nik1703

What are the differences between the T56 and M29? (aside from ratios) Is the M29 as bulletproof as the T56?

BizZzatch350

iTrader: (33)

The M29 as well as the M28 are both Borg Warner T56s just like the 94+ cars. When you say M29, M28 and MN6 all your doing is refering to the RPO code. It's like a 10 Bolt, you had different RPO codes that started with a "GU" for different gears, but all in all it's still the same 10 bolt housing. The differences as you already know are in the gearing and the torque ratings. From Borg Warner the M29 was rated 400TQ instead of 450TQ like the 94-97 MN6, the M28 was rated at 360TQ. The M29 shares the same first to fourth as the "MN6" T56 found in C5 Zs. The story around the camp fire was that gearing was changed due to cags a feature which 93s didn't have on either M28 or M29, not a strength issue with the trans. From what I have been told by trans builders, certain parts are weaker then the 94+. Best bet would be to call some one like D&D.

Colin91Z

iTrader: (9)

So what's a M28 then? Different ratios than the M29?

nik1703

Cool, good info. I do have an M29, wanting to see if all the info I read about T56's stands true for M29's as well

BizZzatch350

iTrader: (33)

They should both be very similar, the big issue is, they are so old now, not a lot of people see or mess with them. Some one would really have to know their T56s to know the differences. Most the shops that build T56s mainly get the LSX stuff, though they may see a 94+ unit time to time.

Yes, 93s had to two different T56s depending on the rear gears. All Trans Ams were M29 cars, never seen a M28 Formula, only M28s I have seen have been Z28s.

1993 Manual/M28 3.36 2.07 1.35 1.00 0.80 0.62 2.73 (GU2)
1993 Manual/M29 2.97 2.07 1.43 1.00 0.80 0.62 3.23 (GU4)

Colin91Z

iTrader: (9)

Interesting, I just so happen to know where a 93 LT1+T56 combo is for sale here locally...I've been tossing around the idea of buying it so I can have the trans as a spare. Plus I thought all 93s had the M29 so I just assumed thats what it was. I'd like to have the M29 gearing in my car.

Any way to tell by looking at the trans whether or not it's an M28 or M29? Can you tell by the tags on it or anything? The owner is a long time friend of mine, he says it came out of a 93 trans am. I can tell for sure that the motor is a 93 (no crossover on intake) but who knows what the car really was...I know the motor/trans combo has been sitting in his garage for over 10 years, and appears to be fairly low mileage...

kgkern01

iTrader: (10)

I have a rebuilt M29 in my car with upgraded shift forks. Externally they look the same as a 94+ T56 except that they have no CAGS solenoid, it is blank where the solenoid would be. That way you could identify it as a 93 T56, however whether it is a M28 or M29, you would have to tell by the vehicle codes, or you could put it in first gear, then turn the input shaft and determine the gearing. Turn the input shaft 3 1/3 times for one turn of the output shaft = M28, right at 3 turns would be an M29.

I love the gearing of the trans, it is like having 3.73's while still having the stock 3.42's, or that 3.73's would be almost like having 4.10's. So I guess you could argue that since you can keep a numerically lower gear, that your 10-bolt may be slightly stronger, since numerically higher gears are known for being more prone to breaking???

Colin91Z

iTrader: (9)

Good idea, I'll go spin the input shaft and count the revoulutions.

An M29 would make my 4.30s seem like 4.56s

BizZzatch350

iTrader: (33)

If it for sure came from a Trans Am it's a M29.

Colin91Z

iTrader: (9)

Thats the problem, I have no way to verify what the car was for sure. Car was wrecked and scraped about 10 years ago.

nik1703

There's a sticker in the glovebox that will tell you what trans the car has. The code for the M29 is "GU4". Don't bother with the spinning of the input shaft, lol.

Colin91Z

iTrader: (9)

I know where the sticker would be located...the problem is the car is not available to look at. It was wrecked 10 years ago, had it's motor/trans pulled, then was sent to the salvage yard...once again, this was 10 years ago. I'm sure the car has been crushed by now.

LT1

iTrader: (1)

BizZzatch350 has already covered this info but i posted this info in another thread not long ago. Just for comparing the gear ratio's here's the info again. BTW that rpo code for GU4 is 3.08

93 F-body with (M28) 6 speed Torque rating 360 lbs-ft. Has 2.73's - GU2
1st: 3.36
2nd: 2.07
3rd: 1.35
4th: 1.00
5th: 0.80
6th: 0.62

93 F-body with (M29) 6 speed Torque rating 400 lbs-ft. Has 3.23's - GU5
1st: 2.97
2nd: 2.07
3rd: 1.43
4th: 1.00
5th: 0.80
6th: 0.62

94+ F-body with (MN6) 6 speed Torque rating 450 lbs-ft. Has 3.42's - GU6
1st: 2.66
2nd: 1.78
3rd: 1.30
4th: 1.00
5th: 0.74
6th: 0.50