Pacbrake misbehaving. Help?

[Bill Sprague]

I apologize for writing a long post, but my Beaver and I are under stess!

For some reason, Beaver forgot to put a Cat in my 2004 Monterey.  I have a Cummins ISC 350.  As a newbie when I bought it, I didn’t know better.  Except for a $600 fuel filter, the drive train has been flawless for almost 80,000 miles.  Even though I don’t have a Cat, maybe you can still help me!

After having a lot of fun at Jim and Gerda Bull’s rally in Grants Pass last week, we drove north on I-5 towards Ellensburg for a Jazz Fesitval.  For the first time in 80,000 miles, the Pacbrake malfunctioned.

On the first downhill grade, I switched on the Pacbrake.  The cruise control disengaged, the RPM kicked up and I felt the braking effect.  Then, for no apparent reason, it up shifted, the RPM dropped and the braking effect went away.  A few seconds later, the Allison down shifted again and the braking effect returned.

Puzzled by the abnormal behavior, I put the Aladdin engine page in the primary scan.  On the next downhill grade it did it again.  I had engaged the Pacbrake with the switch, the Aladdin showed that “2” was selected and it down shifted to “4” from “6”.  After about a half minute, the selected gear changed from “2” to “6” , the Allison shifted and the braking effect went away.  Then it reselected "2" and went back to normal down grade operation.  The abnormal pattern repeated itself on the next couple of downgrades.

Befuddled, I phoned Marty Schenk on my (hands free!) cell phone to brainstorm.  I don’t know if he knows anything, but I had him on speed dial (grin!). The chassis voltage was fluctuating from 13.8 to 14.1 and my chassis batteries are 7 years old so I had convinced myself the computers were not happy with that.  Marty talked me out of that idea.  We agreed that a shut down and restart at the next rest stop might re-boot the computers.  He also remembered a thread on the Cat board about a faulty relay.  

I pulled into the next rest stop, shut down, did the usual walk to the back of the motorhome, returned, restarted and pulled out to attack the next hill.  On the next couple of downhill grades it repeated the same bad behavior.   The re-boot didn’t work.

It occurred to me that, instead of letting the Pacbrake do it, I could tell the Allison what to do with the arrow buttons on the keypad.  On the next downhill grade I engaged the Pacbrake, verified that the cruise control canceled, verified that “2” was selected, watched the shift to “4”, pushed the down arrow 4 times (to back up the Pacbrake signal) and waited.  It worked normally.  There was no “hunting” of the “selected” gear.   At the bottom of the hill I disengaged the Pacbrake, pushed the “D” button to end the “2” selection and reengaged the cruise control.  This worked consistently on the next couple of downgrades.    

To further the troubleshooting, I tried switching the Pacbrake off and on a down grade while the transmission was selected to “2” with the arrow key.  I could feel the braking effect change confirming the Pacbrake valve was operating.  
 
Soon, I was out of the hills of southwest Oregon and am satisfied that I can continue to drive safely by backing up the Pacbrake by downshifting with the arrows.  

My theory is that the Allison is working properly as long as it gets the a command from either the Pacbrake or the arrow keys.  I think that the Pacbrake may be sending an initial downshift signal to the Allison, but then the signal drops out.  That suggests the wiring from the dash switch is OK to the Pacbrake, but not to the Allison.

What sends the signal to the Allison?  Does it come from the dash switch, the Pacbrake or a relay? Where should I look for the simple stuff like wires and fuses?  What other ideas might you have?  Where are the best Pacbrake technicians in the Northwest?

Thanks in advance!

Bill

PS:  I’m looking forward to seeing a lot of you in Harrisburg!

[Gerald Farris]

From your description, it sounds like a bad relay is the most probable cause for your problem. A fuse or wire will very rarely cause an intermittent problem like you described, although a poor connection will cause a similar problem, but a poor connection will almost always get much worse quickly from arcing when it starts.

I do not know were the components are located on your coach, but they should be in the LF electrical bay.

There will be Pac Brake technicians at the FMCA rally in Redmond if you need their services.

Gerald

[Bill Sprague]

Gerald,

Thanks for the suggestions.  Unfortunately I got "cross scheduled" and won't be at Redmond.  I'll survey the electrical bay and check my files for a wiring diagram.  

On today's drive heading west down I-90's Snoqualmie Pass the Pacbrake worked perfectly.  While using it, it occurred to me that something lightly touching the accelerator would have caused the Pacbrake to do what it did.   Since I know better than doing that with my foot, it may have been that something like the GPS power cord was bumping part of the accelerator.  I should know better than that too! Some dust, dirt or loose dog fur could be keeping the pedal from fully returning to the idle position.  If that turns out to be the case, I feel pretty dumb!

Whatever it is, I'm still on the hunt.  

[Larry and Heidi Lee]

Bill, I experienced a similar condition when I purchased my 05 Monterey a couple years ago. The rig would slow down going down steep grades but would upshift and I would have to slow back down with the service brakes so much that I was overheating the brakes. Something was wrong! I finally figured out the air solenoid that actuates the Pac brake was stuck so I wasnt getting any braking assistance at all! I removed the solenoid, cleaned it with some WD40 and it's worked perfectly ever since.  

[Bill Sprague]

[quote author=]Bill, I experienced a similar condition when I purchased my 05 Monterey a couple years ago. The rig would slow down going down steep grades but would upshift and I would have to slow back down with the service brakes so much that I was overheating the brakes. Something was wrong! I finally figured out the air solenoid that actuates the Pac brake was stuck so I wasnt getting any braking assistance at all! I removed the solenoid, cleaned it with some WD40 and it's worked perfectly ever since.  [/quote]
Thanks for the advice.  Pacbrake makes packages their own synthetic lube for that.  They say it should be lubed at every service but I've noticed that in my seven annual oil changes I've had to ask for it.  Now I have a bottle of my own.  Although it seems to have healed, I'll give it a couple of drops.

[George H. Wall]

Where is this solenoid located?? THANKS!     George Wall

[Bill Sprague]

Where is this solenoid located?? THANKS!     George Wall

Here is a link to the Pacbrake lube instructions:  http://www.pacbrake.com/index.php?page=maintenance-4

On my Cummins it is on top of the engine and the easiest way to get to it is by lifting the hatch on the bedroom floor.  I don't know where it is on a Cat.

[Larry and Heidi Lee]

Hey George, on my 05 Monterey the air actuator is located under the upper engine cover in front of the bedroom closet. You'll need to just follow the air lines from the actuator down to the solenoid. The air solenoid itself was buried under a bunch of wiring and was a royal b**** to reach so I ended up making a bracket and mounting it up on top where it can be easily serviced in the future. It amazes me that the failure of this little device that fits in your hand nearly killed me while decending the Kingsbury grade in Tahoe.  

[George H. Wall]

Thanks for the reply, I'll look for it when I get a chance as I bought some of the lube for it!!

[David Rudisill]

Bill:

Does the Pacbrake light go off and on while it's malfunctioning? If so, it could be a defective switch on your console.

I added a foot switch to mine several years ago. It's a lot easier to find than the switch on the console when in a hurry to start slowing down. It has the added advantage of being momentarily on, so shutting it off involves simply lifting my foot. I use the console switch on long grades.

[Joel Ashley]

At the risk of starting controversy, I add that the exhaust brake unit in our '06 Monterey with a C9 Cat, and accessed via the wardrobe floor hatch, says Jacob's on it, not Pacbrake.  Apparently both companies make both types of devices, engine retarder and exhaust brake.  The difference is described below, as per Pacbrake:

"The similarity between a Pacbrake exhaust brake and a “Jake” brake is that they both play a part in retarding the speed of diesel trucks. However, they are significantly different in many ways. A “Jake” brake is a brake which is attached to the top of diesel engines and slows diesel engines using the engine’s compression process. ‘Jake’ brakes are used on larger diesel engines (e.g. Semi’s) and cause an appreciable amount of noise when used but can provide increased retarding power. Pacbrake makes a series of “Jake” engine brakes for larger vehicles.  The Pacbrake exhaust brake is different from the engine brakes. It is attached after the turbocharger in the exhaust system and works on the process of backpressure. It is used most often on Class 4-7 trucks. Noise is not a problem with the Pacbrake exhaust brake."

Our Jacob's Exhaust Brake requires some routine maintenance, especially before extended storage, though I admit to neglecting it;  it's not something one thinks about when winterizing for storage.  You might think about it, though, when pushing the switch on a hill elicits no response  ??).  

I don't know about a "solenoid", but the unit visible through the top hatch is an air cylinder, used to open and close the valve in the exhaust that creates the restriction and thus slows the engine.  The restriction is more effective at higher RPMs, so the transmission should downshift, or you should manually downshift it if necessary.   During storage, moisture trapped in or around the air cylinder can rust, causing operational problems later.  Beaver/Monaco recommends lubricating the several moving parts on the air cylinder platform with silicone spray - I concur with that;  the oils in WD-40 may only attract dirt, so though of some effect, it isn't preferrable to silicone.  Use pliers to move the cylinder ram back and forth a few times and work silicone into it as well as the knuckle joints.

Gerald or others more technically inclined than me may wish to add to or correct my take on things.

-Joel

[LEAH DRAPER]

Joel
Is your Cat C9 a 400hp or 425hp?  I've never had the closet engine access door opened.  I guess I better do that and find out what I have in my Cat C9, 425.  I assume it is a PacBrake (exhaust type) as I sure don't have the braking power I had on my Jake Brake, 99 Thunder!  It is actually kind of scary when you not used to the difference.  I am also sure that I am not yet skilled in using it on 4-6% down grades.

I use it a lot in traffic/city driving and notice that the window immediately changes to 2/4.  Is that what yours does?

[Joel Ashley]

Leah-

Brett Wolfe at the CAT Club is the best at explaining this, and I am certainly no long-experienced veteran, but here's my take:

The exhaust brake circuit is telling your Allison control to select 2nd gear (to get RPMs up for the best braking effect),  though the transmission computer will not allow the downshift all the way to second if you have some speed up.  Probably you are going less than 65mph (the approximate point where any faster will engage 6th gear if actually selected) and are in 5th gear to begin with, so the transmission computer downshifts one notch to 4th.  Thus your panel shows 2/4:  2nd selected but actually in 4th.  Of course, the proper technique on downgrades is to not allow the coach to get on much speed off the hilltop in the first place.  This is the first coach I've driven with any kind of auxilliary braking, so I'm not experienced with a Jake Brake (compression retarder);  but I have had no trouble with the exhaust brake slowing the rig.  I just have some throttle technique issues that sometimes make the coach "lurch" on downhills with the exhaust brake on - the brake cuts out when my speed drops too far and I hit the "gas" to pick it back up, then the coach stutters again when I let off the gas and the brake kicks back in.  I've yet to get an absolutely smooth technique down pat.

Over time, CAT increased the horsepower ratings on the C9, as minor design changes allowed them to, and as most engine manufacturers do.  I believe in years prior to our 2006 model, the HP was 350?  By our year, a 400HP was available, and that's what's in ours;  in our 37 footer, it is more than enough power.  By your model year apparently, the HP went to 425.

Our exhaust brake, as earlier indicated, is made by Jacobs, the name behind the "Jake Brake", which is actually an engine retarder, not an exhaust restrictor.  The exhaust brake on your Contessa may be made by either Jacobs or PacBrake, but either way it should be checked to make sure it's working properly for you.  On my coach, I open the hatch on the platform between the bed and the wardrobe, rather than the hatch in the wardrobe.  The brake and its air cylinder mounting plate are immediately under the hatch and off to the street side of the engine top.  It is relatively easy to get at, and you should be able to use a can of spray silicone and some pliers to make sure the air cylinder mechanism is lubed and functioning.  Our owner's manual actually describes and illustrates all this, so you might want to check your book;  look in the index under Brakes and then Exhaust Brake.

-Joel

[Bill Sprague]

It only malfunctioned one day.  Two days of driving since then it has been fine.  We leave on a two week trip through WA, ID, WY and MT on Monday.  I'll find out more then.

On the '04 Monterey, Beaver had a clever dash design with all the warning lights lined up in a straight row across the top.  The really neat part is that the steering wheel blocks half of them.  By adjusting the tilt you can choose which have to ignor.  The day the Pacbrake acted up I forgot to monitor the lights, because they were in the hidden group.  Instead I was using the Aladin.  

[Bill Sprague]

It is relatively easy to get at, and you should be able to use a can of spray silicone and some pliers to make sure the air cylinder mechanism is lubed and functioning.

You might consider the lube Pacbrake sells in the small plastic bottle. I bought some at the Cummins Northwest Coach Care shop in Coburg, OR.