Exhaust brake

[EngineerMike]

I was just spelunking my way thru some pre-Vansco chassis wiring diagrams, and noticed in a dash wire loom- both Engine Brake loom turn-out/plug connector and PacBrake turn-out/plug connector. I guess in 02 manufacturing year they were set up to build either way.

[Dr4Film]

Originally Posted by Pusherman

Not exactly correct regarding it won't do anything until the speed drops to 55 mph.

The exhaust brake will engage immediately; the transmission pre-selects a pre-programmed gear and starts to downshift to this gear selected, but the Allison is smart enough to not downshift until the coach is at a safe RPM so as to not damage the transmission or engine.

The engine braking is most effective at higher RPM's, so you may not feel the effect of the exhaust brake until it does downshift.

Mine was pre-programmed from the factory to downshift to '2', which I found too aggressive, so I had it re-programmed to downshift to '4'. I can always manually downshift to '3' or '2' if needed.

Pusherman's post is the most accurate one out of this entire thread.

First off, don't confuse the operation of an Exhaust Brake with that of an Engine Brake. They are two braking systems that perform COMPLETELY different.

If you want to get the best performance out of your PacBrake Exhaust Brake, then have the upgraded PRXB unit installed. Next keep your speed between 35 and 53 mph. That's where exhaust brakes are the most effective. The Allison usually shoots for 2nd gear when the exhaust brake is activated unless people have had theirs reprogrammed for a different gear. However, it will not go to that gear until the speed has been reduced enough to safely go into 2nd gear. YOU have to reduce your speed to allow the Allison to downshift to the next gear and so on unless the grade is low enough for the exhaust brake to do it for you.

If the coach picks up speed then trounce on the brakes to drop the speed within a safe range, usually 8-10 mph less than before you trounced on the brakes. Then when it creeps up again do it again until you have reach the bottom of the grade safely.

Do NOT ride the brakes!

If the grade is such that the coach maintains a safe speed while descending the grade then you don't have to do anything except steer.

The exhaust brake will automatically disengage at 15-20 mph.

Dr4Film ----- Richard

[Algoma]

Originally Posted by EngineerMike

I was just spelunking my way thru some pre-Vansco chassis wiring diagrams, and noticed in a dash wire loom- both Engine Brake loom turn-out/plug connector and PacBrake turn-out/plug connector. I guess in 02 manufacturing year they were set up to build either way.

That is probably why another member noted he had a 2 position brake switch even though he had the ISC with PAC brake.

[mel s]

IMO, few owners/drivers, (including me), understand exactly how an exhaust brake is supposed to work, (aka: what braking advantage it provides depending on the engine RPM, the vehicle speed and the gear the Allison transmission is actually in).

BTW, IMO that's also true of nearly all MH systems/components, (chassis and/or house), whether electrical, mechanical, pneumatic, or hydraulic.

Mel
96 Safari

[Rich and Cork]

OK, the best way to figure out your Pac Brake and its effectiveness is to find a hill and go down it. On mine it will shift automatically to 4th as soon as I hit the brake. Feel how it slows you down. Then try going slower and shift it down to 3rd, 2nd and 1st. Note how your braking reacts to adding more throttle in the lower gears. Find a steeper hill and repeat. In my opinion, this will give you confidence in understanding your brakes and the exhaust brake. Note also that the exhaust brake is only an aid....it will not bring your coach to a stop. Even with an exhaust brake you can do a job and heat your brakes to the point they will not work.....I have done that a couple of times.

[Algoma]

Originally Posted by Rich and Cork

OK, the best way to figure out your Pac Brake and its effectiveness is to find a hill and go down it. On mine it will shift automatically to 4th as soon as I hit the brake. Feel how it slows you down. Then try going slower and shift it down to 3rd, 2nd and 1st. Note how your braking reacts to adding more throttle in the lower gears. Find a steeper hill and repeat. In my opinion, this will give you confidence in understanding your brakes and the exhaust brake. Note also that the exhaust brake is only an aid....it will not bring your coach to a stop. Even with an exhaust brake you can do a job and heat your brakes to the point they will not work.....I have done that a couple of times.

I hate to drag this topic any further but I think you need to test the effect of downshifting as opposed to the exhaust brake. If you are descending a hill and select 4 manually you will notice a definite braking effect. Now switch on the exhaust brake and notice the difference. Not as much as you would think. I live in the mountains and do this regularly. In 4 on a steep descent my speed will slowly creep up, but a quick shot of exhaust brake will bring me back to 55mph. I then toggle the exhaust brake on and off to maintain my speed.
Regarding previous comments, I never leave my exhaust brake on as it will fight the cruise control and prevent coasting when conditions permit that.

[mel s]

Originally Posted by Rich and Cork

On mine it will shift automatically to 4th as soon as I hit the brake. .

Algoma
If/when the 12V PacBake switch is in the ON position AND the PacBrake is activated, (in your case when you hit the service brakes?), the transmission doesn't "shift automatically" into 4th gear....
The electronics automatically "select" 4th gear, but the transmission doesn't actually "downshift" into 4th until the vehicle speed drops to a speed that is "safe" for both the engine AND the transmission.

BTW, some automatically "select" 4th gear and some, (like mine), "select" 2nd gear when the PackBrake activates.

Mel
'96 Safari

[Algoma]

Mel, I think you are commenting on a remark made by Rich and Cork, not by me. But I agree with what you say.
My last comment was to encourage owners to see how much slowing effect they get just by using the gears rather than assuming it was all PAC brake.
With most vehicles being automatic these days this is probably a lost art, but I still drive a manual car and a motorcycle so I get lots of practice using the gears to slow down.

[mel s]

Originally Posted by Algoma

Mel, I think you are commenting on a remark made by Rich and Cork, not by me. But I agree with what you say.
My last comment was to encourage owners to see how much slowing effect they get just by using the gears rather than assuming it was all PAC brake.
With most vehicles being automatic these days this is probably a lost art, but I still drive a manual car and a motorcycle so I get lots of practice using the gears to slow down.

Algoma

I did mean my comments for Rich and Cork...(I used an incorrect salutation).
Sorry.

BTW, I agree with your comments about the slowing affect of exhaust brakes.

Mel

[gatorv]

Yes that was me in Canyonlands camp ground. What a crazy week.
Which Coach was yours? The one near the entrance or the one behind me? I only saw three.
I walked by both several times but no one was out to say hello.
I got the wheels , calipers and shoes off mine today.
The Hubs are to heavy . Will have to get help.

[Rich and Cork]

Originally Posted by gatorv

Yes that was me in Canyonlands camp ground. What a crazy week.
Which Coach was yours? The one near the entrance or the one behind me? I only saw three.
I walked by both several times but no one was out to say hello.
I got the wheels , calipers and shoes off mine today.
The Hubs are to heavy . Will have to get help.

I was the one near the front. We got back late most days. We were only able to have a nice cocktail time one evening. Another evening a couple of us had to go back to repair one of the group's rig on Pritchett Canyon and did not get back til after 11. We were actually there for 11 days.

[gatorv]

I'm not retired so 11 days is not an option. Hopefully it will be soon. My Canyonlands neighbor rolled on his head on Pritchett. We did a little more relaxing than any hard stuff. Took a break this year. Hopefully we will meet up one of these days? Have a good one.

[wydeglyde]

Diesel engines do not develop back pressure from compression in the way that gas engines do.

When you take your foot off the throttle, fuel is cut and you will start to slow because you are no longer adding power, however they do not slow in the same way as a gas engine. Diesels take a lot longer to slow down, this is why manufacturers add engine brakes to assist braking.

Pretty sure I am correct about this.

[Algoma]

Originally Posted by wydeglyde

Diesel engines do not develop back pressure from compression in the way that gas engines do.

When you take your foot off the throttle, fuel is cut and you will start to slow because you are no longer adding power, however they do not slow in the same way as a gas engine. Diesels take a lot longer to slow down, this is why manufacturers add engine brakes to assist braking.

Pretty sure I am correct about this.

I am pretty sure you are totally INcorrect.