Im planning a 3800 sc swap for my 85 se next spring so i can have it all setup for when i get my liscense. I was wondering if the stock auto tranny will work with the 3800 sc. The one thats in the car has only 20k on it from the rebuild the previous owner had done and he had everything thing replaced. I want to use this to save some costs and im not going to be beating on the car just maybe getting on it every once in a while. So will it work with the 3800 sc?

It will work, just like the manuals work, but reliability is very very bad.

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Ultimate 3800 swap thread

Ok thats what i was looking for. I no it wont be like the HD tranny that comes out of the 3800sc cars but im not planning on beating the car it would just be for normal use and maybe getting on it once in a while. Would the mounts for the 3800 still be the same though because doesnt the getrag move when you put in the 3800.

If you are talking about the stock auto tranney that came with the 3800,yes it will work.
(You wouldn't want to try and use the Fiero Auto tranney,because the gearing is much smaller and I have no Idea if the Fiero Auto would work).

[This message has been edited by James Bond 007 (edited 09-26-2007).]

nope the stock auto that came in the 85 2m6. I was talking to another fiero owner that said it will bolt up and fit with the stock 125 or whatever its called but the decklid hinge has to be modified to fit. True or not?

I'm pretty sure everybody here will agree that this is not a good idea. The 125 might work bolted up, but the SC engine puts out a lot more power, so the durability is going to be very questionable (doesn't matter if you 'beat' on it) and the gearing is going to suck for your new engine. Save yourself a lot of $$$, headaches, and time by putting the 4t60 or 4t65 in there from the start. I think if that means waiting a few months on doing your swap, then wait.

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Christian Thomas
87 Pontiac Fiero GT Burgandy/Silver 5.7L ZZ4 5spd, 88 suspension, C6 polished wheels, C5 Z06 brakes, Konis, poly'd, Spec Stg 3
301rwhp/345rwtq
Stovebolt Powered!!!!!
06 Cobalt SS/SC w/ LSD (the slow DD)

quote Originally posted by CTFieroGT87: I'm pretty sure everybody here will agree that this is not a good idea. The 125 might work bolted up, but the SC engine puts out a lot more power, so the durability is going to be very questionable (doesn't matter if you 'beat' on it) and the gearing is going to suck for your new engine. Save yourself a lot of $$$, headaches, and time by putting the 4t60 or 4t65 in there from the start. I think if that means waiting a few months on doing your swap, then wait.

I agree,(I've heard the 4 speed automatic has Great Freeway Cruzeing Speeds Too).

[This message has been edited by James Bond 007 (edited 09-27-2007).]

I was worried the durability wouldnt be there but i dont want to have to redo the shift linkage and every thing for the swap and the transmission only has 20k on new every thing inside and out. Might have to decide weather or not i want to do it.

The TH-125H Fiero transmisson will bolt up to the 3800SC, and if you did a few simple mods like adding a TransGo shift kit, it should work reliably. However the TH-125 is a three speed auto and the 4T65eHD is a four speed auto that uses heavier internal parts and has a wider range of gearing. . You would be better off with the 4T65eHD as the cruising RPM's would be in a more comfortable range but if you just want to bolt up and go a Th-125H trans is a possible (but not the best) option.

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87GT 3.4 Turbo- 0-60 5.2 seconds
2006 3800SC Series III swap in progress
Engine Controls, PCM goodies,
re-programming & odd electronics stuff
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I would like to do the entire thing and do it right because if i was messin around one day or something and blew the tranny id be beside myself and wouldnt i have to make my own mounts then because it would be in a different spot than it would be if it were bolted up to the hd transmission. Also does the shift linkage and stuff have to be changed or not when the hd tranny goes in or is it simpler than that. I wish i couldve found a 3.4pr instead, i want to have some more power rather than rebuild the motor but all my options are striking out. Looks like i might just go with a 3.1 turbo if this turns out not to go well to.