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Pontiac of the Month

Pedja's 1968 Firebird

2019 March
of the Month

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I've got a 1970 T-37 Tempest, which i recently learned through PHS is nowhere near original, so ive decided to swap the motor from a 350 2v to a 455, the 455 i purchased came with a TH400 attached, but is from a 1970 bonneville. The T-37 as of now has a TH350, So I guess my question would be what would need to be changed, if anything, to put the bonneville TH400 into the Tempest or would the TH350 handle the stock 455?

 

Thanks, Sam

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 Only thing you might have to change is the location of the crssmember either forward or backward....It's very Possible could already have the frame predrilled from the factory to relocate it...Also the transmission yoke will have to be changed too...Possibly the length of the driveshaft depending on which tailshaft the TH 400 has...Will also have to have the electric kickdown switch...As the TH 350 kickdown is a mechanical cable...Should be a pretty straight forward swap.....

Edited by TWO LANE BLACK TOP

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11 hours ago, TWO LANE BLACK TOP said:

 Only thing you might have to change is the location of the crossmember either forward or backward....It's very Possible could already have the frame predrilled from the factory to relocate it...Also the transmission yoke will have to be changed too...Possibly the length of the driveshaft depending on which tailshaft the TH 400 has...Will also have to have the electric kickdown switch...As the TH 350 kickdown is a mechanical cable...Should be a pretty straight forward swap.....

Nice thing is the electronic kickdown switch and the rest of the parts are readily available from most of the A-body and performance catalogs. 

When I swapped Lucy from a TH350 to a TH400, I didn't have to drill the holes for the TH400, they were already predrilled on my car. However, I did have to get a longer emergency brake cable made, which I got from Inline Tube, who are local to me. 

One suggestion, depending on what you do with your car. I wish I had gotten a BOP-bolt pattern TH200 4R (overdrive) given all the highway miles I drive with Lucy. You can build them up to hold the power of a 455. If a GSX Grand National can run a TH200 4R, so can Lucy!

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The T400 from the bonnie is longer which will require you to cut & balance the driveshaft & then make a new trans cross member as the trans will sit farther back under the car. You can use the t350 as it will bolt right up to your newer 455 & will hold the power the stock engine puts out.  If you use the t400 you'll have to change the driveshaft & trans output to. The T350 uses vacuum to shift it so all you need to do is hook it right back up the way it comes out.  If in the future you build up the power of the 455 maybe you'll want to change to a T400 trans , but get the correct one that will bolt in without a bunch of changing item ,,, just in case your on the road & break down , that way it can be fixed without a lot of problems. 

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