Exhaust Brake

[Skip426]

Originally Posted by TheKassman

I have a 1998 36 SDS
when I flip on the exhust brake my tranny goes into 4th. I get lots of braking but isn't that just engine braking as in down shifting? I didn't think that was how an exhust brake worked.

The exhaust brake/trans downshift program , can be altered , with the appropriate shot tool ; my coach the down shift can go as low as second.
The program can be set , for second , forth or manual downshift.
Diesel engines , provide very little hold back , even on the downshift, so they require , exhaust or compression brakes to aid them.
As mentioned these brake systems work best at higher engine RPM.
You could try this to confirm exhaust brake operation .
On a down hill, at about 45 MPH , manual down shift to 4 forth, observe the amount of engine hold back, then switch on the exhaust brake to confirm operation , with the amount of additional hold back.

[JohnBoyToo]

our 2011 with the allison 3k engine brake and tranny does a surprising job of bringing down near 40k lbs... and the tranny will downshift very quickly all the way down to second when really stopping quickly....

unfortunately have had to test slamming on the brakes twice to avoid idjuts... why our engine brake is on all the time.

from our manual:

When the auxiliary brake is activated, the variable geometry turbocharger will restrict exhaust gases causing increased back-pressure within the engine.

Increased back-pressure slows the speed of the engine resulting in braking action. The amount of engine braking power developed is relative to engine speed (RPM). When the auxiliary brake is activated going down a hill, it will help control road speed or sufficiently slow the road speed until the
transmission can automatically downshift to the next lower gear. Downshifting automatically occurs from high gear down to second gear.
Certain road conditions and engine speeds may require the transmission be manually shifted down in order to generate adequate engine RPM and increase the engine brake effect.


NOTE: The brake lights will illuminate while the exhaust brake is applied.
Caution: Activating the exhaust brake switch does not cancel cruise control.

[whalepirot]

Originally Posted by AKOne

You may find this helpful: https://pacbrake.com/wp-content/uplo...7/08/L5046.pdf

Indeed, thanks. A newb here, so pardon the Q. Does the 2007 FDDS w/400hp ISL use this brake? I use Low and Hi regularly.

[Old Scout]

…..nope, 2007 ISL400 uses a true engine compression brake-- "Jake"......

[Skip426]

Originally Posted by Old Scout

…..nope, 2007 ISL400 uses a true engine compression brake-- "Jake"......

I'll add that calling the compression brake a " Jake " brake , even though it's made by Jacobs , is confusing , because Jacobs also manufactures , exhaust brake systems.

JMHO. An engine brake system , with a " high/low " , " 1/2 " or a "1/2/3" control switch , will be a compression brake , because exhaust brake systems are on/off.

[Old Scout]

...confusing?

[whalepirot]

Thanks for all that. I luv lerning.

[wolfe10]

From an article I wrote many years ago for the FMCA magazine:

Engine Brakes

There are three different braking systems used on different diesel engines: Exhaust Brakes, Engine Compression Brakes and Variable Geometry Turbo Brakes

Exhaust brake: literally a "flap" which closes off exhaust flow just downstream of the turbo in the exhaust system. This causes back pressure (55 PSI on ours) which generates braking power. With the Allison transmission, it is usually tied with downshifting of the transmission to the "pre-selected" gear (usually 2nd or 4th). Think of it as a potato stuffed in the tail pipe.

Engine Compression Brake (aka: Jake brake) The exhaust valves are opened as the pistons reaches TDC (Top Dead Center) on the compression stroke after the engine has done the "work" of compressing about 18 volumes of intake air to 1 volume . If the exhaust were not let escape by the compression brake's opening the exhaust valves (i.e. coasting with brake off), the "compressed air" would mostly be returned as power to the engine forcing the piston back down. With the Jake brake on, the engine works to compress air in the cylinder, then the air is let out. This generates quite a lot more braking force than an exhaust brake. The smallest engines to offer an engine compression brake are the Caterpillar C9 and Cummins ISL.


Variable Geometry Turbo: The vanes reverse or aperture closes (depends on engine manufacturer) to create back pressure with much the same effect as an exhaust brake.

[gmcgene]

Brett,
Thanks for the explanation. Didn't know about variable vanes.

[Old Scout]

….Alpines didn't get the variable vane turbo technology until the 400ISL Pegasus engine model in 2005. Pretty sure only engine brake option for the OP in 1998 with the 350ISC was a PAC brake. Not sure, but also think I heard that some of the earliest Alpines may have had 330s, and still would have had a PAC....

[wolfe10]

Yes, only type of "engine brake" on the Cummins C engine is an exhaust brake with PacBrake being the most common.

[whalepirot]

Originally Posted by Old Scout

….Alpines didn't get the variable vane turbo technology until the 400ISL Pegasus engine model in 2005.

Then, my 36' '07 must have the variable vane, unless it was optional.


Now, to find whatever maintenance is required.

[Old Scout]

...don't know about any recurring maintenance for the variable vane turbo [which was std equip, not an option] on the newer Pegasus engines.....but you do need to follow the recent forum threads on compressor air leaks and the turbo vane control box mounted on the top of the engine valve cover...

[Renipladlo]

All - First read my post "New to Alpines" and read the 1st paragraph. Other brands owners will give you advice which is WRONG for an alpine.

When going downhill, do NOT allow the engine RPMs to exceed 2300, you will blow it up at around 2500, this is straight from Cummins. When going up hill, shift down to 4th gear and keep engine RPS around 2100, this will keep the HYD pump on high speed and give you max cooling at the radiators fans. Remember, never go down faster than you went up the hill, brakes get hot, you want to use the engine/exhaust break for all of it as much as possible. On my coach, when I engage the engine brake, the transmission automatically shifts down to 4th gear, this is the way they are supposed to work, don't have exhaust brake, but assume it is similar, it should shift down to 4th gear too I believe. The exhaust brake needs some maintenance I think, search here in this forum for that information.

Long down hill stretch going into Las Vegas, never touched the brake pedal, used the high/low engine brake, and it worked fine. If new to diesels engines, take driving course, they have NO engine braking without either an engine or exhaust brake, not like a gasoline engine. DO NOT REPROGRAM SYSTEM TO CHANGE any braking or accelerating perimeters which were set at the factory by Cummins/Allison. Bad things can happen.

One last point-see all the time in Parks, folks put their rear wheels in the air and not in contact with the ground, now tell me which wheels have the emergency/parking brake again???? Hanging any wheel in the air without support is not good for the air bags, nor the suspension, put blocks or ramps so all the wheels have something under them, my major pet peeve this is.