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

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jvm051

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Kelly,
No dice at Home Depot or Lowes. You got any part numbers or chain stores that will have in this size or did you order online? If so who is your hookup sir?
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You should see our hardware department.

Shoot me a message on FB. I'll send everything out to you sir, as long as you post pics in here ;)
 

Draklia

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Just my thoughts. Seems to me the bolt size just isn't large enough to give the clamping force needed to keep the bolt out of shear. Have you seen if there are signs of the bushing sleeves marring from not enough clamp force at stock HP levels?
Probably the best thing, though probably not feasible is bumping up to a much larger bolt, course you'd need to know the forces and all that jazz to size appropriately to get the clamping force that will eliminate movement. Guessing the move up to 9/16 bolt isn't adding that much to increase the clamping. But, glad you are taking the time to try to improve what can be done.
 

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Just my thoughts. Seems to me the bolt size just isn't large enough to give the clamping force needed to keep the bolt out of shear. Have you seen if there are signs of the bushing sleeves marring from not enough clamp force at stock HP levels?
Probably the best thing, though probably not feasible is bumping up to a much larger bolt, course you'd need to know the forces and all that jazz to size appropriately to get the clamping force that will eliminate movement. Guessing the move up to 9/16 bolt isn't adding that much to increase the clamping. But, glad you are taking the time to try to improve what can be done.
You are absolutely correct.

I have stated this many times on this forum, that the bolt diameter is the most important part....NOT the grade of the bolt. These issues have been going on for quite some time now, and I have been working to try and prevent them. This is why it took us so long to release our diff kit, so we could test various bolt configurations.

I worked with GForce engineering on their 9" Kits. They use BMR Billet bushings for the diff mounts, and per my recommendation - use a larger center hole with a 16mm 10.9 bolt.

As for these solutions for these stock-ish set-ups...I was going to use a 5/8" fine thread bolt. This would raise the TQ spec to approx 180ftlbs with roughly 25%more clamp load...but I wanted to use the 9/16" fine thread bolt first as it is only "drill the bushing and go"...as it will work with the current diff kits out there, and also work well with the stock bushings if one chooses to do so. When going larger, it requires modifying more than just the OE bushing sleeves.

Nonetheless....the diameter of the entire 9/16" bolt from the shank to the thread base is significantly larger, and placing the shear loads on the shank that is 14+mm will provide a much better solution.

To answer your question, yes, we see the mating surfaces compromised on stock cars. I have shown pics above that should enable people to be able to go check and see if their mating surfaces have lost their initial torqued position, without too much effort.

A few things I think the OEM could have done with this is to make the diff mount ears interlock to the bushing....OR they could have gone up on the surface contact areas of the diff mount ears and the bushing sleeves. Or of course, simply used 16mm or 18mm diameter bolts. The latter being what I would have loved to have seen.
 

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You are absolutely correct.

I have stated this many times on this forum, that the bolt diameter is the most important part....NOT the grade of the bolt. These issues have been going on for quite some time now, and I have been working to try and prevent them. This is why it took us so long to release our diff kit, so we could test various bolt configurations.

I worked with GForce engineering on their 9" Kits. They use BMR Billet bushings for the diff mounts, and per my recommendation - use a larger center hole with a 16mm 10.9 bolt.

As for these solutions for these stock-ish set-ups...I was going to use a 5/8" fine thread bolt. This would raise the TQ spec to approx 180ftlbs with roughly 25%more clamp load...but I wanted to use the 9/16" fine thread bolt first as it is only "drill the bushing and go"...as it will work with the current diff kits out there, and also work well with the stock bushings if one chooses to do so. When going larger, it requires modifying more than just the OE bushing sleeves.

Nonetheless....the diameter of the entire 9/16" bolt from the shank to the thread base is significantly larger, and placing the shear loads on the shank that is 14+mm will provide a much better solution.

To answer your question, yes, we see the mating surfaces compromised on stock cars. I have shown pics above that should enable people to be able to go check and see if their mating surfaces have lost their initial torqued position, without too much effort.

A few things I think the OEM could have done with this is to make the diff mount ears interlock to the bushing....OR they could have gone up on the surface contact areas of the diff mount ears and the bushing sleeves. Or of course, simply used 16mm or 18mm diameter bolts. The latter being what I would have loved to have seen.
Short of major machining to get a 3/4" bolt in there I wonder if there is anyway to increase the surface friction of the mating parts. Wonder if there is such a thing as something that would be like double sided emery paper or something along those lines that could make the sleeve bite into the mounting surface. Just thinking of a ultra-thin badass star washer, but not really, more of a gritty substrate? Just dreaming I suppose.
 
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I like your thinking! I can try and test if I have time.

Due to the smoothness and hardness of the diff ears though, I am going to guess surface area will trump grittiness. Just a wild guess.
 

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So I did the Steeda Diff Bushing Insert Kit (your kit wasn't available yet, Kelly).

I don't think I even had 1,000 miles on the car, and did the install the same time as the CB005 & Ford Performance Track Pack suspension install. Apparently, during assembly at the factory, the passenger side rear bolt that threaded into the front bushing may have been installed improperly, as removal of that bolt was a bear, and took a significant amount of force just to get the bolt out. It appeared that the bushing was either split in 2, or some other issue with thread stripping/damage at the half-way point.

Because I was working on it over the weekend, and didn't want to drop the entire rear diff mount, order new bushings, replace all 4 mounts worth of bushings, and have the car down for nearly 2 weeks waiting for parts, etc., I decided to install the kit's new grade 8 bolt into the damaged bushing. It took over an hour of basically re-threading the back half - thread in, back out, thread in a little more, back out, etc, etc. At this point, if the bolt ever needs to come back out, so too will the bushing, which is going to be a much bigger job as the diff mount will need to be dropped. And the amount of twist of the factory rubber bushing while I was "re-threading" the back half of the bushing was pretty bad. The replacement bolt is at least holding the factory bushing together, and the Steeda kit is providing the reinforcement needed to keep things tight back there for now. We'll see how long that will last with HPDE events.

Eventually, I will make a decision on an aftermarket bushing kit to install, but am in no hurry to tear the entire rear end apart to do that particular job.

So yeah, that design has some major issues, as even the factory can't get the install right from the get-go.
 
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Agent_S550

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So I did the Steeda Diff Bushing Insert Kit (your kit wasn't available yet, Kelly).

I don't think I even had 1,000 miles on the car, and did the install the same time as the CB005 & Ford Performance Track Pack suspension install. Apparently, during assembly at the factory, the passenger side rear bolt that threaded into the bushing may have been installed improperly, as removal of that bolt was a bear, and took a significant amount of force just to get the bolt out. It appeared that the bushing was either split in 2, or some other issue with thread stripping/damage at the half-way point.

Because I was working on it over the weekend, and didn't want to drop the entire rear diff mount, order new bushings, replace all 4 mounts worth of bushings, and have the car down for nearly 2 weeks waiting for parts, etc., I decided to install the kit's new grade 8 bolt into the damaged bushing. It took over an hour of basically re-threading the back half - thread in, back out, thread in a little more, back out, etc, etc. At this point, if the bolt ever needs to come back out, so too will the bushing, which is going to be a much bigger job as the diff mount will need to be dropped. And the amount of twist of the factory rubber bushing while I was "re-threading" the back half of the bushing was pretty bad. The replacement bolt is at least holding the factory bushing together, and the Steeda kit is providing the reinforcement needed to keep things tight back there for now. We'll see how long that will last with HPDE events.

Eventually, I will make a decision on an aftermarket bushing kit to install, but am in no hurry to tear the entire rear end apart to do that particular job.

So yeah, that design has some major issues, as even the factory can't get the install right from the get-go.
I had a very similar situation with my Steeda kit. Would've happened with BMR's too given my stock bushing sleeves were incorrectly threaded. I still intend to drill mine out to 9/16" and just thru bolt the entire thing.
 

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Had some time earlier to put the 9/16" through bolts in the front mounts.

Dropped the cradle, drilled the bushings and that's all she wrote. Perfect fit and should work great.

I used a crows foot socket and torqued them to 130ftlbs.
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Thank you for all the information that you are providing, Kelly. This is something to keep in mind in the future when my car becomes more of a spirited driving and track use car instead of my daily :D
 

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So, you just drilled the threads completely out and drove a bolt all the way through and Nutting on the end to make it work? Pun intended.
 

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Well the plan was to get the front through bolts installed today, but due to some unforeseen issues with my friend who was going to be performing the surgery on the car, it has been postponed till next weekend. I will update the thread when we have it completed.
 

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Kelly, trying to collect together the hardware I need for a thru bolt on the whole thing. Have part numbers so I can make sure the quality/grade is up to par?
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