Help troubleshooting jake brake wiring, please!

[bevans6]

I am trying to figure out the mis-wired jake-brake system on my bus.  MCI MC-5C, 1980.  It has a hi/lo switch, but seems to have been wired as though it was one speed only, although the buffer/rack switch seems to be wired to solenoids on both heads.  It would really help if I knew where some of the connections where located, so that I could buzz them out and see what's what.

My schematic in my manual shows the wiring goes to a "K" inside a triangle inside a circle.  The legend doesn't say what or where that "K" connection is physically located.  From there it goes to a "2" inside a circle.  that is supposed to be an engine terminal block stud, but I don't know where that terminal block is located, although I did find a vertical terminal strip right near the oil pressure sender manifold.  Is that it? 

If anyone knows where the "letter inside a triangle inside a circle" connections are, that would help me a lot.

Thanks, Brian

[NJT 5573]

Hi Brian.

I don't know how to chase the X's and O's, but I would just start with a volt meter at the dash switch.

If you have power to and thru the switch I'd move to the solenoids at the heads and check again there. If there is voltage, they may need to just be used to prime themselves. You should also chase the power through the throttle switch and the clutch switch, thats about all there is to it.

A 2 stroke Jake does not always have much noticable braking power. Thats probably why the heads are wired togather, you need them both anyway.

The throttle closed switch is on there to keep you from blowing the heads off the engine, so be careful if you decide to have the Jake on with fuel going into the engine.

[JackConrad]

     Our 73 MC-8 uses the following shapes with wire numbers inside them: Front panel-parallelogram, Rear panel-rectangle, AC junction box-triangle, Remote control panel horizontalstud block-square with circle inside, Remote control panel vertical stud block-diamond with circle in it.
    I think the circle/triangle with K is the appropriate pin in military type bulkhead fitting in the side on the rear panel as it shows it between the rear panel terminal 11 and the engine block terminal strip that is located near the oil pressure sender manifold on our MC-8.
    With the master switch on and the Jake Brake switch on, you should have power at the engine block terminal. If you do not start at the front switch and work your way  back intil you find no  power.  Jack

[Jerry32]

yes the buffer sw shud have power on it when the jake sw and master are on. another test is to apply power to the buffer sw and run the engine . Rev the engine up and let it off rapidly and see if the jakes apply for a short time. Jerry

[luvrbus]

Does your bus have a manual or auto tranny and which type buffer switch do have and also do you want a 2 stage brake.The wiring on a 1 stage with the auto is simple hot wire from the Jake switch to the buffer switch from there a wire to both heads.
On a 2 stage it requires 4 wires all going back to the control switch then the buffer switch breaks the power to the control switch releasing the Jakes if you have a clutch start from the clutch switch these things can be wired so many different ways just keep it simple.


good luck

[bevans6]

Well I wired it up the way I thought it wanted to be, as a single system, with the power coming from the front buss bar through the dash switch, now have power on the buffer switch.  With the engine on and the switch on, there is power at the buffer switch, and no power at the solenoid terminal side.  when I manually advance the throttle lever to full and release (the procedure in the book) the solenoids energise momentarily and I hear the jake exhaust note.  As I  did this a few times it got more pronounced, and when I ran the engine at a higher speed to get 40 psi, then did the full throttle/release, I got a fairly strong jake sound.  Would this mean they are now working?  what does bleeding the jakes do, does it happen automatically if I just run the bus normally, or do I need to do it from time to time?

Thanks for the help, and particularly the info on the mil-spec plug and the engine terminal strip.  Great stuff.

My total confusion started when I was trying to trouble shoot this as a hi/low system.  With that system, per my schematic, the power starts at the back, goes through the buffer/rack switch, then goes up to the front panel switch, and back again to the solenoids.  It's tough to successfully trouble  shoot something that isn't actually there...

Brian

[NJT 5573]

Brian,

The Jake uses oil to hold the valves open. When the O rings get old they pass the oil and fill with air. Sometimes they can sit for weeks and some drain overnight. Since they are now working, the most you will probably find is a 30 second pause before they start working after you throw the switch.

[JackConrad]

Congratulations, sounds like you got er done.  Yes, bleeding the Jake Brake is an automatic thing.  Jack

[bevans6]

Thank you all very much.  At the end of the day, it's a nonstandard install that would have worked all along, if it wasn't for a corroded connection at the dash switch and the power lead being disconnected at the buffer switch.  No power being sent to a disconnected buffer switch will make Jake unhappy every time... 


Brian

[JackConrad]

  No power being sent to a disconnected buffer switch will make Jake unhappy every time... 
Brian

Yeah, and you do not want Jake unhappy when coing down a big hill.  Jack