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Hi newbie here from over the pond in the UK.
I have a 1975 firebird which i want to resto mod, i have managed to source all my parts but now have reached a brick wall. I want to get rid of my stock pontiac 350, TH350 and 2:73 open diff so i’ve got a LS1 from a 99 corvette on its way over here, I have an LSD with 4:11 gears ready to go on, but i’m totally stuck with what transmissions i can bolt upto the corvette LS1 as i believe these are trans axle. Parts aren’t as readily available over here in the Uk as they are over there so i really need something that will bolt straight up. I’m getting confused with input shafts and splines and all that so i haven’t a clue what i’m suppose to purchase. Any help would be greatly appreciated.
I put a LS1 from a 2000 Corvette in my El Camino, and had the same issue. The Corvette LS1 has a flexplate that the front of the driveshaft attaches to. I had to replace that with a standard flexplate. I think I used one from a Camaro. Then I used a 4L60E from a 1999 Camaro. Below you can see the old flexplate and the new flexplate.
You can use the TH350 as well. It will bolt up and you can buy the correct flex plate. Depending on what speeds yiu drive 4.11 gears are pretty high. The 4l60e will give you a different first gear than the th350 , and overdrive at .84 to one I believe instead of the 1to1 final drive with the th350.
The th350 will need a kick down cable for throttle downshifting, while the 4l60e will need correct harness and ecu, as well as a 12v positive that goes away when the brake pedal is depressed ( torque converter lockup)
If it were me, I would do the 4l60e 3.55 or maybe 3.73 gears, but these parts are readily available around here. Are you planning on modifying thecengine( cam supercharger, etc)? The 4l60 in stock form won’t handle much power, and cammed don’t work well with stock converters IMO. If you buy a 4l60 please keep in mind they make ones for v6 cars as well, they are a little weaker and have different converters.
I've used LS1 and LS3 engines on number of LS swap projects. Some of the engines were stock and some had small to medium cams. The 4L60E's were completely rebuilt with upgraded parts. Never had fail but I didn't try to brake it either. When I'm looking for a core I tell the supplier I need a 4L60E out of a 2002 Camaro.
would go with 3.73 gears. Plenty of low end and reasonable RPM's going down the motorway.
I like about a 2800-3000 rpm stall converter. Buy a billet type if you can afford it. I like Circle and Yank.
Good luck with your project.
Depending on the engine ECU your using, you may need a 600 dollar (give or take) transmission controller, and have the eco neutered to thinks running a manual, or if the ECU is compatible with a 4l60E it will need a bit of tuning to shift like you might want..
The later "ls" family Corvette was a torque tube car.. Transaxle in the rear,, like some of the EU marques..
I believe if you tear apart the setup in that pic of the corvette flywheel,, you'll find thats a regular flywheel/flexplate behind a adapter/spacer assembly for the torque tube connection.
Been a long time since I was under a Vette so consider this amateur advice..
thanks for all the advice guys.
i’ve been offered a T56 which is currently mated to a vortec 5.3. in a gen 3 trans am
it has a mcloud clutch slave and an ACT performance clutch and comes complete with flywhee and shifter too. he said i can have pedal box and linkages too. i’m picking up a custom made drive shaft to fit a T56 for a gen two trans am tomorrow.
The LS1 i have coming over was mated to an auto so does the ecu need reprogramming to let it know it’s now running a manual?
The ecu will probably need vats removed, when that’s done the automatic transmission things can be removed. The t56 will work well with 4.11 gears as the final ratio is .50 to 1. It should be noted that all C5 ls1 engines were drive by wire, so to make it work you will need the pedal and TAC module ( matched) along with with the wiring. If you decide to go to cable drive, it can be programmed as well.
The ecu will probably need vats removed, when that’s done the automatic transmission things can be removed. The t56 will work well with 4.11 gears as the final ratio is .50 to 1. It should be noted that all C5 ls1 engines were drive by wire, so to make it work you will need the pedal and TAC module ( matched) along with with the wiring. If you decide to go to cable drive, it can be programmed as well.
Vehicle anti theft system. It is integrated with the key and the ECU to let the car know it’s not being stolen. With a stock ECU (if you are using that) the engine will start for a second or two and stall without deleting it from the ECU.
When I bought my LS1 it came with a 4L60e bolted up to it from a Corvette with a truck bellhousing and a F-body converter. When I went to try driving it for the first time, it
would not go anywhere. After pulling the trans in and out a few times, we found out the input shaft was different on the Corvette 4L60Es and would not
seal inside the F-body converter. I ended up putting a truck input shaft in it from an 07 Silverado (perks of being at a dealer an having core transmissions to swap parts). Swapping that input shaft fixed everything and I was able to then build pressure. Depending on what your plans are with the vehicle, if you get the 4L60E, you might want to build the transmission up with beefier parts for the common failing parts.
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LS1 transmission 
