Teach me about Jake Brakes

[Paladin]

Ok you Jake guru's, I understand the principal of Jakes but what I don't understand is the real mechanics of them.
I heard from a friend of mine that he may be able to locate some use Jakes for me. I'm assuming that there is nothing really wrong with used but what I'm wondering is how many parts are there to a kit for a 71 series excluding the switches? What parts might need to be scrutinized for damage or wear or are frequently missing when you buy a used kit? Are there different stages or kits?
I'm sort of guessing that I might not want to try an install myself or am I wrong? What's involved? What adjustments are required?
Does anyone have a ballpark estimate on what a used Jake goes for?


Mucho thanks,

-Dave

[Utahclaimjumper]

Dave I installed mine before I knew better, requires removal of racks, valve bridges, and retorqueing of same, adjusting the racks and resetting the valve adjustments and injector adjustments.  you will also need higher valve covers and a bump out in the tailgate. Not for the mechanicly challenged.>>>Dan

[HB of CJ]

He he he.....we, (I) were just talking about Jakes, soosss, here gooosss.  A Jake brakes works, (or soosss I was told) by slightly lifting the exhaust valve(s) during the compression stroke.  This creates work by compressing the air and heating it.  About 70% of the heat stays in the cooling system, about 30% goes out the exhaust pipe along with a boss sound.

This slows down the pistons and eventually the coach.   The valves are controlled/powered by the oil pressure inside the mill.  A single stage works all cylinders at once, a multi-stage works either 2, 4, 6 or 8 pistons, or a combination of whatever number you have.  A dash or stalk mounted electrical switch controls what happens.

Plenty of used Jake assemblies available for the older stuff which we run.  You can either buy used and piece it together or buy a complete new, rebuilt or used assembly with everything you will need including the very neat necessary genuine "Jake Brake" switch identity tag surrounding the Jake Brake switch.  Does a Jake work?

Yeah.  In a light weight coach application, very well in fact.   Sossss good in fact that going down gentle hills when icy, Jakes are NOT a good idea.  May lock up the drivers.  Going down steep hills at speed keeps you OFF the service brakes, which is also a good idea.  A Jake can absorb a greater percent of the rated mill's horsepower.  $Cost$ anywhere from $100 to $2000 per cylinder. 

[Nick Badame Refrig/ACC]

It's simple

buah buah buah buah buah buah buah buah

See...

Nick-

[Barn Owl]

Yeah.  In a light weight coach application, very well in fact.

In my lightweight 4106 I need to modify mine to a two stage (easy to do, just the time involved). I'm tired of hitting my head on the windshield every time they activate.

All joking aside, mine can be annoying because it works so well. I added a momentary foot switch so I can use them like a brake and it saves me from hunting for the toggle switch; works great.

[akroyaleagle]

Dax, I wouldn't recommend trying to install your own unless you are capable of running the rack.

Used Jakes are fine. You can go to jacobsbrake.com and see all the parts and information you seek I believe.

Personally I would have them installed by a 2 stroke mechanic. There are many on this board. I would have them rebuilt with new solenoids and fuel crossovers. I know that will raise hackles among the "cheap as I can" crowd but you do not want to get them installed and find you have a crossover leak. Crossovers are cheap. I bought a new set for $8 each on Ebay just to have a spare set. There are O rings on the crossovers that have to be rolled in right or you will pump fuel into the oil.

The installation cost will be minimal if you have it done because it is just a little more work when a tuneup is done and you get a retuned bus.

I bought new Jakes for my eagle. They are pretty spendy.

I sold a set of used jakes that came with my 92 for $750 and threw away the crossovers because I did not want the buyer to come back and claim that I ruined his engine by selling him a bad jake.

On my 71 and the 92 the jakes are set to 55 clearance. Detroit recommends 65 and most routinely set them to 60. Mine work great on the Eagle with the 740 Allison. My rig is over 50,000# with the trailer and cars. I can leave the Interstate at 70mph and will have to let up on the jake before the stop sign. Saves a lot on brake shoes too.

[DrivingMissLazy]

Joe, I also ran my valves at.055 and the improvement from the .059 or .063 recommended by Jake was truly significant.
The one thing I can not remember is was this setting for hot or cold?

Richard

[belfert]

Yeah.  In a light weight coach application, very well in fact.

In my lightweight 4106 I need to modify mine to a two stage (easy to do, just the time involved). I'm tired of hitting my head on the windshield every time they activate.

I could only wish mine worked that well.  I have a Series 60 and have had the Jaeks tuned up at a Detroit dealer.

The Jakes certainly do help, but it doesn't seem like they do all that much.  They probably are working 100% since I have nothing to compare against.  Some of the grades on I80 through Utah I still had to use the service brakes occasionally even with the Jake on high.  I guess it was better than some of the trucks where we could smell their brakes burning up.

I know some of the folks here with Jakes have said they can't always run them on high on some fairly steep grades as they slow down too much.

[DrivingMissLazy]

Brian,

I think you need to find another mechanic. I have traveled every E/W interstate several times, including I-80 thru Utah and I do not think there are any grades where I ever had to use the service brakes. This was with a 40,000 pound coach and always with a 4X4 Toyota pickup. If they (the Jakes) are working properly, you will know it!
Richard

[Barn Owl]

One of the reasons mine work as well as they do is because my bus weighs #24,500 dry.

[Paladin]

So how many parts are there that make up a complete Jake kit excluding maybe the valve covers? If you were to buy a used Jake from someone how would you know if it was all there and working?


-Dave

[HB of CJ]

Yeah again, a wel-tuned, set up Jake does work very well in a Coach.  Another subjective answer; back in 1970 or sossss, (are we that old?) my assigned 1963 Crown school bus weighing about 30000# loaded could come down the Ridge Route (North bound) at about 40 mph at about 2000 rpm in 4th gear without touching the service brakes.  That's a 6% grade with 50 kids.  The Jake was absorbing more power than the 743 inch 220 Cummins could put out.  Pretty inpressive. 

[JackConrad]

Parts include the actual Jake Brake (usually 1/2 are "masters" & 1/2 are "slaves"), same Jake fits both 71 & 92 series engines. Bridges (71 & 92 series are different), different fuel pipes  (aka "jumper lines"), longer bolts (to attach Jake Brakes & taller valve covers), and buffer switch. You will also need the Jack Brake wires that have the fittings that screw into the cylinder head to get the wire from outside the engine to the Jake Brakes.  Jack

[buswarrior]

As a Jacobs Engine Brake does its job via using engine compression, it works better at higher RPM.

If the engine is loafing in the lower part of the RPM range, you won't get as effective retardation.

Try selecting a lower gear, get the revs up higher and then try the Jake.

You may be pleasantly surprised!

happy coaching!
buswarrior

[TomC]

Jake brakes, in my opinion, are a necessity.  On any of the 2 stroke engines, they can be adjusted to hold back your bus on a 6% grade, if not, they are not adjust correctly.  When I had my truck with the 8V-92TA, I was going up and down the Grapevine (6% grade for 5 miles) everyday, and could go down the grade with 80,000lb and only tickle the trailer brakes 3 or 4 times-getting to the bottom with essentially cold brakes on the tractor.  On any of the 4 stroke engines, they should work very well, especially on the Series 60-they have extremely good Jakes-if not, find someone who knows how to adjust the Jakes.

Now as to how the Jakes work.  The Jakes are a hydraulically powered (engine oil pressure) device that mounts over the valve train.  When activated, a solenoid opens and allows pressurized engine oil into a chamber that pushes a rod down to the top of the injector rocker arm.  When the injector rocker bumps up it pushes the Jake rod up which creates the hydraulic pressure that at the same time pushes the exhaust valve open.  Since this happens at the top of the compression stroke, all the pressure from the compression stroke is released causing the rapping sound in the exhaust.  On a normal deceleration cycle on the engine, the compression stroke causes the engine to work to compress the air, but also on the down stroke of the piston, causes the engine to pickup speed again with the compressed air, so that's why a Diesel has very little compression braking on its' own.  When the Jake is activated, the engine is working to compress the air, but when the air is released at the top of the compression stroke, all that work goes out the tail pipe (causing the noise) and then the engine has to work again to pull the piston back down again under a vacuum.  This is why you get some smoke on the initial activation of the Jake because it is pulling under vacuum any residual oil that is normally being held back by air pressure-like in the air box.  Hope this helps.  Good Luck, TomC