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Will the transmission from my 93 G20 4.3 work in my 86 G20 305?

Old February 9th, 2015, 2:36 PM
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Default Will the transmission from my 93 G20 4.3 work in my 86 G20 305?

my 93 G20 has finally had it. I'm wanting to save parts from it for my 86 G20, The trans is fairly new in the 93 and has overdrive. Will it bolt up and work?
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Old February 9th, 2015, 4:51 PM
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The overdrive is likely the 700r4, and your 86 is likely the turbo 350. They are both vacuum driven, but I am not sure on the swap. It should be okay, but not sure. I think you may have to think about driveshaft length, and so on....
Also, the cost of rebuilding a 350 is way cheaper than rebuilding the r4. Also, the axle ratio on both vans might be diff. My 1990 vandura with the 305 and turbo 350 got 16 mpg. While my 1995 g20 350 with the 700r4 only got 13. So overdrive is not the only consideration for fuel economy....
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Old February 11th, 2015, 3:22 PM
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How do I tell the difference? I'm new to Chevy . Had GM's in my teens but that was a while back. Is it stamped on the pan anywhere?
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Old February 11th, 2015, 3:23 PM
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also the trans in the 86 is weird. I have to let it warm up or it just doesn't want to work.
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Old February 11th, 2015, 5:13 PM
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That I am not sure....not a tranny expert. Try google, and maybe someone here in the forums that is will chime in.
Did you get a quote on just rebuilding the 86?
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Old February 11th, 2015, 7:17 PM
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NO honestly I dont have a bunch of money forthat. I was hoping to just swap it in.
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Old January 26th, 2016, 5:16 PM
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Default Won't be a direct fit

Originally Posted by berekhhnd View Post
NO honestly I dont have a bunch of money forthat. I was hoping to just swap it in.
The 93 uses a 700r4 and the 86 uses a th400. Same bellhousing but different crossmember and different trans lengths. Your th400 shaft will be to short for the 700r4 and the 700r4 uses a TV cable (throttle valve) which controls upshift and downshift. No vacuum on 700r4. It also has a lockup converter which needs to activate in overdrive and requires a switch to engage it only in overdrive. My recommendation is find another th400 they are cheap now
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Old November 1st, 2016, 9:16 PM
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I know I'm replying to an old thread, but didn't they switch to the 4L60E in 1992? Even if you could make it fit with the cross member and driveshaft, you will need a computer to run that transmission.

Last edited by mvusse; November 1st, 2016 at 9:16 PM. Reason: spelling
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Old November 24th, 2016, 3:07 PM
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Here's the info I recently got. the tranny in my 1988 G20 is slipping. It's the 700R4 with overdrive. Ironically a new guy I work with used to rebuild trannies. He was going to hook me up with a THM350. He said it was about 1.25 inches shorter than the 700. He said the yoke should have enough travel to be able to slide out and reach. If not we might be able to move the carrier bearing to split the difference. Switching to TH might require a vacuum line but the wire harness might not hook up except for the neutral safety switch. If you search on Autozone's website for trannies for chevy vans by year you will likely see when they switched to the 700.
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