Scott Hamel

This is prob the oldest question in the trans threads..lol

i have a 1973 cutlass with a 68-69 toronado 455. the car still has the th350 from the factory.. with the 455 it seems to be killing the transmission.. so i would like to beef it up with the th400.. i know i need the kickdown setup for the gas pedal.. i have the transmission. my 2 Questions are will i need to replace the flex plate ( im going with a acc converter ) says i can use on dual bolt flex plates.. and the crossmember that the th350 is bolted to.. does that need to be changed? i know the 400 is a little longer. and i'm sure i'm going to have to shorten my drive shaft?

any help from you guys would be great to make this a easy job. i want to get it swapped over before i store the car for these crappy NE winters.

455man

Just move the cross member back. There were bolt holes for it in my 72. Not sure about the flex plate. There was no issue with my change over.

oldcutlass

Is it a BOP T400? Yes the Xmember gets moved back, drive shaft needs to be shortened, Ebrake cable setup will need to be modified. Yes, you will need a kickdown switch assy.

I believe the flexplate is the same for either trans. Make sure your bolt pattern for the torque converter is correct and I would boost your stall up 500 RPM for a stock 455.

All in all it's a simple swap.

matt69olds

If you don't have a 400 to install, rebuild the TH350. A TH350 will easily handle a stout 455 with the right upgrades. Rebuild the trans with careful attention to end play, use a wide bushing for the direct clutch, dual feed the direct clutches (either with a shift kit or do it internally) and machine the direct clutch piston for 5 clutches instead of the factory 4.

Scott Hamel

i have a TH400 out of a delta 88, tomorrow i'm dropping it off to my trans guy. he's going to pull the pan see what it looks like inside? i'm told its has low miles.. if it looks good he's going to do a shift kit, front and rear seal, filter/pan gasket. if it looks crappy then he's just going to a rebuild.. $500 with a master kit & labor. well all this stuff is going on i'm shopping around for a limited slip diff, because i has the stock one legger in there and all the damn thing does is spin tire. this is my first olds 455 and as a lot of you know there TQ monsters! all my other rides were small block chevy's and none had the TQ this thing has.

oldcutlass

Sounds like a plan.

Scott Hamel

so the transmission could use a rebuild.. i didn't see that coming ~ as i stated above its out of a 1974 delta 88 so its a long tail. should i even bother swapping it over to a 4'' tail well its apart? i don't know what would be cheaper cutting my driveshaft to fit or finding a short tail output shaft and housing? and i mite still need to cut the driveshaft because its a th350 thats in the car now... i mean if i leave the long tail and just cut the shaft to fit it's not like i'm going to be changing the transmission anytime soon again. i have to move back my crossmember and do the driveshaft.. but the biggest pain in the butt with this swap is installing a kickdown for the th400.. i know people say its no big deal but i wish it was just a cable like the TH350. and i'm sure i will need a new yoke for the th400... not sure of the splines. gotta love it X) in the end it will be well worth the effort

oldcutlass

Believe me the easiest part of swapping in a T400 is the kickdown. It's the rest that's time consuming. I would not use the long shaft.

Why don't you just get your T350 rebuilt? It would be much easier and cheaper.

Scott Hamel

you think the th350 will hold up to the 455? its seems to take forever to shift when i get on it hard? i have to let off the gas for it to shift. it would be easy to just have him redo the th350 but i thought the TQ would kill it again.. because its weak for sure at this point! and when i drop it in low 1 i hear a grinding sound? i don't know if the linkage it messed up or the trans is just shot to hell

oldcutlass

The crunching noises concern me, but the shifting issue under light throttle can be as simple as faulty modulator. How does the fluid look, pretty pink?

Scott Hamel

the fluid looks fine in it.. it shifts ok normal driving.. its when i get on it , then it seems like the motor is going to pop before the damn thing shifts

oldcutlass

I'd take it to a shop and have it checked out if you have a concern.

rjohnson442

you can wire the the th400 with a 12v switch and not have to worry about all the linkage and flip it when you want. I put a momentary swich in on mine, down shift with the button. I have no linkage and it still downshifts if I punch it w/o hitting the switch

Scott Hamel

well the car went out today to get a new Vinyl top.. so hes going to have it for about 4 days.. after that its going to the body shop to instal a new door glass. THEN i can bring it to the trans guy.

Intragration

I'd use the TH350, no mods to the car and it will sap a little less power than the TH400. If you do go with the TH400, some Cadillacs used a kickdown switch located on the carb. I haven't looked into the differences, but this might be easier to locate than parts for the pedal kickdown switch.

Scott Hamel

i'm still on the fence on this one guys. i mean my car is not going to be a 10sec drag car but it's not a sled by any means. i have the th400. and the th350 thats in the car now.. i'm getting the car back from Valley Auto top.. (New Vinyl top) then its going to my transmission guy. like i said not a 1/4 killer but i do drive her hard ( insert childish comeback here HAHA ) but i'll see what unfolds. thanks for the advise guys.