Professional or DIY transmission rebuild
 

My MSM has 102k miles on the clock and my synchros are starting to show their age. Most of them are actually close to perfect but I just started noticing that occasionally they are not quite as buttery smooth as they use to be. The third gear synchro in particular has been pretty bad ever since I bought the car. I want to rebuild the transmission and replace all the seals and synchros in order to get back to a like new transmission feel.

I have no reason to believe that anything else in the transmission needs to be replaced other than the seals and synchros because I have never been locked out of a gear or had any problems other than when I shift fast or at high rpms into third and just a tad bit of clunk when I fast shift into other gears like the synchro just barely makes it there before I do.

My question then is should I attempt to rebuild the transmission myself or have it done professionally. This is my daily so either way I am going to have to purchase/borrow a 5/6 speed to swap in while my 6 speed is being rebuilt.

I found that ISC racing (which is not too far from me and is reputable.) will rebuild the transmission for $425 all synchros and seals included. The price only goes up if other hard parts are damaged. This route seems like a good deal and I know it would be done right.

However, I kind of like the idea of taking my time and doing the rebuild myself. I have searched quite a bit on this forum about rebuilding a six speed but never really found out how much this would cost me to do it myself. I also do not know if it is a good idea to do this myself or if there is a high chance that I will fuck it up and regret my decision. I like to do as much DIY as I can because I like to learn as much as possible but if it is not going to be substantially cheaper and does not make sense I will just have ISC do it for me.

I know Hustler rebuilt a transmission or atleast I think he did. Anyone with experience rebuilding one have any opinion or thoughts for me?

I'd PM AbeFM. I know that he at least attempted to rebuild his transmission after 3rd gear wound up in a small pile at the bottom of it. Not sure how it ended, but perhaps he can offer some pointers.

Will do. Thanks for pointing me in the right direction.

Maybe dumb question, but have you tried different lube? It can make a huge difference.

I have changed the transmission fluid. It didn't really help. Like I said the only synchro that is a real problem is the third gear synchro and it is way too far gone for fluid to save it.

Just a little input frorm my experience. I rebuilt a 914 transmission, pretty much a vw transaxle. It was simple enough and the only things I replaced were syncros and sliders/selectors. That being said I was doing it with a guru along side me and he provided all the 'special' tools.

I don't know if the miata tranny would require special tools but that should be considered. Also, setting bearing preload may be needed and that seems daunting to me.

That being said, I have 0 experience with miata transmissions.

What would be interesting to find out would be if the AP2 S2k carbon fiber syncros fit in the miata/rx8 6 speed. The transmissions are "from the same model line" from ASIN. Same with the toyobaru and IS200. The s2k version looks very different on the outside but may have most of the same guts so the synchros may work, and they're amazing syncros and not very expensive from honda.

And on that note, if the gearsets swap...

I'll look into that. I will probably ask ISC what they think but I doubt I will just order some synchros to try.

Make sure to post up your findings in this thread.

I've rebuilt a 5sp before, nothing special actually fairly straightforward.

But I've heard people ( Sav among a couple others ) say the 6sp is a completely different animal and way more difficult and complex. Never popped one open myself, so I'm not sure.

I wish some of these people with experience rebuilding a six speed would chime in. I messaged AbeFM and am currently awaiting a response. If I do undertake this task I will be sure to document it thoroughly because I am suprised at the lack of available information on it.

You do already have the manual for the 6 speed right? I think the pdf is something like 65megs alone. If you don't shoot me a pm and I will see if I can get it hosted for you somewhere.

I am pretty sure I downloaded it on my laptop but I will check to make sure. If I don't have it I will shoot you a pm.

Hey Ryan, what did you end up doing? I found this thread, my Transmissions is having exactly the same issue. I wish ICS was closer, to ship it round trip is over $200.

Thanks
Jeff

He hasn't done anything yet.

FWIW, my 3rd gear syncros were always complaining until I switched oils, both upshifting and downshifting. I'm using shockproof now.

No rebuild yet. I ended up replacing my hydraulics which helped some but I am going to try some of that motocraft tranny fluid sold by ford dealerships. Apparently it works wonders with brass synchros.

Ok thanks.. I'll try that too. Possible cheap fix.

Is this what you mean?
Genuine Ford Fluid XT-M5-QS Full Synthetic Manual Transmission Fluid

Thats it. You can get it at any dealership and skip that obsurd $12 shipping charge.

That's what I have in my 6spd right now. Don't judge too fast, you have to give it some time. There is an initial improvement that's slight but not awesome, but it keeps getting better over time. Over the course of a few months it makes a noticeable improvement. At least that's how it was with the 2 6spd trannies I have owned. I suspect it's from people who put GL-5 into the trannies :vash:

If you do rebuild the 6spd, please post a ton of pics!

I like how all the reviews are for Mazda's.