When I pressure washed my engine(pd4903 with 8-71, I made an enormous discovery! I have Jake's on one head. I have been told that this was normal to avoid the 'bump' on the engine rear door.
My problem is I cannot find a switch to turn them on. On my panels in the operators station,all switches are labeled and no extras.
I was wondering(while at work) do they come on when the brake is applied. I would like to use if needed , but need some guidance.
Come on Roadrunner and give me a call.
Big John
I don't know your setup, but assuming they are wired, you could use a tone generator to trace where the wires go.
Cannot imagine Jake's being on one head only, unless the PO needed to make a head change and the mech needed them for his tool box. There's more hustles out there than you can imagine...especially when they know a rig is for sale.
Generally speaking, there's a Master Switch for the Operator to make the choice on/off along with a switch on the clutch and one at the governor (so when you take you foot of the fuel pedal they will come one).
You might have inherited someones idea of how to do something wrong...but I wish you the best in your search.
NCbob
Bob, with the help of John Vickers, we have located a wiring diagram of the pd4905 with jakes. It only has them on inboard head and was an option. They do operate as you stated. When you appy brakes, with switch on, they operate.
Possible more people have this setup , but as I, did not know.
thanks for your replies.
FWIW, I believe that it's common for Jakes to be able to be activated in stages, ie: one head at a time. my bus has a switch and a wiring diagram for two stage Jake operation - one head or both heads, and I have read about 6 cylinder operation where you can switch on two, four or all six depending. I therefore don't see an issue with only one head having them installed.
Brian
Since you have them on one head, why not complete the job and install on the other head (course you probably will have to modify the rear engine hatch-I just cut out the cylinder head cover and let the cylinder head poke through-sort of cool seeing the valve cover). Properly adjusted to Don Fairchild specs, coming down the northbound Grapevine pulling my car, I have to switch between 1 and 2 cylinder heads because it slows me down to much (5 miles of 6% grade). Good Luck, TomC
You keep mentioning the brake and I want to make sure there is no confusion.
The jake will work while braking but it is not the brake pedal that activates it it is pulling completly off the throttle that does it.
It can also, normally, be disenguaged by again stepping on the throttle OR depressing the clutch pedal just slightly if the trans is a manual.
No Joe. It is wired through the brake light relay and comes on when you lightly touch brakes. Of course this is the way it was installed and could be changed. There is a switch on dash(mine was labeled wrong) to completely turn off.
Big John
That's interesting. Does that mean that if the Jakes are wired that way (via the brake light circuit) that a buffer switch is not needed?
RE the need for a buffer switch:
Wouldn't you still need to be sure the injectors are at no fuel before the jakes engage?
If you have them wired so that they come on when the brake light is on, AND you have no buffer switch, the engine will stall every time you have the brakes on. The buffer switch is needed in all jake installations (on two stroke MUI anyway) so that the jake solenoids cannot come on when the engine is at idle. The test to see if the buffer switch is working correctly is to put a test light on the switch lead that goes to the jake solenoids, rev the engine up to medium/high speed, snap the speed lever to full off - the light should come on as the engine speed falls, and go off at about 900 rpm, and stay off as the engine returns to idle. You should be able to hear the typical "jake" rattle in the exhaust, and the engine may stall. Basically the buffer switch only allows signal to the jake solenoids when engine speed is over 900 rpm, AND the speed lever is full off.
That is the buffer switch control of the jake system, the primary control. There is always some other secondary control system, differing per the manufacturer's installation and/or the whim of the guy who screwed up/modified/fixed the original installation... The secondary controls switches could be a clutch switch (no jake action allowed unless the clutch pedal is up), a foot switch, a dash switch, apparently a brake light switch. I personally find the MCI installation to be completely satisfactory and totally logical - it has a dash switch for on/off, the clutch switch so that the jakes only engage when the clutch pedal is up, and the buffer switch for over-all control. The most common use I have for the jake brake is rolling down hills, both brake and throttle full off, so having to press the brake pedal enough to make the brake light switch operate would not satisfy that condition, you'd be constantly riding the brakes with that, with enough air pressure to trip the light switch at the very least.
My thoughts, fwtw...
Brian
Thanks Brian,
I was thinking something else. . . . .
Kyle, what I don't know is if the injectors get set to "no fuel" when the jakes are on/buffer switch is live, etc. Or if they are at idle setting. What I think of as "no fuel" is when the engine stop lever is set. At least, I hope so, I set the engine stop lever on whenever I am manually rotating the engine for some obscure purpose.
The engine stop lever is sorta like the start button in windows - you turn it on to make the engine go off...
Brian
The buffer switch just makes the use of the jakes easy. You can do without it and just use the switch on the dash to turn them on or off. But if you are going down 95 at 2oclock am and accidentally hit the switch causes someone to just about have a heart attack. untill he figures out what happened.
don't ask me how i know
uncle ned
Thanks for all the input. It does have the buffer switch and will not rattle at idle. I'm going on a trip shortly and intend to researce this more 'in operating conditions'. Yesterday , on my driveway, it work as previously described,and you just touch the brake pedal.
Big John
Brian, the Jake's work in the no fuel postion with the buffer switch,when the governor takes it to idle the Jake's are disconnected
good
Along those lines of the buffer switch, if you're climbing a hill with your gas pedal on the floor, when you peak the hill and if you keep it floored, the Jakes will come on when the top engine speed has been reached and the governor goes to no fuel position. Sort of a wierd sensation to have the Jakes on with your gas pedal on the floor. Good Luck, TomC
I have a Master Switch on the Drivers side console with a cover (much like Beechcraft used on their landing gear switch..you have to lift the cover to switch them on) and a quick swipe at the cover thurn them off in town traffic.
I couldn't have made a better investment.
NCbob