I was just wondering if anyone knew where I could find out some information on a T56 6 speed conversion. I don't know alot about these newer setups, so maybe someone can enlighten me? My 68 427 just dynoed at 500.4 HP and 509ft libs of torque. The car has 308 gears and a M-20 or 21 Transmission. I'm considering switching out to a 411 gears with the T56 double overdrive conversion. Any help appreciated.

 

There are many who have done this conversion. I am doing it on mine as my project progresses. You need to decide whether you want the hydraulic throwout bearing setup or the manual fork type setup. I am using a T56 from a 97 Camaro but converting it to the LS style hydraulic throwout bearing type.

You can use the search function here and specify C3 Tech in the forums. Search under T56 or 6 speed conversion, etc. LOTS of info available.
You can also check out the LS1Tech website and search under transmissions. Lots of info there also.

Good luck

Bman

 

Here is my list of things to look at.

I am converting from a auto to a T56 Magnum so my list has a few things that are extra's for me. ( adding a clutch pedal )

First you need to look at a T56 from a factory car vs a T56 Magnum.

I went with the Magnum so I can use the existing mechanical speedo.
The Magnum has both mechanical and electronic. You will still need a adapter for the mechanical since the T56 magnum I believe uses a ford housing. But they can be purchased from many.

For clearence issues. You may need to cut a bigger hole and will need a offset shifter.

Also the T56 is longer so the slip yoke is further back in the tunnel and may not fit without some triming.

Also I found I had to install the transmission in 2 steps. First Bell Housing to Engine, then Transmission to Bell Housing, and still 1 bolt requires me to prefit in place and struggle to get a socket on.

T56 vs T56 magnum requires difference cross members. You will need cut yours out if it is not removeable.

Will you need to modify the drive shaft. Need a slip yoke with straps so you can install and remove easily.

Wire in electrical connections for backup and nuetral circuits.

I went with a Hyraulic clutch system. Easier for my conversion.

You can purchase all of the parts needed if using a T56 production unit.

Between American powertrain. bowtie overdrives. Hurst etc there are a few to get parts from.

With the T56 Magnum the only item I could not purchase 100% is the crossmember. ( need a custom mod from bowtie Overdrives )

Now the big item is indexing the bell housing. This procedure is not the same for the T56 vs a TKO.
See this
If you are doing all the work yourself plan / test / plan / test

I have spent many hours testing each step to make sure I do it right the first time.

There are many people that have documented theie steps. Read them all and you will learn something from each. This is not a weekend job unless you have experience with custom fab work and installing transmissions.

Good Luck... But plan and think things through many times before starting down the road.

 

I just finished mine in my 69 small block vette ,it was a 4 speed.leave the 308 gears for now , get the close ratio t56 with the 266 first gear and 63 6th gear you will freakin love it.then if you want more change to maybe a 370 rear end.I did the complete t56 magnum brand new , and im using the throw out bearing type, not hydrolic clutch, it works great.I modified the crossmember to make it a bolt in.I have every part number you will need from throw out bearing to the right ball stdd.just try to mount, not try to you have to mount tranny up in the tunnel as high as you can so the drive line angles will work.the hole you have to cut in the top of tranny tunnel is very small, use the american powertrin off set shifter and i beleive the 1310 trans yoke to clear tunnel, and a 6023 quick time bellhousing.I have to say the 6 speed trans iswith out a doubt the single most best imrovment you can do to a late model vette, followed by the borgeson steering box.

 

Did you get the white lightning shifter (what part #), and do you have any leaking problems. (they are known for leak problems)

For the Drive shaft slip yoke does the 1310 give enough clearence. I know the 1330 yoke doesn't fit. Do you have any dimensions that the 1310 yoke needs. Thanks....

Did you do anything with the bell housing indexing or just go with the stock dowel pins / locations ?

 

Does the T56 have sufficient torque rating for you engine? I selected TKO600 transmissions for my 68 SB and 70 BB. These are 5 speed trannies. They have really high torque ratings...sorry I forget now what the torque ratings are. The TKO600 was at one time the standard manual trannie in the Viper. For my 68, with a ZZ4 SB engine, the TKO600 is overkill...doesn't need that much torque rating. For the 70 BB, this is what I need for torque.

For both cars, I have 3.73:1 rear ends. 70 miles per hour at about 2000 rpms. The rear end in the 68 is from Tom's Differentials and is slightly upgraded from the stock rear end. The rear end for the 70 is also from Tom's Differentials..but it's his "Super 10 bolt," large diameter half-shafts, larger U-Joints, fine spline axles, "tuned" diff housing made of high strength components,etc. For extra torque, you can buy a Tom's 12 bolt diff. With all the good stuff, I've read that the rear end can tolerate 1000 hp. I think my super 10 bolt is good for about 800 hp...can't be sure.

With pretty much street tires, the stock C3 rear end is good for about 550 hp. That's pretty astounding for a early 68 car. That's what the L88's ran. With drag tires, the stock C3 rear end will grenade with this amount of HP, from what I've read.

 

The T56 Magnum is the aftermarket version of the TR6060. This is what is in the latest bad boy Viper, C7, Mustang. It will take ~700 lb/ft.

 

Tremec T56 Magnum is rated for •700 lb-ft. of torque capacity.

TKO 600 •Up to 600 lb-ft. of torque capacity.

This is from the tremec website.

 

Check out Silver Sport Transmissions shiftsst.com .

All of the advice above is good stuff but is the hard way to do things. Silver Sport will have a kit to bolt the transmission in the car with all the fixins. They were formally known as Keisler transmissions and developed install kits for these transmissions with mounting brackets engineered for the car the transmission is going in, necessary cables, even a new shift pattern label. The kit includes everything, but the best part is that the shifter in the transmission is modified to fit your car in the factory location.

I have the TKO 5 speed kit for the project car I am working on (70 coupe) and was very pleased with the quality of everything. I cannot comment on fit myself since I have not put it in the car yet but by all accounts I hear it is good to go.

Give them a call.... They can help.

Matt

 

They (SST) have most of what you need, but no crossmembers, offset shifter (for T56 magnums in C3 corvette if you buy their T56 then they mod the shifter for you. If you already have a T56 they wont sell the shifter ???) but between Silversport, American PowerTrain, Hurst Drivline and others you can get everything you need. As stated above if you want a complete kit then you can go the TKO route. Many have described the TKO as a almost bolt on process. For a T56 you will need to make it fit, get the correct drive line angles etc and source parts from at least 2 vendors or do your own fab work. No easy way to install a T56 magnum in a C3 corvette yet. I guess it depends on what you call easy. People with great fabrication skills everything is easy just takes time.

Consider all the posts and learn as much about the complete install process, then decide on what your body, mind and wallet can take.
I was aware of all the challenges for installing a T56 magnum and only missed the slip yoke clearence issue. A little more massaging of the tunnel is required for my 78.

 

Awesome replies! This gives me alot of information to get started. Thanks!

 

so far no leaks with the shifter, and as far as the dowels go I used what they gave me from quick time, I need to look at my notes.

 

just to let you know you will really love that 6 speed, I have both the 6 speed and a tremec 5 speed both great transmissions, but if you can afford the t56, then by all means do it 6 gears is much better.

 

How do you like the feel of the shifter, how does it compare to the stock that came with the tremec ?

 

OK, did this swap a couple of years ago. Magnum T56 behind a 496 BBC. Already had the crossmember made removable several years previously.

Transmission: Magnum T56 with 2.66 1st and .63 6th. Works great with my 3.73 12-bolt rear.

Crossmember: Bow Tie Overdrives T56 crossmember. Had to trim the pad to fit with the Magnum (slightly different location) but it was an easy swap. Used poly tranmission mount shimmed up a bit.

Shifter: 2nd gen (70-82) Camaro shifter for the T56. Disassembled the shifter. Rotated the mechanism 180 degrees and reassembled. Comes right through the stock console hole. Cut down an old Hurst stick.

Bellhousing: Quicktime from American Powertrain set up for a mechanical clutch pivot ball.
http://americanpowertrain.com/i-8425...l-linkage.html
Also from Hurst: http://www.hurst-drivelines.com/?pro...um-with-collar
Noticed that they also have an adapter (http://americanpowertrain.com/c-3145...gm-magnum.html) that will let you use the stock bellhousing.

Clutch: Mcleod RST Street Twin. Great clutch. Mechanical linkage upgraded with spherical rod ends. Nice and smooth.

Yoke: 1310 takeapart yoke. Had to trim and reglass approx 2x3" area of tunnel just forward of the passenger side inner seat belt.

Driveshaft: Made locally. 1310 solid front, 1330 solid rear U-joints.

 

I have not tried the stock shifter, I needed the off set so went with american powertrain.

 

Thanks for the post. I thought the Tremac TKO 600 was a lot stronger. I made some quick checks that it looks like you are correct. Damn.

So I have a TKO600. Looks like it is not as strong as I thought. The Tremac T56 you say is rated at 700 ft-lbs. Any comments about 5 or 6 speeds that get you above the 600/700 foot pounds of torque? Maybe I'm mistaken, but I think Tom's Differentials sells C3 differential's that are rated up to about 1000 foot pounds. If this is accurate, transmission torque ratings for performance C3' trannies need to be pretty high....they need to get up to Tom's torque values. Maybe I'm mistaken....comments? Thanks

 

I use to work at American Powertrain. Both the TKO600 and the T56 are rated at 700 ft-lbs. They offer a high torque upgrade that involves complete teardown, and having all the gears and shafts Cryo treated and RIM polished, and reassembled. This mod will raise the torque rating to 900 ft-lbs.

 

Keep in mind that the spread from 1st gear to top gear is generally about the same between a 5 speed and a 6 speed. A 5 speed has one overdrive and a 6 speed has two. There are exceptions but this is generally true. Also keep in mind that the lowest Gears are the strongest and the higher gears are the weakest. You should never plan on performance driving in an overdrive gear. If your rear end gears are to high or low you might find that You can't use the 1st gear or the top gear. You are way better off using the 1st gear and not the top gear. Otherwise you are skipping the strongest gear and using the weakest. A five speed Trans is generally smaller and lighter. I have a C4 with a factory 6 speed. For cruising the interstates I always shift from 4th to 6th gear. Once in a blue moon I use 5th gear just to see if its still there.

 

I have an LT1 T56 with 3.70 rear gears. I use 5th gear on the highways, and 6th gear on the interstates, but occasionally on the highway will drop it in 6th gear which quiets the ride with my Hooker sidepipes and Max Flo baffles, with rpms at about 1550 in 6th and 2250 in 5th at 60 mph.