Transmission Interchange - will this work?

The 3 & 4 clutch packs on my wagon went - but I have a 1987 Chevy G20 sitting around that recently blew its engine - Can i steal the transmission from that?

The 1991 wagon should have the same transmission, correct? 4L60 / TH700R4?

Yes, but there will be a few stronger parts in your 91 than the 87. Just double check to make sure the G20 doesn't have a TH400.

Thanks Jay,

Do you think it would be a better idea to have the existing transmission rebuilt?
Maybe upgrade the internal parts at the same time, since it will already be pulled apart vs. just switching in the other transmission?
I figure between pulling the van transmission, pulling the wagon transmission and re-installing I am looking at a solid weekend spent under vehicles...

How many miles are on the old transmission.Would it need a rebuild as well?

if the van trans is 700r4,. i would pull it and put a hd2 shift kit in it,.
shift kits really do extend the life of 700 r4's,..along with an auxilliary cooler

Nick had schooled me prior on the value of external coolers. I probably should add a temp gauge to actually see what's going on.

The van has only 88,000 miles on it according to the seller when i bought it, but I am assuming it to be 188,000 based on age. So most likely due for a rebuild in the near-ish future
The wagon transmission has 250,000 miles on it... and as far as I know has not been rebuilt previously.

Have the one in the car rebuilt. You may have a different tailshaft/housing, and the VSS gears may be different as well. Get the "beast" sunshell, and have the other parts upgraded while you are at it.

With a little ingenuity, you can plumb in a trans cooler from an LT1 car, and it will bolt up to your core support. I did that on my 454 conversion. The lines for the cooler are metric, and the lines on the 91 are SAE. The lines are also smaller on the 91, so you have to get adapters for the cooler. I found the adapters at O'Reilly's and made the lines with the SAE fitting on one end, and metric fittings on the other. I used the same size lines as the 91 in the easy to bend lines from O'Reilly's with the SAE fitting already on them, and put the metric fitting on the other end with a double flare. I used a coupler to attach the top original line to the one I made to go to the cooler. The other line goes from the top of the radiator tank to the other end of the cooler. You also need a tubing bender, so you do not collapse the tubes. The line from the top of the tank to the cooler does a 180 after leaving the tank, and that is the only quirky bend. I am currently replacing my radiator because of an incident with an electric fan, but as soon as it is back together, I can take some pictures.

Pics would be awesome - I have a line bender from another project...I was looking at getting upgraded parts put in, just wasn't sure if it was worth the cost of the rebuild.
I will look into the cooler, will need to do some more research on that.

Long term plan is to replace the engine with a slightly built 350 (not LTI) or something newer. But that will need to wait a while.

Here are some pics of the line routing for the LT1 cooler in my OCC. You can do this with any radiator to get more cooling.

The first pic shows the connector and 180 degree bend. The 180 in the green line goes under the hoses. The connector requires that the upper line be bent to pass the top of the radiator.



The lines go across the top, and down to the LT1 oil cooler. You can run the lines wherever they suit you. There are adapters from the lines to the cooler.



This is just a look at how the OEM line goes into the bottom of the radiator. You can see the upper line, and the curve of the custom line. I do not have the fans installed in these pictures.