Cracked Diff Carrier

testrider

testrider

Active Member
I've just been nosing around under my car this morning changing the rear shock absorbers and I noticed what I think is a small crack in the diff carrier. It's on the top flange next to where the mounting bolt passes through and into the floor of the car.


So, the question is how worried should I be about it and is it easy to repair/reinforce?
 

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Fairly common fault actually. Not too hard to fix though, support the diff on a jack and you can remove the carrier and weld up the cracks and reinforce the holes by welding on some thick washers or similar. Just bear in mind the correct placement of spacers between the carrier and the rubber mounts and be sure to adjust as required depending on your repair.
 
Most of the P6s I've had have suffered with this. One diff started knocking heavily - when the carrier end came off!

I thought it was a V8 problem but my 2000 has already been repaired there, & that would have been before 1978! :|

As stated, fairly easy to sort.
 
Thanks guys.

I don't have a lot of experience repairing this type of thing so just to clarify, obviously I'll need to clean it up first but, do I just weld over the crack or do I need to grind a V shape into it?
 
If you try to grind a "V" into it there will be nothing left, just clean it up and MIG it, do it from both sides if you don't get good penetration.
 
Thanks Harvey.

Is it worth trying to make a brace across from the top and bottom flanges to stiffen it up or not?
 
Yes ish. Alan Ramsbottom welds a complete plate across the back of it to form a box section - but of course then has to provide a replacement mount for the panhard rod. He tells me it is a nightmare trying to keep the whole assembly from distorting when doing this. If you did go down this route then you ought also to triangulate the panhard rod fixing onto the diff plate. The diff twists quite badly under torque, which is why it is always the nearside diff mounting that fails first. Any modification to the panhard rod to resist twisting will be well worthwhile.

Chris
 
I have never heard of this problem effecting Rovers in Australia. Maybe it is a byproduct from the high degree of corrosion that is so common with U.K based cars.

Ron.
 
I don't think it's a byproduct of corrosion Ron. Testrider's is nice and clean in that respect. So have others been that I've seen. Possibly Australia has rather more open and less congested roads than the UK and hence less stopping and starting. I'm pretty sure it's the initial application of torque starting from rest that does the damage to both the mounting plate and the rubber bushes in the shell. It should therefore be most prevelant on autos, with the famous Borg-Warner thump taking up drive. (and yes, I know it shouldn't if the box cables are adjusted correctly and the idle is set nice and low - but when was the last time you saw one that was set like that? Apart from your own of course!)

Chris
 
chrisyork wrote,...
I don't think it's a byproduct of corrosion Ron. Testrider's is nice and clean in that respect. So have others been that I've seen. Possibly Australia has rather more open and less congested roads than the UK and hence less stopping and starting. I'm pretty sure it's the initial application of torque starting from rest that does the damage to both the mounting plate and the rubber bushes in the shell. It should therefore be most prevelant on autos, with the famous Borg-Warner thump taking up drive. (and yes, I know it shouldn't if the box cables are adjusted correctly and the idle is set nice and low - but when was the last time you saw one that was set like that? Apart from your own of course!)
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Hello Chris,

The traffic angle maybe a possibility, although Sydney's traffic is pretty crook most of the time, but then never having been to the U.K I cannot really make a comparison. I have had to replace the near side diff mount on two occassions. In 1990 with 93,754 miles covered, the original 1974 factory installation was replaced with the new mount running till 2007 with 199,448 miles seeing its replacement (so 105,694 miles for the second mount). The near side is now on its third genuine mount whilst the off side still retains the original 1974 factory installation, and it remains in perfect condition. I always check every 6000 miles or so the torque on the main retaining bolt along with the two mount retaining bolts,..and have found on more than one occassion that the main bolt in particular required nipping up to the correct torque setting. This also effects the near side bolts much more so than the offside.

I am lucky in that my transmission has never really thumped when selecting drive,..max 650 rpm idle speed helps in this regard. Keeping the transmission mount plus the pinion extension case mount in good condition and replacing when necessary I am sure also helps minimise thumping through the drivetrain, and of course ensuring that the torque on the bolts securing the afforementioned mounts is as it should be.

Ron.
 
Thanks for all the replies on this subject. I've managed to find a NOS diff carrier so I'm going to fit that instead of repairing/modifying the old one.

Interesting that the idle speed maybe a contributing factor here as both of the people who have tuned the car over the past few year have set the idle to 950(ish)rpm to help the alternator provide charge in traffic, so I'll probably turn it down a bit when I get chance.
 
testrider said:
Thanks for all the replies on this subject. I've managed to find a NOS diff carrier so I'm going to fit that instead of repairing/modifying the old one.

Interesting that the idle speed maybe a contributing factor here as both of the people who have tuned the car over the past few year have set the idle to 950(ish)rpm to help the alternator provide charge in traffic, so I'll probably turn it down a bit when I get chance.
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Interesting point :) We had a few customers who did a lot of winter traffic work in London and we fitted a different alternator pulley to cover the same issue :wink:
 
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