Why is the MTX weak?

[Macgyver]

Is it just because of the diff pin problem, or are there other issues?
My engine and trans will be coming out before I paint the car so I can freshen up the bottom end with a crank and bearings and also detail the engine compartment. I plan to weld the diff pin in place while it's out.

 

[zach44102]

Fix the diff. then third gear blows up.

 

[jayro]

For a pretty much stock or even a modified NA car, the biggest weakness in the trans is the diff. Poor design and poor lubrication causes it to fail and when it does alot of times it puts a hole in the case. After that it is 3rd gear. 3rd will usually hold upto about 300ftlbs of torque. After that it will start to shred.

Alot of the durability of the trans has to do with your driving style. If you beat on it repeatedly it will eventually fail. Remember it is basically a somewhat beefed up ****** GT trans. It was never made to handle a ton of power/abuse and most of the enternal wear parts (syncros and blocking rings) are no longer avialable.

 

[jelloslug]

The reason that 3rd gear gets damaged is that the input shaft start to flex when you bump up the torque by quite a bit. That flexing lets 3rd gear unmesh enough with the output shaft so that it can strip under the extra load. Unless you add forced induction or nitrous all the time it's not going to be an issue.

 

[Macgyver]

That's what I expected and wanted to hear. I don't plan to abuse it as I understand parts for it are scarce. Thanks!

 

[kevinspann]

If you don't plan to abuse it, replace the roll pins in the differential pins and leave it at that.

 

[rubydist]

The 3rd gear issue is due to the cluster gear shaft not being large enough (not strong enough) for high torque situations. It holds up just fine at stock power levels.

The diff pin issue is very nearly related to burnouts and other abuse. The 4 mtx tbat i have had apart have not had issues with the roll pins.

 

[Macgyver]

This diff uses roll pins to hold the pin in place? It's not like an 8.8 or just about any other rear driver with the threaded pin? So what happens? A guy lets go with a one wheel peel, the spiders gears go crazy, fuse to the pin causing the roll pins to shear and then the pin flies out? I've seen that same scenario on older Chrysler FWD transmissions.

Just judging from the overall condition of my car I'm inclined to believe it hasn't done too many burnouts. It's a shame, I have 2 manual transmission hi-po cars, and neither one can safely do a burnout. My other car can leave a hundred mile long dotted line...once.

 

[jayro]

This diff uses roll pins to hold the pin in place? It's not like an 8.8 or just about any other rear driver with the threaded pin? So what happens? A guy lets go with a one wheel peel, the spiders gears go crazy, fuse to the pin causing the roll pins to shear and then the pin flies out? I've seen that same scenario on older Chrysler FWD transmissions.

Yes, that is what happens. To avoid this people will make a ring that slides over the diff and is welded to all 4 pins, oe people have welded in supports between the 2 small pins and the ring gear rivits at an angle. The ring idea seems to work a little better. With the angle brce you have to watch out for clearance issues. Just make sure you get really good *********** on the welds or else they wont hold.

 

[mcrowe3797]

Yes, that is what happens. To avoid this people will make a ring that slides over the diff and is welded to all 4 pins, oe people have welded in supports between the 2 small pins and the ring gear rivits at an angle. The ring idea seems to work a little better. With the angle brce you have to watch out for clearance issues. Just make sure you get really good *********** on the welds or else they wont hold.

I agree, having the diff pins shear off one went through the case ande the other one got sucked into the gears It is expensive to get fixed. I just bought a used trans and got a use qualfie. Still always a little nervous about beating on it from time to time.

There is a guy i know modifying a wrx/sti trans or Lancer evo trans to bolt to our motor. He has gotten a lot done so far. Reinforced a lot and modified a lot. Once it is done it should be able to handle pretty much anything you can throw at it. :woo-hoo:

 

[Bob Gervais]

Because heavy pile of shit with fast motor.

 

[rooster]

I guess I better take it easy then....
Oh shlt... Too late

 

[intimdatr]

There is a guy i know modifying a wrx/sti trans or Lancer evo trans to bolt to our motor. He has gotten a lot done so far. Reinforced a lot and modified a lot. Once it is done it should be able to handle pretty much anything you can throw at it. :woo-hoo:

its only taken him about 5 years.

 

[mcrowe3797]

its only taken him about 5 years.

He is fabricating everything from trial and error. Modifying our case to fit sti internals is a BIG job. He is getting close to getting it on a dyno he told me a little while ago

 

[RonPorter]

Well, there were virtually no tranny issues, diff pins or otherwise, for the first ten years when the cars were newer.

My original '89, which had a LOT of smoky burnouts for the 182K I drove it, didn't crack the pins until 200k with the next owner. I also changed the fluid regularly.

NOW....I owned a highly abused (so it seemed) '95 MTX witth only 80K miles. Blew the diffpins after about 5 runs at the strip. Tranny was totally rebuilt (Thank Youy, aftermarket warranty!!). Drove it for a few months through the winter. Went to the strip again. 5-6 runs, pins blew again. We suspect it's a loose tolerance in the carrier with neglect over miles. Got a used ~93k-mile tranny out of a '91. Beat that one for another year with zero issues.

For the stock car, the tranny is fine. Young 'uns don't remember that BW & Muncie 4-speeds would regularly die back in the 60s on musclecars at far lower mileages.

Go to forced induction, especially on an old tranny, and bets are off.

 

[SHOtime2511]

Show me a FWD transmission from the same era that is any better.

 

[mcrowe3797]

Show me any 4 door sedan from that era that could compete with the sho? lol

 

[RonPorter]

Show me any 4 door sedan from that era that could compete with the sho? lol

535i.

That was my original choice in '89, but I had this idea to buy a used 328 Ferrari GTS in a year...........

Also a coupla MB, but IIRC they were mostly autos. Don't remember if the MB 2.3 16-valve was still made then, but it was a few years earlier.

From the USA? None.

 

[mcrowe3797]

its only taken him about 5 years.

535i.

That was my original choice in '89, but I had this idea to buy a used 328 Ferrari GTS in a year...........

Also a coupla MB, but IIRC they were mostly autos. Don't remember if the MB 2.3 16-valve was still made then, but it was a few years earlier.

From the USA? None.

Also look at the price difference between them.... come on lol

put 5k into the sho and its back on top

 

[zach44102]

I love blowing trannys