I shattered my 2nd gear synchro
 

I was talking on the phone as I left work today, so I allowed my 1985 GSL to warm up while I finished my conversation, so it was warm by the time I got behind the wheel. I was parked on a very wide street (a lot of big rig traffic) with a 35 mph speed limit. So, as one does with an RX-7, I accelerated up to 7000 rpm in 1st, then went for 2nd.

I was greeted by the worst transmission grinding noise I've ever heard. Puzzled, I pushed the handle back up into neutral and coasted a bit. I went for 2nd again and got a slower, not-as-bad grinding noise. I clutched out in neutral and reved up to about 2k, then clutched in and felt it slot into gear. I drove around a bit in second and confirmed there was nothing wrong with 2nd gear, and proceeded to double-clutch shift into 2nd every time on the way home. Which is really annoying to do from 1st gear, it takes at least 2 seconds.

So, I'm pretty sure I destroyed my 2nd gear synchronizer. 2nd gear sounds like those old cars from the early 1900's with unsynchronized gearboxes. I have never dealt with a transmission problem before. What are my next steps? Is it realistic to try rebuilding this transmission or should I find a used one?

I think I need to change the fluid, I don't want shattered pieces of synchro floating around in the bottom of the casing, but if I'm just going to buy a different transmission anyway, what's the point?

I think your best bet is to try and find a used gearbox in good condition. If you can find one that has lower miles and the fluid that comes out of it looks ok, you are probably good to go. I think a true rebuild will be very $$.

I have read about trans rebuilds, there are basic rebuild kits available with replacement bearings,synchros etc. Your damage may require more than that.

Drain the fluid and see what it looks like?

there is a guy local to you, Barry Hartzel, who rebuilds these transmissions, he has lots of experience from Pro7 to Spec Miata, it runs around $1000.

Thanks guys,

Since transmissions at local salvage yards run $200-$250 and I could therefore buy 4 of them for the cost of one rebuild, I'm not going to pay a shop to rebuild it.

However, I am curious if I would be able to rebuild it in my garage. I'm curious about this part for sale on Atkins Rotary:
https://www.atkinsrotary.com/store/8...01-17-245.html

The only problem is I don't know I can replace this part using the tools I have at home. Are the gears press fit onto the trans input/output shaft? Or can I disassemble the transmission, install the part, "Lap in" the synchro ring (as suggested by RacingBeat) using lapping compound and hand-turning the synchro ring, then clean everything up and reassemble everything and reinstall? Has anyone done a transmission teardown at home?

Both on principle and because my RX-7 is far from my only car, I would rather do an at-home rebuild and clutch replacement than buy a used transmission with an unknown history. My trans has no other problems besides the 2nd gear synchro. But I don't want to buy a synchro ring and disassemble my transmission just to find out I'd need a hydraulic press or a machine shop to replace the synchro ring. At that point I will be wishing I just had a replacement trans.

tl;dr Is it possible to replace the synchro at home or does that require hydraulic presses/specialized tools?

You will need a hydraulic press. You might be able to buy one reasonably cheap from Harbor Freight.

Here's a nice guide for a rebuild

I contemplated rebuilding one a while back.

The biggest hurdles I remember are:
-finding/making really long jaw pullers
-there's a recessed nut that the OEM uses a special super long socket for. Some DIYers cut off a socket and weld a bar to it to make a wrench, but then torquing it is a little tricky.
-finding a way to drive the gears back on. Stacking everything with the bearing housing on a press might work.

I have posted this doc somewhere else and have lost it. This is a compilation of info that I put together in case I ever wanted to rebuild one of my FB transmissions. Dangit, it's 6mb. I'll compress it tomorrow and upload it.

Also some other info.
https://www.rx7club.com/1st-generati...ebuild-994843/

This article may help if you decide to take on the challenge by yourself.

Article link: https://www.cartechbooks.com/techtip...nd-techniques/

FC Transmission Walkthrough
 

See Attached

Mazda Type M Transmission Walkthrough
 

Credits and source given in document.

Hmm... so maybe rebuilding it would be something I could do after all! I'll definitely consider it. The benefit of having a transmission to swap in is I can get my car out of my 1-car garage, rather than having to leave it in there indefinitely while I work on the transmission. Considering my garage is the only work area I have for my 3 cars and another 3 cars owned by my friends, that makes me nervous.

Maybe I should get a replacement gearbox and then rebuild the one I took out, maybe I can sell one of them. Hmm...