So you just sourced Miata trans and had someone do the input shaft mod for you? Does the fc shifter still fit the same way since it's just the internal parts being changed?

Turns out my weird shuddering is happening in more than just 1st gear. On my drive to get coolant flushed i noticed it quite a bit. Although it seemed to come and go in later gears. It leads me to believe that maybe something is loose. It feels like most of it is coming from under my seat.

The mod is essentially putting the Miata gears into the RX7 transmission housings so the rear housing and shift linkages are still all RX7. Though technically you could swap some Miata stuff over so you could run a Miata short shifter if you wanted. They're much cheaper for some reason. It sounds straightforward but it's a pretty complicated task. You have to completely disassemble the transmission to get to remove the input shaft. I posted a how-to on here a while back detailing the process per the FSM.

Describe the 'shudder'.

Like the engine is missing? Clutch chattering? Suspension shunt?

A good local standup guy (in Northern VA that is) is selling a NA FC trans with the Miata gears on it. I don't want to cross post threads, but if you are interested, I can get you in touch with him (or pm you his FS thread)

I have those injectors and new connectors if you want them. You cover shipping and they are yours.

its more of a heavier vibration coming from under my butt. I looked on Mazdatrix and actually found a trouble shooting guide for that sort of thing. I've basically narrowed it down to bad u-joints, trans mounts, or bad ring and pinion (crap i hope not because those are pricey). So i started cheap and ordered the trans mounts. Ill just work my way up from there until I've replaced it all.

Feel free to post the link here or PM me. I may not be in a position to buy it now but I'd love to know the price. Or see if i can work out a deal with him.

Heck yeah Ransom. Text me 406-450-4103.

Texted ya. I will get them ready to send out Monday. I will just ship them and we can figure it out. If I get an address

Ransom you da man!

Have you inspected your trans mounts? Most likely they're bad considering the age and exposure to oils which turns them into a mushy mess. I've seen this on a few 2nd gens. I've had some completely separate.

Good choice, if you don't have the aluminum shield for the mount closest to the exhaust I'd recommend getting it.

Yeah I'm hoping that will make a difference. I'm not sure about the shield though. It looks like all that is still present but i could be wrong. Its been so long since I've been under one and worked on it that I'm having to re learn a bunch.

Just to elaborate more on my inspection yesterday. I laid under the car for about an hour or so just looking around at stuff, trying to move it, etc. Nothing was obviously loose or easily moveable. Bushings are obviously worn which I'm sure is a contributing factor to the vibes I'm getting.

Bushings will be coming soon as well but i figured trans mounts would be a better first place to start. I ordered a new trans brace as well. I'm contemplating dropping the trans and just cleaning it up when i do the mounts. Its just nasty and has what smells like gear lube on it but I didnt notice any leaks. I guess it would be a good idea to drain it and refill as well. If i do drop the trans.. is there anything else i need to do before i put it back in?

get snot slinging drunk.

There will be bolts missing if that happens!

If it's trans mounts, it'll make a LOT of noise on shifts...
Anything from a thud to a BANG during the shift is your typical sign of failure.

It's uncommon that bad trans mounts induce a shudder during driving though, but this could be a symptom of something else...


-Ted