Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 13, 2025 ...

exhaust brake problem

July 09, 2011, 08:33:08 pm

we have friends here now that have a monico Windsor with a 5.9 cummins and 3000 allison. It has a problem with the ex retarder not cutting in and as we have just replaced the ex manifold and a bunch of other stuff on it the last few days we also took thegate valve assembly apart and made sure it was all ok and cylinder worked too. It does not operate on removing your foot off fuel and the fuses are ok and it seems to be sending a message to the pad selector for Allison and showing it is selecting 2 in the 6 range. Does anyone have any ideas what to look for as they will be doing some heavy mountain climbing on leaving our place in a few days??? I was showing him our Forum and he was very impressed with the knowledge and help everyone gives. So I thought you may be able to help him
John

Quote Selected

Re: exhaust brake problem

Reply #1 – July 09, 2011, 09:10:19 pm

John, I can only respond to what I know bout the Pac brake on the 1993 U225 with the Cummins 5.9. There is an electrical activation switch under a sheet metal plate or box under some of the fueling mechanisms on the passenger side of the engine. You can barely see it from above but it can be located from below. The older models of Pac Brake had a very simple 1/8" metal rod that hung down just forward of the return springs for the throttle. As the throttle plate came to an idle position it would push the L shaped rod forward which activated the Pac Brake. Later models had a slightly more sophisticated mechanism in that it had a roller on the bottom of the L to reduce friction and wear. If the rod got moved or got bent it would not activate the switch at the top of the rod. Jeff and Carol S. had a problem with the wires coming loose on this switch and somewhere under their transmission that caused their Pac Brake not to work.

My suggestion is to make sure the Pac Brake switch on the dash is hot a putting electricity back to the engine compartment. If so then go under the coach and look up under the engine on the passenger side for the throttle springs, then look for the activator rod and make sure it is pushed forward by the throttle plate when it is at idle position. If so, check the wiring to the switch at the top of the rod to make sure it is passing electricity through the switch when the rod is pushed forward. If both or those are working, see if you can trace part of the wiring to a switch on the transmission for the trans lockup. Beyond that, I can help no further.

Good Luck!!!

Quote Selected

Re: exhaust brake problem

Reply #2 – July 10, 2011, 11:19:35 am

John,
  I've got the coach that Kent referred to that had the loose wires. I've since fixed it. This is also a Cummins 5.9. It actually had three problems and maybe your friend can check for these if it is a similar setup. First, one of the air hoses that actuates the exhaust brake cylinder was crushed. Two,  the wiring to a microswitch was REAL funky. And three, the microswitch may have been just a tad loose. Take a look at these attached photos. One of them shows a bracket with two slots. That's what the microswitch is mounted to. It's a real simple deal. When you touch the throttle, the switch disengages the exhaust brake. Anyhow, he might take a look at that switch. It's hard to show in a photo but on mine it is on the right side, almost directly below the cruise control mechanism. Good luck to him.
jor
 

Quote Selected

Re: exhaust brake problem

Reply #3 – July 10, 2011, 02:11:14 pm

OK, what is working properly (because the transmission shift pad indicates the "pre-select gear"):

Exhaust brake switch, fuse, throttle position indicator and wiring to transmission.

From the transmission ECM, the 12 VDC signal goes to the air solenoid that powers the exhaust brake.  Either the wiring to it is bad or the solenoid is bad as you have already verified that it is working mechanically.

Disconnect the 12 VDC positive wire at the exhaust brake air solenoid.  From any 12 VDC positive source on the engine, apply that 12 VDC positive to the exhaust brake air solenoid-- do not backfeed the wire from the transmission ECM. The exhaust brake should snap closed when power is applied (as long as there is air pressure) and snap open when the power is removed.  That will tell you if the solenoid is working. If it is, that would suggest a wiring or relay issue between Allison ECM and the exhaust brake air solenoid.

Brett

Quote Selected

Re: exhaust brake problem

Reply #4 – July 10, 2011, 02:31:16 pm

Thanks guys for these ideas. We are finally getting to it to see what may be the problem. Been busy. Will let you know what we find (if we do)
john

Quote Selected

Re: exhaust brake problem

Reply #5 – July 10, 2011, 05:45:20 pm

well it looks like the quick exhaust valve on the actuating cylinder for the gate valve is faulty and does not allow the air to escape and let the cylinder shaft go back . We have tried to get it working (success twice) but no more so in the morning I will get hold of the company in Ontario to find a dealer here somewhere. All else works ok. Thanks all for the help. It put us on the right track.
John

Quote Selected

Re: exhaust brake problem

Reply #6 – July 10, 2011, 08:18:55 pm

The Pac Brake guys at the FMCA in Albuquerque told me that the most common problem is lack of lubrication of the piston assembly or use of the wrong lubricants. They sell a high heat oil but said that if neglected too long the cylinder and or the flapper must be replaced. I trust this one can be rehabbed with use and then kept lubricated in the future. An entire new unit was $750 and they said it was much more positive braking than the older units.

Quote Selected

Re: exhaust brake problem

Reply #7 – July 10, 2011, 09:24:36 pm

I am sure we can fix this once we get the new "Humphry-quick exhaust air valve" and put it on the cylinder.
Weve had a busy 2 days as we have taken off and replaced the exhaust manifold on that Cummins and fixed a few leaks, replaced oil filters and engine oil and then the 2 Allison Filters and replaced the oil in that with Amsoil Torque Drive. On mine we have replaced all filters (fuel and oil) and done the same on the Allison, and the fuel filter(one with water seperator) on the genset. Tomorrow I do the r+r on the hydraulic oil and filters. Saved quite a bit in labour costs and now know all is done right.

Quote Selected