New transmission help

[coolseanj]

My v30 1987 has a 454 automatic trans. I'm assuming it has a th400. How do i find out for sure? I know it only has 3 speeds.
I am thinking of putting a 5 speed automatic in. But i don't Know what trans i can put in or how. I'm worried about the computer and size of other trans. How can i found out what trans to look for and how to install

 

[QBuff02]

i'd be willing to venture it has a th400 in it. Unless it's been swapped at some point. look at the shape of the pan on it and you'll know for sure.

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[Matt69olds]

The 700 (also known as 4L60) will be the easiest swap. That trans was available in a lot of trucks starting in the early 80s, making parts easy to find.

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[Frankenchevy]

With a GM auto, it’ll be 4 speed then jump to 6 speed. A 4L80e is the 4 speed lockup version of the th400. That’s the route I’m going.

It’ll require a transmission controller and an adapter for your existing transfer case. If you have an np208, @HotRodPC just posted a video of a guy that does a how to involving the 208 and a 2wd 4L80e.

 

[RoryH19]

With a GM auto, it’ll be 4 speed then jump to 6 speed. A 4L80e is the 4 speed lockup version of the th400. That’s the route I’m going.

It’ll require a transmission controller and an adapter for your existing transfer case. If you have an np208, @HotRodPC just posted a video of a guy that does a how to involving the 208 and a 2wd 4L80e.

x2
4L80e is the overdrive version of the TH400.
Almost guarantee that's what you have behind a 454.
700r4 will give you OD without a computer but IIRC they were never behind a big block from the factory.
You will need a standalone computer to shift the trans.
I believe 91 was the first year of the 4L80e.

Gearvendors will also give you OD behind your TH400

 

[Poppy 87]

With a GM auto, it’ll be 4 speed then jump to 6 speed. A 4L80e is the 4 speed lockup version of the th400. That’s the route I’m going.

It’ll require a transmission controller and an adapter for your existing transfer case. If you have an np208, @HotRodPC just posted a video of a guy that does a how to involving the 208 and a 2wd 4L80e.

GM did use the 5 speed Allison automatic transmission, but I think it was used with the Duramax engines.

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[bucket]

GM did use the 5 speed Allison automatic transmission, but I think it was used with the Duramax engines.

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It was used behind the HD line of trucks too, behind the 8.1 big block. It's a big transmission, which is supposedly why it was not used behind the 8.1 in the 2500 Avalanche and Suburban. Or the Duramax vans.

 

[Craig 85]

It was used behind the HD line of trucks too, behind the 8.1 big block. It's a big transmission, which is supposedly why it was not used behind the 8.1 in the 2500 Avalanche and Suburban. Or the Duramax vans.

I wasn't used in Suburbans and vans due to floor clearance. I had a 2001 GMC 2500HD with an 8.1. Look at the bumpers between the 1/2 tons and HD trucks. The HD trucks got a 2" body lift. I used the GMC since it's more noticeable. Look at the rear corners of the front bumper. The filler on top of the bumper is taller than the 1/2 ton. Also in photo #3 & 4 you can see a raised lip on top of the rear bumper to help fill the gap with the bed floor.

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1500 Bumper/gap

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2500HD Bumper/gap

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[bucket]

I wasn't used in Suburbans and vans due to floor clearance. I had a 2001 GMC 2500HD with an 8.1. Look at the bumpers between the 1/2 tons and HD trucks. The HD trucks got a 2" body lift. I used the GMC since it's more noticeable. Look at the rear corners of the front bumper. The filler on top of the bumper is taller than the 1/2 ton. Also in photo #3 & 4 you can see a raised lip on top of the rear bumper to help fill the gap with the bed floor.

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1500 Bumper/gap

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2500HD Bumper/gap

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Yeah, I only said supposedly because I wasn't 100% sure of the reasoning. I was pretty sure it was floor clearance though. The light duty 2500's used the same bumper filler as the 1500. I know that when the "Duraburb" conversions are done, they usually employ a tapered body lift. Presumably to fit the larger radiator support, and more clearance for the Allison too.

But anyway, the Allison trans is probably a tight squeeze in a square too.

 

[coolseanj]

Thank you all for your advice!

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[HotRodPC]

GM did use the 5 speed Allison automatic transmission, but I think it was used with the Duramax engines.

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And the 8.1 Big Block. 6.0 and 6.2 LS Engines got the GM transmissions.

 

[bucket]

And the 8.1 Big Block, 6.0 and 6.2 LS Engines got the GM transmissions.

2500 HD and 3500 trucks with the 8.1 got the Allison too. Standard 2500 trucks were not available with the 8.1, but 2500 Suburbans and 2500 Avalanche both got the 4L80e even when equipped with the 8.1 big block.

 

[HotRodPC]

2500 HD and 3500 trucks with the 8.1 got the Allison too. Standard 2500 trucks were not available with the 8.1, but 2500 Suburbans and 2500 Avalanche both got the 4L80e even when equipped with the 8.1 big block.

True, but yes Allison did come behind 8.1's. I would have bought a 2500 Avalanche if it got the Allison but it didn't as you mention. The 2500 Avalanche had rear leaf spring suspension and 8.1 was the only engine option. So I opted for the 1500 since it didn't have the Allison. I had 2 different Avalanches that I bought brand new. A 2002 and a 2003.

 

[bucket]

True, but yes Allison did come behind 8.1's. I would have bought a 2500 Avalanche if it got the Allison but it didn't as you mention. The 2500 Avalanche had rear leaf spring suspension and 8.1 was the only engine option. So I opted for the 1500 since it didn't have the Allison. I had 2 different Avalanches that I bought brand new. A 2002 and a 2003.

The 2500 Avalanche frame was just a 2500 Suburban frame. I always thought it was odd the Avalanche came standard with the 8.1 but it was optional in the Suburban.

I also thought it was weird that the Avalanche was later available without all the cladding, but ONLY on the 1500. The 2500 was stuck with the goofy plastic.

 

[Poppy 87]

Interesting info on the truck frames. I asked our fleet sales manager at work ( I am a GM tech) why the Duramax wasn't available in the SUVs and he said that due to the frame configuration the engine would too high up, changing the center of gravity, thus creating a rollover concern that the General wasn't willing to risk. Truth or rumor I don't know

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