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Author Topic: Th400 rebuild  (Read 3836 times)

Offline st3vomettler

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Th400 rebuild
« on: June 05, 2015, 10:06:28 pm »
Is it hard to rebuild a th400?
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77 c10 Silverado 350 nv3500 5spd

Offline Engineer

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Re: Th400 rebuild
« Reply #1 on: June 05, 2015, 11:51:44 pm »
No. Not hard at all.

Probably the easiest automatic transmission ever.

One of mine survived for a couple of years in a mud truck where the owner never hooked up the fluid cooler........for real.
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2002 Chevy 2500HD 4x4 8.1/ZF6sp RC/LB
2001 Chevy 2500HD 4x4 6.0/4L85E EC/SB
1997 Chevy Blazer 4x4
1994 Chevy K-2500 4x4 C6P 5.7/4L80E
1979 Chevy K-30 4x4 4sp 4.10
1977 Chevy K-30 4x4 4sp 4.10 454

Dad of an Eagle Scout, and a Life Scout

Offline st3vomettler

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Re: Th400 rebuild
« Reply #2 on: June 06, 2015, 10:14:43 am »
Ok I had to take it out because the output shaft is messed up. I took the valve body off and the output shaft had a lot of play in it to were it shudder so bad it slowed down while going 63
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77 c10 Silverado 350 nv3500 5spd

Offline st3vomettler

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Re: Th400 rebuild
« Reply #3 on: June 06, 2015, 12:48:42 pm »
How do I get the last bit of gears out of the transmission
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77 c10 Silverado 350 nv3500 5spd

Offline Engineer

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Re: Th400 rebuild
« Reply #4 on: June 06, 2015, 04:41:24 pm »
If you took the valve body off there should be a 12-point headed bolt with a hole through the middle of it that holds the center support in. Take that out and the entire gear train should just slide out.
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2002 Chevy 2500HD 4x4 8.1/ZF6sp RC/LB
2001 Chevy 2500HD 4x4 6.0/4L85E EC/SB
1997 Chevy Blazer 4x4
1994 Chevy K-2500 4x4 C6P 5.7/4L80E
1979 Chevy K-30 4x4 4sp 4.10
1977 Chevy K-30 4x4 4sp 4.10 454

Dad of an Eagle Scout, and a Life Scout

Offline st3vomettler

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Re: Th400 rebuild
« Reply #5 on: June 06, 2015, 08:10:56 pm »
Is ether of the shafts on this move at all
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77 c10 Silverado 350 nv3500 5spd

Offline Engineer

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Re: Th400 rebuild
« Reply #6 on: June 06, 2015, 10:41:43 pm »
There is a big snap ring that holds the rear output shaft into the planetary ring gear. Take that snap ring out and that all comes apart.
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2002 Chevy 2500HD 4x4 8.1/ZF6sp RC/LB
2001 Chevy 2500HD 4x4 6.0/4L85E EC/SB
1997 Chevy Blazer 4x4
1994 Chevy K-2500 4x4 C6P 5.7/4L80E
1979 Chevy K-30 4x4 4sp 4.10
1977 Chevy K-30 4x4 4sp 4.10 454

Dad of an Eagle Scout, and a Life Scout

Offline st3vomettler

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Re: Th400 rebuild
« Reply #7 on: June 07, 2015, 09:26:10 am »
Is there a way to tell if it's going bad?
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77 c10 Silverado 350 nv3500 5spd

Offline Engineer

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Re: Th400 rebuild
« Reply #8 on: June 07, 2015, 06:56:07 pm »
Visual inspection would be a reliable and cheap method.

If it all looks ok it probably is.
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2002 Chevy 2500HD 4x4 8.1/ZF6sp RC/LB
2001 Chevy 2500HD 4x4 6.0/4L85E EC/SB
1997 Chevy Blazer 4x4
1994 Chevy K-2500 4x4 C6P 5.7/4L80E
1979 Chevy K-30 4x4 4sp 4.10
1977 Chevy K-30 4x4 4sp 4.10 454

Dad of an Eagle Scout, and a Life Scout

Offline st3vomettler

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Re: Th400 rebuild
« Reply #9 on: June 07, 2015, 08:55:46 pm »
It looks ok but when I got it apart I notice some big pieces of metal in it
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77 c10 Silverado 350 nv3500 5spd
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