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Old 05-05-2009, 12:30 AM   #1
RedRocketS10
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Default TH400 Line Pressure adjustment?

Hutch, looking for a little shortcut here. Line pressure in my fresh 400 is 155 @ 3000 RPM in park... Looking to go to 175 or so. It has a medium blue spring of unknown origin, new pump, all the goodies.

How much would be a good starting point to shim up the regulator spring? .060"? I really have no idea how these regulators react to shimming.

I think 175 will be adequate with the Alto power paks and a Griner brake. Combo is ~890 HP N/A SBC, 3000 pounds. Don't want to "waste" horsepower with a super high line pressure- let alone get into intermediate problems.

Your thoughts?

Thanks!
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Old 05-05-2009, 01:30 AM   #2
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Default Re: TH400 Line Pressure adjustment?

If you have no shims , just the 4 tang washer on the regulator you will need .140"- .160" under the 4 tang to get to 175.

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Old 05-05-2009, 09:27 PM   #3
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Default Re: TH400 Line Pressure adjustment?

Quote:
Originally Posted by RedRocketS10 View Post
Hutch, looking for a little shortcut here. Line pressure in my fresh 400 is 155 @ 3000 RPM in park... Looking to go to 175 or so. It has a medium blue spring of unknown origin, new pump, all the goodies.

How much would be a good starting point to shim up the regulator spring? .060"? I really have no idea how these regulators react to shimming.

I think 175 will be adequate with the Alto power paks and a Griner brake. Combo is ~890 HP N/A SBC, 3000 pounds. Don't want to "waste" horsepower with a super high line pressure- let alone get into intermediate problems.

Your thoughts?

Thanks!
You could use an adjustable PR regulator will adjust with a allen wrench 150-250.
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Old 05-05-2009, 11:56 PM   #4
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Default Re: TH400 Line Pressure adjustment?

Quote:
Originally Posted by RedRocketS10 View Post
Hutch, looking for a little shortcut here. Line pressure in my fresh 400 is 155 @ 3000 RPM in park... Looking to go to 175 or so. It has a medium blue spring of unknown origin, new pump, all the goodies.

How much would be a good starting point to shim up the regulator spring? .060"? I really have no idea how these regulators react to shimming.

I think 175 will be adequate with the Alto power paks and a Griner brake. Combo is ~890 HP N/A SBC, 3000 pounds. Don't want to "waste" horsepower with a super high line pressure- let alone get into intermediate problems.

Your thoughts?

Thanks!

A TH 400 Has two boost valves, A wild guess you have the wrong boost valve in your pump.

Measure the boost valve's small end and it should measure around .482 . The medium blue spring and two horse shoe shims (no more than two) under the 4 tang washer that centers the spring should give about 180 PSI.

This valve has one raised identifying ring around the small diameter shank part of the of the valve.

The boost valve in question has a diameter of about .455 and will give about 150 / 160 PSI. It is not as common as the other boost valve, has no identifying marks on it. (normally out of B.O.P. transmissions. never seen it in a Chevy trans).

Nothing will come out right unless the proper boost valve is installed in the first place. it is as much if not more important than the spring.

Don't get the outer sleeves mixed up, as there are no markings on them.
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Old 05-06-2009, 12:30 AM   #5
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Default Re: TH400 Line Pressure adjustment?

I'm seeing 175-180 @ 2000 RPM with .158" worth of shim in addition to the .070 horseshoe and the tanged washer. Pressure seems fairly solid, it bobbles with the lope of the engine. Run it up to 3500-4000 RPM, levels out at about 175. Tanged washer pilots on the PR valve enough to keep it in place. I will check the boost valve at a later date, as far as I know it's as GM had it, but who knows- the parts are 35 years old. I have the pressure regulator with the orifice cup plug, in the proper pump half. I'm surprised the boost valve is used, isn't that usually used with downshifts, low vacuum and such in stock transmissions?

I may have to pull this thing apart again anyway. With the wheels off the ground and idling at 2000 RPM, 1st, 2nd, and 3rd all appear to turn the tires at the same speed. Brake works, holds up to a converter flash of 6000 RPM. Reverse works, wheels turn at about 20% of the speed in any forward gear. Both neutrals will turn driveshaft, but its normal drag- you could probably stop the shaft with your hands.

Pulled the tranny down last night to alter converter feed restriction and double checked all clearances and endplays. All looks well. Cooler pressure ended up a touch higher than anticipated, it's 70 PSI. Target was 40-50.

Going to drop the pan after taking it for a test drive tomorrow and check for a hydraulic cross leak if the road test isn't right.

Thanks for the help everyone!
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Old 05-06-2009, 01:34 AM   #6
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Default Re: TH400 Line Pressure adjustment?

Doesn't sound too bad. Don't test gears on the jack stands , you won't feel any shifts. 70 in the cooler is fine. Ideal would be 60-65 and im sure it will end up there when its hot.

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Old 05-09-2009, 12:47 AM   #7
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Default Re: TH400 Line Pressure adjustment?

Thanks Hutch! Will be getting on the track soon to test.
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