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Old 12-02-2019, 10:50 PM   #1
tom400
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Default turbo 400 high gear problem

got a T400 manual forward pattern valvebody, 34 element drum etc done and fitted up to a solid roller big block chev powered vehicle.. low and intermediate working fine as well as reverse on road test.
problem is with high gear seems to have bugger all drive very weak


put the pressure gauge on and have come up with these readings


brakes applied rpm around 1100
neutral 80psi
drive 200-210psi
2nd 200-210psi
reverse 95psi


drive has 200 there so im not sure if theres anything else i should try before removing the trans?
any help here appreciated.
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Old 12-02-2019, 10:53 PM   #2
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Default Re: turbo 400 high gear problem

What does the gage do during shift when it acts up?What is pressure during 2-3 @ wot?
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Old 12-02-2019, 11:01 PM   #3
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Default Re: turbo 400 high gear problem

hi chris i will check now. Just some more info.. valvebody only has the one checkball in the bathtub low reverse and the detent solenoid location has a plate blocking off the hole on the seperator plate.
also the the boost valve in the pump is not ground. the modulator valves large land is ground. No modulator obviously
sonnax oring boost valve and pressure reg fitted.
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Old 12-02-2019, 11:13 PM   #4
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Default Re: turbo 400 high gear problem

Ok when i make the shift from 2nd to 3rd the gauge quickly drops to around 80psi then goes back to 200
i havent done the wot test yet as my hose isnt long enough to bring into the car with me.
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Old 12-03-2019, 05:00 AM   #5
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Default

The pressures seem right.

As silly as this may sound, make sure there is enough fluid in it. In top gear they have the most fluid in use, and it is slinging it around when the internals are moving, not when stationary. Even if sucking a little air when pan level drops could cause an issue. The FULL mark should be right around the pan gasket, if not a touch over.
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Old 12-03-2019, 07:05 AM   #6
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Default Re: turbo 400 high gear problem

Thanks for the reply paul i checked the dipstick and full is just above the rail. before i posted it was a little low when checked in park engine running. thought it was my problem till i took it for another test drive and problem remained. I have since dropped the pan which was clean and removed valvebody. which is a ptc/promatics item. everything looked ok shift valves seem free to move etc . i removed the servo cover and servo assembly which is correctly assembled and 1/2 spring not broken. i then removed the front servo and its assembled correctly as well. Then i got to the modulator plug removed and found its large land does not have a flat ground on it.. could this possibly be my problem? The boost valve is not ground. I tried calling ptc 3 times today left message but no reply!
Thanks
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Old 12-03-2019, 08:09 AM   #7
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Tom, give me a call tomorrow, 0414977521.
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Old 12-03-2019, 09:00 AM   #8
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Default Re: turbo 400 high gear problem

According to your pressure drop on the 2-3 it is shifting. Does it have a lot of stall speed and you can't feel the shift? Reverse pressure is weak so it's doesn't sound like the large land on the booster is active.


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Old 12-03-2019, 05:09 PM   #9
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Default Re: turbo 400 high gear problem

Hi Hutch hope your well. yes it has some stall its an 8 inch built using the sonnax race kit with diode.
yes is hard to feel the shift. It all seems to lead to the direct drum doesnt it..
Tom
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Old 12-03-2019, 11:27 PM   #10
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Default Re: turbo 400 high gear problem

Direct drum seems fine condidering 3rd gear pressures are ok.


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Old 12-03-2019, 11:51 PM   #11
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Default Re: turbo 400 high gear problem

Converter is too loose. Hi gear pressures prove that the direct clutch is not the culprit. High gear shift places all of the load on the converter which makes it FEEL like a slip. Tighten it.
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