4 Speed / 5 Speed Transmission Question
Thread Starter
Heel & Toe
Joined: Sep 2020
Posts: 22
Likes: 4
4 Speed / 5 Speed Transmission Question
Hey everyone,
so I’ve been doing a lot of thinking lately regarding my Super t-10 that I removed from my 74 convertible C3. Upon further study I see that the input shaft has 0 rings on it, leading me to believe it is not original and a 3.42 1st gear ratio; therefore prone to failure — so I’m looking to get some input on transmission options. I am swapping out the original 350 for a mini blown 350 that’s currently making 450hp at the crank and don’t want to go through the hassle of reinstalling this tranny just to have it fail.
also, I’ve found that my rear diff has an “HO” code stamped on it, meaning it’s from a later year C3 and either has 3.55 or 3.08 gearing. I’m not sure which of the two it is.
i am considering a 5 speed swap ( in fact it’s more preferable), but I’m not looking to break the bank on one. I know there’s SST, Modern Driveline and American Powertrain kits available that are direct swap, but $4k is a bit much for me to lay out at the moment.
perhaps there is another company out there that makes direct fit swaps? Or does anyone know of modding GM production 5 speeds so the shifter will be located in the correct spot?
thanks!
so I’ve been doing a lot of thinking lately regarding my Super t-10 that I removed from my 74 convertible C3. Upon further study I see that the input shaft has 0 rings on it, leading me to believe it is not original and a 3.42 1st gear ratio; therefore prone to failure — so I’m looking to get some input on transmission options. I am swapping out the original 350 for a mini blown 350 that’s currently making 450hp at the crank and don’t want to go through the hassle of reinstalling this tranny just to have it fail.
also, I’ve found that my rear diff has an “HO” code stamped on it, meaning it’s from a later year C3 and either has 3.55 or 3.08 gearing. I’m not sure which of the two it is.
i am considering a 5 speed swap ( in fact it’s more preferable), but I’m not looking to break the bank on one. I know there’s SST, Modern Driveline and American Powertrain kits available that are direct swap, but $4k is a bit much for me to lay out at the moment.
perhaps there is another company out there that makes direct fit swaps? Or does anyone know of modding GM production 5 speeds so the shifter will be located in the correct spot?
thanks!
Le Mans Master
Joined: Mar 2004
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From: Little Rock AR
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Last edited by stingr69; Oct 17, 2020 at 12:26 PM.
Melting Slicks
Joined: Nov 2006
Posts: 3,412
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From: Apple Valley, MN
Check your diff code again. Likely it is an “OH” which is a 1978 or 1979 3.55.
I’d recommend you look for a good used TKO600. I would bet there’s somebody out there who has or is installing a Magnum 6 speed because they want the latest and greatest.
I’d recommend you look for a good used TKO600. I would bet there’s somebody out there who has or is installing a Magnum 6 speed because they want the latest and greatest.
Thread Starter
Heel & Toe
Joined: Sep 2020
Posts: 22
Likes: 4
as far as the 5 speed swap goes, I may have found a used SST kit for sale with 1k miles on it; waiting for confirmation on whether it’s a 500/600. Current owner is selling because he’s upgrading to a 6 speed funny enough. Exciting stuff!
Drifting
Joined: Mar 2009
Posts: 1,461
Likes: 361
From: Monson MA
My apologies — I did mean “OH” code. I see that the 78/79 have the 3.55 OH code, but the 80 has a 3.07 OH code? I’m not sure which gear is in this rear, but I suppose I could find out by rotating the wheels and counting how many times the driveshaft rotates?
as far as the 5 speed swap goes, I may have found a used SST kit for sale with 1k miles on it; waiting for confirmation on whether it’s a 500/600. Current owner is selling because he’s upgrading to a 6 speed funny enough. Exciting stuff!
as far as the 5 speed swap goes, I may have found a used SST kit for sale with 1k miles on it; waiting for confirmation on whether it’s a 500/600. Current owner is selling because he’s upgrading to a 6 speed funny enough. Exciting stuff!
Melting Slicks
Joined: Nov 2006
Posts: 3,412
Likes: 1,823
From: Apple Valley, MN
You are spot on regarding counting the number of revolutions the driveshaft turns per one full revolution of the wheel.
The ‘80 differential is a completely different design than the 63-79. Apples and oranges so pay no attention to those in your case.
The ‘80 differential is a completely different design than the 63-79. Apples and oranges so pay no attention to those in your case.
Thread Starter
Heel & Toe
Joined: Sep 2020
Posts: 22
Likes: 4
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Thread Starter
Heel & Toe
Joined: Sep 2020
Posts: 22
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haha glad to know I was on the right path. And thanks for the knowledge! So I now know I have 3.55 gears in the rear (which I think I’ll be very content with)
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You are going to have a fun little car when you get that motor and tranny in. I would go with the 5 speed no matter if its a 500 or 600. It will handle the torque you are putting out at 6 psi and if its the first gear you are worried about you can torque match it with the rear end gear. I am/ ws in the saem boat as yo ubut fouund a used McLeod 5 speed that I had to sent back to get the gears and some internals fixed. It was well wotrth the cost and I wont ever go back to a 4 speed unless its a temporary replacement while the 5 speed is getting worked on