8.25 Diff questions

[airkiller]

Ok, I have been restoring/ COnverting a 74 Duster from a 904 with 7.25 rearend to a 833 with a 8.75 rear end. I bought a rearend off Craigs list and it look pretty good to me but as it was latter found, the diff has some issues, at least I think it is the diff. The rearend came with new upgraded axels and green bearings already installed on the axels. The guy I bought iot from is a hobbiest and told me the whole system, hosing, diff and axles were ready to be assembled and installed. It is installed and running but I have a growl from the rearend at 30-60 mpg and it gets louder when I let off the gas and hold in the clutch. It will make nopise almost to the point when the car stops. It sounds like a bunch of rocks boucing around in the case. No when I looked at the diff before installing it, I noted no issues with it. I talked to a local diff shop and they think it has an issue with the pinion bearings. I have rebuilt my 727 in my Road Runner and have been a Aviation Mechanic for a long time, so delicate and complicated devices don't scare me but I think a diff is a demanding build. I have a 489 case and need a bebuild kit. I also have a 741 case that was going to go into the Road Runner. Which one is better if any, and has anyone built these up. Can anyone give me some pointers. Thanks./

 

[vwmoparguy]

I would say something definitely in the r/p setup or bearings. When you push in the clutch and coast, you are narrowing down what it could be. Pretty much eliminating a trans prob.

Before doing anything drastic, I would jack the car up and check wheel bearings, and grab the drive shaft yoke and check for any abnormal movement...side to side and up and down, this is what you're looking for in wheel bearings as well....abnormal movement.

Next would be to remove the diff section. If you get this far, I'm sure your problem will be evident.

The diff is not a demanding build. It's just out of your comfort zone. You can do it!

 

[1970Duster]

If your going to rebuild the center section, rebuild the 489. It is stronger then the 741

 

[res1vw21]

I would rebuild the 741 case and put it in the A body and the 489 case in the heavier, more powerful RR, just like ma mopar did. Also the 741 is by no means a bad unit, people have been running them for years without issues in street cars, slicks and lots of power are when you start finding your weak links.