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turbo 400 diagnostics

Discussion in 'The Garage' started by merace19, Apr 15, 2006.

  1. merace19

    merace19 1/2 ton status

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    Got a m1008 or m1028. The transmission has a high pitched whine and will not go forward. It will go backward after i rev the engine. But once engaged it acts normal in reverse. what could be the problem?
     
  2. hack500

    hack500 1/2 ton status

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    this is just a guess but if the fluid is at the right level, I'd say the pump went bad and/or the clutches in the forward gears may be too worn.
     
  3. 85-m1028

    85-m1028 1/2 ton status

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    If the bellhousing has a HD stamped on the side then its a turbo 475 and another tell of it being a 1028 also the vin will have a H read ( 1gch34j) m1008 have a g read (1gcGd34j) a NP205 t-case and a vin with (1gbhd34j) will be a m1031, this should help you figure that out!! no forward movement reverse ok mean the oil pump assembly and seal rings are shot *check the torque converter or the foward clutch housing , first I'd try dumping few quarts of ATF in there *dex3 "these trannys take alot of fluid" and see if that does anything !! the accumulator piston for the front band is ceramic and prone to breaking causing fluid to leak past it and it wont apply the front band this will not affect the drive range only the low1, I got an aluminum replacement when I rebuilt mine cost me a few days "just a heads up"
     
  4. cbbr

    cbbr 1 ton status GMOTM Winner

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    I thought that the m-1008 had a NP208?
     
  5. 85-m1028

    85-m1028 1/2 ton status

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    THATS CORRECT!!!!!!!!!!!!!!!!!!!!:wink1:
     
  6. merace19

    merace19 1/2 ton status

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    The vin is 1GCHD34J0GF312340 AND ACCORDING TO THE PRIOR POST I DO HAVE A M1028. I fixed the vacuum hose to modulator and the truck now goes forward and shifts but there is a whine coming from the transmission. I thought it was the altenator but i got real close to them and then under the truck and there is a whining noise. The truck does not shift right either so i still believe a rebuild is in order to get it right. When going from P to Drive i have to wait a second or to before it grabs. Same if i go from drive to reverse, I have to wait a second and then it grabs. Could this just be a stopped up filter?????:(
     
  7. diesel4me

    diesel4me 1 ton status Premium Member

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    Yup!..

    My 69 GTO's TH400 whined like a siren after I got it stuck in a snow covered field one winter,and had to rock the s*** out of it to get it unstuck for 30 minutes!....it was slow to engauge the gears when cold too,and had some slippage after that too!..:doah:

    I dropped the pan as soon as I was able,and it was FULL of what looked like coffee grounds from a perkolator!..I assumed it was clutch material,and thought to myself I'd better start looking for another tranny..but to my suprise,after replacing the filter and fluid,the siren noise stopped,and I drove it two more years after that,and the tranny shifted great!..I bet the clutches were close to being junk though...:doah:

    So,yes,a clogged filter could cause whining and slippage,by starving the pump for oil,which = low pressure to apply the clutches..I'ts worth a shot,a filter is only ten bucks or less probably...:crazy:
     
  8. merace19

    merace19 1/2 ton status

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    Yeah i dropped the pan yesterday. It looks like it was never changed. Fluid still red but slightly darker. No smells. Very fine black paste was around the magnet in the pan. No metal. The filter seemed stopped up. I poured fluid into the inlet and waited for it to come out to end that suppost to go to the trans and it was slow to come out. So i will be replacing that today. The pan on the outsiide was nasty from years of dirt and rust. But the inside looked like a crome bumper super clean almost like someone polished it.
     
  9. merace19

    merace19 1/2 ton status

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    Changed the filter and put it back together and it runs like a champ. No whining, solid shifting now. I thanked god on that one too. As i did not want to pull the transmission. And the 900 or so bucks it would take to fix it i can get some better springs and shocks. Maybe a set of tires.
     
  10. 74BBPowerHouse

    74BBPowerHouse Registered Member

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    Dont mean to steal of this post.... But im buying a Th400 with a HD on the housing.... What does that mean?
     
  11. 85-m1028

    85-m1028 1/2 ton status

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    means its a turbo 475!!
     
  12. merace19

    merace19 1/2 ton status

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    I have researched it and asked a few people. I asked a transmission guy and he said he would swap me my transmission for a rebuilt 400 he had for $350. Got me to wondering what did i have that could be worth him swapping it out for so little. When i told him i was keeping the core if i needed a trans and his price jumped to 900.
     
  13. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    From the little that I know, the TH475 is indeed "HD" in every sense of the word. Bus trannies!
     
  14. 85-m1028

    85-m1028 1/2 ton status

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    If a chevy 4wd turbo 400 is rare then I would say the 4wd 475 is ultra rare, the only real difference I know of is the use of straight cut planetaries that have more side loading cappacity, "just stronger" but I dont see why one couldn't just pull the planteries out of a 2wd 475 and slap em in a K housing
     

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