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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Trukk on March 17, 2009, 11:00:52 pm

Title: TH 350 TH400 Swap
Post by: Trukk on March 17, 2009, 11:00:52 pm

My TH 350 trans started slipping today. How much advantage is gained my changing to a TH 400, and how much conversion work would it take on a 78 Chevy 3/4T 2x4? Are the 350 and 400 the same length? Same output shaft size?

The truck is powered by a 350cid and will be towing a 6000-lb load 1600 miles two to three times a year. The rest of the time it is a driver.

Sorry for the Jr-grade questions - I'm new the old Chevy's and have a lot to learn about interchange.

Title: Re: TH 350 TH400 Swap
Post by: werewolfx13 on March 18, 2009, 12:15:01 am

Build a 700r4. Better mileage, and with those demands, you don't need a 400.

Title: Re: TH 350 TH400 Swap
Post by: Blazin on March 18, 2009, 06:52:36 am

700R4 would be nice if rebuilt to heavy specs. But the TH350 is a great transmission as well when rebuilt correctly. Not to down play the TH400, but they are not physical the same length. Require other minor mods as well. If you can get a whole parts C20 with a TH400 in it it wouldn't be to bad.

Title: Re: TH 350 TH400 Swap
Post by: enaberif on March 18, 2009, 07:11:57 pm

Quote from: Blazin on March 18, 2009, 06:52:36 am

700R4 would be nice if rebuilt to heavy specs. But the TH350 is a great transmission as well when rebuilt correctly. Not to down play the TH400, but they are not physical the same length. Require other minor mods as well. If you can get a whole parts C20 with a TH400 in it it wouldn't be to bad.

Cept the TH350 on the highway is horrible.

Title: Re: TH 350 TH400 Swap
Post by: Trukk on March 18, 2009, 07:49:18 pm

Thanks for the info guys. The 700r is a later 4 speed auto I assume? How much of a direct bolt in is one of those?

PS - It turns out I already have the TH400 in this truck. Once I looked underneath I found the info from the original seller to be incorrect.!!