phone :
9 am to 5 pm
eastern time
We are an authorized Jake Brake dealer with over 20 years of experience. We sell and install brakes to fit
71 & 92 Series engines.
NEW! We now offer a Jake Brake monitor/analyzer for your dash.
Now you can know if your Jake Brake is working correctly.
This is how our Jake Brake analyzer /
monitor is wired.
If the brake is on low only one light will be lit.
If it is on high both lights will be lit.
When any one solenoid fails the light won't light.
If there is a broken wire under the valve cover or anywhere else the
light won't light.
If there is bad connection the light won't light.
All of these problems can visually be detected, so even if you can't HEAR the difference, you can always SEE when the
brake isn't operating properly.
read HOW a Jake Brake
Simply stated, energizing the brake converts a diesel engine into an energy absorbing air compressor. This is done by opening
exhaust valves near the top of the compression stroke, releasing the compressed charge into the exhaust. The energy used to
compress the charge without a firing cycle acts as the brake.
Referring to the schematic drawing, exhaust blowdown occurs as follows:
1. The energized solenoid valve permits engine lube oil to flow under pressure through the control valve to both the master
piston and the slave piston.
2. Oil pressure causes the master piston to move down, coming to rest on the injector arm clevis.
3. The injector rocker arm clevis begins upward travel (as in normal injection cycle) forcing the master piston upward and
directing high pressure oil to the slave piston. The ball check valve imprisons high pressure oil in the master-slave piston system.
4. High pressure oil causes the slave piston to move down, momentarily opening the exhaust valves, while the engine piston is
near top dead center position, releasing compressed cylinder air to the exhaust manifold.
5. Compressed air escapes to atmosphere completing a compression braking cycle.
We rebuild Jake Brakes and test them on our own design test stand. Here we can control the oil pressure and adjust the brake
to suit your engine and it's oil pressure
Read a discussion of how a Jake Brakes work and how to check and fix them
It is our observation that 90 % of the Jake Brakes on coaches don't work to their fullest potential.
Our experience shows us that the main problems are electrical.
Low oil pressure to the rocker arms on 2 cycle Detroit Diesels is also a common cause of trouble.
Next week we will begin to explain what this means.
We better start by talking about the electrical circuit of a typical Jake Brake installation. There are 2 typical ways of having
the electrical circuit look.
The early installations had only 1 wire, positive, through 3 switches & series.
The later installation was wired with a low performance and a high performance option.
Typically the power for the Jake Brake is taken from the power panel at the front of the coach. It is wired from the panel,
through a circuit breaker, to the driver's control switch. From there it is wired to the clutch switch (unless the coach is
equipped with automatic trans.). Next, the wiring goes to the buffer switch located at the side of the governor at the engine.
Finally, the wiring goes to the Jake Brake solenoids on the heads.
The power is picked up from the front panel, then goes through a circuit breaker to the clutch switch (unless automatic).
Next the wiring goes to the rear of the coach to the buffer switch. From there it goes back to the front to the driver's control
switch. After that the wiring has two wires going back again to the rear (one for each half of the Jake Brake system).
On the first version 1 wire runs the length of the coach. On the second version, there are 4 wires running the length of the
coach to support the partial braking option. We feel that this is a source of 4 times the potential problems with almost no
benefit. The driver can and usually does control his Jake Brake with the control switch whenever he or she feels it is
Next week we will explain how to fix the most common problems we
have experienced.
So please keep checking back
With the early version: If your Jake Brake doesn't work, you should first check for power from the front panel through the
circuit breaker or fuse to your control switch. If you have power there, turn on the switch. You should now have power at
the clutch switch (if used) and to the buffer switch. You can check all this with either a test light or a volt meter. If you have
power at the buffer switch, you have eliminated all the wiring in the coach except for the engine compartment. Next, make
sure that the buffer switch is in the no-run position. You should now have power to the solenoids under the valve covers.
With the 4 wire version: If your Jake Brake doesn't work, you should first check for power from the front panel through the
circuit breaker or fuse to the clutch switch (if used) and to the buffer switch. If you have power there, you must make sure
that the buffer switch is in the closed position. Now you can check to see if you have power to the driver's control switch. If
you do have power, turn the switch to high. You should now have power to the Jake Brake solenoids on both banks of the
engine. Once again, this can all be checked with either a test light or a volt meter.
You have now reached the place where most problems occur. There are two types of electrical problems under the valve
covers. First you could have a shorted wire caused by worn insulation which will blow the fuse or constantly pop the circuit
breaker. This leaves you with a Jake Brake that is not working at all. The second possibility is an open circuit caused by a
broken or loose wire. This will cause one or more cylinders to stop working while still giving you some brake. These
problems are caused by the heat and vibration of the engine. The solution is to replace all the under the valve cover wiring
with newer style wire. These wires have more and finer strands to flex better and silcone type insulation that resists heat and
doesn't harden and crack.
Because of the location of the engine, engine noise may be muffled by the interior of the coach, making it difficult to
hear the Jake Brake working.
We have a solution to this problem. We designed an electronic unit that lets you visually see that the Jake Brake soleniods are
properly working. Therefore, it is also a diagnostic tool as well as a visual indicator whenever the Jake Brake is engaged.
Now that we are done with the electrical part we want to get involved in the hydraulic part of the Jake Brake. The Jake Brake
is supplied with oil that comes to the rocker arms of the engine. The oil pressure and oil flow, therefore, are important to
having satisfactory Jake Brake operation. The oil enters into the Jake Brake housings through solenoid valves, flows through a
control valve and is trapped in the Jake Brake housing between two pistons. With the piston extended and making contact
with the injector rocker, it has no choice but to push against the valve bridge to open the valves slightly to exhaust
compressed air out of the cylinders, thereby making a giant air compressor out of your engine and absorbing energy.
Next we will talk about the most common hydraulic problems and how to fix them.
Since the oil flow and oil pressure to the rocker arms on the 2 cycle Detroit is low to begin with, it is very important that we
don't have any oil leakage to the Jake Brake housing for proper operation.
A common problem is oil seeping past the seals at the crossover tubes from one housing to another. Also, due to vibration, the
crossover tubes sometimes crack or break. So if there is any doubt that the Jake Brake is functioning properly, remove the
valve covers, start the engine, manually press the solenoids and visually inspect for oil leaks.
If you have no oil leakage and still have poor Jake Brake performance, the problem may be low oil pressure to the rocker
arms. In that case we can rebuild your Jake Brake with special control valve springs, new style control valves and new style
rocker arm pedestals that allow you to adjust the Jake Brake to new tighted settings. The other choice is to rebuild your engine
and thereby increase oil pressure to original specifications.
This concludes our discussion of "the Jake Brake". We hope that you found it informative.
We also install the direct mount Driveline Brake on Prevost Le Mirage and the DL-model MCI coaches.
call: BERNARD BUS PARTS & SERVICE. We ARE your one stop repair shop. CALL BERNIE in Quakertown, Pa.