Rear end issues

[spdbrake]

Yes it is sheared. The clue is the hang-nail thread where it snapped. Machine bolts and screws area chamfered 360 on the end to prevent cross threading. You also need to add the missing fender washer (large area washer under the head)
Your earlier pic:



which is also allowing the diff to shift aft due the two aft mount bolts being loose. You will have to drop the diff out of the car to extract the broken bolt.

While its out you might as well go in with Poly bushings
https://www.ecstuning.com/b-ecs-part...02447ecs04kt2/
https://www.ecstuning.com/b-ecs-part...02447ecs01kt1/
You don't have to go with ECS parts there are plenty of alternative brands for these items.

If your going to James Yale's shop let him advise you and procure the parts for you.
Nothing worse than bringing your box of parts to a shop and expecting them to assume all the risk. "Bringing your own eggs to Denny's" is the common term.

Another thing I'd ask James Yale while its in his shop is upgrading your front diff bolt to 14mm VS the stock 12mm
https://www.ecstuning.com/b-condor-s...me36diffbu~cd/

[SBSerpent]

Originally Posted by spdbrake

Yes it is sheared. The clue is the hang-nail thread where it snapped. Machine bolts and screws area chamfered 360 on the end to prevent cross threading. You also need to add the missing fender washer (large area washer under the head)
Your earlier pic:



which is also allowing the diff to shift aft due the two aft mount bolts being loose. You will have to drop the diff out of the car to extract the broken bolt.

While its out you might as well go in with Poly bushings
https://www.ecstuning.com/b-ecs-part...02447ecs04kt2/
https://www.ecstuning.com/b-ecs-part...02447ecs01kt1/
You don't have to go with ECS parts there are plenty of alternative brands for these items.

If your going to James Yale's shop let him advise you and procure the parts for you.
Nothing worse than bringing your box of parts to a shop and expecting them to assume all the risk. "Bringing your own eggs to Denny's" is the common term.

Another thing I'd ask James Yale while its in his shop is upgrading your front diff bolt to 14mm VS the stock 12mm
https://www.ecstuning.com/b-condor-s...me36diffbu~cd/

I was told by a reputable BDR builder that Backdraft removes the 12mm bolt and replaces it with the 14mm bolt when they install these BMW differentials. Is that not the case?

[Soundkillr]

Originally Posted by SBSerpent

I was told by a reputable BDR builder that Backdraft removes the 12mm bolt and replaces it with the 14mm bolt when they install these BMW differentials. Is that not the case?

I can tell you this...I just ordered the bmw brace kit for mine....it comes with a bolt smaller than mine so I would believe bdr does use the 14mm bolt

Mine is sheared as well...and I bought the kit that came with the bolt. So unfortunately I have to find a source for a hardened 14mm bolt...because the one in the kit is too small .

[bobcowan]

Originally Posted by Soundkillr

I can tell you this...I just ordered the bmw brace kit for mine....it comes with a bolt smaller than mine so I would believe bdr does use the 14mm bolt

Mine is sheared as well...and I bought the kit that came with the bolt. So unfortunately I have to find a source for a hardened 14mm bolt...because the one in the kit is too small .

It had a hardened bolt in there to begin with. And that's why it's broken now.

I know I'm going to get a lot of flack for this, but I'll say it anyway. Hardened, grade 8/10.9 bolts are extremely strong along their length, and are great when you need high clamping strength. But in cross section they can be brittle. When subjected to lateral stresses, they will eventually crack and break. Which is what happened to you.

BDR tried to get around that by replacing it with a bigger bolt diameter. Sometimes that works. But here we are.

High grade bolts - 10.9, 12.9 - should only be used for high clamping strength in single shear if there is a locating dowel, or in double shear. Never in single shear in a high vibration environment. .

When I install the support bracket, I will use a grade 8.8. Which is about equivalent to a SAE grade 5. 75,000 psi is plenty in that application.

Carroll Smith once said, "There's no place on a race car for a grade 8 fastener."

[169mph]

Originally Posted by SBSerpent

I was told by a reputable BDR builder that Backdraft removes the 12mm bolt and replaces it with the 14mm bolt when they install these BMW differentials. Is that not the case?

I can confirm that my differential had a 14mm bolt. I assumed it was 12mm. I stopped at a mom and pop hardware store on my way home today to see if they sold 14mm bolts. Most of the automotive stores only carried 12mm. I got lucky. I planned on tapping the differential tonight and ordering a new bushing but it looks like all I need is new bushing. Regardless I plan on replacing all the differential bushings and replace the differential cover gasket.