Diff housing - Same or different across models?

Quagmire

Active Member
Morning everyone,

Before we go any further, I have a confession to make - i have never changed the oil in my diff. I regularly check it is still up to level, which it always is, as it doesn't lose any.

The reason for this is that I have never been able to undo the drain plug! I have spent many hours on and off trying to get it out over the last few years with no success. My last resort will probably involve the welder as that tends to be good at freeing off stuck bits.

Anyway, back to the question.

Are all diff casings the same? I am thinking out loud here in case the worst happens with the extraction of the drain plug and I need to source another...

Thanks
 
Hi Quagmire,

According to the 3500/3500S spare parts book, there is only one part number for each part that comprises the casing. The housing has part number 556611 and the cover 556612.

Ron.
 
AFAIK 2200 & V8 casings are the same, just different ratios, the 2000 has different casings but the same ratio as the 2200.
 
Hi, Harvey, Are the two halves of the casings a matched pair in as much as they are machined together? I was led to believe they can't be swapped about, the same as bearing caps on a block.

Colin
 
Hi, Harvey, Are the two halves of the casings a matched pair in as much as they are machined together?

I think they're probably supposed to be kept as a pair, like a lot of other things, and that's what I'd always try to do, but as there are separate part numbers for the two halves then there's obviously the scope to mix and match otherwise you would only be able to buy them as a pair. If you look at the 3500S manual gearbox, you can only buy the main casing and the top cover as a pair.

ISTR changing the diff cover half at one time or another, but I can't remember why, if that were the case, I never had any problems afterwards.
 
The diff cases are not matched, so you can mix and match. I've replaced the cover side on two rear ends without any complications other than resetting the gear tooth pattern. That said, having to set up the crown & pinion clearances is a powerful incentive not to do that. I believe the gearbox case and lid are matched because of the holes for the shift rods are bored half in the case and half in the cover, and the forward face of them has to mate with the bell housing.

Actually, now that I think about it I didn't have to reset the gear tooth pattern, I just had to re-shim the cover's bearing race to get the same nip.

Yours
Vern
 
The reason for this is that I have never been able to undo the drain plug! I have spent many hours on and off trying to get it out over the last few years with no success. My last resort will probably involve the welder as that tends to be good at freeing off stuck bits.
That seems to be a common problem - mine is the same, I'd be interested to find out how you do manage to shift it.
 
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