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This happens on some S550 mustangs when launched hard. BMR and Steeda offer upgraded bolts for mustangs to try and help solve the problem. Some people (such as myself) drilled out the threads in the bushings and diff and through bolted them. This holds it much more solid and allows you to use a bolt that place the load on the shank of the bolt instead of on the threads. After seeing this I might consider doing it on my RS.
 

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I don't want to scare anyone and from my googling, I'm the first/only report on the forum. I cannot remember if we torqued them to spec, I think yes. It's hard to say when exactly this happened, I just started hearing a clunk in the back from the RDU moving. It was not after any particular event or hard driving. The only thing I can think of is somewhat recently, maybe 1 or 2 weeks ago, I was sitting parked after starting the car and texting on my phone. Forgot car was still in gear and let the clutch out while on brake. Loud bang and engine stalled. I drove the car pretty hard after that to see if I broke anything.. that's my best guess.
 

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@Hank @tedsRS I'm going to chime in, I haven't broken a bolt yet. That being said I was getting some noises from the back end. I got under the car this past weekend and realized that my RDU was moving all around. Here's what happened: The large washers that ship with the powerflex inserts keep the bolts from completely engaging all the threads in the RDU. Although my bolts were torqued, they were not completely inserted due to the additional thickness of the washers and the inserts. Looking at the thickness and at how the stock inserts are recessed, there is probably a cm or more that the threads aren't engaged with. I'm hoping that pulling the washers and reinserting the bolts will alleviate the movement. I'm concerned I may have jacked up the threads since the bolts weren't fully inserted. I am going to run the inserts without the washers and see if they just fall out after getting squeezed all around.
 

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Is it worth getting a class 10.9 bolt that's about 1cm longer than stock? As long as it doesn't bottom out?

I'm considering the yellow bushings at some point in the future.
 
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Is it worth getting a class 10.9 bolt that's about 1cm longer than stock? As long as it doesn't bottom out?

I'm considering the yellow bushings at some point in the future.

I already have mine sitting in my garage:

345846


I was just waiting for some wrench time to come up.

Reading about all this bolt snapping makes me think about a couple of things, base from @Hank 's install:

345847

  • How much of the threads are threaded/in contact before and after the install? If i base it on the discoloration on threads, that would be 11 threads in?
  • The bolts has tips that does not have threads, that makes me think at least that part and a thread or three are recessed out?
  • Getting thinner washers might help?
 

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I already have mine sitting in my garage:

View attachment 345846

I was just waiting for some wrench time to come up.

Reading about all this bolt snapping makes me think about a couple of things, base from @Hank 's install:

View attachment 345847
  • How much of the threads are threaded/in contact before and after the install? If i base it on the discoloration on threads, that would be 11 threads in?
  • The bolts has tips that does not have threads, that makes me think at least that part and a thread or three are recessed out?
  • Getting thinner washers might help?
If you look at the photos on @Hank 's install page and on this thread, there are only a few turns worth of threads sticking out. With the added thickness of the bushing and washer, you might lose enough thread engagement to matter. Not sure what other people have seen who have installed these parts.
 
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As you said might be worth getting longer bolts?

Powerflex should have indicated/included longer bolts.
 

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As you said might be worth getting longer bolts?

Powerflex should have indicated/included longer bolts.
I can tell looking at the images posted here and at Hanks images that with the std bolts you are going to be around 8-10mm short of the std thread engagement. I mean seriously, when are you guys going to figure out that the majority of these "special parts" are just **** or at the very least in some way shape or form introduce some half arsed suspect engineering element into the equation.
I'm trying to think of an aftermarket supposed upgrade that actually enhances the OEM 100% without some suspect engineering involved.

Ciao
 

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My desktop computer died 2 weeks ago. Although difficult to post on my iPhone, here are my thoughts on this discussion.

I just went out and measured the (3) RDU bolts and mounting locations on my RS. The front RDU mount is ~26 mm thick. Each rear RDU mount is ~33 mm thick. I’m not taking the RDU bolts out again, but I’m almost positive the (3) mounts are fully threaded.

The (3) RDU mounting bolts are all M12 (12 mm diameter). Didn’t measure the pitch, but they appear course (1.75). The factory manual calls out for 66 lb-ft of torque on these (3) bolts, so based on torque charts online we can deduce the (3) RDU bolts are class 8.8.

I’m no materials expert, but I’m guessing the RDU is sand cast aluminum, A356-T6. The minimum thread engagement chart below states a M12x1.75 fastener in a nut material (RDU housing = nut material) of A356-T6 requires 25.8 mm.

It would appear the rear RDU mounts are sufficient with the OE bolts + Powerflex inserts and washers. The front RDU mount, however, seems just a few mm short of optimal due to the OE bolt not being fully threaded.

Based on these findings I will continue to monitor the Sharpie marks that I have on all fasteners that I have removed and/or replaced due to my RS modifications. If I detect movement in the front RDU bolt I will consider replacing it for a longer bolt.

References:

Bumper Automotive exterior Tire Automotive tire Auto part
Auto part Vehicle Engine Car
Auto part Tire Automotive tire Metal Carbon
 

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@Hank , did you remove the OE washers (the small one right below the bolt head and the cross shaped washer)?

I did notice you kept the small washer just right under the bolt, that might be worth a thread in.
 

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@Hoonigan , merge with :

 

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Incase anyone was dying for an update, I got my car back. Thankfully all covered under warranty. They had it for about 2 months. Replaced the RDU.. apparently the aluminum alignment faces were all ****ed up from the rdu not being fully supported. Took about a month to get RDU sourced and another month to get some special torque to yield bolts that they didnt know they needed until they went to install the new RDU.

Everything is good now. They even allowed me to purchase new powerflex inserts and reinstalled them for me lol.

Sorry I failed to get any pictures. I'm just happy to have my car back.
 

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Incase anyone was dying for an update, I got my car back. Thankfully all covered under warranty. They had it for about 2 months. Replaced the RDU.. apparently the aluminum alignment faces were all ****ed up from the rdu not being fully supported. Took about a month to get RDU sourced and another month to get some special torque to yield bolts that they didnt know they needed until they went to install the new RDU.

Everything is good now. They even allowed me to purchase new powerflex inserts and reinstalled them for me lol.

Sorry I failed to get any pictures. I'm just happy to have my car back.

No pictures?! Unacceptable!

LOL
 

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Incase anyone was dying for an update, I got my car back. Thankfully all covered under warranty. They had it for about 2 months. Replaced the RDU.. apparently the aluminum alignment faces were all ****ed up from the rdu not being fully supported. Took about a month to get RDU sourced and another month to get some special torque to yield bolts that they didnt know they needed until they went to install the new RDU.

Everything is good now. They even allowed me to purchase new powerflex inserts and reinstalled them for me lol.

Sorry I failed to get any pictures. I'm just happy to have my car back.
If the bolts are torque to yield then they should not be reused. Anyone that has done this should consider buying new bolts... now. My 2 cents.
 

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My desktop computer died 2 weeks ago. Although difficult to post on my iPhone, here are my thoughts on this discussion.

I just went out and measured the (3) RDU bolts and mounting locations on my RS. The front RDU mount is ~26 mm thick. Each rear RDU mount is ~33 mm thick. I’m not taking the RDU bolts out again, but I’m almost positive the (3) mounts are fully threaded.

The (3) RDU mounting bolts are all M12 (12 mm diameter). Didn’t measure the pitch, but they appear course (1.75). The factory manual calls out for 66 lb-ft of torque on these (3) bolts, so based on torque charts online we can deduce the (3) RDU bolts are class 8.8.

I’m no materials expert, but I’m guessing the RDU is sand cast aluminum, A356-T6. The minimum thread engagement chart below states a M12x1.75 fastener in a nut material (RDU housing = nut material) of A356-T6 requires 25.8 mm.

It would appear the rear RDU mounts are sufficient with the OE bolts + Powerflex inserts and washers. The front RDU mount, however, seems just a few mm short of optimal due to the OE bolt not being fully threaded.

Based on these findings I will continue to monitor the Sharpie marks that I have on all fasteners that I have removed and/or replaced due to my RS modifications. If I detect movement in the front RDU bolt I will consider replacing it for a longer bolt.

References:

View attachment 345894 View attachment 345895 View attachment 345896

@Hank just checking in if there's any changes at your end on this?
 

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I forgot to reply to you. No changes. Bolts have not moved after torqued.
 

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The rear two inserts for me have been fine. I’ve had the front vibrate looose though, also add the fact it’s brutal to install, you need to trim a few mm off to get it to insert
 

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The rear two inserts for me have been fine. I’ve had the front vibrate looose though, also add the fact it’s brutal to install, you need to trim a few mm off to get it to insert

Which part did you trim?
 

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I'm assuming the torx bit (and hoping not the insert), but I used stubby bits and it all went together ok -- no trimming anything. I also used a crows foot on the stubby bit to torque it. From what I recall, the most difficult part is getting the RDU to line back up to put the front mount bolt back in.
 
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