Anyone that already rebuilt a MTX , get in here.

[Phoenix]

I already welded my diff on my good tranny , but this one I picked up had a diff pin ejected.

I got another half case , now I was wondering if anyone done a rebuilt without doing the whole shimming process with success.

If I can escape that , it would be nice.

If you never done this , please stay quiet , dont wanna hear about the ''by the book shit''

 

[gmorrell]

I've done plenty of MTX-IV Frankenmissions from collected/graveyard parts, and I've over-shimmed them to survive in forced induction cars as well.

In general, Mazda was pretty decent about their manufacturing and machining tolerances, so you should be able to move the shims with a set of shafts to pretty much any pair of case halves. If you have a selection of shaft shims, mic them and use the thickest ones, as Mazda tended to shim these pretty loose, so it won't hurt. As long as it's not going into a forced induction car, it will probably be just fine.

I would at least check the clearance on the diff bearings, and try to get close to factory preload, as these are pretty heavily loaded bearings, and if they're too tight, or too loose, they won't live long.

"Igor, go find me an MTX-IV differential, and this time get a fresh one."

"Yeeessss, Master..."

 

[Toolman]

I have swapped a number of gearsets into different cases, as I have been through a few. Some lasted longer than others. None were shimmed to any sort of spec. I would shim the diff though, as GM suggests.

 

[kevinspann]

Thanks for asking Phoenix, I needed this info as well. And thanks Gary, for all of your knowledge/experience.

 

[Toolman]

As long as it's not going into a forced induction car, it will probably be just fine.

And what is the suggestion for FI SHO transaxles?

 

[AREA 91]

And what is the suggestion for FI SHO transaxles?

BUMP to Gary!!!!

 

[jedhead]

I did a quicky rebuild without shimming. The tranny lasted about 5k before the bearing supporting the diff exploded. I used the shim selector tool the diff on the third rebuild and no shim was needed. One way to determine the size of the shims without using the shim selector tool is to use lead solder wire as a shim and measure the thickness the solder compressed to when the transaxle was assembled.

Bob

 

[AREA 91]

Good info Bob (I already knew that .

I want to know about shimming the input shaft and main shaft (tighter) in high HP applications.

 

[luigisho]

You try getting in touch with Josh from SHONUT? He should have good input on this for you.

 

[zak]

gmorrell and transmission shimming

gmorrell had carefully calculated the thermal expansion of the aluminum case and the transmission shafts (I got him some of the data specific to the alloys used, please don't ask this was in the late 1990s IIRC). Aluminum has a higher themal expansion than steel, so at operating temp the shafts can be a bit loose. He then shimmed the shafts such that at operating temp (200 F? can't recall) the case would still be holding the shafts in a slight bit of compression, or at least neutral.

This kept the shafts from flexing as much (in theory anyway) and may have kept the gears in better alignment, both possibly increasing the torque limit of the MTX-VI. These tightly shimmed transmissions (and it is possible to go too tight) seemed anecdotally to live longer on forced induction SHOs, in particular the break one (or two) third gear tooth problem.

Several transmissions were built in this manner, Ransom's, the ShoNut's, etc. Have asked Gary to swing over here and add his comments.

 

[kevinspann]

FWIW the one I put together without proper shimming is still working fine after 2k miles. Time will tell though...

 

[Toolman]

My results varied, sometimes my 3rd gear would last 5k miles, sometimes 12k miles, or somewhere in between. FWIW, I mas making over 400ft lbs much of that time, and I drove the car like it was meant to be driven. IMO, unless you have a horribly mismatched case/shaft/shim, something that would cause it to be very loose, I think you will be fine in a NA situation. But boosted, I would suggest having someone with some experience shim it tight for you.