General Boards > Technical Support
Pacbrake misbehaving. Help?
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:
--- Quote from: ]Bill:
Does the Pacbrake light go off and on while it's malfunctioning? If so, it could be a defective switch on your console.[/quote ---
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.
--- End quote ---
Bill Sprague:
--- Quote from: Joel Ashley --- 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.
--- End quote ---
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.
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