Wondering if y'all could help me diagnose the source of these drivetrain noises.
I hear either bearing or syncro noises when the car is running. Quiets when I press the clutch to the floor. Makes sense, right? How can I tell if replacing the bearings associates with a clutch job will do the trick?
Or, if I'm getting syncro noise, how can I tell? I guess I'm fooling myself a little, because the noises sound different in each gear. Does that definitely mean syncro noise?
Right now I have "normal" manual gear oil (just changed) in the box. Should I try something heavier? Lighter? More expenseive? Mix with ATF (that sounds scary to me). I'm willing to replace the clutch, if its bearings are worn out, but would like to avoid a box rebuild.
It's a 5-speed 85 GS with only 79k. It sat for a couple years ... maybe corrosion formed on the syncros that weren't submereged in gear oil? Is that a kooky theory?
Thanks!

 

Every car i owned that made a noise and then went away when clutch was pressed in was either pilot bearing or Throw out bearing. You could have syncro noise as well i am not a tranny guru but i run 80 weight in my trannys in the summer!

 

Sounds like a throw out bearing.

Syncros dont rust, they're brass or some kind of brass alloy

 

Sound like the throw out bearing to me,,, just my 2 cents
Cruz

 

Just for ***** n' giggles - a 12A box i took apart.
The brass looking teeted thingies are the syncros

 

+1

 

Throwout bearing. Usually people change both the TO bearing and the pilot bearing at the same time so the noise gets attributed to the PB (better symptom for PB is clutch chatter). There's an outside chance that the input shaft bearing is shot (from the car sitting idle a long time, lube dripping away and water condensing on the exposed bearings: it happened to me once, but since then I upgraded to a topnotch transmission lube (redline for me, but there are many others, like Amsoil, Royal Purple, etc.).

Heck, why not replace all 3? Easy enough once you drop the transmission. Not too expensive, either. The input shaft bearing is almost always shot, so is the PB, and the TO fails after a certain mileage anyhow.

In fact, why not replace the old transmission with an SE transmission which gives a taller 5th gear. I did it on my 83GS and I LOVE that tall gear!

If you can't get an SE tranny and would like the higher 5th gear, maybe you can change the gear yourself (I don't know if this is feasible, maybe someone else knows) and you can get the gears cheaply (new they are about $500, gasp!), and you don't need the car as a DD and have a few hours to dedicate to it, you can even disassemble the transmission on the bench and upgrade it. Not too hard, and all you usually need is internal/external retainer clip removers, brass hammer and ordinary wrenches. Then you can upgrade the gears yourself. I haven't done this with an RX-7 transmission but have with others. It's actually fun (I think) because you do it all on the bench, no heavy lifting and hauling, it's clean, the parts gleam prettily, and you learn how everything in that box works. It gives you a better appreciation of a mechanism which is quite precise and almost delicate but able to transmit great power and survive many shocks. You will henceforth treat that lovely little thing with greater care and appreciation. And you'll always treat it to a good lube!

 

Thanks for the advice, all. I've torn into a gearbox before (on a Triumph Spitfire) but the part that was trashed on that car (layshaft, I think?) was not available/very expensive, so I've never put one back together!
If it comes to it, I'll rebuild the trans (new syncros and maybe a taller 5th) but I'll definitely start with the bearings associated with a clutch job.