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Author Topic: what is a buffer switch on a jake brake?  (Read 1617 times)
kbunnystarr
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« on: February 15, 2007, 03:32:45 PM »

i have read there should be a high and low on the JAKE brake switch, i have just on and off, is that ok too?
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DrivingMissLazy
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« Reply #1 on: February 15, 2007, 04:56:03 PM »

Kristine, the buffer switch is mounted in the rear off the mechanism that controls the throttle opening. When you let off the throttle, the buffer switch contacts close and let the Jakes operate thru the control switch that you have up front.
If you have the throttle open, even just a little bit, the Jakes will not work. You do not want to be accelerating and braking at the same time.

Most Jakes are set up with a high. low, and off. It is very nice when descending long grades and full on is too much braking and all the way off is not enough.

It would be very easy to convert yours to hi-low- and off. Next time you are in WV I will be glad to do if for free.
Richard

i have read there should be a high and low on the JAKE brake switch, i have just on and off, is that ok too?
« Last Edit: February 15, 2007, 05:18:18 PM by DrivingMissLazy » Logged

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« Reply #2 on: February 15, 2007, 10:44:13 PM »

One point about the buffer switch that makes it so expensive is that it works off the governor, rather than directly off the pedal.  It closes the switch only when the engine is in a no fuel position.  So going down a hill with the Jakes on with your gas pedal on the floor, if you get to the top of the governor speed setting and the governor closes off the fuel, the Jakes will activate even with your gas pedal mashed on the floor.  Good Luck, TomC
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DrivingMissLazy
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« Reply #3 on: February 16, 2007, 08:22:09 AM »

Tom, you have really confused me. Not that it is too hard to do, but I have read your post several times and I really can not understand what you are saying.
First, I can not understand why you would be gong down a hill with Jakes on and full throttle. If you want to increase speed it would seem that you would simply turn the Jakes off.
It seems like it would be kinda foolish to leave the Jake switch on all the time while traveling thru rolling country. It would seem to be a sure method of reducing your MPG.
Perhaps I am missing something and you can enlighten me.

The buffer switch is a standard off the shelf switch made by MicroSwitch. I do not understand why it would be expensive. I never replaced one, but it could be ordered from any electronic supply house.
Richard

One point about the buffer switch that makes it so expensive is that it works off the governor, rather than directly off the pedal.  It closes the switch only when the engine is in a no fuel position.  So going down a hill with the Jakes on with your gas pedal on the floor, if you get to the top of the governor speed setting and the governor closes off the fuel, the Jakes will activate even with your gas pedal mashed on the floor.  Good Luck, TomC
« Last Edit: February 16, 2007, 08:25:31 AM by DrivingMissLazy » Logged

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« Reply #4 on: February 16, 2007, 08:38:45 AM »

DML- the point I'm making is that the buffer switch is not just a throttle pedal operated on/off switch.  Rather an on/off switch that is operated by the governor.
The going down a hill example was just demonstrating one of the ways the switch operates.
So going down a hill with the Jakes on, if you have your foot on the floor, when the engine reaches governed speed and continues to increase in rpm, when the engine speed gets high enough where the governor shuts down the injector rack, the buffer switch will be closed and activate the Jakes-even though you still have your gas pedal floored.
I know when going through rolling hills, I leave my jake on.
Bottom line, the buffer switch is activated when the governor goes to no fuel position, whether it be at the top rpm caused by the bus overpowering the engine into overspeed, or of course when just coasting.  This is why the Jake doesn't kill the engine when it comes down to idle.  When the governor gets down to idle, it opens the buffer switch since it is going from no fuel to idle.  Just showing an example of how it works.  Good Luck, TomC
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DrivingMissLazy
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« Reply #5 on: February 16, 2007, 10:00:09 AM »

Tom, that is just backward from everything I have read or experienced.

In adjusting the Jake buffer switch, it is adjusted so that it closes about 25 rpm above idle. I feel this is correct since I have adjusted mine a couple of times and watched other mechanics do the same. It is a fairly critical adjustment and may take several times to get it right. The engine should be up to operating temperature when this adjustment is made

Quote
This is why the Jake doesn't kill the engine when it comes down to idle
The Jake quits operating well before the engine comes down to idle and it has nothing to do with the buffer switch. The Jakes quit working at about 1000 rpm as the oil pressure drops to the point that it can not hold the exhaust valves open. At least that is the way it operated on my 8V92. The dropout point will vary from engine to engine depending on the condition of the engine.


Quote
DML- the point I'm making is that the buffer switch is not just a throttle pedal operated on/off switch.  Rather an on/off switch that is operated by the governor.
[/b]
The buffer switch is operated by the rack coming back to fully closed position.

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I know when going through rolling hills, I leave my Jake on.
To me, this would be the same as putting on the brakes every time you start down a grade whether you need them or not. I would think this would adversely affect your fuel mileage.

Richard

« Last Edit: February 16, 2007, 10:02:25 AM by DrivingMissLazy » Logged

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« Reply #6 on: February 16, 2007, 11:41:36 AM »

Does the Buffer switch also control your High idle RPM?
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DrivingMissLazy
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« Reply #7 on: February 16, 2007, 11:46:03 AM »

I believe so. I think there are actually two microswitches, one for high idle and one for Jakes on the same assembly, but I can not find my Jake manual and I have forgotten. Hopefully Tom or one of the others will know the full answer.
Ricahrd

Does the Buffer switch also control your High idle RPM?
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« Reply #8 on: February 16, 2007, 07:26:51 PM »

Richard, it is the original equipment buffer screw that you adjusted to a 25 RPM increase in the idle speed.

If you have a high idle function with the original equipment, a small air solenoid is mounted in it's place, and adjusted in a similar manner.

If you install Jakes, and have the benefit of the governor control of the Jakes, the high idle solenoid is replaced with a buffer switch.

If you want to save the high idle function, it requires a special switch that allows the use of an air solenoid with it. I don't recall if the solenoid was built in or the switch allowed use of the original air solenoid.

At least, this is what I found when we had our Jakes' wiring upgraded at Southern Oregon Diesel a couple of years ago.

This means that the buffer screw position on the governor is serving three purposes; it still serves as a buffer, it provides the on-off switch to the Jakes and it provides for high idle.

I hope this helps.

Tom Caffrey
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lloyd
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« Reply #9 on: February 16, 2007, 09:47:24 PM »

A two stroke diesel has a buffer screw that is adjusted to remove the hunting at idle. A jake micro switch is used to control the jake operation. The micro switch is opened closed by a rod (which goes through the center of the buffer srcew) that is controled by the governor, so when the throttle is opened up the micro switch is opened and the jakes are off. When the throttle is released the governor goes to a no fuel postion and the micro switch closes and the jakes come on, until the engine speed slows down to the point where the governor decides to give the engine more fuel to keep the engine from stalling. Of course this all happens with the dash switch for the jakes turned on.
Lloyd
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TomC
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« Reply #10 on: February 16, 2007, 10:22:41 PM »

That's what I was saying, but Lloyd said it in a simpler way.  When you say an open switch, that means it is off.  A closed switch means it is connected.
On most 2 strokes you'll loose oil pressure when coming down in rpm to the point where the Jakes stop working-like at 1000rpm-well before it hits the buffer switch adjustment.
Once again-the buffer switch is mounted to the governor and gets its control from the governor.  The injector racks are also attached to the governor.  Without the governor, you'll have a wildly crazy engine to contend with.
Being on the west coast like I am, my definition of rolling hills is probably different than those of you east of I-25.  Rolling hills, I mean where going down hill the bus gains more speed than you want, hence using the Jakes to control excessive speed gain.
I've had both 8V-92 and 8V-71 both with Jakes with the buffer switch control, and both act the same.  When the engine goes into no fuel position, the buffer switch closes completing the circuit allowing the Jakes to activate.  This can happen anywhere between idle and high end governor limit.  If the engine rpm exceeds the top rpm limit the governor pulls back the rack to no fuel position, no matter where the gas pedal is at-including mashed on the floor.  No fuel, buffer switch closes, Jakes can activate.  Good Luck, TomC
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DrivingMissLazy
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« Reply #11 on: February 17, 2007, 06:52:57 AM »

OK. Thanks for the explaination Tom and Lloyd. I guess our terminology is somewhat different, but we are saying the same thing.
Regarding leaving the Jake switch on, I think it is just a matter of preference. I run all the western routes for tens of thousands of miles, but generally left the Jakes off unless I actually needed them. I suspect that if driving a heavy loaded 18 wheeler I would have done the same as you as the speed would have increased so fast.

That's what I was saying, but Lloyd said it in a simpler way.  When you say an open switch, that means it is off.  A closed switch means it is connected.
On most 2 strokes you'll loose oil pressure when coming down in rpm to the point where the Jakes stop working-like at 1000rpm-well before it hits the buffer switch adjustment.
Once again-the buffer switch is mounted to the governor and gets its control from the governor.  The injector racks are also attached to the governor.  Without the governor, you'll have a wildly crazy engine to contend with.
Being on the west coast like I am, my definition of rolling hills is probably different than those of you east of I-25.  Rolling hills, I mean where going down hill the bus gains more speed than you want, hence using the Jakes to control excessive speed gain.
I've had both 8V-92 and 8V-71 both with Jakes with the buffer switch control, and both act the same.  When the engine goes into no fuel position, the buffer switch closes completing the circuit allowing the Jakes to activate.  This can happen anywhere between idle and high end governor limit.  If the engine rpm exceeds the top rpm limit the governor pulls back the rack to no fuel position, no matter where the gas pedal is at-including mashed on the floor.  No fuel, buffer switch closes, Jakes can activate.  Good Luck, TomC
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