Techie Diff Question!!!

[M3GTR]

I have an uprated (60% or possibly more) 3.63, short case, LSD. The gears in the diff are shot as three teeth on the pinion broke off. However, I also have an open, long case, 3.63 diff.

Question is this... I know you can unbolt the driven gear from the actual diff unit, so will I be able to swap the good pinion and the driven gear from the long case open diff, bolt the ring gear to the uprated diff, use the pinion from the large case diff and put it all back into the small case?

[M3Compact]

will I be able to swap the good pinion and the driven gear from the long case open diff, bolt the ring gear to the uprated diff, use the pinion from the large case diff and put it all back into the small case?

No. (Assuming by short case and long case you're meaning the 6 bolt and 8 bolt?)

The small case diffs use a 168mm crown wheel, the large case use 188mm, the LSD units aren't interchangeable.

[agent006]

http://www.quaife.co.uk/catalogue/page7.htm

You know you want to.

[M3GTR]

will I be able to swap the good pinion and the driven gear from the long case open diff, bolt the ring gear to the uprated diff, use the pinion from the large case diff and put it all back into the small case?

No. (Assuming by short case and long case you're meaning the 6 bolt and 8 bolt?)

The small case diffs use a 168mm crown wheel, the large case use 188mm, the LSD units aren't interchangeable.

Good question as they are both 6 bolt. The case itself is slightly shorter but the cover on teh back has an extended arm (the bit that the diff bush sits in) to reach the normal mounting point. Where would the extra 2 bolts be on an 8 bolt unit? Any pics on the web of the two side by side?

[M3GTR]

Update:
This is the style of what I have called the "Short case". Things I can see that are definately different are that the drive cups where drive shafts attach to the diff are closer to the case, and the length of the the prop shaft coupling sticks out further from the body when compared to the long case.

Short (small) Case

[Martinaston]

Can you not just put the clutch pack in the good case ?

[M3GTR]

Easier said than done I think. If I can change the ring and pinion for free, I'll do that. Worst case is a clutch pack (if I can find an uprated one) or a new pinion and ring from BMW.

[jonbuoy]

As they're both 6 bolt rear back plate's usually indicate's they're a small case diff. 8 bolt rear back plate mean's big case diff.
I'm not saying i know the answer to your question but have you not got the time to try the idea?

[M3GTR]

Yeah but I figured I'd ask here first to save the hassle if someone already knows if it can be done.

[jonbuoy]

PM "Jhonno" mate, he seem's to know his stuff with diff's, might save you some time aswell

[M3Compact]

I'm a bit confused by this.

I haven't seen many small case diffs, but if (as appears likely) both of your diffs use the smaller crown wheel and pinion (168mm) it should all be interchangeable.

It's much easier to swap the LSD unit over in to the good diff, than swapping the pinion in to a different casing.

[M3GTR]

I know it's easier to swap the whole LSD unit, but it's an uprated diff unit that has the knackered teeth so I need to change the gear set that is in the other diff to the uprated LSD. The problem is that the diff casings are different so I needed to know if the gear sets are interchangeable.

[M3Compact]

I know it's easier to swap the whole LSD unit, but it's an uprated diff unit that has the knackered teeth so I need to change the gear set that is in the other diff to the uprated LSD. The problem is that the diff casings are different so I needed to know if the gear sets are interchangeable.

Ah sorry, misunderstood.

So presumably there's a reason why you can't use the LSD unit that you have in the other diff casing with the good CW&P? (Does swapping the flanges help, or is the other casing from a different model that won't fit the E30?)

[Taffy]

I'd love to jump in now and say you need to do this and I've done that but I really don't having a chuffing clue! Speak to Russ Paul, he's not a million miles away from you and he might have rebuilt it in the 1st place

[M3Compact]

Is this diff being used in a 325?

[M3GTR]

I'd love to jump in now and say you need to do this and I've done that but I really don't having a chuffing clue! Speak to Russ Paul, he's not a million miles away from you and he might have rebuilt it in the 1st place

I'm getting silly quotes from people to do it though Dom and I know I can do it myself with the right parts.

Yeah it is being used in a 325. The good diff is ok, but I don't want to mess with the plates if I can aviod it as I know it has been uprated a lot. Bolting a new crown gear to the uprated LSD is doable but I want to try an avoid buying a new set from BMW....which funnily enough are still available!!

[Demlotcrew]

If you have a small case the gears/clutch pack are not interchangeable so the answer to your question is no!

Get another small case at the same ratio swap the clutch pack and run that.

Andrew

[M3GTR]

UPDATE!
After checking out with BMW I can still get a brand new crown wheel and pinion for £270+vat full wack so I need to find a trader to get them at trade price!. I think that's going to be the best way to go I think.... better than finding a worn set and hoping for the best anyway!

[e21Jason]

Hi

E21's run the small case, also 4cly e30 you buy a car for that price of the wheel.

Try richard at fritz and see if he has an open e21 diff in the right ratio, also martyb has a e21 qualife unit for sale.

Jason

[M3Compact]

Is small case (168mm/6 5/8") big enough for a 2.5L?

[Taffy]

Give me a shout if you need some help Paul, I have an account at my local BM dealers

[M3GTR]

All stripped down now and yeah, no swap possible! So, does anyone know the part number for the oil seal at the front of the diff? The one that the propshaft attaches to. Also, Looks like I'll need to replace the bearings. ETK is pants for this stuff unless I'm not using it right!