Ever since I got my 1993, #135, ZR-1 the rear end has made noise. It was just whine on coast. But a month or so ago it started make a whirring noise on power. First not much but then it got very noticeable. I know from past post when I had to change the pinion seal that the 4:10 gear set in my diff was the smaller Dana 44 set. I do not know which previous owner put this gear set in, but it was likely 25 or so years ago, probably 20K to 30K miles. So, I set about pulling the diff, not that hard to do, I have past experience from my 1985 track car doing this job. Well, not too surprising there are two broken teeth on the pinion gear. I am a little surprised it drove as smoothly as it did.



I exchanged some emails with Marc H. and he provided me with some part numbers for the best carrier and ring and pinion for a replacement 4:10 gear set up. Also, he said that he had not found any of the gear sets in a while.

So, set out to see if I could find any parts to rebuild my diff with a proper set of Super Dana 44 gears. After some searching on the internet, I located the proper Spicer Trac Lok carrier (Spicer 74299X), and a set of Supper Dana 44 4:10 gears.


The carrier I got form a place called Iron Wings Sales, the gear set, the Mopar part number (P5007043), is an NOS set I found on ebay.

Once I get the bearing and shim kit, SKF, I will take everything to a guy in Boring, Oregon, about 80 miles from me, to have the old removed and set up the new parts. I found this guy by calling Tom Wong, a very good GM tuner/builder located in Vancouver, WA that I have used in the past on my 85 C4 track car and my C6 Z06. Tom does not do differentials, but he gave me the name and number for the guy he uses. I called this guy, and he has rebuilt these C4 diffs before and has the tools necessary, also said they were a PIA. I will take everything to him in a month or so when I get back from some travels.

An interesting thing I see on the top and bottom surface of the diff where it attached to the C beam is some fretting/pitting. Someone, likely the previous owner that did all the mods to this car, put the beam plates on the bolts that attached the C beam to the diff and transmission tail housing. They seemed to be tightened correctly, not to tight or to lose.


Top surface


Bottom surface

I'll update once the diff is rebuilt and the car driving again.

Brian

 

Greetings, Great post, im anxiosly anticipating the results as I am trying to diagnose diff noise issue as well. My issue is exactly like the description in the following post in another section here:

"I'm at my wits end regarding a vibration I'm experiencing with my bone-stock, 29k mile LT4. It's a low, booming sound coming from behind the seats. The sound doesn't appear until about 65mph. It's present when accelerating or deccelerating, but it really gets loud when coasting. Clutch in, in gear - or in neutral, clutch out, it's significantly louder. Engine speed has no effect. I have replaced the rear wheel hub bearings, all 6 u-joints, and I've had the driveshaft professionally balanced. At this point, I'm beginning to accept the problem is the differential or the output assembly of the transmission. I'm not qualified to rebuild my Dana 44, let alone a ZF-6. I'm wondering if anyone has experience with an issue like this. Could a differential bearing or gear alignment cause this? What about the things in the tailshaft of the transmission? Is there anything I can do to try to isolate this before I start tearing apart the rear of the car? My next step is to take the diff out and to a reputable shop for a rebuild. Any advice would be appreciated. Thanks in advance."

Could the issues be the same?

 

Update 9-27-2025
The diff. has been rebuilt with the parts I mentioned in my initial post. See photo below:

Below are a couple photos of the old pinion. Of course you can see the two broken teeth, and you can see that this is a standard D44 pinion and had a sleeve welded to it to fit it in the Super D44 case of the C4 Corvette. It worked but not for that long. Too bad it is so hard to find the proper 4:10 gear set for our cars.



I have cleaned the diff. and cover and then reinstalled the cover. Next steps are to reinstall the diff. in the car and get everything back together and take it for a test drive.
Brian

 

Impressive work


thanks for posting the images

 

This is some seriously impressive work!