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Diff repair opinions

sdh2903 - 6/1/13 at 06:48 PM

Hi All

Last year I took a punt on a cheap M3 LSD, Opened it up today with the intention of starting to strip it as the bearings are shot. However I found that 2 of the lugs on one of the internal flanges have broken off as you can see in the pic below:

diff

This is how the flange should look:

diff2

Is this repairable or should i just bin it? The flange is cast so presume if it can be repaired it would need lugs Tig welding on?

fregis - 6/1/13 at 07:21 PM

if you produce disc which is mounted on you all the bolts. Pressure it higher flatness and do not need to weld
or make |_ _|

[Edited on 6/1/13 by fregis]

sdh2903 - 6/1/13 at 07:37 PM

Ahh good idea, make a doubler ring to fit over the top and fit some longer bolts. Cheers for that!

If it was only 1 missing i probably would just leave it, but, as the 2 are next to each other it definitly needs sorting.

Cheers
Steve

snapper - 6/1/13 at 08:04 PM

Welding cast is not simple
The process is very involved not a simple case of mig or TIG especially as there are some serious forces going through a diff

sdh2903 - 6/1/13 at 08:22 PM

quote:
Originally posted by snapper
Welding cast is not simple
The process is very involved not a simple case of mig or TIG especially as there are some serious forces going through a diff

Agreed, would you anticipate any issues with using a retainer ring over the top?

umgrybab - 6/1/13 at 11:57 PM

A retainer ring is more likely to back off over time and then that leaves the piece open to simple fracture. Welding is not simple but its not at all difficult in the great scheme of things, I mean you're building your own car. Welding and a retainer ring may be the best solution, but I'd be sure to lock wire those bolts. They've been loosened off and the cast sheared once so there's a good chance the housing is slightly oblong in those locations.

trextr7monkey - 7/1/13 at 12:48 AM

Although we have a decent welder any critical jobs like this are entrusted to local engineer/blacksmith who tends to be doing this kind of stuff on a regular basis - not expensive and he knows exactly how to preheat components so no stress in finished work etc
I'd try and suss out someone of similar calibre in your locality
atb
Mike

cliftyhanger - 7/1/13 at 07:06 AM

However, worth having a think about this. Where are the missing bits if not in the diff somebody may have been in there before and given up. Likewise the bearings, plus how are the CWP??
It may have been sold on as it isn't worth repairing. I have no idea how much they fetch, but you may be better off just buying a good one?

sdh2903 - 7/1/13 at 08:07 AM

All offending missing bits were in the oil, judging by state of gasket and how tough it was to get the back plate off I would say its not been open in a long while. It definitely needs further stripping and checking before committing to any repairs.

It's getting to be a pretty rare diff as its from a 3.0 non evo M3 with a 3.15 ratio. They fetch anywhere from 200 up to 4-500 for a real good one so it's worth pursuing.

Oddified - 7/1/13 at 10:04 AM

I would say just make a complete new end piece out of steel, then it would be 100% right.

Ian

MarcV - 7/1/13 at 12:28 PM

Wouldn't it be possible to grab this part out of another diff? Or is it specific to the M3 diff?

bi22le - 7/1/13 at 12:32 PM

quote:
Originally posted by MarcV
Wouldn't it be possible to grab this part out of another diff? Or is it specific to the M3 diff?

That was my thoughts. There must be busted M3 diffs out there that have this peice intact.

sdh2903 - 7/1/13 at 01:45 PM

quote:
Originally posted by MarcV
Wouldn't it be possible to grab this part out of another diff? Or is it specific to the M3 diff?

This had crossed my mind as its only a bearing race flange really, it also looks very similar to the one in my open diff. I'm just trying to get my copy of Bmw TIS working to see if I can cross reference the parts. Realoem used to have the exploded parts diagram but not any more.

I'm going to pull the drive flanges and the lsd out later and have a good look at everything to see if anything is chewed up and re-assess whether its scrap or not.

sdh2903 - 7/1/13 at 08:08 PM

Well cracked it open and split it apart today. Not only was there the 2 bits of casting but also one of the allen bolt heads had sheared off! (did come out easy though)

diff3

diff4

Checked over the CWP, pinion and all the internals and there are no marks on any teeth so i suspect none of the metal chunks have been through the gears. However the clutch plates do look a bit worn.

diff5

diff6

The cause of the graunching was the input shaft bearing, it was completely shot, i suspect through incorrect torqueing and the fact that the dust cover and seal were bolloxed.

I'm going to drop it into a local diff/gearbox place but I suspect its going to be too pricey. Ive done some research and the bearings are around Ł100 for the proper SKF items and the clutch plates are Ł94+shipping+import tax plus Ł30 for dust covers and a bit more for some decent oil. So with the cast repair plus an overhaul I suspect I won't see change from Ł400+

I think I will keep the CWP and pinion then I can swap them into my open diff as they are all interchangeable.

[Edited on 7/1/13 by sdh2903]