Jacobs Exhaust Brake

BlueLine · 03-06-2011, 06:43 PM

Thats what it says on the dash switch, "Jacobs Exhaust Brake". I wasn't sure it was truly working because it really didn't slow me that much. I've read several posts and this seems to be common. I have a VMSpc and one post suggested I monitor my intake temp when I flip the Exhaust Brake switch, and I should see an immediate temp spike of about 50 degrees in intake temp. I did see this spike on several applications, but no dramatic slowing, but I decided that maybe this was norm and everrything was functional because of the temp spike. I also wasn't satisfied with the difficult to reach location of the toggle switch that activates the brake which was on the lower right side of the dashboard next to the parking brake, soooo I moved it and changed it to a large lever flat paddle toggle switch and placed it in a non used switch position in the upper mid level right side of the dashboard, and very easy to reach. NOW........nothing happens when I actuate the switch. I checked the switch with the ohm meter and it's functional. I checked and I do have 12V to the switch. Iv'e checked every fuse and circuit breaker I could see or find, but nothing. I even reversed the black and white wires to the switch and still nothing. I've read on some past posts to check the relays. I have 3 located on the side of my fuse panel, but they are all unmarked and I have no idea what they may be for and I can't locate a drawing showing them. I also checked back on the actuator itself but found nothing but a neumatic hose connection. The only electrical I saw back there was 2 bendix type relays mounted on the frame on a plate near the actuator.
Any help would be appreciated

J Walker · 03-07-2011, 06:55 AM

So your intake temperature is not spiking now when you apply the exhaust brake? Moving the switch should not change the exhaust brake operation. Perhaps the brake piston has stopped working. You had problems before you moved the switch. You don't seem to be getting automatic downshifting. Troubleshooting an exhaust brake can be a job for the professionals. You can check the obvious things like loose connections or sticking brake piston but beyond that there is not much you can do.

BlueLine · 03-08-2011, 06:44 PM

Thanks Jim, When you refer to the brake piston, do you mean the pneumatic one directly linked to the linkage that operates the valve?

J Walker · 03-09-2011, 07:33 AM

Quote:

Originally Posted by BlueLine

Thanks Jim, When you refer to the brake piston, do you mean the pneumatic one directly linked to the linkage that operates the valve?

George
That is the one. I can't tell what chassis you have but if it is Freightliner I would go to Gaffney and let them fix it after you exhaust everything you can do. I had an exhaust brake mis-wired when new and two local Freightliner shops took over six weeks to fix it. Thank goodness for warrantees. I later had occasion to have Gaffney technicians work on another difficult wiring issue and they solved in a few hours.