A 275-45-20 has a radius of 351mm with a RC of 2304mm. For a 10km journey one wheel will turn 4442 revs and the other 4340. So the diff pinnions will have to make 102 revs over the course of that journey. Thats one diff rev for every 44 wheel revs in 100m driven.

To put that in context, drive one circle at full lock and the diff pinions will rotate 5 times.

The effect on the VC will be half of that, 1 rev for every 88 wheel revs, factored by the crown wheel ratio so I believe it is insignificant in the short term.

So IMHO, I wouldn't do it long term, but for 2 weeks it wouldn't bother me.

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If those were indeed the tyre sizes and both were worn the same amount and everything was perfect maybe not. But if one was half worn and one was nearly new what can you expect it to do to a already whining diff. Improve it? It obviously had some effect, whine went away with odd tyres on, when proper tyre put back whine worse. No need for a calculator to work that one out.

op2: this should be good!