Early last spring I began noticing a noisy input shaft bearing on my car. Gradually it got worse. I tolerated it through last summer's driving season here in the Midwest. Just figured I'd address it over the winter when the car hibernates anyway. That was nearly a costly mistake...see below:



The car/transmission has about 118K on it. The previous owner set it up for autocross and I also autocrossed it about 4 yrs. But AFAIK, it's never been tracked and it's adult street-driven otherwise. Shortly after I bought it 11 yrs ago, I started running synthetic gear oil. First (I think) M1, then Redline MT90 and most recently NEO 75w-90 HD. Didn't watch it close, but averaged about 20k miles between changes.
In a nut-shell I'm not sure why this bearing went bad, but a BIG word of caution. Don't wait like I did. When the shop got it apart they showed me the main-shaft which had been galled slightly. He was able to clean it up with some fine emery cloth, oil and time to where he felt comfortable re-using it. The shop has a good rep, so here's hoping he's right. He also said that if I'd driven it much more that main shaft would have been toast. And it runs about $500 from Mazda (Ray @ Malloy). I didn't check MAZDACOMP.
The up-side is I ended up having a pretty comprehensive rebuild with new bearings, brass, shift forks etc. Haven't been able to drive it much due to bad roads, but what little I did suggested dramatic improvement. Took the opportunity to change fuel filter while the trans./PPF and drive-shaft was out, and added a LW flywheel (thanks adamc for input)

 

Ouch!! Good catch. What are your thoughts on just sticking with the Mazda specific tranny oil since you aren't running high stress, continuous, track duty on this one?

 

Mine was completely toasted too but it had a lot of track miles on it at the hands of the PO.

 

Honestly I don't know what to think. I figured synthetic would be an improvement and maybe added protection from exactly the issues illustrated. Both the Redline and the NEO came with their own following and good reputation here and elsewhere and I changed it on a semi-regular basis. And IIRC, both are GL-4 or GL-5 Maybe "just one of those things"?
I actually had two quarts of NEO 75w90 HD and about 1/2 quart of unused Redline 75w-90 (from diff) sitting on the shop shelf. Since this was almost exactly what I needed, I mixed them to fill it up following the rebuild. I'm assuming that it's OK to mix two brands???

 

Damn, Jim....that sucks! At least you were able to fix it without TOO much drama. As you note, it COULD have been much worse.

 

Whats a noisy input shaft bearing sound like?

 

Can be really noticeable in neutral with the clutch pedal released. I could hear mine really well when the sound was reflecting off the garage wall. Mine sounded like a "dry" scraping/grinding noise.

 

All the boxes that I've pulled have that bearing brinelled, usually a nice slurry in the area it spigots as well. Doubt oil or use has much bearing on whether any one particular box will be affected....unfortunate Mazda legacy using a decades old design.

 

There's a vid in post #16 ----> https://www.rx7club.com/3rd-generati...aring-1045877/