Drivetrain Clunk from the rear at 10 mph coming to a stop

zack2001

Member
Dec 11, 2019
20
1
13
Lansing, MI
I had 4.10 gears along with an aftermarket 7.5" rear end rebuild kit installed in my 2005 V6 about a year ago. Recently, a clunking noise began coming from the rear of the car while coming to a stop, and it happens at exactly 10 mph. About one week ago, I took my car to the same mechanic shop that I had the 4.10 gears installed due to a howling noise while going around turns at low speeds, and it turned out my differential fluid was leaking and my axle bearings were bad, which I had them fix. They also let me know that when they had taken off the differential cover, barely any fluid came out.

When it was done being fixed, the mechanics believe the rear end rebuild kit I had them install was bad. After reading the one star reviews it seems like there are complaints about the lack of shims and the bearings being bad.

Along with the clunking at 10 mph, my rear end still makes a lot of whining and howling going around turns even after getting the axle bearings fixed, although it did help reduce the noise a little bit. Friction modifier did get added to the fluid when the axle bearings got fixed, and when I got the 4.10 gears installed I made sure I bought synthetic gear oil (75w-90) with friction modifier in it, so I don't know if that has to do with anything, I hope adding this will help explain things better.

Today, I lifted the rear of my car up and checked the driveshaft for play. With the car in park, I can turn it clockwise a little bit (it stops itself from turning any further), but it clunks as I'm doing it. I also spun one of the rear tires forward and the same clunking noise gets made. Is this normal? I can post videos if asked.

Link to rear end rebuild kit: https://www.americanmuscle.com/rearendrebuild1.html
 
  • Sponsors(?)


StangNet created a new car social app called knowmoto! Add your Mustang or post a photo in the knowmoto app and enter for a chance at a $100 gift card from LMR. Click the LMR Logo for more about the knowmoto Mega Thread!

KRUISR

5 Year Member
Apr 16, 2015
782
292
83
51
When the shop replaced the bearings, did they do the pinion bearing too or just the axle bearings? If low on oil the pinion bearing could be bad too.

If pinion bear changed, did they make sure it was set up correctly again (like you need to do when you change gear set)?
 

zack2001

Member
Dec 11, 2019
20
1
13
Lansing, MI
When the shop replaced the bearings, did they do the pinion bearing too or just the axle bearings? If low on oil the pinion bearing could be bad too.

If pinion bear changed, did they make sure it was set up correctly again (like you need to do when you change gear set)?
They didn't tell me anything about a pinion bearing, they only let me know about the axle bearings and leaking diff fluid. Could the pinion bearing be causing the issues I'm describing?
 

KRUISR

5 Year Member
Apr 16, 2015
782
292
83
51
If the pinion bearing wore due to low/no oil, the clearance between the pinion gear and ring gear could be increased and out of tolerance. That added clearance could cause clunking. If they pulled the pinion gear, did they replace the crush washer or just reuse the old one (some reuse but add an additional shim/spacer) and tighten some more (that could cause added clearance as well).

Are your U-joints on the drive shaft "tight". Worn U-joints can cause the clunking as well.
 

zack2001

Member
Dec 11, 2019
20
1
13
Lansing, MI
If the pinion bearing wore due to low/no oil, the clearance between the pinion gear and ring gear could be increased and out of tolerance. That added clearance could cause clunking. If they pulled the pinion gear, did they replace the crush washer or just reuse the old one (some reuse but add an additional shim/spacer) and tighten some more (that could cause added clearance as well).

Are your U-joints on the drive shaft "tight". Worn U-joints can cause the clunking as well.
How can I check for bad u-joints precisely? I get a clunking shifting from Park to Reverse, but in ChrisFix's video about u-joints he says a symptom of them being bad is a clunk from Drive to Reverse, or Reverse to Drive, which I'm not experiencing. I'm not experiencing any constant squeaking like he says, but I do hear a squeak from either the front or the rear when hitting bumps real hard at low speeds. I know you can also test for play in the u-joint with the car in neutral but I haven't had the chance to do that yet.
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
736
276
73
57
Memphis TN
"When it was done being fixed, the mechanics believe the rear end rebuild kit I had them install was bad. After reading the one star reviews it seems like there are complaints about the lack of shims and the bearings being bad."

Reading between the lines he's telling you the diff or center bearings are bad too.
 

KRUISR

5 Year Member
Apr 16, 2015
782
292
83
51
I would think that drive shaft U-joint play is too much. Start there and replace both ends.
 
  • Like
Reactions: 1 user

zack2001

Member
Dec 11, 2019
20
1
13
Lansing, MI
UPDATE: Took my car to my mechanic and he took the diff cover off and spun the diff around with the car in neutral. The pin bolt was really loose and there were some squishing sounds coming from the diff as it got spun so hopefully a higher quality rebuild kit will solve all of that. When spinning the driveshaft, only one tire would spin unless you gave a lot of effort into spinning the driveshaft and clunking could be heard inside the transmission while spinning it?? There was also grease leaking out both u-joints so once there's a performance driveshaft back in stock I'm going to buy one of those (has the U-joints pre-installed, all I have to do is just bolt it on).
 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
31,501
12,847
234
Box behind Walmart
www.stangnet.com
The eliminates my idea. I was going to suggest checking for a hooker in the trunk. :shrug:


Sounds like you found the issue though.


Grease leaking out of the U-joint doesn't necessarily mean anything. Depending on the type of U-joint, they are serviced with new grease until you see the old grease begin to come out. Some folks don't do a great job of cleaning up after themselves.

If you suspect the U-joints, apply new grease and wipe them down. Go for a spin and wipe them down one more time. They should weep too much after that. The important thing to check would be to get hold of the driveshaft at each end to see if there's any side-to-side movement.

You [can] get sealed U-joints. Those do not have grease fittings. They tend to not be as robust as the greaseable U-joints IMO.
 

zack2001

Member
Dec 11, 2019
20
1
13
Lansing, MI
Well this is odd... Why and how would a BAMA tune cause the rear end clunking? The clunking all started after I put an 87 performance tune made by BAMA on the car. I did a "Return to stock" on my car and the clunking noise is gone?? Now when I come to a stop I don't hear any abnormal noises like when I had the performance tune on the car. The performance tune was also causing other issues, like making me run too lean, rough idle, and for some reason it took forever to shift out of 1st gear when coming from a dead stop, I had to lift my foot off the pedal if I wanted the car to go into 2nd as if the car had a manual transmission. If I didn't lift my foot off the gas, it wouldn't shift until the engine reached redline, no matter how much input I put on the gas pedal, which was weird. With me returning the car to stock, my car idles and shifts fine now..

That still doesn't excuse all the play in the driveshaft though, I still plan on getting that checked out as well as getting my rear end rebuilt with a higher quality kit.
 

7991LXnSHO

10 Year Member
Sep 1, 2010
4,991
1,491
184
Kearney, NE
The eliminates my idea. I was going to suggest checking for a hooker in the trunk. :shrug:


Sounds like you found the issue though.


Grease leaking out of the U-joint doesn't necessarily mean anything. Depending on the type of U-joint, they are serviced with new grease until you see the old grease begin to come out. Some folks don't do a great job of cleaning up after themselves.

If you suspect the U-joints, apply new grease and wipe them down. Go for a spin and wipe them down one more time. They should weep too much after that. The important thing to check would be to get hold of the driveshaft at each end to see if there's any side-to-side movement.

You [can] get sealed U-joints. Those do not have grease fittings. They tend to not be as robust as the greaseable U-joints IMO.
The Hooker in the trunk was a good thing to check for. Especially if the owner uses more Ethanol than the car.
The u-joint robust thing depends on your use. The grease zirc and passages add a potential weak spot under big loads and shock loads (drag strip, towing). But dry U joints are soon dead, cooked U joints. So if there is a choice, I usually recommend greaseable ones installed with the zirc on the compression side during forward acceleration.
 

zack2001

Member
Dec 11, 2019
20
1
13
Lansing, MI
My mechanic called me today and told me I need to look for a rear differential carrier assembly (I have only found just the carriers for a 7.5" rear end, no pre-assembled 7,5" ones) and to find a new carrier and bearing kit, but looking that up, I haven't found anything related. However, looking at differential rebuild kits for my car, some of these kits include carrier bearings, pinion bearings, the various shims, and more. If I order the part linked here, will that be good enough for him? It seems like it would be, but correct me if I'm wrong


Edit: He said he needed a new carrier assembly with the spider gears and whatnot already in it, and since there are none that I could find, I'm currently looking at just getting an entirely new rear diff with everything in it already instead of hunting down every individual part
 
Last edited: