Both my SE and GSL make this "whine".

The GSL's rear went quiet for about a month right after I had the axles out last summer to swap in SE pattern axles. I dont know why the sound came back, or what it is.

 

On this: "3. Removed & inspected LSD. Reinstalled with redline gear oil"

Did you add the GM LSD additive like someone else mentioned above? If you don't add this, the LSD plates aren't properly lubricated and will cause a grinding sound typically when turning (*I know that's not your primary condition...). If not, it's worth adding the GM LSD stuff to be sure that's not it - because it's a couple of ounces of possible prevention.

Good luck, and watching for the outcome on this one, as I'm doing my rear axle bearings as soon as my engine swap is complete.

 

I bought Red Line gear oil that says it contains the additive for the LSD, so I did not add anything else. Do you think I need to? Like you said though, I have heard that only causes chatter when turning. I have constant noise when accelerating or decelerating that doesn't match this "chatter".

I will definitely keep working on this problem but it is lower on my priority list for now due to some idle issues (which you helped me with, LongDuck!) and another car I am working on as well. I will definitely post back when I figure it out. Thanks for the help

 

It couldn't hurt to add the few liquid ounces of the correct GM stuff just so you don't have to wonder, and wouldn't you feel better if that fixed it?!

Good luck, and post back when you can dig into it further,

 

I just bought a 1984 RX7. I have the same problem a persistent whining/grinding noise coming from the rear end. The sound changes depending on if I am accelerating.
I did replace the 2 rear bearings, the collar ring and the oil seal that goes on the housing. Whining noise with accelerating is still persistent.
I removed the diff, all the components look good. I don’t really want to spend any money on diff parts as derSchwamm did and replace multiple parts with no fix.
Was there a find for the noise and what was the fix??

 

Hey there! I after reading about your problem and attempts to fix it, I think I might know what your issue is. I ran into this problem very recently. The sounds you're describing are most likely caused by the pinion bearing. I had a bad rear pinion bearing in my GSL rear that was making a whirring sound at higher RPMs and a grinding sound at lower RPMs. Unfortunately, I believe the only way to check this is by disassembling the differential. You might go ahead and try a turning torque test before you disassemble it completely. I'm not saying your issue is definitely a pinion bearing, but from my experience that seems the likely issue.

 

Thanks for the response. Did you replace both the rear and front pinion bearing and oil seal? Since all my components look good is there a way to check the pinion and ring for ware by checking there teeth depth , do you know?

 

Robin,
You will need to replace the carrier bearings, front and rear pinion bearings, crush sleeve, and the pinion seal. When I say you need to replace the side bearings, this is my OPINION. I'm only saying this because if your pinion bearings are bad, then there is PROBABLY some excessive wear on the side bearings too. That is up to you. As far as checking the pinion bearings without disassembly you can do the turning torque test. Go to this site Mazda RX-7 Manuals and Wiring Diagrams and use the 1985 Factory Service Manual (FSM) to properly perform the test. The FSM can also aid in assembly and setup of your differential after replacing components. Let me know if I can help with anything else.

 

I have not yet figured out the cause of mine but I'm pretty sure it's in the differential itself, just based on the noise. I'm sure it's a bad bearing somewhere. If anyone else with this issue beats me to fixing it, let me know what worked