How common is the diff mount shearing?

[lear]

This is the cross member bolted to the top of the diff that locates on the chassis with two tubular bushes. It snapped clean through on both sides under braking on a track day today. The boot floor is cut away on mine so easy to see. Is this a common failure?

[redwedge5]

Is this the actual cast aluminium diff. mount that has broken. They can crack and break at each end near to where they are attached to the chassis. There are two versions. The later had an extra piece welded on to improve strength. I had to replace mine which suddenly went after braking/rapid deacceleration.

[lear]

That's the one. Mine broke either side of the centre plate that bolts to the top of the diff. Is it easy to find replacements or do they need to be made up?

[redwedge5]

www.tvrcarparts.com have them listed for sale under the differential section.

[NTEL]

Had a couple break on my old Taz racer. They are a weak point. You would be better using the old mount as a templete and making a steel replacement. Easy to do if you are handy with a tape measure, welding set, grinder and drill. If not, any good fabrication shop will be able to do it for a reasonable price.

[GV]

NTEL said:

Had a couple break on my old Taz racer. They are a weak point. You would be better using the old mount as a templete and making a steel replacement. Easy to do if you are handy with a tape measure, welding set, grinder and drill. If not, any good fabrication shop will be able to do it for a reasonable price.

Good idea...There's a place I've used - they've made my outriggers including mounting plates and my front suspension mounts. Their specialty? Is making metal parts for the catering industry!!

[lear]

Thanks all. Will look into getting a steel replacement made up. Guess it is a good time to refurb the brakes, replace the exhaust and polybush the rear suspension!

[lear]

Gratuitous picture of the sod:

[Number 7]

I've maned to break 2 - one on an '86 350i with the earlier type beam, and one on my current modified 400se, with the later type beam. ETA - just seen your pic and you've got the early version. If you buy a new one, it should have the extra reinforcing.

[JR]

Number 7 said:

I've maned to break 2 - one on an '86 350i with the earlier type beam, and one on my current modified 400se, with the later type beam. ETA - just seen your pic and you've got the early version. If you buy a new one, it should have the extra reinforcing.

Good 'photos.
For the OP: note that the later one is a new casting, not a bit welded in. You don't hear of many of this type failing. If you get one fabricated then note the weight and strength differences between steel and cast aluminium. The steel one will need to be made from thinner plates and would be best with web stiffeners in the area where number 7's later mount broke.

[shpub]

JR said:

You don't hear of many of this type failing. If you get one fabricated then note the weight and strength differences between steel and cast aluminium. The steel one will need to be made from thinner plates and would be best with web stiffeners in the area where number 7's later mount broke.

Probably due to the 540 bhp I was putting through it at the time.

I also broke the steel replacement but the new version with lots of strengthening has coped.

[lear]

Thanks very much guys. I think I will try to go the steel route. Thinking about it, the mount must come under enormous stress under braking, particularly when coming down the gears at the same time. Will see what Dave Batty recommends as he will do the work. At least my enormous access hole makes getting to the bolts a little easier!

[JR]

shpub said:

JR said:

You don't hear of many of this type failing. If you get one fabricated then note the weight and strength differences between steel and cast aluminium. The steel one will need to be made from thinner plates and would be best with web stiffeners in the area where number 7's later mount broke.

Probably due to the 540 bhp I was putting through it at the time.

I also broke the steel replacement but the new version with lots of strengthening has coped.

To be fair, that is triple the power originally designed for. I think that three or four elongated web stiffeners to each side would work.

[TVRleigh_BBWR]

I'm sure a new one of the later style will be ok, remember your one is at least 20 year's old.
So unless you have a stupid about of power, then it should be fine for another 20 years.
I have the later style on my racer, with 230 BHP Rv8 and not broken it, despite a few off, and running slicks.

[voltage_maxx]

lear said:

Gratuitous picture of the sod:

Do you have any other pictures of your access hole? I'm probably going to cut one into my 350i, as I'm taking all the rear end out shortly.
I'd be interested to see how you cover up the hole and what it looks like with all the carpets back in etc.

[lear]

voltage_maxx said:

Do you have any other pictures of your access hole? I'm probably going to cut one into my 350i, as I'm taking all the rear end out shortly.
I'd be interested to see how you cover up the hole and what it looks like with all the carpets back in etc.

I do but I don't think mine is an example you'll want to follow! It's really only a track car (albeit road legal) and much of the boot floor has been removed to accommodate the roll cage and make for easier brake pad replacement/bleed and accessing the adjusters on the shocks as well as a disposal system for all those spare sockets.... It definitely fits under 'rat look'!

[lear]

Can anybody tell me what the risks are of driving the car with the diff mount broken? Obviously wouldn't be dumping the clutch and slamming on the brakes but wondering if I could drive it slowly for 15 miles to be repaired? I guess most of the strain would be on the lower mounting frame. Struggling to find a convenient recovery service for Saturday albeit recognise driving it may be a stupid idea...

[JR]

lear said:

Can anybody tell me what the risks are of driving the car with the diff mount broken? Obviously wouldn't be dumping the clutch and slamming on the brakes but wondering if I could drive it slowly for 15 miles to be repaired? I guess most of the strain would be on the lower mounting frame. Struggling to find a convenient recovery service for Saturday albeit recognise driving it may be a stupid idea...

I don't know but I can tell you that I drove my car for over 100 miles before the problem was diagnosed without any adverse effects on the car.

[TVRleigh_BBWR]

A few of the racers have completed races with it broken, so should be ok to drive.

[mk2 24v]

shpub said:

Probably due to the 540 bhp I was putting through it at the time.

I also broke the steel replacement but the new version with lots of strengthening has coped.

i think the amount of torque your wedge chucks out might have more to do that rather than the hp though Steve