Volume X, Issue 4, Page 101


4/8/2008

Mike,

A friend of mine bought a used pro mod powerglide for his Mustang and it has a JW case with an ultra bell and seems to be experiencing a problem when he applies the brake. The car seems to creep forward as if the reverse clutches were not holding. We did a pressure test on the reverse clutch and the needle was bouncing from 90 to 210 but stayed around the 200 as we brought the RPM up a little but as soon as the brake was applied the pressure dropped to about 15psi. We've replaced the valve body and rear support thinking there may have been a leak there. Mike, any leads to this problem would be greatly appreciated.

Juliano
Ottawa, Canada

Juliano,

Holding power in the transmission is determined by friction surface and apply pressure. So first, we need to check the pump: it has to be in good shape, nice pocket, about .002 clearance across the top of the gears in the body. A loose pump, of course, will drop pressure, especially when the fluid warms up. Normally on a pressure test, most brakes will drop from 200 – 250 psi to 50 psi and then immediately return to approximately 5 – 10% of the original pressure. The low band is on when you get the shifter in first gear. When you push the brake button, it applies the reverse clutch pack if the piston is pretty large, so the fluid requirement can be big, especially if the piston travel is too much. Normally, we will set the reverse pack at .050 - .060 with a 5-6-7 clutch pack. Of course, the more clutches, the more holding power, but also the more drag. I think that you probably have a pump issue.

Thanks,

Mike

Mike’s Transmission
Lancaster CA
(661) 723-0081
www.mikestransmission.com

 

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