| Author | Message | ||
| Tom Dessert (Mci5er)
Registered Member Username: Mci5er Post Number: 109 Registered: 12-2005 Posted From: 96.39.162.176 Rating: N/A |
Can someone explain the mechanics of a jake brake on a 8v71. Master switch applies 24 VDC power to the dash mounted toggle, once closed what happens next ????? Thanks Tom | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 1187 Registered: 12-2000 Posted From: 74.4.55.77  Rating: |
The power from the dash switch goes through a buffer switch on the governor to prevnt Jakes from working unless fuel setting is at idle position. If fuel is at idle, buffer switch allows power to go to the electric solenoids on the actual Jake brake. The solenoid opens which allows engine oil to flow into Jake and the oil pressure opens the exhaust valves at the top of the compression stroke,releasing the compression. This basically turns the engine into an air compressor making it use power instead of creating power, thus causing the vehicle to slow down. The lower the grear the vehicle is in the stronger the braking effect. Jack | ||
| Tom Christman (Tchristman)
Registered Member Username: Tchristman Post Number: 163 Registered: 1-2006 Posted From: 66.218.33.156 Rating: N/A |
To expand a bit on Jack's explanation-yes the solenoids in the Jake units on top of the valve train allows the pressurized oil from the engine to enter the Jake unit, which then lowers a piston to the injector, so when the injector hits (remember the injectors are in no fuel position), it pushes up against the hydraulic cylinder with engine oil in it, which flows over to the exhaust valve hydraulic cylinder pushing down on the exhaust valves to open the exhaust valves at the same time the injector is going to fire-which is at the highest compression ratio-hence that sudden release of compressed air (and the extra exhaust noise), is also a release of energy creating the engine drag for braking. Good Luck, TomC | ||
| Tom Dessert (Mci5er)
Registered Member Username: Mci5er Post Number: 110 Registered: 12-2005 Posted From: 96.39.162.176  Rating: N/A |
Thanks Guys .... a friend just got his first bus and the jakes arent't working. So your explanations helped me understand how they work and given me some idea were to start looking for his problem. Tom | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 941 Registered: 8-2006 Posted From: 99.62.10.149 Rating: N/A |
Jack has my vote from before, and a little clarification will help. As stated, power is fed from the master through the dash on-off switch, and maybe then through a clutch switch, or an auto trans switch, then through a micro-switch, (called a buffer switch) which "feels" the position of the fuel RACK, (not the throttle.) The fuel rack must be in the no fuel position, which only occurs during shutdown, OR WHEN THE ENGINE IS BEING TURNED BY THE DRIVELINE FASTER THAN THE THROTTLE POSITION. The Jake solenoids feel the injection lobe on the cam, and when they are electrically energized, allow oil pressure to pull the rocker down, which opens the exhaust valve(s) at the top of the compression stroke. Some previous owners have added switches to throttle pedals, etc... Jake brakes CANNOT operate under power or idle, period, or the engine will die. Probably the failure to operate is due to a blown fuse caused by a short somewhere, or a loose connection, or the buffer switch out of adjustment. At idle, use a meter or a test light on the buffer switch to see if there is power on ONE side of it. (In the vee, below the gov. with two wires on it, one goes into the valve covers, the other goes to the rear junction box.) Power present on one terminal at idle means the buffer is out of adjustment, no power means no power from the front, due to electrical problems, or the clutch switch. An auto trans will have to be in forward to send power to the buffer. HTH, whew, G | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 815 Registered: 8-2006 Posted From: 74.32.95.26 Rating: |
Good advice is to download a manual from Jake it's free. Take extra care when adjusting the buffer switch always do it with engine idling never set it above 25 rpm above the idle speed if you screw the switch in to deep it can cost a engine. Do you know what switch he has they have 3 different ones,and they can be wired dozens of different ways. The first thing to do is make sure the holding cylinder and arm is working on the throttle before trying to make any adjustments to the mirco switch if he has the fast idle mirco switch (Message edited by luvrbus on December 26, 2009) (Message edited by luvrbus on December 26, 2009) | ||
| Bruce Henderson (Oonrahnjay)
Registered Member Username: Oonrahnjay Post Number: 514 Registered: 8-2004 Posted From: 69.143.41.152  Rating: N/A |
George, is the buffer switch normally-closed at idle/open at no-fuel? Or vice-versa? | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 477 Registered: 10-2003 Posted From: 74.244.14.221  Rating: N/A |
Luvrbus is correct....get the buffer adjustment wrong.....and it doesn't take much...you can end up with a runaway. | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 327 Registered: 3-2006 Posted From: 216.198.139.38  Rating: N/A |
Tom Here is the Jake Brake link. http://www.jakebrake.com/support/parts-and-service-literature.php?engine_mfr=3&engine_mode l=28&jacobs_product=26 | ||
| L James Jones Jr (Jamo)
Registered Member Username: Jamo Post Number: 121 Registered: 11-2007 Posted From: 24.59.114.207  Rating: N/A |
Uh oh...you guys are starting to scare me. My bus came with the Jakes, but not working. There is no switching (that I know of) to keep the Jake "off" while you're using the engine for power. We just wired a spring type toggle switch (springs back to its neutral position) & mounted it on the stick. The plan was to hit the toggle when I wanted to Jake. What happens if I hit this toggle when I'm putting the coals to the ol' girl? Maybe it's a good thing that something must not be right under the valve cover as the Jake will not operate. The bus is tucked away in the barn for the winter, so no messing with it until spring for me. | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 328 Registered: 3-2006 Posted From: 216.198.139.38 Rating: |
Jamo Jakes are nothing to be afraid of. They help when stopping and desending a hill. You must have a switch on the dash somewhere to turn it on and off. There is a switch on the throttle housing on the engine to prevent it from coming on when the accelerator isn't at an idle position as well as one on the clutch to turn it off when you depress the clutch. Look for the switches and try to trace the wiring as these buses didn't come equipped with Jakes so the previous owner must have installed one. Bill | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 816 Registered: 8-2006 Posted From: 74.32.95.26 Rating: N/A |
James your unit could be wired with no switch on the dash so many ways for Jakes to be wired yours maybe one that is hot all the time with only the buffer switch controlling it. With the laws in different cities and town now it is best to have a switch on the dash like Bill said. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1766 Registered: 12-2000 Posted From: 76.69.141.64  Rating: |
Reading between the lines, there are so many ways to wire Jakes WRONG... get your Sherlock Holmes hat on and do some sleuthing as to how it might be wired. Assume nothing the previous owner did was correct unless you can prove it right. happy coaching! buswarrior | ||
| L James Jones Jr (Jamo)
Registered Member Username: Jamo Post Number: 122 Registered: 11-2007 Posted From: 24.59.114.207 Rating: N/A |
Ohhhh, I'm not afraid of the Jakes. Drove truck for 15 years and several had Jakes. I like 'em and I'm happy to have Jakes on my 4104. What I am worried about is if I may do damage to the 6-71 with my way of thinking. With the toggle I have (as described in my last post), my Jakes will be always in the "off" mode, until I flip and hold the toggle on my shift stick. I release the toggle, it springs back to neutral, and the Jakes go back to their "default" off setting. Guess what I'm asking is if there's an idiot switch within the works under the valve cover to keep me from trashing the engine if my toggle gets pushed while throttling up. I have no clutch/accelerator/throttle to Jake switches on my bus...that I've found anyway. We just ran the wires from the shift stick toggle straight to the wires at the valve cover. Does that make sense to you guys?? I've been known to do half-assed stuff when necessary. I'm trying to avoid full-big-assed screwups. Thanks.... | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 329 Registered: 3-2006 Posted From: 216.198.139.38 Rating: |
Jamo From what I can remember if you accidently turn them on when accellerating it won't hurt anything but will just cause a cloud of smoke out the tail pipe. You will have no power as you are opening the exhaust valves when you should be creating power and dumping the compression out the pipe. Maybe Don Fairchild could chime in and clear up things. Bill | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 817 Registered: 8-2006 Posted From: 74.32.95.26 Rating: N/A |
James that is the reason for the buffer switch it will disengage the jakes at around 900 rpm that is where I have mine set anyway. | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 1052 Registered: 7-2006 Posted From: 75.209.180.115 Rating: N/A |
Interesting comment about the "puff of smoke", Bill. I note that mine does that quite frequently when Jakes are applied...not on acceleration; seems to be when they have not been used in a while. After a few "switches", it seems to stop. ...Curious. RCB | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 331 Registered: 3-2006 Posted From: 216.198.139.38 Rating: N/A |
Chuck Are you sure you don't have a leaking injector? Oil analyize will tell you. Air box drains blocked so you get a build up of unburned fuel in the engine and when you use the Jake a few times you are clearing it up. Is the throttle switch or buffer screw set at idle? Just some suggestions. Bill | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 942 Registered: 8-2006 Posted From: 99.62.10.149 Rating: N/A |
Jim, 1. No damage will be done if the Jakes come on under power, as Bill says, you will get a lot of smoke, and NO power if the Jakes come on under power. 2. The buffer switch feels the fuel rack, and only allows the Jakes to operate when the governor has the fuel rack in the no-fuel position. 3. Bruce, the buffer switch is open unless the fuel rack is in the no-fuel position. 4. If the buffer is bypassed, and the manual switch is left on, the engine would smoke and die when it gets down to idle speed, if the oil pressure doesn't go too low for the Jake to operate first. So, simple test. Turn the manual switch on at idle. If nothing happens, its properly wired thru the buffer. If it coughs and dies, its hard-wired from the wheel to the valve covers. My personal advice: There is a correct statement above that Jakes are more effective in lower gears. But remember that after the Jakes release the compression pressure, the lower half of the connecting rod bearing has to pull the piston down with no "compression help." So, whatever you do, don't over-rev it! G | ||
| Gary Stacy (Stacytruck)
Registered Member Username: Stacytruck Post Number: 1 Registered: 12-2009 Posted From: 75.170.75.150  Rating: N/A |
I am the friend that Tom (Mci5er) was talking about and today I ended up just hard wiring to get power to the jakes, I have power to the buffer switch, but I couldnt get power through the switch no matter what I did. So to get the jakes working I hard wired for now until I can get either a new buffer switch or find out what my problem is. thanks for all the info and I hope to become a productive member. | ||
| Bruce Henderson (Oonrahnjay)
Registered Member Username: Oonrahnjay Post Number: 516 Registered: 8-2004 Posted From: 70.60.107.113 Rating: N/A |
Thanks for that clarification, George. I wish that there were Jakes available for my engine. On my engine, the "rack" is internal and it is not available. On a DD, can the rack be moved by hand? If so, you should be able to see the action of the switch (engine not running but power on to the buffer) by power on/off on a VOM as you move the rack, right? (Message edited by oonrahnjay on December 28, 2009) | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 336 Registered: 3-2006 Posted From: 216.198.139.38 Rating: N/A |
Gary Welcome to the world of busnuts. Good luck with the Jakes. I'm sure you will figure it out. | ||
| Ralph Peters (Ralph7)
Registered Member Username: Ralph7 Post Number: 92 Registered: 3-2004 Posted From: 75.209.32.212 Rating: N/A |
Gary, The jam nut on the buffer switch has a seal on it to prevent oil leak there. Do not over tighten. The switch is a micro switch, so disconnect both wires and use a light. IF you check the switch while it is installed you need to know if the switch is contacting the rod in the govenor. Remember with engine stopped the govenor is full throtle, not at idle, or shut down. So to check the switch with the engine off, disconnect both wires, power one wire, use a light on the other, push the shut off to off, and hope the govenor contacts the switch. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 818 Registered: 8-2006 Posted From: 74.32.95.26 Rating: N/A |
Gary, the point I was trying to make is set the buffer switch with engine at idle screw it in till the engine is about 25 rpm over idle then back it till you have a normal idle. I have a 8v92 in my shop now that the owner set the jake with a light and meter. A 8v92 is not pretty when they are turning 4000rpm | ||
| clint hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 563 Registered: 1-2009 Posted From: 24.129.234.224  Rating: N/A |
...welcome GS. if you should find any BBS information usefull & you use it or even just pass it on, then you have become a productive member in my books. ~The bottom line to me is about saving these machines, least they become our only redeming technological feat left as reminders to the future that not every thing that we made was planned obsolesence junk motivated by cheat & gain in a society of disfunctional genuis. But hey I am just a bus nut, so what do I imagine anyhow? | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 944 Registered: 8-2006 Posted From: 99.62.10.149 Rating: N/A |
Bruce, You are exactly correct! So is Ralph in his instructions above. With a dead engine, the governor "sees" idle throttle, and RPM of less than idle speed, so it tries to get the engine up to idle speed with what little pressure it has left as the engine dies, and the stop lever is released. So, the rack will be laying somewhere above no fuel, and can be pushed either way. All the way to 'no fuel' (stop) should indicate closed on a VOM. A light and meter is kind of like a belt and suspenders isn't it? Sorry, I just couldn't resist. How far in did he turn it? With no mousetrap on the 92 series, and the rack being held open by the buffer, the gov couldn't stop it, so I assume it blew up before it could be hit with a CO2 fire extinguisher, or the buffer unscrewed? I don't know as I would want to be wrenching on a runaway? G | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 819 Registered: 8-2006 Posted From: 74.32.95.26 Rating: N/A |
guys, so many prople try and set the idle with buffer switch on 92 series that have the tamper proof govenor that is were they get into trouble. I am telling you a fail safe method that I have used for years along with a pair of vise grips on one of the fuel rods. screw a buffer switch in a 1/8 of inch if it close on adjustment and it is off to the races. His problem was a bad switch with the fast idle option one of the good ebay buys a 600 dollar switch for a 100 bucks good luck | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 1055 Registered: 7-2006 Posted From: 70.212.212.121 Rating: N/A |
Luvr...what about Cummins? (220 with turbo) I know absolutely nothing about Jakes, but I do know that something is not just perfect with mine....never has been. (8 years) I do have a manual, but suspect that is not what is needed to correct my particular situation. One of the posts above suggests some things I am going to try to look for,(ie, hard wired) but I hardly know where to begin ....so on some sunny day, I will begin at the dash switch..  Thanx RCB |
