Learn me Manual transmission internal issues

hokay, I haz a problem.

My 1987 Mazda RX7 NA has a 5 speed manual. I am pretty sure it is nearly identical to a miata gearbox internally.

The problem is that the box "snicks" into 3rd and 4th gear. In other words, it seems like it grinds a tiny bit. It will go in gear, but sometimes it is a little notchy.

I tore apart the box to look at it. This is fairly easy to do with these gearboxes and allows you to see everything still together. The "geartrain" does not get dissassembled at all (it comes out complete).

I have found nothing wrong with the box. The block rings (some people call them synchros - the brass pieces) look pretty darn good. No discernable wear that I can see.

The only thing that is not in spec is the 3/4 shift fork. It has about 1.1mm play in teh engagement ring. It also seems that it is "opened up" a little. In other words, if the engagement ring is 3" o.d., the shift fork is 3.175 or so I.D. The spec for the gap between teh shift fork and engagement ring is .8mm max with a .2 to .3mm standard.

Can this actually be causing my shifting issues? If so, can you explain how it would cause the issues?

Thanks!

Rob R.

I have nothing to add except that thinking about touching the inside of a transmission make me pee a little

I think I will take that as a compliment

I worked for Tremec transmissions in Mexico during college (for 1 summer).

The problem I have is that the transmissions I dealt with were all brand new. No wear. I have zero experience working with a worn "newer" transmission.

I took apart and inspected a saginaw 4 speed a while back. I don't see how they could make a saginaw any simpler. If you want to understand how a trans works and want to mess with one, pick up one of those and take it apart. It will teach alot!

However, as I said, I have no experience with broken / worn parts. Any help is appreciated!

Thanks!

Rob R.

Easy, too much slop prevents it from going all the way in with force from the shifter. I bet when you really hammer on it, it shifts great?

Maybe? I NEVER really hammer on these transmissions. With all the torque we are producing, I don't want to hurt it.

Actually, as the issue developed, I took it easier. So that seems to make sense with your theory.

Rob R.

Shift forks are a wear item on heavily used transmissions. Most likely is your problem.

In reply to wvumtnbkr:

Shifting it hard will impart more momentum on the synchro, taking up the slop from the wear of, shifting it hard. Though riding the shifter will also do that.

Dont just inspect the syncro "teeth" also wear on the cone where it hits the matching surface of the gear. Also, check for wear on the gear dog faces as well as the matching parts of the hub slider.

I think getting a look at the synchro rings requires taking it farther apart than he currently has it. Not that that's a bad thing, but it does carry the potential of still not finding a smoking gun and wondering what to do after that.

wvumtnbkr wrote: I think I will take that as a compliment

you should, Im serious, theres nothing I can think of thats more terrifying than the inside of a transmission...maybe midgets dressed as clowns, but not much else

http://www.amazon.com/Rebuild-Modify-Transmission-Motorbooks-Workshop/dp/0760320470/ref=sr_1_1?ie=UTF8&qid=1377625472&sr=8-1&keywords=How+to+rebuild+manual+transmission

Written by a GRM'er.

I think those transmissions are pretty common, used in many different cars/trucks and are fairly well known. Go slow, document it as it comes apart and you should be fine.

you should, Im serious, theres nothing I can think of thats more terrifying than the inside of a transmission...maybe midgets dressed as clowns, but not much else

Automatics are a lot scarier than old manuals. The only thing i dont like about working on manuals is ever having to use a shop press. I've never liked using shop presses. Not all of them need it, though.

Vigo wrote: I think getting a look at the synchro rings requires taking it farther apart than he currently has it. Not that that's a bad thing, but it does carry the potential of still not finding a smoking gun and wondering what to do after that.

Seeing as how it only has issues in 3rd AND 4th, I'd take a gamble and just throw a new 3/4 fork and maybe some bearings at it.

well, I ordered 2 new blocking rings (the brass parts) and a new shift fork.

We shall see if that cures what ails.

Thanks all!

Rob R.

Also check any shift bushings, I just had the shifter seat bushing thingy in my toyota pickup crap out and the damn truck would barely go into 3rd and not go into 4th at all. I figured it had to be a bent shift fork, nope new shift ball seat bushing and shifter nylon seat thingy and the transmission was back to shifting. The ball seat bushing actually had disintegrated into a paste leaving on the seal.

Vigo wrote:

you should, Im serious, theres nothing I can think of thats more terrifying than the inside of a transmission...maybe midgets dressed as clowns, but not much else

Automatics are a lot scarier than old manuals. The only thing i dont like about working on manuals is ever having to use a shop press. I've never liked using shop presses. Not all of them need it, though.

The only thing scary about automatics is the valve body. The mechanicals are pretty simple.

In reply to benzbaronDaryn:

New bushings were installed. Good thought though!

iceracer wrote: The only thing scary about automatics is the valve body. The mechanicals are pretty simple.

Easy peasy on VB's. There are TONS of available diagrams for them, either in the shift kits or tech repair manual.

I hate rebuilding manuals. Last one I did was for myself. I put everything into spec and it shifted like crap, too much shift pressure and mildly whined. Besides that, I LOVE driving them. Go figure.

True, on the valve bodies.