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

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BMR Tech

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Hello M6G!

I wanted to take a moment and share some information on the differential bolt issues that have arisen since the S550 has become such a popular platform to modify.

As many of you know, BMR has been developing and testing S550 Chassis and Suspension components since the release of this new platform. Since we only concentrate on chassis and suspension components, we are usually able to develop the most knowledge from experience. Gaining this knowledge from experience takes having your products out being tested rigorously. As with previous platforms, we typically have more products out being used for record setting performances, early-on, than most others. This, combined with our testing in house allows us to really get a grip on what the car needs, wants and does not want. Hence my diff housing failures, diff bolt failures, driveshaft failures and so on.

Computer and electronic testing and modeling only goes so far - the true test is on the street and race tracks. :headbang:

One area of concern when modifying the S550 with more power and more grip, are the rear differential mounts. The reason I have put so much emphasis on this area is because, when these bolts break it can cost the user a significant amount of money and down time to repair.

We (BMR) wait to release some of our components, so that we can feel confident that they are a design that will work and provide a trouble-free operation. This is why we waited to release our BK051 Kit...so we could make sure to the best of our capability that the rear bolt upgrade was going to be sufficient.

Now that we have been shipping hundreds of these BK051 systems out, I am getting most of my customers telling me that they are not performing the rear bolt-upgrade due to the amount of work involved. Naturally, this bothers me and I strive to find better solutions that will not result in push-back from the customer.

I recently (several months ago) acquired for myself, another S550. I bought this car for strictly testing purposes. I commute 97 miles each day, and take the car to the road course AND the drag strip. The drag strip is more abusive on these IRS components short term...so I have been focusing on that lately.

On to the pictures that should help explain what is happening when these Stock and Aftermarket Diff Mount bolts fail.

-The OEM Fasteners are mounted with the shear path right on the threads of the bolts

-The Front Bushing is threaded, and the housing is non-threaded

-The Rear Bushing is non-threaded, but the diff mount is threaded

-Not only are the loads hitting the threads when the clamping force is not sufficient, but there is also a gap that is promoting that shear!

-
Pay close attention the the bushing from my Blue 2015 car. Check out how deformed that bushing sleeve is!

-There is more info that I will be posting in this thread. I would like for this to become a good thread with tech and input from everyone. Members, vendors etc.

I will share some other pictures later on that show "symptoms" and signs of issues.

*pictured in these photos are 12.9 Upgrade Bolts and some other pieces that will be in our new coming "Differential Hardware Upgrade Kit" - which will work on stock vehicles and BMR or Steeda Diff Kit Equipped cars.

:cheers:
Upgrade VS Stock.jpg
Upgrade VS Stock 2.jpg
Front Factory Mount.jpg
Rear Factory Mount Threaded.jpg
Stock Rear NA PP Car 1.jpg
Rear Bushing From BluBallz 1.jpg
Front Bushing Slop.jpg
Front bushing hole misaligned.jpg
Front bushing hole aligned.jpg
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s550v6

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Awesome!
 

jvm051

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Followed you over from the FB post Kelly. So I finally had a chance to get a better look at the pictures and it looks like there are sleeves inside the stock aluminum bushings to fill the void, combined with the upgraded 12.9 bolts, thus negating the need for the through bolt on the rears for those that do not want to to go the extra mile and drill out the diff cover. You mentioned the through bolt is still the better option, but if the void is still present with the through bolt, is the likelihood of the bolt still shearing still present, OR is the upgrade to install the sleeve in conjunction with the through bolt. Will this require the removal of the through bolt again? I ask due to having to remove my halfshafts to install, and would prefer to be done at this point, but if this is the FIX, then it is what it is.

Another question partially due to the Quality Engineer/nerd in me, with regards to the new bolts and the sleeves. I see the pictures of the distorted aluminum in the factory bushings, and I'm curious if the likelyhood of the distortion still being present after the bolt and sleeve upgrade, since the aluminum is still softer than the bolt. Since the bolt still tightens down to the BK051 bushing in my situation, and there will be some flex from the bushing, I'd think there is still opportunity for deflection present, and the possibility distorting the softer aluminum from the factory bushing, eventually leading to damage of the bolt? I am just curious your thoughts on this?
 
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Followed you over from the FB post Kelly. So I finally had a chance to get a better look at the pictures and it looks like there are sleeves inside the stock aluminum bushings to fill the void, combined with the upgraded 12.9 bolts, thus negating the need for the through bolt on the rears for those that do not want to to go the extra mile and drill out the diff cover. You mentioned the through bolt is still the better option, but if the void is still present with the through bolt, is the likelihood of the bolt still shearing still present, OR is the upgrade to install the sleeve in conjunction with the through bolt. Will this require the removal of the through bolt again? I ask due to having to remove my halfshafts to install, and would prefer to be done at this point, but if this is the FIX, then it is what it is.
Well. Unfortunately I do not know if still having the gap is going to be a significant difference, with your current modification.

But what I do know is:

-I have not seen a failure on a 1000hp stick shift car with your same bolt arrangement

-Your through bolt arrangement is a 12.9 grade and can be torqued to a higher value than the 10.9, although slight...that additional amount adds significant clamping force and will likely allow the mating surfaces to stay in place. Remember, the issue isnt necessarily the gap...but the surfaces "slipping"....which enables the bolts to contact the sleeve with force.

-Your diff kit arrangement is helping to support the bolt, and helps prevent it from shifting in the sleeve and contacting as the pictures show.

-If contact happens on your current set-up, the impact is likely low due to the inner and outer support (diff insert kit / diff cover tolerance) of the bolt....AND, if it does impact....that shank isnt breaking :cheers:

-Lastly and most important! The spacers we will be offering will pop right in for you! Remove the nut on the rear side...slide the spacer over the bolt and into the bushing, re-install nut. Woot!

Another question partially due to the Quality Engineer/nerd in me, with regards to the new bolts and the sleeves. I see the pictures of the distorted aluminum in the factory bushings, and I'm curious if the likelyhood of the distortion still being present after the bolt and sleeve upgrade, since the aluminum is still softer than the bolt. Since the bolt still tightens down to the BK051 bushing in my situation, and there will be some flex from the bushing, I'd think there is still opportunity for deflection present, and the possibility distorting the softer aluminum from the factory bushing, eventually leading to damage of the bolt? I am just curious your thoughts on this?
I do not think this would happen. The reason is because the fit is very snug. The deformation you see is from the bolt shifting and "smacking the ever living snot" out of the sleeve.

So the solution is, higher clamping force so that bolt does not utilize that gap...or fill the gap...or both.
 

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Well let me know when the bits are ready I will give em a shot.
 

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Kelly, in your original post you talked about getting another S550 strictly for testing purposes. I tried to tell my wife I needed to pick up another Mustang GT "strictly for testing purposes", but she wasn't buying what I was selling. I tried to convince her that picking up a manual trans GT to complement my auto would provide a complete testing platform to assist all those who are testing this platform and making improvements. All she does is roll her eyes. I just can't win...
 
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LMAO

Well, speaking of diff bolts. I have an issue over the weekend...and had to leave my car up in the air. Didn't have a 14x2 tap nor a 12mm Hex wrench. My wife was NOT happy about this, especially since our daughter had her b-day party this weekend and I think my wife was embarassed. haha! Not sure how much more she can take.

The funny part is, my blue car is in the garage completely ripped apart too... She loves it....
Stocktonaut on Stands.jpg
 
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Back to diff bolts! Got some super good pics and info to share tomorrow. ;)
 

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The struggle is real....
 

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Here is some solid info. This is from my 2016 PP GT pictured above on jack stands.

This car has 7700 miles. It has a tune, KN Filter/mishi tube and Pypes Mufflers.

It has been to 2 road courses (on street tires)...and to the drag strip 3 times. One drag strip visit on street tires wheel hopping a little....once on 20" MT drag radials, no wheel hop and once on Hoosier Slicks launching at 5500+ cutting 1.5~ sixties.

I want to clarify....the diff has NOT BEEN TOUCHED. These pics of the witness marks and shifted diff are from the factory diff mounts and TQ settings etc.


Driver Side Rear Bushing Slipping 2.jpg
Insert Installed Rear Bushing.jpg
Front Driver Side Bushing Slipped.jpg
Front Driver Side Bushing Re-Indexed.jpg
Front Pass Side Bushing Slipped.jpg
Front Pass Side Bushing Re-Indexed.jpg
BK051 Rear With upgraded Hardware and Sleeves.jpg
 
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Kelly

Ok where can I find the instructions for the upgrade install? What is the part that is so hard for everyone and what should be ordered?

sorry if I have missed something in a post but I just want to make sure I understand.
 

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This thread make me want to buy them again. Even though they are already installed. Good info!
 
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For those of you have have a BMR or Steeda Diff Insert or Lockout Kit....and want the ULTIMATE solution, check this out.

You will need the following:

(2) 9/16" fine thread bolts that are 4.5" long (grade 8 or higher)
(2) Lock Nuts
(2) Washers
(1) 9/16" or 14mm Drill bit (to remove the threads in the front bushings)

You will gain access to the front bushings by lowering the cradle enough. Drill / ream out the bushings....insert these bolts and tighten everything up. Not too bad!

Some cliff notes:

-The 9/16" Fine Thread bolts below are 14.14mm at the shank
-The 14mm Bolts used for these are <14mm at the shank
-The 9/16" bolts are 1mm larger at the thread base, which makes them much stronger
-The 9/16" bolt is the best way to increase (drastically) shear strength
-Using a one bolt design, through bolted, is much stronger in EVERY way.

Here ya go!
UPGRADED THROUGH BOLTS.jpg
Shear path on upgraded through bolt.jpg
Through Bolt VS Standard Insert Kit.jpg
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