Engine/Transmission (1994 - 1998) Jacobs/Cummins e brake info plz

[PorterS]

Hello all... Tried a search and after looking through pages and pages of info I can't really find what I'm looking for. I just bought a 97' 2500 4x4 auto out of Tennessee. It has a Jacobs exhaust brake under the hood with a micro switch and throttle lever at the inj pump. Also a switch in the cab. I've installed two Pacbrake brand ebrakes with the micro switch at the gas pedal but haven't ever seen one of these. The brake does not work. Solenoid does not click hence the valve doesn't engage. After glancing at the microswitch it appears that either it was loosened up and moved out of the throttle levers way purposely or rattled loose and moved too far away from the lever to engage the brake. How do these things work on the 97' auto's? I know they use the converter to slow the truck, but how do they lock the converter? I haven't seen any other items on the truck anywhere such as a controller... Wouldn't know where to look or what it looks like... Will it hurt anything to fire the truck, and at idle in neutral, depress the microswitch and see if the brake works? Thx in advance TDR members. .

 

[ScottLewis]

A guess, and only that, is that the switch serves as a "mystery switch" to lock up the converter. This was/is commonly used method to force the T/C into lockup when the brake is used. My '98 uses a controller from BD to lock the T/C and a microswitch at the throttle to engage the brake. Do a search on "mystery switch" and you should find lots of info. Essentially, it grounds the circuit of the PCM that locks the T/C. You have to remember to turn it off when coming to a stop or it will kill the engine.



Checking out the microswitch while idling in park won't hurt anything, in fact my '98 e-brake is engaged most of the time at idle.



Good luck,



Dan

 

[hsmith]

I am pretty sure on the 12 valvers, mine included, all the ebrake does is restrict the exhaust. If the main switch inside is on, the micro is the one that energizes the relay to apply vacuum to the brake. These switches can move and not function. Loosen the two mounting screws and with the engine idleing, move the switch to make the button contact the throttle. You should be able to feel a click and the relay should open the valve and apply vacuum to the brake. Have to play with the adjustment sometimes to make it repeat. I have also had to replace my relay at the vacuum valve once. Cummins part and a bit pricey!

 

[Bob V]

The switch you have is one of the early versions of the brake, they later updated to the in cab switch due to problems with the engine mounted awitch staying adjusted. Without a "mistory switch" to keep the tc locked , and mods to incresse line preasure when your foot is off the throttle, the brake will not slow you down much and will cause transmission damage,

 

[PorterS]

Thx for the replies guys... Bob that is what I was concerned about. . Wear on the torque converter/transmission with the use of this brake. Is it useable or not? BTW the brake does work... I fired it up with the cab switch hot and pushed in on the microswitch. The brake opens and closes as it should

 

[ScottLewis]

Without some means of locking the T/C the brake won't do much more than slow the engine. While many will correctly say that the e-brake places stresses on the T/C and transmission, many more have used them with only minor mods. I had a BD PressureLoc installed at the same time I had the brake put on. I also got the AutoLoc controler which I was told would put less strain on the transmission.

The pressureLoc increases pressure on the clutches, etc. at lower speeds than stock. I converted the AutoLoc to act more like a TorqlLoc because I wanted even more braking. The truck now has over 100K miles with probably 60K towing a 11K+ fifth wheel. I replaced the T/C at about 90K because I started getting nervous and wanted something beefier. It was still working fine.

I would never again tow anything as heavy as my RV without an exhaust brake, I like them that much. If you don't tow you don't really need the brake although I use mine all the time on both trucks.



Dan

 

[GAmes]

I have a Jacobs brake, but not an auto. I turn mine on during cold mornings to warm the engine faster at idle. Doing that won't hurt it. It has a microswitch that the throttle switch activates and a toggle switch in the cab. Somewhere I think I have all the original paperwork, that I could scan and send to you if you want it and I can find it.

 

[PorterS]

Thx for the info. . Games, I have all the paperwork. , thx for the offer. It came with the truck. I think I scored a pretty good deal on this thing. It was traded into Sexton Dodge in Knoxville, TN. This is the fourth one I've had in 6 years : ) Just can't get away from these 12 valves... The truck actually just had a brand new DC transmission, converter, and lines put on it in Oct 06... The older fella was in New York pulling his fiv'er and the transmission went out at 122k miles. . So he bought a brand new transmission and had it installed same day to the sum of 4500 bux :--) The truck is spotless on the inside... It's a 97' quad cab 4x4 2500. Has a fiberglass bed cover, e brake, brand new Michelins and 127k miles. Stock down to the air filter as far as mods go... I gave 11,900. 00 without knowing about the new transmission. The dealer didn't know about it either. On my way back to Alabama, I was going through some paperwork in the console and found the ticket and warranty info on the transmission!! I almost turned the truck into a pine tree magnet!!! Was beside myself to say the least.



So the question is: should I mod the transmission to pick up some line pressure (maybe lengthen the life of it) and use the ebrake? Or leave it alone and don't use the brake? I do not plan to mod the engine at all, it gets 19mpg and don't wanna lose that... I do tow quite often though... Bobcat, backhoe, etc... . What would you guys do? I've never had a ebrake with an auto.

Thx again. . Scott

 

[GAmes]

I get as good or better mileage with my plate and advanced timing. I can't imagine having an EB and not being able to use it. If it was mine I'd put in a mystery switch, and if the transmission wasn't up to it, then I'd mod the transmission.