Transmissions and DrivetrainNeed help with your trans? Problems with your axle?
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I have a TH400 trans I am wanting to install a trans brake what is all invalved in installing one into my trans and is it worth it to put one into my car I have a mild built 468 bbc 12.1 to 1 compression and 4.11 gears with a 4200 stall
The transbrake is a different valve body however the transmission needs to be disassembled for internal modifications as well. All TH400 transbrakes are reverse pattern. PRN123 instead of the normal PRN321
A transbrake allows you to launch up to the converter's true stall speed. Using a 2-step, you can launch at any rpm up to the stall speed. For best performance, providing you can get traction, you launch right around where the engine makes peak torque.
alright good deal I just got my old th400 all apart so I can use the case because I just found a crack in my new trans case can I swap all parts over to the old case without any problems?
Should be able to but be sure to upgrade the sprag and what not while your installing the transbrake setup. Brakes are very hard on sprags. Also make sure you get a converter that can take the type of abude your going to thro at it.
__________________ 1983 Z28 Camaro
10.48 @127MPH Pump gas flat tappet cam getting ready for next season.... maybe 9's ;-)
1967 RS/SS 396 Camaro
Restoration in progress
The sprag can be cheaply replaced if it's an early style TH400. The later versions use a different drum with the weaker sprag and the 34 element sprag won't fit.
A transbrake won't destroy the sprag. The sprag is usually destroyed when coming out of the water box in second gear and hitting dry pavement, stopping the wheels suddenly. Always come out of the waterbox in third gear.
There has been many a trans that has come of the brake and cracked the sprag as well as the waterbox. Just saying this from seeing several friends and their aftermath.
Without taking it apart and physically inspecting the sprag, you need to know what year the transmission is. There should be a data plate on the passenger side of the case.
The Direct drum that accepts the better sprag was in the 64-71 models but 71 was a changeover year so it may have either. If you have a later model, you can buy a new drum that accepts the 34 element sprag.
Although I now use a powerglide, I still have 2 TH400's in my garage both with the better drum and sprag. One still has a transbrake in it.
heres the number i got off the side of the trans on a tag the numbers are 468 70-OF-27406 what year would that make it anyone know thanks Eric
also i just got the transbrake today its a coan brake I don't know if it is a good company but I got it for a deal at the place by my house for 340 with tax
Last edited by transam360; 05-21-2009 at 08:45 PM.
1970
OF = Olds Delta 88 with a 350 engine
27406 = serial number
An Olds engine has a different bellhousing bolt pattern than a Chev. Is it an Olds pattern or does it have a dual bolt pattern so it can be used on BOP and Chevys.
Even if it's a BOP bolt pattern, the internals can easily swap into a later Chev pattern case since it's one of the better older models.
Are you sure the O is really an O and not a C? If it's a C then it's a Chev tranny
Across the center on both sides of the tag there should also be a C on one side and an F on the other.
OK, a 1970 CF TH400. It was in a full size Chev. Probably a station wagon. It had a 400 engine in front of it. A very good candidate for a performance rebuild.
I am installing the brake now i just have one question in the instructions it says discard front band is this the band they are talking about? O yea by the way the trans brake is a coan coa-22020
After orifice has been drilled, drum is ready for reassembly. Before installing piston remove and discard center lip seal in drum. Install piston. Discard 16 stock release springs and replace with 16 new springs furnished. Replace retainer and snap ring. Assemble clutches and steels. A.050 - .060 clutch pack clearance is recommended. Install drum, discard front band, and reassemble transmission.
Discard the band. It's an extra part that won't be used. Somewhere in those instructions, it should have said to remove the servo piston and plug the gallery hole. The servo piston applies the band. Without a servo piston, you don't need the band.
All the front band does is provides engine braking in second gear. It also slows the release of the direct clutch pack by acting like an accumulator.
Don't forget to install a 34 element sprag before putting it all back together.
1983 Z28 Camaro 
