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Speedy

Mystery Diff Noise Solved (I Think)

82 posts in this topic

I had been getting a weird clunk/tapping noise from the rear area of the car, right behind the driver seat.  It would happen when on/off the pedal or when taking off and it seemed to make the clutch want to chatter more as well.  I had a hunch it was the rear diff bolt that's toward the front of the Getrag and was afraid I'd either cracked the housing or torn the bushing.

 

I couldn't see anything on my Race Ramps so went over to my buddy's shop today to borrow the lift.  He and I walked around the chassis checking things and found that rear diff bolt a bit loose.  We snugged it up but I waited to get home and torque it when I had the specs as it's just a 15mm bolt and quite long.

 

Torquing that bolt is a major PITA.  It has a washer with integrated nut up top in the cross beam that is recessed pretty deep.  After about 15 mins of fiddling I got the 17mm deep socket on it and was able to torque it the bolt to 48 ft/lbs.  This got rid of the slop and about 90% of the noise.  I'm still hear a slight tap when I let the clutch out which leads me to believe the bushing is getting worn.

 

I'm guessing that's going to be a pretty big job to replace and I will likely just do the rear cradle bushings with it.  May be a project for over the winter, but something I'll do at his shop after the bushing horror stories I've read.  Any advice appreciated.

 

The only other thing we found was the carrier bearing in the DSS Chromoly DS had about 3/8" of play in it.  Not sure if that's considered normal or not?  It's not making contact with anything, will just move up and down a bit when you muscle it around.

 

Keep an eye on those bushings if your racing on the regular.

 

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Speedy, That is a common problem. HHP has an aluminum bushing that replaces half of that pinion mount you are describing. 70..

 

http://www.highhorseperformance.com/HHP_Racing_Solid_Rear_Differential_Pinion_Support_p/hhpsrbil.htm

 

That may be the ticket.

 

takes 15 minutes to replace the pinion bushing.

 

Seriously?  Fill me in.  Remove the bolt and it'll drop out?

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Not sure I'm ready for a solid pinion support bushing.....it may transmit too much NVH for me as I drive on the street A LOT.  Anyone know of a poly version?

 

Visually the bushing looks "OK".  It's just making a bit of noise even though it's torqued to spec which leads me to believe it's compressed a bit past spec.  Not 100% positive though.

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Also you shouldn't have needed to put a socket on the nut. Normally if you let the weight of the dif hang on it, it won't move so you can tighten it. But if the threads are jacked it's a pain as you found out. I took a deep socket and cut it down to the perfect size for just such an occasion.

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I had the car on Race Ramps when working on it.  I could hear the scraping sound of the nut spinning.  I've not had one of these in my hands, is that further evidence of failure?

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If the weight of the dif still allowed the nut to spin, I wonder if the upper rubber piece is toast, you should have not heard it "scrape".

Hopefully I'm able to post these off my phone. But this is what it looks like.

post-821-0-50937700-1451933557_thumb.jpg

post-821-0-42803200-1451933570_thumb.jpg

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Those help for sure.  I had to use a mirror and a flashlight to get creative and figure out what size that nut is.  17mm is correct ins't it?

 

As I was trying to tighten the 15mm bolt I could definitely hear the top turning and scraping, kinda like a crusty sound like there was some dirt in that pocket turning with everything. 

 

If it's really just 15 mins I may as well just swap it out.  Will probably take me 45 as I'm not the Hemi Jesus though lol

 

Is there a poly that's any good or just go back with stock?

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Yup it's a 17. I don't think it's worth it if they do make a poly. I've seen too many of the getrags busted to consider going to a more solid mount. It's one of the few things I'd leave on stock rubber. Normally a bushed mount anything is designed to allow the assembly to move X amount. So imho having one portion of it more or less fixed and not touching the case mounts might make it worse. I don't think there's enough movement overall to make it worth it. It's not like the cradle where we know it'll ocsolate 1/2" when loading n unloading.

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Got it.  I'll take a look and see what I see.  Thanks for the pics and info.  I'll grab a spare and pull mine to see how it looks and just swap it out.  The top half just lifts out of the pocket once the bolt is removed?

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Speedy,I have the HHP mount and didn't notice any difference in NVH. I don't think its a true solid mount siince you still use the bottom rubber. I think its a good mod to help keep everything square. 

 

 

Also, If you have trouble removing it you can try a cargo strap pulling down on the diff. this will keep friction on the upper mount so it doesn't spin.  70..


Fit auto cars too or only Getrags?

 

Stevo

I believe it is for all LC/LX cars 70..

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Got it.  I'll take a look and see what I see.  Thanks for the pics and info.  I'll grab a spare and pull mine to see how it looks and just swap it out.  The top half just lifts out of the pocket once the bolt is removed?

Yes, use the bolt to push it up out of the cradle until you can grab it. It's PITA if you have fat fingers.  70

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Speedy,I have the HHP mount and didn't notice any difference in NVH. I don't think its a true solid mount siince you still use the bottom rubber. I think its a good mod to help keep everything square. 

 

 

Also, If you have trouble removing it you can try a cargo strap pulling down on the diff. this will keep friction on the upper mount so it doesn't spin.  70..

I believe it is for all LC/LX cars 70..

Good to know. I went on the HHP website and it did not mention auto or 6 speed.

Thanks,

 

Stevo

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Those help for sure.  I had to use a mirror and a flashlight to get creative and figure out what size that nut is.  17mm is correct ins't it?

 

As I was trying to tighten the 15mm bolt I could definitely hear the top turning and scraping, kinda like a crusty sound like there was some dirt in that pocket turning with everything. 

 

If it's really just 15 mins I may as well just swap it out.  Will probably take me 45 as I'm not the Hemi Jesus though lol

 

Is there a poly that's any good or just go back with stock?

Stock or the HHP aluminum. No poly it's crap.

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Stock or the HHP aluminum. No poly it's crap.

 

Agreed, poly is garbage. Destroyed after 1st pass. The 2 bushings at the rear of the diff are beginning to crack. 

 

2014-07-01_22-23-51_699.jpg

 

 

20150406_173255.jpg

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Damn.  Poly = crap.  Got it.  I'll just replace it with stock and hope that solves it.  If so, the stock bushing lasted 6 years of pretty hard driving.

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Damn. Poly = crap. Got it. I'll just replace it with stock and hope that solves it. If so, the stock bushing lasted 6 years of pretty hard driving.

What is the part # speedy

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I had the same issue with the hhp solid pinion mount. Pinion bolt backed out a bit and it sounded like a hammer hitting the underbody when I lifted. Little thread locker and problem solved. There is added nvh with the solid hhp product.

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What is the part # speedy

 

The bushing is two pieces, upper and lower.  I went ahead and got a replacement bolt as well for good measure.

 

4578085AA - bushing half

4578191AA - bushing half

6509315AA - bolt

 

I get a discount but the parts should all be about $30.

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Thanks to Hemi31 for giving me the heads up this was an easy bushing to replace or I may have put it off.  Once I got it out, I'm glad I didn't wait.  Both the upper and lower bushing were shot.  Bolt was fine but for less than $3 I figured to go ahead and replace it anyway.  There was probably 1/4" of play between the metal washer and rubber bushing on the top half, and the bottom was smashed flat.

 

challenger_pinion_bushing_repair_05_web.     challenger_pinion_bushing_repair_06_web.

 

If you have a Getrag and make any power at all, or drag race frequently, I'd suggest putting this on your regular maintenance list.  Erik was right, the swap only took about 15-20 minutes.  Getting the original out was easy, getting the new one in a bit more of a challenge as you have to hold the top have while tightening the bolt, but no big deal with a 3/8" ratchet, deep well 17mm socket and a short extension.

 

To recap, my symptoms were a clunk/tap sound coming from the rear when I let off the clutch, or eased on and off the gas.  Occasionally shifting between gears was a bit more stiff than usual indicating some bind back there as well.  Not good obviously.  Mine happened pretty suddenly and seemed to occur shortly after I went to the DRs.  Maybe all those 0-60 runs I did finally killed it.  Car has a tick over 23,000 miles on it and I can't count how many drag strip runs.  Lasted a pretty good while for a stock part on this car I think.

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