C9 CAT ENGINE BRAKE

[LEAH DRAPER]

Am after some information from others with the C9 engine brake.  At times it appears not to work, but perhaps I don't  understand how it supposed to work.  There are times that I flip the switch and nothing appears to be happening, and nothing shows on the Allison panel to show that it has engaged.  Is there a speed limitation at which it will turn on/engage that I am not aware of?  My understanding that this is a CAT product right?  Do I have a problem that I need to have CAT address?  Other times it acts like I would expect, I flip the switch and it engages.  Anybody know what is happening?

[Marty and Suzie Schenck]

It depends on how the parameters were set up. Some models the cruise control master switch must be in the off position for the engine brake to work and others it will work by just letting off of the accelerator and others you must let off and then tap the brake. Or it could be as simple as something under the throttle pedal not letting it return to the full rest position. Hope that is of some help. Marty

[Gerald Farris]

Also keep in mind that exhaust brakes will not engage below 1000 RPMs.

Gerald

[Keith Moffett Co-Admin]

Leah
We have the 3126 CAT but I suppose the systems are similar.  Our "pacbrake" manual suggests inspecting the connections and using a touch of silicone spray lube on the pivot points.  I brush off the dirt, plug and unplug the wires a few times to clean the contacts and hit the shaft and cam with a spray of WD-40.  Takes perhaps 5 minutes.  If yours is dirty/stuck it likely wont kick in every time.  Do I have this right Gerald?

Merry Christmas
Keith and Carol

[Gerald Farris]

Keith,
You are right on all exhaust brake equipped coaches up until the DPF (Diesel Particulate Filter) equipped coaches were introduced. On the DPF equipped coaches (like the one the question was about) there is no external linkage to maintain because the exhaust back pressure is generated by a variable geometry turbocharger instead of an air cylinder that controls a valve like your coach uses.

On the DPF equipped coaches the variable geometry turbocharger is controlled by the Cat electronics using either a solenoid or a step motor that does not require external lubrication.

Gerald

[Tim Westman]

Leah,

On my '09 Contessa, the "engine brake" (through use of the variable geometry turbocharger that Gerald described above) operates significantly different than my Pac Brake on my old '05 C-9.  My old unit was set up to engage whenever I backed off on the throttle if the cruise wasn't engaged and the switch was on.  If the cruise was on it would not engage until I exceeded the set point by about 10 MPH with the throttle off.  The new one will NOT engage if the cruise on regardless of speed and set point.  I also strongly feel that the new technology (variable geometry turbocharger) is anywhere as effective as my old Pac Brake and is difficult to feel at higher speeds.  I have found that if I need more braking power the best thing to do is to manually downshift one gear with the switch on and braking is more effective than either transmission or brake alone.

Tim Westman

[Larry and Heidi Lee]

Keep in mind when you flip the switch your transmission will automatically downshift possibly giving you a false illusion that the exhaust brake is operating. Did the "exhaust brake" lamp located on your dash ever light up in the past? I didnt know my exhaust brake was not working until I smoked my brakes going down a long steep grade. What I found was the electric air solenoid that controls the exhaust acctuator was stuck. I removed the solenoid, cleaned and reinstalled it and the system has worked perfectly ever since. I would remove the engine access cover located in your bedroom and ask someone to flip the exhaust brake switch and see if the actuator is moving or not. I do have a 05 C9 as well.

[Larry and Heidi Lee]

The electric air solenoid in the picture was buried so I relocated it to the top of the engine for future maintenance purposes. The actuator can be seen in this picture.

[Richard And Babs Ames]

If you lubricate you must use high temperature silocone lube as prescribed by Pac Brake. The over rev control on the Pac Brake program prevents the transmission from down shifting so fast the engine over revs (thank goodness) and at the higher gears the effect of the engine brake  is not so obvious.  On ours the Pac Brake stops working at 15 mph and second gear and it can be programed to stop after different gears.