Exhaust brake inoperative

[Happycarz]

Ever since new in June '07, my exhaust brake would not hold me back, whereas on my last two Monacos, it would. It downshifts fine, but doesn't really hold me back to the point of having to use the service brakes or else over revving the engine and forcing an upshift. Not what you want to do on a 6% downgrade. A few times at slower speeds, like in city streets, it did a good job. I would even try selecting 4th gear and turn on/off the exhaust brake switch and could feel no difference most of the time. So, I change the Jacobs E- Brake to the new PacBrake, at my expense. Still, the same results. Bah! Well, not to give up, I have been working on it for the last two days on my way home from Camp Monaco.
First, I hooked a fused wire to the chassis battery post in the front run bay and ran it into the cockpit. Then I wired it to an on/off switch and ran other wire back to the front run bay, where I connected it to wire labeled "spare #1"�. I next found the "spare #1"� in the engine bay, added a length of wire, and used a blue Scotchlock to connect it to the wire feeding the 12volt side of the exhaust air solenoid. (When voltage is applied to this solenoid, coach air pressure is sent to the exhaust brake actuating cylinder, engaging the E-brake.) I even added a led light at my switch in the cockpit, hooked between the solenoid side wire and ground.
Now for the test drive. Exhaust brake switch on, down hill, transmission in 4th, led light on, but still picking up speed. Turn on my switch and bingo, I start slowing. Woohoo! So, what gives? Have you figured it out?
I hooked my trusty Fluke DVOM between the solenoid feed wire and ground and headed down the next hill and repeated same sequence. The exhaust brake relay is only feeding 11.2 volts to the solenoid. When I flip my auxiliary switch, my meter jumps to 13.6 volts and again I start slowing. Aladdin Jr. is reading charging 13.9 volts. I then swapped relays, seeing if the original had high resistance in the contact – to no avail.

When I called Monaco in June with this E-brake issue, I was told it was my driving habits. Hmmm, I wonder if he was one of the 600 laid off?
Since Monaco will not supply a wiring diagram, I guess I be back on the phone with tech support.

[Happycarz]

Ever since new in June '07, my exhaust brake would not hold me back, whereas on my last two Monacos, it would. It downshifts fine, but doesn't really hold me back to the point of having to use the service brakes or else over revving the engine and forcing an upshift. Not what you want to do on a 6% downgrade. A few times at slower speeds, like in city streets, it did a good job. I would even try selecting 4th gear and turn on/off the exhaust brake switch and could feel no difference most of the time. So, I change the Jacobs E- Brake to the new PacBrake, at my expense. Still, the same results. Bah! Well, not to give up, I have been working on it for the last two days on my way home from Camp Monaco.
First, I hooked a fused wire to the chassis battery post in the front run bay and ran it into the cockpit. Then I wired it to an on/off switch and ran other wire back to the front run bay, where I connected it to wire labeled "spare #1"�. I next found the "spare #1"� in the engine bay, added a length of wire, and used a blue Scotchlock to connect it to the wire feeding the 12volt side of the exhaust air solenoid. (When voltage is applied to this solenoid, coach air pressure is sent to the exhaust brake actuating cylinder, engaging the E-brake.) I even added a led light at my switch in the cockpit, hooked between the solenoid side wire and ground.
Now for the test drive. Exhaust brake switch on, down hill, transmission in 4th, led light on, but still picking up speed. Turn on my switch and bingo, I start slowing. Woohoo! So, what gives? Have you figured it out?
I hooked my trusty Fluke DVOM between the solenoid feed wire and ground and headed down the next hill and repeated same sequence. The exhaust brake relay is only feeding 11.2 volts to the solenoid. When I flip my auxiliary switch, my meter jumps to 13.6 volts and again I start slowing. Aladdin Jr. is reading charging 13.9 volts. I then swapped relays, seeing if the original had high resistance in the contact – to no avail.

When I called Monaco in June with this E-brake issue, I was told it was my driving habits. Hmmm, I wonder if he was one of the 600 laid off?
Since Monaco will not supply a wiring diagram, I guess I be back on the phone with tech support.

[Robin_M]

Harry,

As you know, with the exhuast brake on, the transmission should be seeking 2nd gear, whether or not the exhaust brake is actually working. If it is properly seeking 2nd gear range with the exhaust brake on, then it sounds like you've got resistance in the EB circuit somewhere. I doubt that you are going to get much help from Monaco tech support on this one. Now that you can demonstrate the problem, I'd take it to a Cummins repair center, or a good truck repair shop qualified by Cummins. Cummins customer care should be able to direct you to one. My bet is that they'd be able to diagnose and fix the problem better than Monaco or an RV dealer.

BTW, did you notice a difference on your boost gage when you flicked your make-shift switch? The boost will be quite low any time you are slowing, but when the exhaust brake is actually working, the boost immediately goes to zero, which is an easy way to tell if it is really working.

[walt2137]

Harry I cant see how the voltage difference to the mac valve would make any difference as 11.2 is enough to switch the air to the calender and if it switches it will close, I would think one of the main reasons that it is not stopping as good as your other coaches is the trans needs to be reprogrammed to select 2nd gear rather than 4th gear.
Be sure to service the pac brake with lube designed for the pac brake, not dyno oil.
I will paste oil info below, this info is a few yrs old.

Silicone will burn off pac brake because of high temps. PacBrake's
lubricant is made by SYNCO (1-800-253-lube; super-lube.com) but is
also marketed under the name "Super Lube" a multipurpose Synthetic
lubricant with Syncolon. Good for temps from -43 to +450 Degrees F.
They also have a SuperLube called "DRI-FILM" which is a self cleaning
lubricant and is rated at -40 to 500 Degrees F. The info regarding
silicone burn off came directly from PacBrake. After going to 7
different stores including 2 Home depots, I located it at Lowe's
Items 65880 $4.48, 11 oz aerosol; Item 93615 $2.94. Check you
Roadmaster lube for high temps!


Walt

[Hillbilly2]

Does sound like a loose connection, changing the relay was a logical move, could be a defective fuse, since you are using a different circuit for the override and it works. That also rules out a bad ground at the solenoid. Is the relay mounted to a printed circuit board? It also could be the problem, if the trace is melted, it would not pass sufficent voltage and current to activate the solenoid.

[Sixpack98]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I then swapped relays, seeing if the original had high resistance in the contact – to no avail. </div></BLOCKQUOTE>

Harry,
I agree with Rob, there is some sort of resistance and it sounds like you have confirmed everything from the brake back to the relay is ok. I would look at the supply side (12v) of the relay for a bad connection or connector. Checking the voltage with a load on the wire tells me there is a bad connection on the +12v supply side. Another possibility is if the 12v splits on the brake side (past the relay) and provides signaling to something in the brake food chain after the relay and you bypassed the faulty connection by directly connecting (thru a switch) to the brake solenoid. If you had the same results with your wire around I would suspect a ground problem but you eliminated that.

mark

[Happycarz]

Robin,
The ECM and TCM are functioning as designed. Exhaust switch on and closed throttle, trans selects 2nd gear . At the test speed, the trans had attained 4th gear. Monaco told me when I had a problem with a circuit, they would address that item, but would not supply me with a coach wiring diagram. I do have a 2007 Camelot diagram, but many revision were made in 2008, especially the front run bay.

Walt,
They switched from Mac valves to KIP solenoids and maybe I just have a weak coil. I tested resistance to ground, .4 ohms.
One of my initial tests was to apply 12v directly to the exhaust solenoid and watch it operate smoothly. I even disconnected the air piston and operated the butterfly valve by hand. No hang ups. Only after these checks, did I start looking at voltage issues. On another note, I thought the circuit wanted to see a brake light signal as when I stepped lightly on the brakes, the E-brake activated. I could not duplicate this again and thought it was only coincidental.

Two things to test further is output voltage at the relay and switch solenoid coils, using one of the KIP dump valve solenoid coils. The input voltage, at both the fuse and relay terminal 30, with no load on the circuit is chassis battery voltage- 12.4v KOEO and 13.7 engine running on fast idle. Now, I am going to run another wire from cockpit to run bay to pin 10 of wire bundle in the VCD labeled harness connector. This is wire is fed by terminal 87 of the relay. If I have good voltage there, but not in the engine compartment, I can change over to the spare wire to remedy the situation. I just need to make sure this wire is not feeding a command signal to ECM or TCM. I believenot, but want to check with Monaco first.

Hillbilly and Sixpack,
I was testing while you were posting. Sounds like we are in agreement.

We will see what the next tests reveal.

[Robin_M]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Monaco told me when I had a problem with a circuit, they would address that item, but would not supply me with a coach wiring diagram. I do have a 2007 Camelot diagram, but many revision were made in 2008, especially the front run bay. </div></BLOCKQUOTE>Harry,

That's really frustrating - especially for people like you who could fix many electrical problems if you had the proper information on hand.

[Flyer]

Harry
I just had my PacBrake checked out at Cummins in Coburg. It seemed as if the downshift would happen immediately, but the valve was sluggish. Cummins did the troubleshoot and found all OK and then attempted to charge me even though I was still in warranty. If you go to Cummins be sure to clarify the warranty issue.

[Pusherpilot]

Our 04 Imperial has the 2 stage Jake brake. When it is selected the trans goes to 2nd gear but usually only goes down to 4th to avoid over revving. Our old Safari Zanzi had a pac-brake tht worked the same way with the trans seeking 2nd. It seemed to have far more braking power than the Jake on our new coach. The Jake will hold the coach on a 6% downhill at 50 mph but you can't start at 60 and expect it to slow the coach or even hold it at 60. I like the 2 stage since it can be switched back and forth to vary the rate of braking. Another trick I learned is to manually apply the toad brakes with the dash controller, but be careful doing that, I've locked up the toad brakes that way!!

[RetiredSKP]

Happycarz,

I had the exact same symptom that you describe on my Freightliner. It turned out to be the small micro-switch that senses that you have indeed taken your foot off of the accelerator pedal. The switch prevented the air cylinder from actuating even though my allison transmission was downshifting when I called for exhaust brake. If yours was creating a high resistance connection, dirty contacts inside the switch, you would see a voltage drop at the cylinder solenoid. Good luck.

RetiredSKP

[Happycarz]

So, I drive all day Sunday with the volt meter hooked to output wire of the E-brake relay and I get over 13.5 volts and the exhaust brake is working fine. Then Sunday night, it quits working. In order to catch it in the act, I pull over and leave everything on, as to not disturb the fault. When checking voltages again in the front run bay, the chassis battery supply cable and fuses were close to 14 volts, with the exception of the e-brake fuse. It had 11.7 volts going into the fuse, with or without the fuse installed. On the green printed circuit board, the circuit is visible and I could probe it away from the fuse, thereby eliminating a cold soldier joint at the fuse holder - same 11.7v.
Now I start checking voltages at idle and fast idle (1100 rpm) with the A/C on and off, with headlights on and off and 8 combinations thereof. Chassis battery terminal stayed close to 14v, but anytime the headlights were on, the e-brake fuse voltage dropped to 11.8v. With headlights off, the voltage went to 13.8v.
Robin,
I took your suggestion and watched the turbo gauge and it did not go to zero unless the e-brake solenoid was actually on. I don't know if that is a cause or effect. Meaning, is the ECM getting an e-brake signal and telling the turbo vanes move, or does the back pressure cause the vanes to move.
For the next few days, I need to pay attention to my businesses and then a call to Monaco and to KIP, the solenoid manufacturer. I use dozes of KIP solenoids in my carwashes, albeit 24v a/c, and have had zero failures. I can call KIP and get the specs on the one in question, as it does have an OE part number on it. And, I didn't try changing the solenoid coils around yet. Just one more test to try.
With this much info, maybe Monaco will have some input other than my "driving habits."�
Oh well, I guess I can't expect this motorhome to last forever.

Flyer,
Now you know what to check - the actual voltage at the air solenoid.

Pusher,
Yes the engine Jake is better than the exhaust brake. Now that I can apply enough voltage to the e-brake solenoid, the 6% grades are no longer a problem. When Monaco first started using the ISL they were equipped with the engine brake. When I saw on the spec sheet for the Camelot and it listed Jacobs brake, I assumed it was the engine brake. I didn't even know that Jacobs was manufacturing an exhaust brake. My mistake!

RetiredSKP,
Thanks for the input. I am getting a voltage signal, just not enough voltage.

[Hillbilly2]

Resistance is being added into the circuit some where between the fuse and the main supply bus, as your voltmeter has just proven, keep moving it back towards the main supply bus and you will find the problem, it may be a tee joint where the headlight fuse pulls its power from. It can be an overheated solder trace, short circuits destroy these very easily. The headlight current may be enough to temporarily heat up the connection, causing it to loose continuity. You could also refeed that circuit from a spare fuse that is not affected by the loose connection.

[Happycarz]

I like the idea of feeding the circuit from another source. Without taking the panel completely out, it would be hard to trace circuits. It looks like in 2008 Monaco put just about all circuits on relays - 33 on the pc board , including the headlights, and 4 off the board.
Maybe I'll check the voltage at the headlight relay, with lights on and off. Also, I can try pulling each relay, esp the headlight relay while testing voltage.
There is one relay marked spare, but was warm, and clicked when I unplugged it Saturday. Apparetly it isn't a spare. I see I have more work to do.