Author Topic: TH350 to TH400 Tranny swap  (Read 11803 times)

Eddie

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TH350 to TH400 Tranny swap
« on: January 31, 2013, 03:24:30 PM »
Will the Turbo 400 interchange with the turbo 350 tranny with out any Mods?.. i'm looking at one and want to be sure it will interchange before i commit..thanks. Eddie

firebirdparts

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Re: TH350 to TH400 Tranny swap
« Reply #1 on: January 31, 2013, 03:47:14 PM »
The rear mount, driveshaft, and WOT kickdown are all different.  Otherwise it's pretty similar.
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Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Grand73Am

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Re: TH350 to TH400 Tranny swap
« Reply #2 on: January 31, 2013, 04:04:30 PM »
And the th400 uses a different, larger yoke.

I think you have to get a th400 shifter cable bracket, or modify your existing bracket.

What engine do you have? Pontiac, I guess? If so, are you sure it's a BOP pattern trans so it will fit?
Steve F.

Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #3 on: January 31, 2013, 04:10:16 PM »
It's a 400 Engine with 400TH tranny. I have the 350 engine with the 350 TH in the car now. Looking to swap up to the larger Engine/tranny, just not sure what all i need to change. I'm pretty sure the Engine should swap out with no problems. just wasn't sure about the Tranny.. so i guess i need to see what a new yoke and rear mount will run..

Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #4 on: January 31, 2013, 04:12:28 PM »
And yes it's a pontiac Engine, 2nd Gen.. Mine is a 72 firebird. the Engine & tranny I'm looking at is a 77 400 out of a T/A

Re: TH350 to TH400 Tranny swap
« Reply #4 on: January 31, 2013, 04:12:28 PM »

Grand73Am

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Re: TH350 to TH400 Tranny swap
« Reply #5 on: January 31, 2013, 04:25:52 PM »
Hmmm. A 77 engine wouldn't originally have a th400 on it. So, I guess somebody put a th400 on the 77 400 engine if that's the case.
Steve F.

yellow1098

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Re: TH350 to TH400 Tranny swap
« Reply #6 on: January 31, 2013, 04:49:02 PM »
What really is the advantage of a TH400 over a TH350?

Grand73Am

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Re: TH350 to TH400 Tranny swap
« Reply #7 on: January 31, 2013, 05:44:59 PM »
Stronger.
Steve F.

tajoe

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Re: TH350 to TH400 Tranny swap
« Reply #8 on: January 31, 2013, 05:49:42 PM »
X2!
"You can sell an old man a young mans car,
but you can't sell a young man an old mans car"
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hdinch

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Re: TH350 to TH400 Tranny swap
« Reply #9 on: January 31, 2013, 06:17:27 PM »
 just swapped a 350 tranny for a 400 on a 73 firebird.  I went with a 400 turbo as it is a stronger tranny and this is sitting behind a 461 stroker.  Not on the road yet but all the parts are connected.  I needed a crossmember...sometimes you can turn them around depends what you had.  You will need the transmission mount. I used the universal one from energy systems.  You also need all the kickdown parts.  So the connector on the pedal and the wiring back to the tranny.  If you do not have that with your harness you can buy a seperate wire.  I used one made for a chevelle.  Goes from the tranny to the kickdown switch on your pedal.  The linkage bracket is also different.  The drive shaft and yoke are also.  If I remember the 400 shaft is shorter and thicker.

Flamn Chkn

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Re: TH350 to TH400 Tranny swap
« Reply #10 on: January 31, 2013, 06:48:00 PM »
just swapped a 350 tranny for a 400 on a 73 firebird.  I went with a 400 turbo as it is a stronger tranny and this is sitting behind a 461 stroker.  Not on the road yet but all the parts are connected.  I needed a crossmember...sometimes you can turn them around depends what you had.  You will need the transmission mount. I used the universal one from energy systems.  You also need all the kickdown parts.  So the connector on the pedal and the wiring back to the tranny.  If you do not have that with your harness you can buy a seperate wire.  I used one made for a chevelle.  Goes from the tranny to the kickdown switch on your pedal.  The linkage bracket is also different.  The drive shaft and yoke are also.  If I remember the 400 shaft is shorter and thicker.

TH400s came with a short or a long shaft depending on what type of car they were going in large cars got the long tailshaft Fbodys got the short shaft also the driveshaft may need to be shortened for some reason mine went in its a little tight but still has some end play so Im not worried about excess pressure on the tailshaft or pinion gear my driveshaft had the brown stripe and seems to work just fine.
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Ben

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Re: TH350 to TH400 Tranny swap
« Reply #11 on: January 31, 2013, 06:50:04 PM »
Don't forget to check if the flywheel on the engine is drilled for both bolt patterns.  Nothing worse than getting an engine and transmission all in and finding the torque converter won't bolt to the flywheel...
Trans Am-less at the moment...

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Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #12 on: February 01, 2013, 09:51:14 AM »
I looked at it lastnight. I was going to pass on it because it had some dirt in the intake. he claims it has always been stored indoors! But he texted me this morning and dropped the price in 1/2 and will deliver it for 250. so i'm going to take a chance on it..worst case i have a core engine and tranny... :D will post pics when i get it with the engine #s..

richduty455

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Re: TH350 to TH400 Tranny swap
« Reply #13 on: February 01, 2013, 11:37:36 AM »
prob a 400 out of a 77 GP....they'll have a400/400
Our Current Birds:
70 Ram Air III auto
71 455 HO T/A auto white (pop's 1st car)
71 455 HO t/a auto blue (pop's)
71 formula 455 HO auto (little bros)
73 SD 455 auto
74 SD 455 auto (pop's)
77 T/A
78 Y88 ws6, w72 4speed 79k
79 TATA 400 4spd 38k orig (pop's)
79 trans am 350
80 y84 455HO doug nash 5 spd
80 T/A 400 pont auto
84 L69 auto areo T/A
94 firebird 3.4 t-top daily
97 WS6 lt1 au

Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #14 on: February 15, 2013, 04:41:38 PM »
Well the deal on the 400/400 went south. the guy never got back to me, Sooo I ended up buying a Rebuilt 350 engine. the guy built it for his 69 Firebird to drive it while the original 400 was being built. and never got around to putting it in the car! still sealed up from being rebuilt.. This will give me a dependable engine for now! Will toss on a 4BBl and run it!.. Was going to toss in a Thump er cam to give it that loping idle. but the guy at the performance shop said i would need stronger valve springs and some other valve work so i passed on doing that..So My question is..do i need to re lube this new engine up before firing it up, since it's been sitting for 6 years?..or just put in the oil and prime it up?..



Re: TH350 to TH400 Tranny swap
« Reply #14 on: February 15, 2013, 04:41:38 PM »



tajoe

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Re: TH350 to TH400 Tranny swap
« Reply #15 on: February 15, 2013, 05:05:38 PM »
Seeing the intake is off, probably wouldn't hurt to drip in a can of STP on the cam, just to help it out. but if nothing else, at least prime the eng. with the dist. out.
"You can sell an old man a young mans car,
but you can't sell a young man an old mans car"
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Flamn Chkn

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Re: TH350 to TH400 Tranny swap
« Reply #16 on: February 15, 2013, 06:33:21 PM »
Nice I hope you get many trouble free miles from that engine what are the casting numbers on the block? Ive never seen a 56 head casting before do you know the specs on those ?


I see its a 70 - 75 casting so it should just bolt right up to the motor mounts in your car
« Last Edit: February 15, 2013, 06:43:57 PM by Flamn Chkn »
Speed is only a matter of Money how fast can YOU afford to go

Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #17 on: February 15, 2013, 07:57:07 PM »
It's a 1972 350 engine that was originally a 2bbl. it came with a 4bbl intake though.

LeighP

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Re: TH350 to TH400 Tranny swap
« Reply #18 on: February 16, 2013, 06:19:15 AM »
get a Pontiac priming tool and throw some oil in the engine and spin the pump over. Pull the valve covers off and look for oil in the top end....you're right to go. Remember....the pump spins anticlockwise viewed from above.

As for TH400s.....you can build a very tough TH350 these days, they're lighter, take less HP to run and you don't need to modify the car to use them (if it didn't come with a TH400). I wouldn't go looking to swap in a TH400 myself. I had a TH350 built with all the good gear for my 455.
Regards,
Leigh

Sydney, Australia
1969 Pontiac Firebird 400 coupe (project)

Former Firebirds -
1971 Pontiac Firebird 455
1977 Pontiac Trans Am
1976 Pontiac Trans Am
1967 Pontiac Firebird 400 convertible
1967 Pontiac Firebird 400 coupe


Flamn Chkn

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Re: TH350 to TH400 Tranny swap
« Reply #19 on: February 18, 2013, 10:41:16 AM »
I agree with Leigh if you dont have to build a TH400 and make it fit, dont. since your 350 wont be putting down the torque like a 455 will.
But I will have to say Ive owned both TH400 T/As and TH350 T/As modified both with Trans go shift kits and yes a TH400 will sap a few more ponies from your HP but I really like how smooth the power is put to the ground with a TH400 My car has a super street fighter stall converter and a transgo shift kit and firm and tight but is as smooth as silk between gears.
TH350 in my sons 73 Camaro with a vette converter and transgo shift kit is pretty harsh between 1st and second and hes replaced his u joints more than once.
Speed is only a matter of Money how fast can YOU afford to go

Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #20 on: February 19, 2013, 10:43:29 AM »
Thanks for the tips guy's!. I will find that prime tool. or cut the shaft off a long straight blade screw driver and use that! and I have decided to use the TH350 until I find all the parts to swap to a 4 speed tranny. Much more fun to drive a stick.. anyone have tips on switching to a 4spd from a auto?..

Eddie

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Re: TH350 to TH400 Tranny swap
« Reply #21 on: February 24, 2013, 11:12:16 AM »
I was doing some # crunching on the Heads and it looks like they are 400 heads. the stamping is 5c heads date stamp is J124 the I/D stamp is 8 so going by these this is what I'm seeing!..> 8 5C 100.04 cc's 2.11/1.66 valve 4.86" 400


Re: TH350 to TH400 Tranny swap
« Reply #21 on: February 24, 2013, 11:12:16 AM »
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