Turbo 400 no engine braking in 2nd gear

[demian5]

Anyone have experience with a broken plastic servo piston causing no engine braking in 2nd gear?

Was the fix as easy as dropping the valve body and replacing the servo piston and sealing ring with a metal one?

It's in my sons 1986 c20 Scottsdale with a 350/th400 combo and only 56,000 original miles. 400s didn't change much between body styles (well except the cheap piston!)

Thanks!

[demian5]

Really? Nobody?

[mongocanfly]

Clinebarger would be the man to answer your question. Give him time

[Bigdav160]

In drive range-second there is no engine braking because power is driven through a one way clutch. In manual second it brings on the band to help hold the sun gear and give engine braking.

So yes, a bad servo piston could cause no engine braking but still work in second gear.

[demian5]

Originally Posted by Bigdav160

In drive range-second there is no engine braking because power is driven through a one way clutch. In manual second it brings on the band to help hold the sun gear and give engine braking.

So yes, a bad servo piston could cause no engine braking but still work in second gear.

Good info. I'll check the manual shift operation!

Should be a simple driveway fix right?

[clinebarger]

Originally Posted by demian5

Anyone have experience with a broken plastic servo piston causing no engine braking in 2nd gear?

Was the fix as easy as dropping the valve body and replacing the servo piston and sealing ring with a metal one?

It's in my sons 1986 c20 Scottsdale with a 350/th400 combo and only 56,000 original miles. 400s didn't change much between body styles (well except the cheap piston!)

Thanks!

It's the Plastic 3rd Accumulator Pistons that break, Not the Intermediate "Brake" Band Servo Piston. Never seen a Plastic Servo Piston in a TH400.

A broken Accumulator Piston will allow L2 oil to leak into the 3rd/Direct clutch circuit & prevent the Servo from applying the Band.

[demian5]

Originally Posted by clinebarger

It's the Plastic 3rd Accumulator Pistons that break, Not the Intermediate "Brake" Band Servo Piston. Never seen a Plastic Servo Piston in a TH400.

A broken Accumulator Piston will allow L2 oil to leak into the 3rd/Direct clutch circuit & prevent the Servo from applying the Band.

All I really know is its a plastic piston that is part of the valve body correct? Should be a simple swap with the exception of just getting a set of gaskets and getting the balls back in the right places (I hope). Going to do in the driveway soon.

[clinebarger]

Originally Posted by demian5

All I really know is its a plastic piston that is part of the valve body correct? Should be a simple swap with the exception of just getting a set of gaskets and getting the balls back in the right places (I hope). Going to do in the driveway soon.

Yep it's in the Valve Body. It's not hard at all, Careful not to mangle up the Governor Tubes!