Community Forums

countrypair · 04-18-2016, 03:28 PM

I don't believe my pac brake has worked from day one. I told the dealership when I bought the coach, I didn't think it was working. They checked & said it was fine. So, here I am 2 years later & I had it checked again! This time at another dealer. Everything is fine except I'm not getting a signal from the ECM to the solenoid valve, which activates the cylinder to the pac-brake. They said I would have to take it to a Cummins dealer because only they have the ability to check for fault codes (proprietary). Any suggestions or thoughts on this problem? I would appreciate any input.

MnTom · 04-18-2016, 06:46 PM

Have you checked for a possible blown fuse or a broken wire? It also could possibly be the brake is stuck in the open position.

palehorse89 · 04-18-2016, 06:52 PM

For some odd reason it may not be "Enabled" in the Cummins Insite program??? They will have to hook it up to their laptop and take a look at it to be sure.

**CountryFit** · 04-18-2016, 08:10 PM

Quote:

Originally Posted by countrypair

I don't believe my pac brake has worked from day one. I told the dealership when I bought the coach, I didn't think it was working. They checked & said it was fine. So, here I am 2 years later & I had it checked again! This time at another dealer. Everything is fine except I'm not getting a signal from the ECM to the solenoid valve, which activates the cylinder to the pac-brake. They said I would have to take it to a Cummins dealer because only they have the ability to check for fault codes (proprietary). Any suggestions or thoughts on this problem? I would appreciate any input.

our names are very alike, countrypair vs countryfit

the packbrake is fed with pressured air pushing the valve to close. to test it, you would just need to check two things:

1) with your hands, or with help of a screw driver, could you push the rod in the cylinder to extend (meaning the valve can freely close or open);
2) when you turn on the brake, do you see the pressured air present. to test this, you will need to disconnect the hose from pacbrake and connect a longer hose to extend the pressuring hose into your bed room. connect an air meter to measure the pressure when exhaust braking is on. with a helper in the bedroom, you operate your coach on the road and he/she watches the gauge...

either does not work, it won't work. trace down the path, solenoid, leaking hose, stuck valve, disconnected wires... good luck.

Darrel · 04-27-2016, 03:42 PM

I have the same problem. The brake switch causes downshiftine but not much retardation. On 6% grades I normally have to slow to 40MPH to avoid manual braking. Hope you find a fix and relate it here.

Have a nice day - Darrel

TonyMac · 04-27-2016, 03:51 PM

Do you get the downshifting schedule and just not the brake activation? The valve requires Pac Brake Lube (Google it). You can use a breakaway line to test valve movement. Tie a thin piece of thread to the valve and something immovable. Drive around and activate the valve. Stop, open the engine cover, see if the breakaway line is broke. The valve itself gets hot, so maybe use a leader of safety wire with a short piece of thread for the breakaway.

"Remember, if she don't find you handsome, she should at least find you handy." Red Green

countrypair · 04-28-2016, 05:18 AM

Everything is operational, except there is no signal from the ECM to the solenoid valve.

TonyMac · 04-28-2016, 05:22 PM

Quote:

Originally Posted by countrypair

Everything is operational, except there is no signal from the ECM to the solenoid valve.

How do you know there is no signal, vice the signal is sent to an inoperative bus or part?

NevadaNick · 04-30-2016, 09:00 AM

It takes alot of rpm's for the engine/exhaust brakes to be effective. What rpm are you getting up to going downhill ?

countrypair · 05-01-2016, 05:04 AM

If I put power directly to the solenoid valve, it activates the cylinder!

countrypair · 05-01-2016, 05:05 AM

2000 -2500 rpm

Dr4Film · 05-01-2016, 05:42 AM

Quote:

Originally Posted by NevadaNick

It takes a lot of rpm's for the engine/exhaust brakes to be effective. What rpm are you getting up to going downhill ?

Quote:

Originally Posted by countrypair

2000 -2500 rpm

With all due respect, speed is more important data than rpm's.

If your speed is too high you will have very little exhaust braking effect versus if your speed is lower.

I had a good working standard PacBrake Exhaust Brake. I switched it out for the upgraded PRXB PacBrake Exhaust Brake due to the weight of my coach and rolling garage that I usually tow. Neither of them will do much at speeds around 55 mph or higher. You should start to see some affect at 50 mph or below.

If your exhaust brake switch is on, when you remove your foot from the treadle in a second or two your transmission should downshift to 4th but the display will say 2nd as that is the "aim" gear of the transmission. You should also feel a slight slowing which should increase as your speed decreases.

I would test this on a flat highway versus a grade.

BTW, when doing grades, I never let my speed get above 51-53 mph as that's when my Allison up-shifts to 5th gear and the coach will "take off".

Also, an exhaust brake is not in the same league as an engine brake so don't expect it to perform the same.

Dr4Film ----- Richard

TonyMac · 05-01-2016, 10:10 AM

Quote:

Originally Posted by Dr4Film

With all due respect, speed is more important data than rpm's.

If your speed is too high you will have very little exhaust braking effect versus if your speed is lower.

I believe the amount of force generated by the engine's crankshaft while the Pacbrake is on, is directly related to engine speed, rpm, and not related to vehicle speed, mph. The higher the engine speed, the more force is generated by the crankshaft while using the PacBrake. However, the effect of that crankshaft force is more noticable at lesser speeds, because the crankshaft force is playing against lesser driveshaft force.

dennis45 · 05-01-2016, 10:22 AM

Quote:

Originally Posted by TonyMac

I believe the amount of force generated by the engine's crankshaft while the Pacbrake is on, is directly related to engine speed, rpm, and not related to vehicle speed, mph. The higher the engine speed, the more force is generated by the crankshaft while using the PacBrake. However, the effect of that crankshaft force is more noticable at lesser speeds, because the crankshaft force is playing against lesser driveshaft force.

Richards post is pretty much bang on in reference to the PacBrake. I think you may be confused with the operation of a Compression Brake (commonly known as a Jake Brake) which is a whole different animal.