Installing a 2G trans in to a 1G or GVR4 is not too tough, but there are several things you need to be aware of. Here are the issues and how to overcome them. Realistically this swap has become quite rare due to the increasing price and demand of a good 2G trans, but if you're like me and found a deal on one that you just couldn't resist then this FAQ is for you.
DISCLAIMER: This modification was done to a '92 Galant VR-4, it should work on 1G's no problem but your results may vary. This is exactly what I did to get it to work on my car and it shifts like butter.
Issues and the fixes for said issues:
1. The 1G clutch slave cylinder bolts are too short, you will need to use 2G clutch slave cylinder bolts (as they're longer of course) to mate up with your 1G clutch slave cylinder.
2. The 2G trans slightly repositions your starter, if you are reusing your 6-bolt starter plate (as I did) then you will have to remove the plate to bore out the starter bolt holes. This means that once you remove your old 1G transmission, you will also be removing the clutch pressure plate, disc, and flywheel so that you can unbolt your starter plate to bore the holes out. SOME people have just hogged out the holes with the plate still attached but I completely removed mine, lined it up with the 2G trans, and then ground the holes out to right where they needed to be. Once you have bored the holes out, you can replace the starter plate, and clutch assembly.
3. You will need to remove the 2G speedo sensor, and replace it with the 1G (cable driven) speedo sensor.
4. I also replaced the reverse switch/sensor with the 1G model. Whether or not you can use the 2G model I am not sure, but the 1G part fits right in so I used that.
5. Be absolutely sure you have the appropriate transfercase for the transmission you're installing. My trans was a '97-'99 model so I had to purchase a '97-'99 transfercase to go with it as the early model '95-'96 transfercases are geared differently.
6. For whatever reason the "small/skinny" bolt on the back of the trans that goes in above the transfercase was not long enough to snug back in to the 2G trans once I had it in place? I had to use a bolt of the same thread pitch but just a 1/2 inch longer. The original felt like it wanted to thread in but just wouldn't take. That might be different for you but it's just something I bumped in to and an easy fix.
7. The shifter arms on the trans are different for the 1G and 2G transmissions, there are several ways to tackle this (including the cutting and welding of the shift-control arms etc.) but you'll see my solution below in the steps. In these pictures you can see the difference between the 1G and 2G "side to side" shifter arm.
1G "side to side" shifter control arm
2G "side to side" shifter control arm
Steps:
1. Remove 1G trans (find another faq on that if you don't know how to do this)
2. Remove the misc. sensors and whatnot from the 2G trans and replace them with the appropriate sensors from your 1G transmission. I used the 2G clutch fork, throwout bearing etc. that were all still in the 2G trans. I also shimmed the clutch fork pivot ball with a washer and greased the ball, clutch fork, clutch fork pads, and throwout bearing shaft while I was in there.
Be sure to REMOVE the big plate that rests on top of the 2G trans as well as all the bolts that sit where the motor mount will be. I left ONE stud on the top of the trans, it didn't have a nut or way to come out and it did not interfere with the 1G motor mount so I just left it up there. Take the 2G shifter cable bracket (the small bracket that holds the cables to the trans) off of the trans, and replace it with the 1G shifter cable bracket.
3. Remove the 2G "up and down" shift control arm (two bolts an viola) and pitch it, replace it with the 1G "up and down" shift control arm.
2G up and down control arm bad.... Get rid of it.
1G "up and down" shift control arm good, remove this from your old trans and bolt it on to the 2G trans. It should fit right in, and be sure it still has the little square plastic bushing on the end.
3. Remove clutch assy and starter plate to bore out the starter bolt holes (or if you think you're slick try your luck with it on the block and regret it later lol) Then replace the starter plate and clutch assy. While you're doing this why not upgrade your clutch?
4. So now your 2g trans is aaaaaaaaaaaalmost ready to go in the last and probably most inportant step is to bend your 2G "side to side" shift control arm to look just like the 1G "side to side" shift control arm. I used a big crescent wrench and just went to town. A few bends later and it was close.... Damn close. I took some rough measurements and it was maybe 1/16th of an inch off from where the 1G arm was and that was good enough for me. Here was the final result of all that bending as well as another pic of the corresponding 1G arm for comparison sake.
1G "side to side arm"
Modified 2G arm after a little lovin' with a crescent wrench and elbow grease. She isn't pretty, but looks better in person and works beautifully.
5. Drain your trans and transfercase, replace with whatever fluids you like, reconnect the shifter control arms to the shifter cables. Now get in the car and run it through the gears. Initially my shifter felt way off, and would not go in to 5th and reverse. This was later determined to be the fault of the shifter cable adjustments UNDER the shifter in the car. We adjusted those cables so that neutral felt right, and then the car went right in to every gear. Done, you now have a working 2G trans in your 1G.
As a side note, the 2G trans I put in my car is a mildly used Shep stage 3 with a 4-spider and it shifts wonderfully. Love this trans, and glad it worked out okay. Hope this helps as most of the info I found was kinda vague. If I think of anything else I'll post it up later.
-Cory
EDIT>>> Just another data point here. Your 2G transmission "side to side" shift control arm may look a bit different if it still has the counter-weight attached. Mine was a worked over shep trans and thus it didn't have the counterweight.
Install a 2G trans into a 1G/GVR4
