T-400 Valve Body Problem and whine - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-13-2011, 02:33 PM
UngerMarkus's Avatar
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T-400 Valve Body Problem and whine

Hi guys!

I posted a thread a couple of weeks ago concerning the problems with my Th400. It makes an anoying whine and doesnīt shift into 3rd gear. I did a pressure test. It has a pretty high line pressure for a completely stock rebuild. 120psi in park at idle.

Today I disassembled the valve body. I had some small metall debris in the pan. The gasket on the case-side was damaged. Please see the pictures I enclosed.

What could have happened here?

What can cause high line pressure?

The modulator works, I have sufficent vacuum and the modulator valve moves freely.

The filter ainīt clogged. The o-rings on the filter tube are sealing properly.


I have a good 1-2 shift and a strong reverse.
When I block the transmission cooler line the whine goes away.

I pulled a line to pump out the atf before I removed the oilpan. Maybe a year ago, I forgot to install the cooler line to the cooler on a th350. The fluid was squirting out rapidly! On my Th400 itīs flowing out slowly!!!

Thanks for your help in advance!

Markus
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Old 04-13-2011, 11:15 PM
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Wish I had a scanner. Arrrg.
From ATSG Manual.

(Causes of High Line Pressure.)

Vacuum Modulator:
1. Low Vacuum.
2. Vac lines leaking.
3. Damaged or wrong Modulator.
4. Mod. valve stuck in Case.

Detent Solenoid:
1. Stuck open.
2. Detent switch actuated or shorted.
3. Detent gasket missing.
4. Detent feed orifice in spacer plate blocked.
5. Mounting bolts loose.

Oil Pump Assembly:
1. Pr. Reg. or Boost valve stuck.
2. Wrong Boost valve & sleeve.
3. Incorrect Pr. Reg. spring.
4. Improper Assembly.
5. Aluminum bore plug damage.
6. Porosity in Pump body or cover.

Valve Body Assembly:
1. Detent valve bore plug damaged/leaking.
2. Detent Reg. valve pin short.
3. Detent Reg valve or Detent valve stuck.
4. Spacer plate to case gasket off location or gaskets reversed.
--------------------------------------------------------------------------

(Causes of No 2nd to 3rd Upshift)

Oil Pressure:
1. Refer to "HIGH LINE PRESSURE"

Governor ***., Feed Pipes, Screens:
1. binding, stuck, leaks, blockages.

Valve Body ***.:
1. Valves, Pistons, gaskets.-- leaks, binding, porosity, seals damaged.

Direct Clutch Housing:
1. Clutch piston or seals.
2. Missing checkball in piston or housing.
3. Porosity.

Center Support & Oil sealing rings:
1. Porosity or crack.
2. Oil sealing rings damaged/missing.
3. Oil sealing ring grooves damaged or worn.
4. Support bolt loose or broken.

Unbelievable, abbreviation for Assembly is edited out.
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Old 04-18-2011, 01:57 PM
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Thank you very much SSedan64!!!

The whine is gone and the tranny shifts beautifully!

When I disassembled the valve-body for the second time, the case-side seperator plate gasket was torn up. I also realized, that 2 springs were definitly not the right ones and 3 valves were a litte burred.

I put in a TransGo Shift Kit and deburred the valves. It works great now!


PS: I just have about 1/2'' slip yoke travel. Is that enough?

Thanks a lot

Markus
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Old 04-20-2011, 08:42 AM
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1/2" DS travel is cutting it close, 3/4" Min. to 1" Max travel is what's recommended.

Are you checking the DS travel with the suspension loaded, weight on rear axle at ride height?
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Old 04-20-2011, 09:46 AM
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Just read your post.

I was intrested in the deburring of your valves. ( I have a similar issue with both my forward and reverse abuse valves, they seemed a bit burred, and are a tight fit.)

Q. Which valve were they??

Q. How did you go about deburring them ??
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Old 04-22-2011, 01:49 PM
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Hi Old Yukon!

I turned the edges of the valves over my thumbnail. Using a small file I removed the burrs. On some surfaces I had some scratches. I polished the spots (wich were minimal) with 800-grid sandpaper soaked with trans fluid.

The 1-2 accumulator valves and the 2-3 modulator valve where the parts burred the most.

Also the valves in the aluminum bushings felt sticky. I was told, they need to fall out of the aluminum bore just by gravity. Put them into the bore and tapped the assembly on the workbench to make the valve sit properly into the bore. As it was moving easily I "secured" the valve in position with a small amount of vaseline.

After dropping the valves into the steel bores, I tapped the valve body with the handle of a big screw driver from both sides.

Make sure all the springs are the right size and spring rate.

Good luck!
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