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1G FWD transmission internals in 2G FWD case

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mr2krazee

Proven Member
179
2
Nov 30, 2012
spokane, Washington
My wife and I recently purchased a 99 Spyder GST with a transmission that only had 2nd, 5th, and reverse. We drove it home like that and kept driving our 6.0 swapped trans am while I looked for a replacement transmission to swap in, I had no luck but what I did have was my 1g FWD GST transmission that shifted flawlessly in my old GST.

I began to research the similarities between the two units and found many similarities so I proceeded to remove the 2g transmission for a hands on side by side comparison. I concluded that the two were nearly identical other than the obvious mounts that were different, the speed sensors also differed between mechanical and electronic.

After having a good friend who is not only a fellow DSM owner but also is a journeyman industrial field mechanic with a strong background in transmission rebuilding agree to lend a hand, as well as several air tools and other various goodies that I do not possess. We proceeded to remove the bolts that surround each tier of the cases.

After carefully tapping the outer most case with a rubber mallet we were able to expose the top two shafts one of which is fifth gear and also the shift fork is exposed. We then removed the nuts off the two shafts exposed. After removing the reverse idler bolt on the side of the cases which was a torx on the 2g and a six sided bolt on the 1g the secondary case was free to come off exposing the full planetary gear system contained within the transmission as well as the differential which on both units was an open style diff unfortunately, no posi.

Oh well the Spyder is just a kwick daily driver. We now removed the roll pins from each shift arm and the gears sets came free, we then swapped the 1g gear sets into the 2g case and reassembled the 2g transmission. I'm pretty sure that covers it for the most part if anybody is interested in doing this or is hard pressed for a transmission for their 2g FWD as they are quite uncommon.

The best part of this is that non-turbo 1g transmissions are identical to their turbo counterparts, so you can find them in yards when you want a cheap setup to get going. I have heard the nt trans is geared a bit higher but I have not confirmed this personally.

We had to swap the 1g primary shift fork into the 2g case as the 2g had one less shift fork dowel hole in it. Nearly every component was interchangeable and the only tools we needed beyond the basics was a set of snap ring pliers on hand in case we wanted to swap synchros between gear sets but the 1g synchros were all nice so we decided not to. After reassembly each gear was tested and all checked out with proper functionality.

So there it is, if you need to do this or wonder if its possible for the everyday budget minded real world do it yourselfer the answer is yes. Transmissions aren't as scary as they are made up to be, that is what I learned today with the help of my good friend Don.

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Have you put this in the car yet? I hope you used the 2g front diff. Many of the part numbers are likely the same but not all. 1g nt transmissions are not the same. Maybe the shafts but likely not as certain ratios are different. I don't have my books any more to look it up. The splines are different from year to year on fwd. If that 1g tranny was 93 94 it is likely the same but 90-92 fwd use smaller axles.
 
Have you put this in the car yet? I hope you used the 2g front diff. Many of the part numbers are likely the same but not all. 1g nt transmissions are not the same. Maybe the shafts but likely not as certain ratios are different. I don't have my books any more to look it up. The splines are different from year to year on fwd. If that 1g tranny was 93 94 it is likely the same but 90-92 fwd use smaller axles.

The splines match fine, that was one of the first things I checked.

And as I stated both were GST transmissions. I should have been more clear on the nt transmissions, I meant they are identical on 1gs, meaning you could technically use one for this. The nt transmissions are very close, obviously not every year matches to every car but I just took a six bolt fwd trans and swapped internals to a seven bolt fwd case. Nearly everything was identical.

On top of it, I don't even know for sure that the 1g trans was actually a factory six bolt trans, I just know it fits a six bolt because I took it off one and have the engine sitting in my laundry room. I know AWD transmissions are much more finiky to swap between, splines, final drive ratios, hell even the dowel pins from the 1g 23 spline trans are ever so slightly spaced different to their predecessors, the FWD transmissions have less variation over the years. But yes, they were smaller in their earlier FWDs, that's why certain years could use an AWD intermediate shaft to get the equal length half shaft mod.
 
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Twicks69 is the tranny rebuild expert (TMZPerformance) on here. You could pm him to find out for sure the differences & compatability.

Good to know, ill be sure to ask him a few questions if I run into any issues. Everything was a direct drop in, and all the gears turned nicely together when shifted into, so I think im going to just install it and see how it drives on friday. Thanks for the input guys. Ill let you guys know how it drives.
 
If it is a complete swap over, shouldn't be a major issue. The big thing to be sure to match to the case being used is the reverse idler gear and reverse idler gear rail as the offset height is different. Case wise, well, as you can see, most of it is very similar.
 
If it is a complete swap over, shouldn't be a major issue. The big thing to be sure to match to the case being used is the reverse idler gear and reverse idler gear rail as the offset height is different. Case wise, well, as you can see, most of it is very similar.

Exactly... found that out the hard way and had to rip it all apart again... shifts like a dream now... great trick to know if your in a transmission bind LOL...
 
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