T125C for 3.4 DOHC? (Page 1/1)
newc14 APR 12, 09:23 PM
I recently purchased a 1986 SE 2.8 that I'm looking to swap to a 3.4 DOHC, my question is can I use my stock T125 transmission with this swap? It's recently been rebuilt and I'd like to keep it for making the swap process that much easier. However if it's not advisable and I have to swap trannys anyway, I figure I may as well go with a 3800SC. The vehicle will be a daily driver mostly, so I need to make sure it's not going to go out on me 1000 miles in.

Thanks for any and all pointers
ericjon262 APR 13, 02:47 AM
the 125c is a crap transmission, I'm sure you could make it work, but I wouldn't even keep it if it was behind a stock duke.

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"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper

Dennis LaGrua APR 13, 04:03 PM
The TH125H 3 speed automatic will bolt right up to the 3.4DOHC engine (using the original mounts) but agree that its not the best trans choice. If worn as most are at this point in time and if you use it for a performance swap it will need a few mods so it will stay together. At the very least you will need to rebuild, extra friction discs to the clutch pack, a shift kit but the bottom line is that the three speed doesn't provide the best driveability and mileage.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

newc14 APR 13, 04:19 PM
Definitely appreciate your guys' input. Sounds like if I'm going to swap up, I'm better off swapping the transmission too. Appreciate the help!
Dennis LaGrua APR 13, 05:00 PM

quote
Originally posted by newc14:

Definitely appreciate your guys' input. Sounds like if I'm going to swap up, I'm better off swapping the transmission too. Appreciate the help!



I believe that engine came with the GM 4T60e 4 speed transmission. It will bolt right up with its stock brackets and Fiero mounts. Not a difficult swap and the ECM and engine vacuum will control the shifting. If you are swapping in a used 3.4DOHC engine be advised that the timing belts were only good for about 60K miles. On any used engine I would recommend doing a cylinder leakdown test before buying or if you can listen to it run.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

newc14 APR 13, 05:42 PM
Thanks for the heads up! I've got a full service shop so I'll likely just do a full service to it before it goes in, new gaskets, new accessories, belts, etc.