| Re: JC-4 Vacuum Pump?? [message #364225 is a reply to message #364219] |
Mon, 24 May 2021 06:05  |
rjw
Messages: 697
Registered: September 2005
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RF_Burns wrote on Sun, 23 May 2021 22:01Richard,
Have you read DaveL's article in the Spring GMCMI magazine about the proportioning vales. If you have replaced your OEM with a brass proportioning valve, you may have limited rear brake pressure.
The "Mod" of the JC-4 wasn't really a high tech "Mod". I believe the internal control circuitry pulled one side of the motor to ground through a Power FET to turn it ON. I just moved wire on the switched side of the motor to the JC-4 ground pin and ran that pin through the relay to ground.... I'd have to look at it again to be sure.
I never changed out my OEM valve to the often touted brass proportioning valve because I never got around to it. As it turned out, Dave showed me his cutaways of various valves and explained what he had learned about them during a visit to his place in March. Consequently, I'm happy I never got around to switching to a brass valve. I've never had better braking, since I installed his disk brakes, the newer 4-bag suspension, 80MM calipers in the front and a still working OEM proportioning valve. However, I don't have a working parking brake.
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com
Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water heaters.
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