14 replies to this topic

[xrocketengineer]

Hi all,
I just finished taking out the differential on my 94 Cooper. My initial assessment is that the gearbox appears to be rebuildable. The differential carrier needs to be replaced. At least one of the ouput shafts has some damage.

Differential Housing


Gearbox Internals




Differential





What is left of the pin, thrust block and pinions


Any other observations or comments? By the way the car is supposed to have just over 70000Km. it broke with no warning.

Cheers,
Ivan

[minidaves]

yeah it happens it must have clonked now and again with a diff pin that worn

[xrocketengineer]

yeah it happens it must have clonked now and again with a diff pin that worn

Yes, it did lately. But it was driven just short distances twice a month. Is this amount of wear to be expected with under 45000 miles?

[xrocketengineer]

I took apart the differential cage and this is how it looks inside:



The output shafts look like this:

This one has a high spot that needs to be cleaned up


This one is more beat up

[Surfbluegarage]

if that was me id be cleaning and inspecting everything as the parts that have broken up will have gone around alot of stuff in the box. plus having the diff pin come out of one end of the diff cage and cut a nice groove in the casing just make sure that you can use the case again as the back casing where the diff bearings sit are line bored from the factory so make sure if your keeping the casing that the new back diff cover matches the casing and holds the bearings firmly after the thrust has been takien up.id also change the whole diff cage and parts as it looks like the planet gears have taken a good chunk out of the cage.
me personally i would fully strip and inspect it and replace the casing as i dont like the look of the chunk missing next to the main bearing in the casing.

[Guess-Works.com]

IMO... Replace the case

Where the diff has taken a small chunk out of the main web, that'll develop into a crack then then potentially a bigger failure further down the line.

[xrocketengineer]

Guess-works I will PM you.

[xrocketengineer]

Well, I am getting a new gearbox from Guess-Works. I will use the old one to play with later down the road.
My question now is the engine. Do I need to do anything with the engine. The oil filter protects the engine from all the metal particles the came from the differential. But what about the oil pump? Does it need to be removed and inspected?

Thanks,
Ivan

Edited by xrocketengineer, 03 March 2012 - 02:33 PM.

[Guess-Works.com]

While it's out no harm can be done by having a look...

[bmcecosse]

May as well check over the crankshaft bearings too while it's out, and if you had been thinking of a cam change - this would be a good time........

[xrocketengineer]

Quoted from the FAQ section:

I will throw my 2 cents worth in here -- I have been running regular, non-High mileage Castrol GTX 20-50 in my classics year round for a l.o.n.g time and it has worked well. Many moons ago, there was a guy called Crazy Mike that had worked at Seven Ent when they were still in Virginia and he heavily autocrossed a ratty looking but very quick classic Mini with amazing success. He ran M*b*l* One synthetic oil as he wanted to have the "best oil" he could to protect the engine/gearbox. Sometime after he switched to synthetic, the car started to experience differential failure. He asked the manufacturer of that oil if there was a problem using their synthetic oil in the classic Mini. He got a reply that their synthetic oil was fine in the engine, also in the gearbox, but the shear forces generated in the differential (which uses the same oil as engine and gearbox) would break down their synthetic oil and they recommended he not to use it. I actually saw that letter, so this is not heresay, and ever since, I have not considered using synthetic in my classic Minis."

Maybe this is proof of the statement. In three years and a little over 2000 Km of using Mobil1 15W-50 this happened.

Ivan

[Cooperman]

There is a technical definition of the damage to that lot. It's one word and it begins with 'F' and ends in 'ucked'!
Have you considered replacing the standard diff with a cross-pin. They really are good for higher powered Minis, although I did manage to break one.

[xrocketengineer]

Guys, I am getting a newly rebuilt box from Guess-Works. So what to do is not the issue. The question is what caused the accelerated wear of the differential pin. The car is a bog standard 1994 Japanese Cooper with just over 70000Km and that appears to be correct. I have owned the car for three years and I have driven it for just over 2000 Km while using 15W-50 Mobil1.
Was the pin worn out already when I bought the car (made out of chocolate syndrome)? Or, the synthetic oil can not take the loading in the differential as stated in the FAQ's and in just 2000Km can accelerate the wear to the failing point. Notice in the pictures that the pin is worn to half of its diameter.
If it is the second case, then potential oil leaks from using synthetic oil people talk about is not even an issue. The destruction of the differential in just a few miles of very light use when using synthetic oil would be the concern.

[Ivor Badger]

Do you spin the wheels a lot, that what seems to wear the pin. As in 40/50 miles on the loose or 200 miles on tarmac rallies.

[xrocketengineer]

Well, maybe the previous owner did spin the wheels a lot. I have been driving the car like the proverbial "old lady". No spirited driving at all. All driving was on paved roads and no more than 55 MPH.

Edited by xrocketengineer, 13 March 2012 - 02:39 PM.