S550 Rear Differential Mount Bolts - ISSUES & RESOLUTIONS: Pics!

[MENTION=9386]Reds197[/MENTION]

BMR Tech said:

Updates?

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I'm just waiting on parts to build up a new differential assembly with all fresh parts, 3.55s and OS Giken diff.

The original differential assembly could go back in now if I needed it to.

Edit: trying to think back to when the bolt might have broken and why I didn't notice that right away. I'm wondering if it didn't break back at the first event last March when I heard a loud snap at startup. I could never find what made that snap and ever since then I had a clunking noise somewhere along the drivetrain that never got worse or went away. Believe me, I tried a few times to figure out the clunking short of taking the rear end apart.

The bolt was broken a few turns into the diff cover so I suppose it's possible it stayed put and felt tight every time I checked them all through the season until now. I guess I'll find out if that explains the clunking I was hearing if it's gone when I get the car back together again.

Edit2: some pics of what I dealt with



(Good thing it backed out easy with the extractor since I can't drill straight)

I have been working with people almost on a weekly basis with this issue.

Figured I would share this option as well, which is very simple and effective - but it is the method that requires the most work.

With this set-up, you drill the front bushings out with a 14mmm or 9/16" drill bit and you have to modify the diff side of the rear diff mounts to sit the "allen head" bolts flush to the aluminum (very easy, usually only the driver side needs a little grinding)

Silver bolts are the fronts. Gold are the rears. All 4 bolts go in from the front of the car, towards the rear and then you torque the nuts down to 130ftlbs.

The shear path on this set-up is shown where the red line is drawn in the photo.

This is my 100% favorite solution.

BMR Tech said:

To add, here is the OE bolt that sheared and the one I replace them with.

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[MENTION=9985]BMR Tech[/MENTION]
What size and length bolt are you using to replace the stock one with?

KAR said:

@BMR Tech
What size and length bolt are you using to replace the stock one with?

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Which method are you referring to?

Referring to Post #94-#95

M14-2.0 x 80mm Length

Thanks for the help

KAR said:

Thanks for the help

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My pleasure. Below is an actual representation of the Stock fastener compared to an M14x80mm Bolt. The Billet spacers match the thickness of the stock front differential housing mounting points/ears - so you can see the improvement where the bushing and the diff mounts meet.

Hope this helps!

Another one. Happened while driving in traffic.

Kelly, pm sent, looking to buy some parts

For those reading, Lethal Performance is about to release a bolt hardware upgrade kit that is a little more heavy duty than the current offerings on the market.

I assisted them with it, and it is the most proven kit that will be offered and can be easily purchased.

It will have (4) High-Grade bolts and (2) rear bushing sleeves to fill the voids.

This kit differs from the ones we offer, and others offer, as the fronts are a through bolt design and DO require drilling out the threads on the front bushings.

I'm just getting started with my 2015. Just picked up a low-mile stock A6 3.55 car which will be a fun/track/weekend car. Definitely not a DD. It's now sitting on Weld bigs and littles and I am hopefully on the way to ~800 whp soon. I need it to be fairly kind on the street, but it's a straight line car. I just read through this whole thread and appreciate this is an issue worth looking at, especially for the setup I have. I recently installed the Steeda kit with the black poly bushings. (I'm not aware of upgraded hardware from Steeda??)

Going back to the beginning of this thread it seems like the options have evolved some. I'm leery about the solid aluminum bushings due to NVH, though I recognize it's the best solution and I'm not ruling it out. Kelly what do you recommend I do from here?

Awesome work here, BTW. I love all the BMR goodies I've installed so far.

Lethal Performance got the kit up on their site, check it out.

https://www.lethalperformance.com/lethal-performance-s550-extreme-diff-bolt-upgrade-kit.html

That kit is the best solution for those of you who don't mind drilling the front bushings out!

rts9364 said:

I'm just getting started with my 2015. Just picked up a low-mile stock A6 3.55 car which will be a fun/track/weekend car. Definitely not a DD. It's now sitting on Weld bigs and littles and I am hopefully on the way to ~800 whp soon. I need it to be fairly kind on the street, but it's a straight line car. I just read through this whole thread and appreciate this is an issue worth looking at, especially for the setup I have. I recently installed the Steeda kit with the black poly bushings. (I'm not aware of upgraded hardware from Steeda??)

Going back to the beginning of this thread it seems like the options have evolved some. I'm leery about the solid aluminum bushings due to NVH, though I recognize it's the best solution and I'm not ruling it out. Kelly what do you recommend I do from here?

Awesome work here, BTW. I love all the BMR goodies I've installed so far.

Click to expand...

Until you get to that big power level you mention, I think the kit you have should suffice. What I would do though is, I would periodically check to make sure the fasteners have not backed out. I see a pattern with kits backing out and causing issues and I am not 100% certain as to why. I rarely see our kits have those issues and I think it is due to us providing lock washers.

Once you reach the big power level I cannot help but to suggest the kit I linked above from Lethal Performance. That is the style that I consider my "go to" to ensure the probability of issue with big power is very low.

Some say I am over concerned with this issue and using scare tactics - but try to tell the people who have this issue and a $2000 bill to repair it.

Hope that helps! :cheers:

BMR Tech said:

Lethal Performance got the kit up on their site, check it out.

https://www.lethalperformance.com/lethal-performance-s550-extreme-diff-bolt-upgrade-kit.html

That kit is the best solution for those of you who don't mind drilling the front bushings out!



Until you get to that big power level you mention, I think the kit you have should suffice. What I would do though is, I would periodically check to make sure the fasteners have not backed out. I see a pattern with kits backing out and causing issues and I am not 100% certain as to why. I rarely see our kits have those issues and I think it is due to us providing lock washers.

Once you reach the big power level I cannot help but to suggest the kit I linked above from Lethal Performance. That is the style that I consider my "go to" to ensure the probability of issue with big power is very low.

Some say I am over concerned with this issue and using scare tactics - but try to tell the people who have this issue and a $2000 bill to repair it.

Hope that helps! :cheers:

Click to expand...

Thanks for the feedback. I will likely order one of the upgrade kits soon as my "big power" is being delivered in a big box today.

Drilling out the front bushing is easy compared to installing solid bushings, so if the upgraded bolt solution is deemed to be "enough," I will do that. I don't plan on beating on the car an abnormal amount, but some extra peace of mind would be nice.