Pac Brake differences

[DBCooper]

Been looking for a used Pac Brake and have come across a couple that were for sticks. What is the difference between the stick and auto Pac Brakes. I know about the exhaust spring issue on the 12 valves. That would be dealt with. Thanks.

 

[SRehberg]

I recently purchased a PacBrake for my auto '96, that was originally for a stick. Before I bought it, I contacted PacBrake and this is what they told me: The holes in the butterfly is the difference between the two transmissions. On the stick, the holes are 31/64"; on the automatic they are 9/32". To use the stick ex. brake on an auto, you will lose approx. 5% retarding power is all. If you want to up the holding power, then they suggested welding the one hole shut (blunt hole, not the chamfered one) then redrilling it to 9/32" or weld it shut and redrilling alongside. With the stock 12V springs, and the PacBrake, this setup is good to 11,000lbs towing per PacBrake. When you upgrade to 60lb springs, you plug the chamfered hole and leave the "blunt" hole open. With both holes open and stock springs, there is no chance of floating a valve per PacBrake, plus providing adequate holding power.



Hope this helps.

 

[krs]

For the 98+ trucks pacbrake uses the ECM to activate the brake when you let off throttle with a stick, but uses a microswitch mounted at the throttle pedal to activate in the auto trucks. The ECM provides a 1--3 second delay of activation so that your brake won't come on during (slow) stick shifts.



There may be differences year to year that I don't know about. Apparently you can buy whatever pieces you need to make a stick brake work in an auto and vice-versa.



Also, just general info: there's little or no braking force in an auto unless the torque converter is locked. DB Cooper, your smart controller takes care of that, I think, or a switch can be installed to manually give lockup when using the brake.