jctelling@juno.com Report post Posted June 1, 2010 My 2005 Excursion (Cat 350, Spartan, Allison Trans) has a PacBrake as well as a Retarder, the latter being controlled by an on/off switch. Can anyone tell me how the PacBrake is activated? I realize that its purpose is to restrict the exhaust flow, but I don't know how it is controlled. Thanks! Share this post Link to post Share on other sites
wolfe10 Report post Posted June 1, 2010 My 2005 Excursion (Cat 350, Spartan, Allison Trans) has a PacBrake as well as a Retarder, the latter being controlled by an on/off switch. Can anyone tell me how the PacBrake is activated? I realize that its purpose is to restrict the exhaust flow, but I don't know how it is controlled. Thanks! You have only one of these devices with the C7 Caterpillar. It will be some brand of exhaust brake. Jacobs makes one, PacBrake makes one, etc. They all work basically the same way: You have a switch at the driver's area that turns on the exhaust brake. When the switch is on AND the throttle position switch says the throttle is closed, a relay sends a signal to the Allison ECU. The ECU then does two things-- starts downshifting toward the "pre-select gear" (you will notice the left window/only window of the Allison shift pad goes from "6" to whatever the pre-select gear is with 2nd and 4th being popular choices) AND sends a signal to the air solenoid on the exhaust brake to open the valve which allows air pressure to activate the exhaust brake butterfly. The butterfly does indeed function as a "potato stuffed in the tailpipe" building about 55 PSI of back pressure to slow you down. There are two other kinds of auxiliary braking devices-- an engine compression brake (only available on much larger engines) and an Allison transmission retarder (only available on on Foretravel and OTR busses as far as I know). And the exhaust brake does need lubrication: http://www.pacbrake.com/index.php?page=maintenance-2 Brett Share this post Link to post Share on other sites
jctelling@juno.com Report post Posted June 1, 2010 My 2005 Excursion (Cat 350, Spartan, Allison Trans) has a PacBrake as well as a Retarder, the latter being controlled by an on/off switch. Can anyone tell me how the PacBrake is activated? I realize that its purpose is to restrict the exhaust flow, but I don't know how it is controlled. Thanks! Share this post Link to post Share on other sites
jctelling@juno.com Report post Posted June 1, 2010 Brett, Thanks for the information. My truck driving buddy has been trying to convince me that there is a switch missing! The PacBrake link that you sent (thanks for that, too) says to 'cycle the exhaust brake manually or electronicall a few times' - how do I do that? JT Share this post Link to post Share on other sites
wolfe10 Report post Posted June 1, 2010 Brett,Thanks for the information. My truck driving buddy has been trying to convince me that there is a switch missing! The PacBrake link that you sent (thanks for that, too) says to 'cycle the exhaust brake manually or electronically a few times' - how do I do that? JT Manually is difficult because you are "fighting" a pretty heavy duty return spring. You can disconnect the arm at the butterfly and manually move it. You can also disconnect the positive wire (signal wire) from transmission to the air solenoid at the air solenoid. Apply 12 VDC from any source in the engine room to the solenoid side ONLY (don't "back-feed" the wire). You can also apply the lube just before you drive and turn the brake on/off multiple times. Brett Share this post Link to post Share on other sites
realbob@seanet.com Report post Posted June 18, 2010 Here comes the newbie to everything. This is my first participation in a forum so hoping this is the way to enter a discussion. Second, I have just purchased a 2006 Phaeton (350 Cat) after having two gas coaches. I am trying to figure out what I am supposed to know and whether I should just take the coach to a repair shop every time something comes up or if (as was the case with gas) I can do a few things myself. Brett pointed out the exhaust brake needs to be lubricated. Based on the site you referenced it looks like this is some linkage and I'm hoping I can just open the floor in the bedroom that gives me access to the engine compartment (nothing but radiator showing at the rear) and this linkage will be in site. Can someone help here. Thanks Share this post Link to post Share on other sites
wolfe10 Report post Posted June 18, 2010 Realbob, Welcome to the FMCA Forum. Yes, there is a learning curve, as with any new complex "toy". Best answer is to get to an FMCA International Convention-- LOTS of free seminars. Read posts here on the FMCA Forum. And with a Caterpillar Engine, consider joining the Cat RV Club (an FMCA Chapter). Their next Rally is two weeks before the Redmond Convention in Newport, OR. I will be doing two 1/2 day maintenance seminars at the Rally: http://catrvclub.org/rally_info.htm Brett Share this post Link to post Share on other sites
