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Old 09-05-2010, 12:10 PM
kwacasey kwacasey is offline
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Presssure readings in 1993 4L60 trans

Just rebuilt my first 700r4 in a 1993 Z28 that I picked up real cheap (due to trans issues). With everything back together the trans seems to shift and work, but lacks holding power. (I am very proud of this)

After doing some pressure testing and searching this and other sites, i found that my base line pressure seems OK but WOT pressures seems low. So, I changed the TV Boost valve and Reverse Boost valves to upgraded over-sized/O-ring units. Below you can see my before and after pressures:

Before boost valves:

Gear base/max
R 75/190
N 75/125
OD 75/125
D 75/125
2 75/175
1 75/175

After boost valves:

Gear base/1500rpm
R 75/240
N 75/150
OD 75/150
D 75/150
2 75/175
1 75/175

*Max was determined by a hand pulling the cable at idle*


Even when the TV cable was adjusted properly i could not get over 10-15 psi change at 1500rpm in any gear. This seems much too low to me.

I have made a few assumptions such as because I can achieve a line pressure reading of 240psi, the pump is able to produce pressure so it most likely is not the problem.

Also, now that i have changed the Boost valves out, they are eliminated from the troubleshooting process, leaving only the TV valve assembly or internal leak.

I suspect SSS, but do not know enough to be confident here. Could it be the TV valve itself? How can i check this in the VB, or do i just have to blindly replace the valve and spring and monitor results?

Any help here would be appreciated, i am really trying to understand my problem and how to go about troubleshooting issues with this trans.

Thanks

KEN
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