difference 350 vs 400 auto
Thread Starter
Instructor
Joined: Feb 2008
Posts: 200
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difference 350 vs 400 auto
I'll be looking at a '72 small block coupe later this week and the owner can't tell me if the auto transmission is a turbo 350 or a 400. What are the external differences that I can look for to identify it? It's not an original engine car, so what it came with from the factory doesn't necessarily apply here. If someone could post a picture of the transmissions or provide me with some clues, I'd sure appreciate it!
TIA
TIA
Le Mans Master
Joined: Sep 2004
Posts: 5,116
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From: Livonia MI
The output shaft on a 400's also a larger diameter. These tranny's weigh more and sap more power. Also, the vacuum modulator position tends to get in the way of the right side exhaust piping. Nothing at all wrong with a well built 350.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
The oil pan on the THM-400 resembles the state of Texas 
; the THM-350 pan is generally rectangular. The modulator on the 400 is on the right side just above the pan split-line; the mod on the 350 is at the right-rear, I believe.
; the THM-350 pan is generally rectangular. The modulator on the 400 is on the right side just above the pan split-line; the mod on the 350 is at the right-rear, I believe.
Pro
Joined: Jul 2005
Posts: 517
Likes: 7
From: Peoria IL
There's nothing wrong with the TH400, don't be afraid of it. It weighs a whopping 9 pounds more than a TH350. They both use the same torque converters, and although the rotating mass is slightly greater in the TH350 it isn't enough that anyone short of a professional race team can tune an engine well enough that the difference can be measured in parasitic loss. People run 10 second quarters pretty regularly with TH350's and 9 second cars often have TH400's. so they can both be very fast.
I wouldn't be afraid of either one of them.
EDIT: Oh, and one other significant difference between them- a TH350 uses a cable connected to the carburetor for passing gear (kickdown) control, while the TH400 uses an electrical solenoid, with an electrical switch on either the carburetor or the pedal. If there's a cable running from the bottom of the throttle linkage down to the transmission, it's a TH350. If it's not there and passing gear works, it's likely a TH400.
I wouldn't be afraid of either one of them.
EDIT: Oh, and one other significant difference between them- a TH350 uses a cable connected to the carburetor for passing gear (kickdown) control, while the TH400 uses an electrical solenoid, with an electrical switch on either the carburetor or the pedal. If there's a cable running from the bottom of the throttle linkage down to the transmission, it's a TH350. If it's not there and passing gear works, it's likely a TH400.
Last edited by dstaley; Sep 6, 2011 at 03:45 PM. Reason: Another difference between transmissions
Team Owner
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