#ZedShed Supercharged Z4 - Diff Repair

[Lee]

Nice treat for us in the shed today. A friends diff on his supercharged Z4 had started making very strange noises. We offered for him to drop it off and leave it with us while we looked into it.

In all her glory.

The M53B30 with a lovely charger hanging off it.

Now down to the nitty gritty, we knew we would be in for a surprise as the noises coming out the diff were awful. About an hour job getting the diff out.

First job was getting the brace off

next was the exhaust, interesting design

Next we removed the roll bar.

then onto disconnecting the half shafts and drive shaft.

There we have it she’s out.

Now for the fun part. Let’s see what’s inside. First we poured the oil out, looking a little metally.

then once we tilted the bucket….

in total we found 3 bolts. Once we looked closer we could see they backed out of the LSD unit. These should normally be locktited aswell as torqued. Can see a bolt missing from the hole.

It’s a shame as it’s caused quite a bit of destruction inside. So much so the crown and pinion will need to be changed.

Damaged the pinion gear.

So the diff is now with our local diff builder. We’ll likely source him a new unit to swap over.

 

[t-tony]

So it's got some questionable history then?

Tony.

 

[Lee]

So it's got some questionable history then?

Tony.

More how the unit was built.

 

[Althulas]

I presume the current owner inherited the diff build? Just wondering if the current owner had it done somewhere and can claim some compensation. Do you know how much bhp it makes @Lee

 

[Lee]

I presume the current owner inherited the diff build? Just wondering if the current owner had it done somewhere and can claim some compensation. Do you know how much bhp it makes @Lee

It’s currently Dyno’ing at 307bhp but It’s actually good for 340bhp. Running a conservative map currently.

The diff builder is known but we’re not into naming and shaming.

 

[Althulas]

Nice figures, shame the S50 is at the top of its tune as one would most likely destroy the engine. Always been impressed with the old super charged cooper s the wife used to have with the pull and the sound was so addictive.
All be good with your contacts sorting the diff out though

 

[Lee]

Update to close this little job out. We still don’t fully understand why the LSD unit failed. It’s been fully stripped down and what is clear is the bolts closing the LsD body failed, the majority have sheered completely. This is very strange as they’re high tensile 12.9 bolts and all had loctite on the threads (stamped at least) our diff builder did say the LSD body is quite small compared to others he’s built for this power and car but still not sure why it failed.

LSD Body look at all the sheered bolts.

Gears are luckily ok.

So to get Stu out of trouble we fitted a 2.5i diff we had on the shelf. This actually works in his favour as the ratio gives him some more acceleration. If he likes the ratio we’ll likely pull the Diff again to fit an LSD, currently all stock non M diffs are open so he’ll get one tyre fire under hard acceleration.

You’ll see this car again in new year for some nice tuning mods. New race clutch and some diff goodies.

Watch this space