84’ 359 Cat 3406 jakes not disengaging with accelerator

@wore out?

 

So is it electrical or mechanical? Never had that problem with Cats but when the C brakes came out they had a lot of those issues. Springs and piston problems in the brake assemblies. Thank you should be able to figure that out with a test light and push on top of the control solenoid. When you push the solenoid the brake should apply. When you let off it should dump oil and stop.

 

Jake switch at the injection pump. Had this happen on my 7FB.

 

Whatever you do, don't let the motor die while the Jake is on, it does horrific damage. There are usually 3 switches, dash, clutch and throttle. Clutch one takes the most beating, and a simple fix.

 

Had this happen with a company truck I was driving once middle or late 80's cat engine, it was the switch at the pump.

 

"Is it bad or out of adjustment?" Probably sticking. Pull back on the linkage and press the switch on and off with your finger to see if it sticks. Or the contacts are worn or burnt.
"how do I know where to set the new one?" So that the switch is in/compressed without pressing on the accelerator. As soon as the linkage is pulled back it should be moving away from the switch until there is separation where the switch and linkage make contact.

 

The switch on 4MGs at least also sets your low idle speed. Screw it in farther for higher idle speed. The jam nut holds the the switch at the desired position.

It is strictly a continuity switch, and likely the problem. It has a little plunger in the tip that is probably sticking. With the engine off you should be able to move the throttle by hand and hear it click, or check it with a test light.