Rear Diff Clunking

Vegas99D1

Vegas99D1

Well-known member
May 5, 2009
187
9
Plano, TX
Got a weird clunk coming from the rear diff (took it to a shop, they narrowed it down to the rear diff). Only happens when going between 20-30mph..just cruising along. If i accelerate, the noise stops. If i slow down/stop, the noise stops. If i go around a easy turn it stops. The shop noticed that the diff fluid was a little "liquidy" (their words). So i had them drain and refill the diff to see if it would stop the noise. No difference. Any ideas? The shop wants to tear down the rear diff to check it out, but for their labor quote just to check it out i can buy a used diff from one of the recyclers.

What do the guru's of Dweb say?

Thanks!
 
R

robertf

Well-known member
Jan 22, 2006
4,790
360
-
check the driveshaft ujoints and bolts, but if that's not it put in a salvage unit. They should be close to free. I know I've scrapped a few.

I've got a ujointed rear I'd let go cheap if you ever made it up to Dallas.
 
Vegas99D1

Vegas99D1

Well-known member
May 5, 2009
187
9
Plano, TX
Yeah, already checked rear driveshaft u-joints, they are fairly new. It's something in the diff is that the shop told me.
 
K

keith13

Member
Feb 11, 2014
7
0
NEW YORK
I just had this happen to me ... the pin that holds the two opposing spider gears in the carrier has worn a slot in the carrier
the pin will eventually brake in half leaving you stuck unless you have a locking cdl
i did not, had to be towed home :banghead:
a reasonably easy fix tho

keith
 
R

robertf

Well-known member
Jan 22, 2006
4,790
360
-
It's a differential design from the 30s. The carrier is weak. If you put a locker in it the major weak point goes away

I broke one in an heb parking lot. It did have over 200k on it and oversized tires and lots of off road time
 
D Chapman

D Chapman

1
Jan 3, 2005
11,746
73
On Kennith's private island
It's a very weak carrier. So yeah, bad design, IMO. Some of the RR's and D2's had a two pin carrier that was much stronger, yet equally as shitty. Your carrier is a ticking time-bomb.

It's a pretty easy job to fix. 30 minutes.
remove rear driveshift on the diff side (4 bolts)
remove both rear wheels (assuming you have alloys)
Remove the five 15mm bolts holding the driveflange on both side and slide the axles out about 5"
Unbolt the diff and remove

From there your options are wide open. You could replace the stock carrier with another stock carrier. This would be the cheapest option.

If you do not off-road or anything, you could upgrade to a True Track carrier and never worry about this again. This is the best option, IMO. ~$500+-

Or you could install a locker. Almost worthless without also replacing your axles with HD's.

As long as you're not removing the pinion gear, which you should not need to, chances are you will not need to reset the gears. You should at least take a measurement before reinstalling, though.
 
K-rover

K-rover

Well-known member
Jan 15, 2010
2,171
66
Raleigh, NC
Ive got 190,000 miles on my stock diffs, and larger tires. This truck gets wheeled often, but I do change the diff fluid every year and run Lucas 85w140.
Ill probably wait till one blows up before I replace it with a locker.

When you drained the gear oil, where there large metal chunks on the magnet? If I were you I would just replace it with a good used stock unit.

Something else you can do is pull the rear shaft and drive it around in 4hi. See if the noise changes or goes away.
 
D

danleym

Active member
Jan 5, 2014
29
0
Colorado
In my experience, if a diff starts making noise, and you've eliminated anywhere else in the driveline, it's time to open it up. I drove around for months with a diff making weird clunking noises, but only under very precise circumstances. This was a full size Chevy Blazer, but it ended up being one of the bearings had completely broken off the side of the carrier. I don't know how it made it as long as it did.

Moral of the story, open up the diff. Or if you don't feel like paying for that, put a salvage one in. Better moral of the story is open up the diff yourself. Not saying you have to learn to rebuild one and set up gears, but pulling it apart to see if anything major jumps out at you isn't all that hard, and would save you a bunch of money.
 
Jagfixer

Jagfixer

Well-known member
Feb 25, 2008
367
3
Millstadt, IL
Most manufacturers of diffs can say they will last 100K. So as they age they wear and get loose. Regular fluid changes and the checking of internals once in a while can make them last long time. So figure age and what maintenance is done. I do mine more than most and only had a crushed pinion sleeve from drag racing with a 30ft boat on back at 90K. Cleaned diff and replaced sleeve and bearings then drove another 100K before trading.
 
M

MC97D1

Well-known member
Nov 30, 2014
63
8
Birmingham, AL
Truetracs are an off road upgrade too. They aren't a locker, but certainly better than an open diff or clutch type limited slip. Many people run them in both diffs and do plenty of off roading. I would recommend the truetrac.
 
chris snell

chris snell

Administrator
Staff member
Aug 15, 2005
3,020
152
Swapping a diff is seriously one of these easiest mechanical things you can do on your truck. It was the first real project that I ever did. The steps are as Dan detailed them. You can get the RAVE manual online and just print out the pages you need and go through the steps. The only "hard" part is getting the diff out of the axle. It's a heavy bitch. If it won't come loose after you unbolted it, put a floor jack under the nose of the diff (where the driveshaft connects) and give it a tiny "pop" to break it loose from the axle. Then, get underneath the axle and work it out and carefully lower the heavy diff onto your chest and roll it to the side onto the floor.

If you've never worked on your truck, the job may take you 3-4 hours going through the steps. Once you've done it, you can do it in 30 minutes or less--it's that easy.
 
Vegas99D1

Vegas99D1

Well-known member
May 5, 2009
187
9
Plano, TX
I ordered a replacement 3rd member from Will Tillery...should be arriving today. Will get it swapped out tomorrow.

Thanks for all the replies/info you guys!

Edit - spelling
 
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