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02-09-2017, 02:40 AM | #1 |
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Join Date: Aug 2016
Location: Lake Forest, CA
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Turbo 400 no engine braking in 2nd gear
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!
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
02-09-2017, 11:38 AM | #2 |
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Re: Turbo 400 no engine braking in 2nd gear
Really? Nobody?
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
02-09-2017, 12:09 PM | #3 |
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Join Date: May 2015
Location: Alabama
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Re: Turbo 400 no engine braking in 2nd gear
Clinebarger would be the man to answer your question. Give him time
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02-09-2017, 01:48 PM | #4 |
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Join Date: Apr 2011
Location: Klein Texas
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Re: Turbo 400 no engine braking in 2nd gear
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.
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02-09-2017, 07:05 PM | #5 | |
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Re: Turbo 400 no engine braking in 2nd gear
Quote:
Should be a simple driveway fix right?
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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02-09-2017, 10:28 PM | #6 | |
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Join Date: May 2009
Location: Fort Worth, TX
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Re: Turbo 400 no engine braking in 2nd gear
Quote:
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. |
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02-10-2017, 12:31 PM | #7 | |
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Join Date: Aug 2016
Location: Lake Forest, CA
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Re: Turbo 400 no engine braking in 2nd gear
Quote:
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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02-10-2017, 08:27 PM | #8 |
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Join Date: May 2009
Location: Fort Worth, TX
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Re: Turbo 400 no engine braking in 2nd gear
Yep it's in the Valve Body. It's not hard at all, Careful not to mangle up the Governor Tubes!
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