| Transmission Pressure [message #305260] |
Wed, 10 August 2016 21:48  |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma:
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Senior Member |
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Does anyone have a transmission pressure gauge on their GMC? I am looking for someone to compare notes with, in actual driving. I am not so much interested in on the stand type tests, or front wheels jacked up sorts of tests, in the GM manual. I want to compare actual driving pressures. The things I am seeing cannot be seen in GM Shop Manual tests or on the test stand.
The one instance I am particularly interested in is the pressure in Drive when under full deceleration. I have textbook pressures when driving except when I let off the gas. When I let off the gas, at any speed from 80 to 15 mph, my pressure suddenly drops to about 52 lbs.(Please note that at times, the RPMs are 3000 and pressure drops to 52.) It remains there until about 15 mph when it suddenly jumps back to about 65 or 70, depending on the heat of the oil. I assume the transmission has downshifted.
My gauge has a red light at 50, and there have been times deceleration has caused the light to come on. My concern is the rear (first out) band in my transmission has slipped and burned out twice. When it does, there is no engine braking. In other words, when you let off the gas at 65, the RPMs go to idle. My pea brain tells me this band is keeping the engine and wheels at speed when decelerating. I wish I had had a gauge on it when that band gave out. I also fear 52 lbs is not enough to keep the band tightly engaged.
I have also noted that in neutral, pressure is normal 65-75 depending on oil temp, and when I put it in drive it takes a sudden drop that turns on the light. I assume this is torque converter, pistons and clutches sucking up oil for a moment and the accumulator cannot keep up.
And yes, I asked Manny about the 52 lbs. He says, "That's too low." I agree.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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