So I'm shopping for a trans for my V8 Miata project and can't seem to find any LS1 T-56s. Do I even need one? Some places say the LT/LS transmissions are the same or at least interchange. Others say they are different or at least not easy to convert. Plenty of cheap ($1000) LT versions around. If they are swappable what would I need to make the LT version work with my LS engine besides the bellhousing?
HELP!
Well, near as I know LS1 and LT1 use the same bellhousing pattern, and the bellhousing to shifter length must be the same as both were used in the same cars.
Only thing I can imagine that might be different would be the spline count on the input shaft or the diameter of the pilot bushing, but I'd wait for more expert advice.
The length of the input shaft would be different as the LS crank is .4" shorter than the older SBC and LT series with regards to how far it sticks out the back of the block. There are options, longer pilot bushings or certain 4.8L flywheels, but finding any actual good information is hard. Lots of speculation and BS presented as gospel by folks who don't really know any better.
oldopelguy wrote: Lots of speculation and BS presented as gospel by folks who don't really know any better.
Thats exactly my problem. The worst part is that the rebuilders lump them all together.
LS and LT bellhousings are different- the pattern is the same, but the LS bellhousing is deeper to compensate for the shorter mounting flange on the LS engine. McCleod makes a modular sfi rated bellhousing system for hooking pretty much any trans to any engine. don't know about cost, tho.
I believe the LT version has an external clutch fork while the LS version does not.
This thread might help: LT1 vs LS1 T56
dyintorace wrote:I believe the LT version has an external clutch fork while the LS version does not.
This thread might help: LT1 vs LS1 T56
Eureka! I swore I searched on that site and didn't find anything. Time to swap conversion parts for the cheaper LTs and see if its worth going that route.
I'm pretty sure Car Craft has run through this in the past year or so.
Pay attention to the shifter as well - you want the F-body shifter location.
Found some good stuff there but not what I was searching for. Anyone have an idea what back issue I should look for?
I really need to re-up with CC.
If you search for info about putting a TH400 behind an LSx motor you get info about which flywheel or flexplate you can use. IIRC, on the autos they use either a dished flexplate, a flat flexplate, or a flat flexplate with a factory spacer. I think that factory spacer behind a stock flywheel is the key to using a small block chevy trans behind an LSx motor. This is all based on memory so results may vary, follow at your own risk, etc...
Why don't you use up the guys at Keisler? http://www.keislerauto.com/
They are the source of all things Tremec, and can probably tell you what you need, and then sell it to you.
The CC article was about using SBC transmissions with the LS engines, but not specifically the T56. Sorry, I didn't keep the issue.
JD, I kept the issue of CC. Send me your address and I'll mail it to you. I may want it back someday.
tuna55 wrote:JD, I kept the issue of CC. Send me your address and I'll mail it to you. I may want it back someday.
I'll try not to make the pages stick together then. 
Revisited: Just scored a GTO unit with for a grand. I figure as long as its not lunched I could always resell it. From the looks of the pics all I need is the F-body shifter assembly. 1st question-can I grab the shifter housing from the earlier and much more common LT1 trans? 2nd question(for Kieth)-does the FM shifter even care what trans you start with i.e. is it just the stick or the stick/plate/pivot assembly?
Streetwiseguy wrote:Why don't you use up the guys at Keisler? http://www.keislerauto.com/
They are the source of all things Tremec, and can probably tell you what you need, and then sell it to you.
This is probably my next call 
The bellhousings will interchange as far as bolt patterns are concerned... you'll just have a couple holes on the block that won't have holes on the bellhousing.
The bellhousing depth is different between them. There are conversion parts like flywheels and spacers, but you might end up spending as much on those as you would paying a premium for the LS T56.
It might make your search a little more productive if you know this: All T56 center cases are the same casting. The adapter plate and tailhousing (along with the corresponding input/output shafts) are what is different. For instance, I took a TNET1247 Viper T56, put a GM front plate and input shaft on it, then bored out a GM tailhousing for the Viper output shaft. I could have swapped to a GM output, but I can't let go of that beefy 31 spline output :)
I say that because (if all else fails) you can just get the one you want and scavenge parts to make it fit anything - early gm, late gm, ford windsor/romeo, mopar... the possibilities are somewhat endless.
Thanks for the info!
A quick look says the one I bought is a GTO LS unit with belhousing and no shifter-making it look almost exactly like the Camaro unit in the picture above. The seller seems to be a good guy and is throwing in both a Corvette and GTO throwout bearing once he digs them out. For the price I don't think I can go wrong. I think I could sell it far a few hundred more than I paid with one phone call tonight.
I tend to buy things on the "bigger idiot" theory. Somewhere there is a bigger idiot than me that will pay more than I did 
Junkyard_Dog wrote:2nd question(for Kieth)-does the FM shifter even care what trans you start with i.e. is it just the stick or the stick/plate/pivot assembly?
It's my understanding that a shifter designed for an F-body will plug into a GTO trans. We might have an aftermarket unit at FM that we pulled out of Elvis, BTW. Generally speaking, we've found the stock parts to work best.
The CTS-V trans needs a new tailhousing. At least, that's what I've gleaned. Never tried to use anything but an F-body donor.
