73 Formula

Formula1973

Formula1973

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Hi All, new member here.

I recently purchased a 73 Formula 350. Now has a decent running 75 400 in it.
It needs some attention, as do most...

Here is my question, The seller told me that the transmission was rebuilt. Upon inspection, it looks super clean and brand new under the car. It also shifts well. When I got it home I looked a bit further...there is a band screw on the passenger side, and a "C" stamped on top of the bellhousing. There is also a big "X" on the pan. (same shape as a TH350, which I thought it was.)

Do I have a lock up 250?? Can it handle the torque coming from a Pontiac 400? The pan is already leaking! This would not have been a deal breaker, as I got the car for a great price. Just mad I didn't look close enough, rookie mistake......I would never have imagined a 250C being behind a 400. The car struggles performance wise for many reasons, but this being a 250C would not help.
Thanks in advance
 
Lockup would have an electrical plug on the side , Reinterduced 1979 due to many TH200 failures. Was mainly used in 6 cylinder cars before that.

Can be built to handle 700HP /650TQ http://www.fbperformance.com/ViewTransmission/?TransmissionID=94

Best bet would be to replace it with a built TH 350. ( piece of mind)

Doug in P.R.:cool:
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Welcome

Pictures, pictures, pictures, your car cannot live forever without pictures.:D
 
Thanks melsg, picture posted.
The holley carb is a old, floods, stalls and fouls plugs. I have a 70 Quadrajet and edelbrock intake to put on it.
Does the TH250C hurt performance?
 
it doesn't hurt performance and will probably work fine unless you do major modifications to increase power
 
Formula1973 said:
Thanks Doug-


Can a stock TH250 handle the 400 torque?
Click to expand...

According to "GM myth" , the trans number is the average torque the trans can handle. (700r4 and 200R4 breaks the so called "myth")

If its an older 400 ( real late 70's emission gagged motor ) then maybe............:rolleyes:

All big blocks got a TH400 , they started to use TH350's on them in the late 70's though.

Th350's can be built to handle about anything and its a direct bolt replacement in your case. Anything else would need the driveshaft shortened and the yoke changed.

If you get a TH350 , measure your current TH250's total length and tail housing since TH350's have 3 different lengths.

Doug in P.R.:cool:
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Thanks for all the help guys,

I am planning a TH350 with 3.73 gears. (now has 3.08)

At some point I will do some modification to the 400. It is a 1975 block with 5C heads, low compression.
Not the thin wall cast block from late 1975, should be a good base.
I removed the carb, an old Holley 1850. The car had a electronic Carter fuel pump mounted to the wheel well. Too much fuel pressure even for a new carb. Was running real rich...
When it got up to speed (20 or 30mph) it pulls real hard and sounds real nice.
Absolute dog off the line though.
Any suggestions would be greatly appreciated!!

Thanks again!!
 
you should really consider a 4 speed automatic with that 3.73 gear and at the same time the Pontiac 068 cam or equivalent. It was used on Ram Air III and HO engines.
 
Agree with Mel with the 3.73's .......either a higher gear ( 3.23-3.42- 3.55) or taller rear tires with the TH350.

About 3100 RPM at 70 MPH with a taller 235/60 /15 compared to your factory 14" tire. ( 205/ 75/14 )

Doug in P.R.:cool:
 
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