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Need Help with Pacbrake

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Gerald Farris:
Jerry,
The term "Jake Brake" is used for the compression brake on a diesel engine that was developed by the Jacobs Company. The only maintenance that is involved with a "Jake Brake" is the periodic adjustment that is done as part of the valve adjustment. The majority of Beaver coaches will only need the one valve adjustment that is preformed early in its life, usually in the 20,000 to 40,000 mile range.

Gerald

Edward Buker:
Jerry,

You won the lottery on engine braking systems when you bought a coach with a Jake Brake. They are a trouble free internal system that basically converts your engine into either a 3 cylinder compressor on low and a 6 cylinder compressor on high. The amount of braking that you get is related to the RPM range the motor is in and generally the range of 1700 to 2100 RPM is desired for braking horsepower. Some understanding of using the right gear for the grade situation is in order. Some grades may require the use of 3rd or 4th gear and slower speed while others may work well in 5th gear. That part will be a learning experience. How it works which was the question, I grabbed this from an earlier post...

Just to add a little more info to Gerald's post about Jake Brakes given it is a bit hard to understand (at least for me) as to how opening an extra exhaust valve momentarily at the top of a compression stroke slows a vehicle down.

 The compression stroke is consuming energy and therefor is providing braking HP. The problem is that if you do not release the compressed air at the top of the piston stroke, it then expands on the downstroke and gives back the compression energy, basically nullifying the energy being absorbed on the upstroke.

 So it is all about changing the pressure of the downstroke that provides the benefit here....it is a great system and does not rely on increasing any compressive forces on the head and pistons and therefor does not negatively affect the long term durability of the engine. We call it a compression brake but it really does not increase compression at all. Just in case anyone else had been scratching their head on that one....

There is one issue with this system that has generated a lot of debate that you should be aware of. Many of the coaches with the C12 and Allison 4000 transmission were programmed by Beaver to go to 4th gear when the Jake is selected. Many of us have had a hard downshift situation and engine RPMs above 2300RPM. The max RPM recommended by Cat is 2100RPM so there is a bit of a personal dilemma here of knowing which gear your coach is programmed to use with the Jake on, what speed would equate to 2100RPM, and personally managing the Jake engagement point. The engine will tolerate a higher RPM then the 2100RPM but it is not recommended and frankly there is no reason to go there. Many of us have had a simple Allison reprogramming done from 4th to 5th gear for Jake use which has allowed a higher highway speed safe engagement point RPM wise. Yours may have already had that change. You can manually select 4th gear if the RPM vs braking vs speed warrants it. Some tend to drive slower and have remained with the 4th gear selection.

This note is not intended to open any debate just to make you aware that there is learning to do here on the Jake subject. Knowing how your Jake system on your personal coach is programmed and how it works is an important aspect of safe driving for these coaches.

Later Ed

Jerry Emert:
yálls knowledge of these complicated beasts never ceases to amaze me and my thanks to you all!  How do you tell what gear the tranny is in?  Mine always says "6"on it.  

Edward Buker:
On the Silverleaf, if you have one, on the drive page upper right numbers will tell you the gear you are in. You can watch the shifts being done by the Allison. You can use the tranny up down arrow to select a gear and the tranny readout pad will follow also. Other systems beside Silverleafs were used but I am not sure of the models and years and if they also had the capability to indicat the gear you are in.

Later Ed

Keith Moffett Co-Admin:
Jerry
I had upgraded the old coach from 'Intellidrive' to a entry level 'Silverleaf'.  I cant imaging that your Thunder didnt come with at least that.  If you dont have one or if you do but like me are just learning how to use it, go to www.silverleafelectronics .  They are in Albany Or. and can set you up or just help you get up to speed.  
I am a fairly cautious driver and still was able to improve mileage significantly.  It also gives you real time transmission sifting, temp. and engine updates.

Just FYI
Keith

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