Common Problems of the T-56

[Knight]

Anatomy of the T56

By far, the most common source of T56 transmissions on the used market is the Fourth-Gen F-body, primarily due to its longish production run from '93-'02. Although the T56 has been used in the Dodge Viper since the early '90s (in addition to the '03-'04 Mustang Cobra, '04-and-up Pontiac GTO, and Cadillac CTS-V), much lower production numbers make them less likely swap candidates. Likewise, the C5 Corvette-with its rear transaxle layout-makes a potential conversion far less appealing. Nonetheless, other than varying rear tailshaft housings, front adapter plates, and bellhousings, the transmission cases and the internal components within them are remarkably similar in each version of the T56. Consequently, many parts from stronger variants of the T56 easily interchange with its more feeble brethren. All T56s feature die-cast aluminum construction, paring mass to a trim 130 pounds.

Breakage

The most common F-body box features an official torque capacity rating of 450 lb-ft, but hoards of racers have subjected them to well over that figure without much fuss. From a durability standpoint, the primary difference between the Viper trans and lesser T56s is its thicker output shaft measuring 1.290 inches versus 1.175 inches. Likewise, the Viper shaft allocates its torque load over 30 splines, as opposed to 27. As far as parts failure from sheer driveline shock is concerned, the output shaft is the first to go.

Although upgrading to a Viper output shaft is a must in hardcore drag racing applications exceeding 900 horsepower, very few street cars actually break the stock piece. In fact, non-Viper T56s can handle close to 750 hp in most street applications. On the other hand, most of the components replaced during a typical rebuild are normal wear and tear items, such as synchros and friction cones.

Improperly setup clutches that don't fully disengage compound the problem. In other words, the T56 has a lot more strength than the average backyard clutch installer has common sense, and is therefore much more durable than its reputation may suggest. Most of the problems people have with their transmission-like grinding or popping out of gear-are due to not addressing the hydraulic system when replacing a clutch.

Regardless of whose fault transmission wear may be, the T56 isn't perfect. Due to its small diameter in relation to the 1-2 shift fork, the factory cast aluminum 3-4 fork is a common problem area. Of course, the 5-6 fork is smaller still, but hard shifts into overdrive are rare. Rebuilds typically include an upgraded steel 3-4 fork along with rugged billet steel keyways to replace the factory aluminum pieces. Furthermore, upgraded carbon fiber synchros further improve resilience to gear banging. All parts are available directly through Tremec, and its distributors.

Repair

Rebuilding a transmission is probably best left to the professionals. Not only is there a harrowing volume of gears, bearings, pins, shafts, screws, and locks in varying sizes that all look the same, but misplacing just one of them can blow up your trans. In comparison, assembling a short-block is a walk in the park. If you're still feeling rather intrepid, a quick look through a service manual will probably change that pretty quickly. It can be done and there is plenty of info on how to do it. There is a sticky listed in this sub-forum where you can download the T56 Service Manual in PDF format.

[2002ssslp]

The Gear Box has a great stage II rebuild kit for 665.00 which addresses all the major problem areas and will handle 650 hp with no problems.

[jrbonds]

I bought that kit. Hoping to get it rebuilt this week. My 3rd and 4th gear are non functioning.

[2002ssslp]

I bought that kit. Hoping to get it rebuilt this week. My 3rd and 4th gear are non functioning.

Same with mine. I was shifting hard from 3rd to 4th and it never game out of 4th gear. the cheap aluminum slider key. I was told this is one of the best kits on the market for the part time racer. Also look into a new shifter with a positive stop.

[Knight]

I shipped my tranny to them a few years ago for my rebuild. I went a little further than the stage 2, but the pricing was very reasonable, and the workmanship was top quality. It's held up to everything I've thrown at it.

Even after a rebuild, the key is to also make sure your clutch and hydaulics are functioning perfectly. If not, this can lead to premature wear and failure. As stated, a good shifter with adjustable stops is a good idea.

[Spikito]

Thats why I'm glad i got a pro-5.0 with the stops....no over shifting...

[BobbyGFirebird]

Dropping in from TramsAm WS6 forum.... I have a '99 4th Gen Firebird TAm and was told by dealer the tranny mount was broken, and was WHY i getting a rattle on harder accell. from about 3-5k rpm. Relieved it wasn't internal engine noise, but how careful i need to be w new OEM GM mount? Street use only and i good manual tranny shifter. Not a hack or a brute.

[SMWS6TA]

Nothing to worry. Gotta remember the car's age is going on 17 years. That's quite a bit of years for rubber. GM Stock rubber is fine to use for stock power (look how long it last) If you go with poly you'll feel more vibrations from the tranny but not like you are now.

If it means anything I still have the stock rubber for my tranny with a 403ci pushing it and with a 8.8 rear. No issues.

[BobbyGFirebird]

i have a great tranny with just 40k miles in my '99ws6, but i do notice clearly a harder, notchy, balking shift into 3rd gear. i've taken to double-clutching technique (which i still don't fully understand!) when going into 3rd in non-spirited driving like freeway. Is it limely the synchros or bent fork? Also, i missed my first shift ever in 4 k miles on this car on WAY to dealer service. Didnt have clutch fully depressed when going from N to 1st at a light. Grinding. Was that the synchros or the actual gears? Thought the gears were always meshed?

[SMWS6TA]

Sounds like synchros.


Do you have the stock Clutch MC?

[35th-ANV-SS]

Double clutching is not necessary in a vehicle that has a synchronized manual transmission like the T56.

With this method, instead of pushing the clutch in once and shifting directly to another gear, the driver first engages the transmission in neutral before shifting to the next gear.

[BobbyGFirebird]

Great advice Gents! Dealer diagnosed and replaced the tranny mount (SO glad I took to a GM dealer where the service techs own a couple of 4th Gen F-bodys!!!) and it eliminated the noise and the car drives like a $999,999.xx Ferrari. Truly. Amazing. Like day 1 factory.

On the double-clutch, does it make it easier for synchros on my problem gear (3rd) if I do double-clutch? I know I don't have to, but I also don't want to damage synchros anymore.

[35th-ANV-SS]

I doubt your problem is synchro related. The T56 is just a pita notchy transmission because of its slide rail design coupled with a sorry hydraulic setup.

Does it shift fine just driving it around normal?

[BobbyGFirebird]

35thAnnSS.... every gear is fine, up and down, EXCEPT going in to 3rd. 6-speed tranny on white/blue 30th Ann. T/Am. I just shift in very slowly to 3rd, giving things time to catch up.

p.s. you guys likely know this already, but Jim McIlvane, the former Center for the Seattle Sonics, NJ Nets, etc. was a photo editor of GM High Tech Perf. magz. I met him at a wedding and subscribed, and a decade later bought the '99 WS6 ! Is he on this forum somewhere? He had the car in your pic, a convertible with a roll cage. At 7'2" or something, he didn't fit in the coupe !!!

[Naaman]

I, too, find that 3rd gear is the red-headed stepchild of my transmission.

I have missed 4th once or twice out of 10,000 shifts, but if there is a gear that can be a problem child, its 3rd. Now that my clutch is all broken in, though, its much better. 1500 miles after the clutch install, I could not, for the life of me, get into 3rd gear above 5k rpms. Now, 3000 miles after, it does fine.

[douglowden116]

I was having alot of issues with miss ed shifts into third . I got rid of that mushy pos factory shifter and installed a Hurst shifter I'm not saying it's 100 percent cured but it is a hell of alot better . The Hurst has a much more positive feel to it than the factory shifter and it's pretty rare now that I miss third gear .

[35th-ANV-SS]

35thAnnSS.... every gear is fine, up and down, EXCEPT going in to 3rd. 6-speed tranny on white/blue 30th Ann. T/Am. I just shift in very slowly to 3rd, giving things time to catch up.

p.s. you guys likely know this already, but Jim McIlvane, the former Center for the Seattle Sonics, NJ Nets, etc. was a photo editor of GM High Tech Perf. magz. I met him at a wedding and subscribed, and a decade later bought the '99 WS6 ! Is he on this forum somewhere? He had the car in your pic, a convertible with a roll cage. At 7'2" or something, he didn't fit in the coupe !!!

The 35th Anniversary LE but in a convertible?

I'm pretty familiar with the T56 Manual 6-speed as that's what I have in my car. What exactly does it do when you try to put it into 3rd? Does it do it whether you are shifting at 2k rpm or 6k rpm?

[Whamhammer]

I was having alot of issues with miss ed shifts into third . I got rid of that mushy pos factory shifter and installed a Hurst shifter I'm not saying it's 100 percent cured but it is a hell of alot better . The Hurst has a much more positive feel to it than the factory shifter and it's pretty rare now that I miss third gear .

I have the factory Hurst shifter in my WS6 but it feels as if the synchros between 1-2 gear arent working. Sometimes I feel it being uppity, and repeatedly move between 1st and 2nd to "clear" the problem up. When its cold outside, it'll "grind" (sounds like a zipping noise). I always thought it was the 1-2 shift everyone had problems with, never heard about third until this thread.

[douglowden116]

How old is the clutch and does it seem to be working correctly , the clutch being worn or bad hydraulics can cause alot of shifting problems also .

[35th-ANV-SS]

I agree, but if it's a clutch issue it would be in every gear, not just some of them.