Jacobs Brake not working-HELP

[waltmoe]

Greetings; my 07 3500, 48RE, 95,000 miles with dealer installed Mopar/Jacobs Brake was installed at time of truck purchase so it would be covered under vehicle warranty.

The Jake brake has suddenly stopped working. The shifter mounted Jake switch is showing a lighted RED LED. When the Jake brake is turned on at the switch I would always hear a hissing from the engine compartment, hissing is the best description I can give. That noise has stopped and there is no function of any kind when the switch is turned on and off.

I checked the fuses, that is the best I can do for now. I have no idea on how to trouble shoot this issue. I have searched the web for installation documentation which I thought might help troubleshooting. Does anyone have any suggestions on what might be causing the Jake brake not to work, is there any typical point of failure of the Mopar/Jacobs brake.

Thanks for any help.....

 

[mwilson]

Troubleshooting is on the last several pages.....


http://www.jacobsvehiclesystems.com/files/support/docs-pdfs/32414 E2_Screen.pdf

 

[waltmoe]

Thank you very much for the information.....

 

[jhenderson]

1st check is to see if the vac pump is ok. Pull the line off the pump and start the truck. It should make constant vac of over 20 inches. If not the pump is bad. You can replace the whole pump or just the vac canister, which is most often the problem. Genos has both.

 

[Prairie Dog]

Am I wrong in thinking that if one hears a constant hiss that there must be a leak in the system?
I know a leak will kill the pump.

 

[AH64ID]

This hiss could also be the exhaust flowing past the brake and thru the fixed oriface.

Mine and my dads both hiss when engaged.

Leaks kill the pumps, if it was loud enough to make noise I don't think the pump would have make it 95K miles.

There is a new HD pump, it might be worth looking at it.

 

[waltmoe]

Thanks everyone for the info... I examined the pump and noticed black oil everywhere.... I just ordered a new pump, it should be here in a few days.. Thanks again....

 

[bigceltic]

Thanks everyone for the info... I examined the pump and noticed black oil everywhere.... I just ordered a new pump, it should be here in a few days.. Thanks again....

Not sure if you have gone through the troubleshooting guide but I had the same thing happen to me (stopped working but light would come on) and I thought it was the vacuum pump but after following the troubleshooting, I isolated it to an electrical issue where the brake was wired into the ECU - the wire had pulled out. I got it reinstalled and the brakes works again. Just FYI.

George

 

[CKESSEL]

Also, don'y buy the replacement pump from Ma Mopar. When mine went out, the Mopar relabled Cummins unit was close to $800. One from Cummins was in the $200 range. Save your money and buy your Cummins parts from Cummins or Genos.

 

[waltmoe]

Update: After completing the troubleshooting process as stated in the install manual there were no wiring issues noted. Since the pump had been leaking black oil I did replace the pump with a Gould pump with the larger pulley. The install is very straightforward, reconnected the vacuum line and started the engine. When engaging the shift handle the Jake Brake switch, the pump made the typical noise. Road test and all is back to normal. Thanks to everyone for their assistance.