Jake Brake Operation

[Joe Magie]

I have a 1992 Beaver Marquis with a Cat 3176 engine, 4 speed Allison Trans and 2 speed Jake Brake.  Can someone out there tell me how the Jake Brake operates.  There is a 3 position toggle switch on my left control panel labeled Engine Brake.  You can position it at  Off / Low / High.  If I am going down a hill (or on flat ground for that matter) nothing happens when I flip the toggle to Low or High.  Is there something else I should be doing???   Joe Magie.

[Dave Atherton]

Joe, how an engine brakes works:  Creating a power absorbing air compressor from your
Diesel engine. With a 4 stroke engine such as your Cat 3176 with engine brake, the piston as
it approaches top dead center on the compression stroke, the exhaust valve is opened, exhausting
high pressure air which means no energy is returned to the piston in the expansion stroke.
the loss of energy is called engine retarding, made possible by a compression release brake
under your valve cover. The switch you have on dash has different setting that will allow one,
two or three cylinders to retard your engine speed down a long grade on slowing down. I
have mention this before when engine valves are checked the piston that controls the engine
Brake has to be backed off and reset to a know value after valves are checked. Many times
this not done correctly and engine brake does not seem to provide the braking as being set
Up correct. Dave Atherton Retired Cat Mechanic

[Steve Huber Co-Admin]

Joe,
To add to Dave's explanation, the Jake will only work if you have completely released the accelerator. I'm pretty sure your Jake will also defeat the cruise control so if the Jake is on in either High or Low position, the cruise will be inoperative. If functioning properly you will notice significant braking when in High and more "gentle" braking in Low.
Steve

[Jerry Emert]

My cruise and Jake seem to work together rather well.  I had read on here that the cruise will not function with the Jake on.  I have to have my Jake on for the cruise to function.  When going down a hill the cruise backs off the accelerator and the Jake comes on and the coach downshifts.  Too scary for me to give up control on steep grades but on normal driving it works well.
Jerry

[Joel Weiss]

My cruise and Jake seem to work together rather well.  I had read on here that the cruise will not function with the Jake on.  I have to have my Jake on for the cruise to function.  When going down a hill the cruise backs off the accelerator and the Jake comes on and the coach downshifts.  Too scary for me to give up control on steep grades but on normal driving it works well.
Jerry

I believe there are three distinct modes for the jake's operation relative to the cruise control.  It's my understanding that CAT dealers can change your coach from one to another.  As I understand them they are:

1. The default mode for most (all?) of our coaches is that the cruise won't operate with the jake on.
2. The mode described in the post above allows the cruise to operate with the jake in the "on" position but not engaged; if the actual speed exceeds the set cruise speed by the specified number of miles per hour then the jake will engage.
3. In this mode the jake is "on" but doesn't engage until the brake pedal is depressed.

Joel

[David T. Richelderfer]

I have found the Jake brake will actuate with the cruise control activated and the cruise control remains in the on position with its previously set set-speed as noted on the Aladdin.

If the coach's speed on a downhill run without the accelerator pedal being pressed gets to about 3 mph over the cruise control set-speed, then the "little Jake" actuates for braking.  At about 5 mph over the cruise control set-speed the "big Jake" actuates.  If the coach's speed continues to climb on a steep enough downhill, then I start touching the brakes intermittently to hold the speed down to my liking.  Obviously, the first touch of the brakes will deactivate the cruise control to the off position as noted on the Aladdin, but the set-speed is not lost.

To activate the cruise again, such as at the bottom of the hill, momentarily touch the accelerator pedal to deactivate the Jake, or switch off the Jake brake momentarily, in order to resume the cruise control to its on position at its previously set set-speed.

I leave the Jake brake switch on its "big Jake" setting most of the time.  A couple years ago I had my Jake brake-Allison interaction reprogrammed so that the transmission does NOT downshift when the Jake brake is activated.

[Joe Magie]

Just wanted to say thanks to all of you that responded to my question about my jake brake problem.  It sounds like I was trying to use it properly.  I took my coach to a diesel shop and hopefully they will  get it adjusted properly.  It would be nice to have it working as it should.

[Edward Buker]

Joe,

It sounds like your Jake brake is not working for some reason and hopefully that will get resolved. I think by your question you are not overly familiar with a Jake brake. Due to the fact that it uses engine compression it is far more effective at higher rpm then at low rpm so you attempt to be in the right gear and at higher rpm levels (but not over your engine rated rpm) to gain the most braking. Most of the time you can just let the transmission do its thing, but there are times when you will want to manually shift. If you can get a little driving lesson from a current owner in its use that would go a long way to getting comfortable with its operation.

One sure telltale that a Jake Brake is operating is the resultant increase in exhaust noise (very loud if unmuffled) and the tone change in the exhaust.

Later Ed

[Dale Wiest]

On my 94 Marquis, if the cruise switch is turned on, but not set, the jake brake will only activate if I step on the brakes. If the cruise switch is not turned on, the jake  will activate normally.

I don't know how it works with cruise engaged going down hills as I have not tried it yet. I like to be in control on hills, not at the mercy of the computer.

[Dave Atherton]

Gentleman, while on the subject Jake brake or compression brake. The engine brake
needs correct adjustment on Pistons operates valves when brake is in operation and
electric connections. I mention this in above post, being out of adjustment, many times
was located in electrical connections. Word of advise about compression brakes,  be very
careful in applying max power in selection or position of switch. Depending on nature
stopping force needed, the torque can very easy twist the short driveshaft and or shear off
bearing caps on u-joints. Dave Atherton Retired Cat Mechanic

[Bill Borden]

Dave,

Questions regarding my C12, I always try to monitor the RPMs so the High Speed Jake will not cause any over spinning.  With HS Jake engaged I try to not allow over 21-2200 RPM, per the dash tach. Is this correct or should I look to a lower RPM level.

Also the Jake adjustment, when should this be checked.  Is there a Recommended service period.

Is there any other service that would accompany the Jake being checked?

Thanks for your advise,

 

[Dave Atherton]

Hi Bill, answer to Compression Brake, most effective maximum compression brake performance is
obtained at speeds 1800 rpms to 2000 rpms. Below 1700 rpms will reduce retarding power a real
lot. Note: the engine ECM will deactivate the compression brake ( Jake Brake ) when engine rpms
falls below 1000 rpm. The operation of Jake Brake with cruise control will depend on engine and
options that are provided by Caterpillar. The ECM will activate Jake Brake when motorhome exceeds
the set speed of the cruise control. The Jake Brake will operate until motorhome has slowed to
one-half mph above set speed of cruise. Switch modes, flat, dry road. Switch ( low ) while driving
On flat, open road with light load. Switch ( high ) for following conditions, Carrying heavy load,
Descending grade. Low setting on switch will activate two cylinders which will provide 1/3 of
Braking H.P.  Med. setting will activate four cylinders which will provide 2/3 of braking horsepower.
High switch setting will activate all cylinders of which will provide max braking power.  Jake Brake
will not affect operation of ABS system, the ECM will deactivate the Jake Brake when ABS senses
wheel slippage or loss of traction. When driving on wet or icy conditions leave Jake Brake in OFF
position. Compression Brake service ( 15,000 and 60,000 miles ) and when you check engine valve lash 150,000 miles etc. Note: anytime you remove engine valve cover the Pistons for Compression
brake and assembly are right on top of valves. Dave Atherton Retired Cat Mechanic

[Edward Buker]

Dave,

Lots of good info in your post. Just so there is no confusion for a new person to a Jake brake system. Dave is pointing out an option where you have three Jake brake positions on a coach control switch activating 2, 4, or all 6 cylinders in Jake compression mode, many Country Coach with the same engines used that feature option. The Beaver switch system had off, lo (3 cylinders) and hi (6 cylinders).

Later Ed

[Bill Borden]

Thanks Dave,

As Ed states you have provided allot of info, it will be helpful for decisions in the future. Thanks again.

In regards to the overspin question, don't we need to watch the RPM when running with High Speed selection? Or did I miss your answer, sorry for the repeat.

Since Beaver set our Jake up to disable the cruise control during operation, how many have had your coach reprogrammed to work in conjunction with the cruise control?

Now I am sorry that I wasn't aware of service adjustment to the Jake to be completed while performing the valve lash adjustment. It was serviced at 40 K. About 10 K ago.  The Cat dealer did not mention the Jake service at the time.

Is the Jake service normally at the same time as the Valve lash?

[Dave Atherton]

Bill, that ok to ask as many question you would like.     First going into the wheel spinning
or loss of traction, what is being explained the ECM will deactivate the compression brake
so ABS system can do its job. I also mention wet slick roads or icy condition leave the compression
brake in the off position. ( for safety ). Checking compression brake for correct adjustment any time
engine valve cover is removed. You mention you had your valve checked or adjusted about
10,000 miles ago. ( at that time you engine compression brake was reset. ) in order to get at
the valve train the compression brake assembly is removed and reinstalled when valve adjustment
is complete. At this point the compression brake pistons were reset to correct value. I have
been holding back on members setting there own valve train and the compression brake. It is
great doing our own work but it is more involved and if not adjusted to correct spec. Damage
can happen to your engine. Dave Atherton Retired Cat Mechanic