Jake Brakes Not Working

[luvrbus]

It's not always a electrical problem with Jakes the engine I am working on now had 2 broken cross over tube and 1 broken plunger

[sledhead]

 luvrbus  glad to see a picture !  nice !

dave

[luvrbus]

The man in the hat Gary made it easy now to post photos 

[Glennman]

I thought I would revive this thread that I started, since it is still concerning my Jake brakes.

Just to remind everyone what is happening with the Jakes... they are installed under the valve covers, wiring is there, micro switch is wired up, relay is installed, a wire feeds the relay from the rear panel near the air cleaner, but I have not been able to figure out why there is no toggle switch at the front operating the brakes, nor which wire at the front drivers window goes to the rear Jake relay.

I used one of those wire tracers that was suggested on this board and found the wire that goes from the relay at the motor area that is connected to the Jake micro switch at the governor to the front main panel under the driver's window (1974 MCI MC-8). The wire dead ends there at connector nut #56 (no other wires are connected to #56). I'm thinking that I simply need to find a power source there at that panel (again, under the driver's window), install a toggle switch to provide power back to the relay, and see if it works.

My question is this: with the bus power being 24 volts, is there any situation where there is both 12 volt and 24 volt in any of the bus wiring (not referring to the house wiring at all of course)?. My concern is that I don't know if the Jakes are 12 or 24 volt. I'm assuming that since the bus is 24, and the Jakes are already installed, then they would be 24 volt. But if the bus wiring has 12 and 24 volt, how would I know which to use? I'm new to 24 volt systems. Also, does my conclusion above sound correct (providing the power at the panel under the driver's window to a toggle switch)?

Thanks for all your help, Glennman

[richard5933]

Looks like someone disconnected at the front end for some reason. If you don't have a switch on your dash somewhere that controlled it, is there a chance you have (or had) foot control for the Jakes? Sounds logical to add power to the system at the front through a switch if you've checked over all the items at the rear, but I'd disconnect the system at the rear temporarily so that you can test the wire in the harness for shorts (just to be sure that's not the reason it was disconnected).

Is it 12v or 24v? Could be either, in my experience. My bus is a 24v GM, and nearly every single thing on the bus is 24v. Imagine our surprise when we discovered that the electric a/c clutch was running on 12v? Luckily we caught the very small print in the wiring diagram before we ordered the new one last year. Also, in working on our speedometer recently I learned that it runs on 12v. Seems that the bus makers were good about mixing things up as needed.

Not sure how you determine the voltage for your Jakes. I'd bet they are 24v, but this is something you should know before connecting. Are the solenoids under the valve covers themselves marked with part numbers or voltage?

Any chance you have a factory wiring diagram which would show the original setup?

[chessie4905]

The older Jake's used the same solenoids for 12 or 24 volts. Now they sell different ones. I think you can check which voltage they are by disconnecting wire at one solenoid and check it's  resistance. I recall Cliff mentioned in past what it should be for the voltage it is for.

[chessie4905]

Just checked. Jacob's vehicle systems has a downloadable pdf. troubleshooting manual with everything you need to know on install/ checking/ diagnosis. Also solenoid resistance numbers listed.

[luvrbus]

It is so damn easy to check with a test light just hook it up to the buffer switch and start flipping the switches or stepping on switches if you have power to the buffer and if they don't work move on,the Jakes will work without driving the bus fwiw

[Glennman]

There are 3 foot switches at the drivers floor, 2 toward the front, and one a bit further back. I know one runs the high beams, but the other 2 (?). I suppose I can check the micro-switch for power at the governor and see if it gets hot when the buttons are depressed (and I can try some of the unmarked, seemingly unused toggle switches too). It just doesn't make sense to me that someone would disconnect them, unless as it was suggested, there is a short or something. I found an old hand written letter that is a description of the bus written by the owner prior to the gentleman I bought the bus from, and he says that the bus was equipped with Jakes. That's how I found out! I doubt that the guy I bought it from even knows what Jake brakes are (nice guy, but he is A-mechanical).

I'll let you all know how that goes. Glennman

[buswarrior]

Highbeam switch, electric horn switch to replace the air horn button, that leaves one for...?

Are all 3 of these mounted in the left step up in the driver's area?

The one under your heel will be for the horn.

Those switches lead a miserable life, foot drippings and being stomped on, they are regular failures.

Happy coaching!
Buswarrior

[richard5933]

I have read about Jakes being installed with a foot switch, even where the switch was a momentary one which had to be held down to engage the Jakes.

The other two? High beams and air horn?

[akroyaleagle]

Could have been disconnected by previous owner(s) to keep inexperienced drivers from using them in icy road conditions., especially if it was commercial operation.

Big surprises happen if a good Jake is activated in icy roads!

[Glennman]

Well, I tested the wire connection at the Jake connection at the governor micro switch by depressing the 3 foot switches (yes, they are at the left foot area, one at the heal, the other 2 at the toe). I turned the key on, had the bus in neutral, nothing. I suppose I could try it with the auto tranny in neutral (?).

It seems to me that if the wire at post #56 at the main panel under the driver's window is all by itself, then it is dead ended there. In other words, aren't those posts used as connectors such that if there was a switched wire from a hot lead, then there would be 2 wires on the post instead of just one? Many of those studs have 2 wires together telling me that the post is a connector in lieu of wire nuts. Is this correct?

I have confirmed continuity from the Jake at the engine compartment to the #56 post at the front. I'll download the pdf wire diagram suggested in this discussion. Thank you everyone.

[richard5933]

Can you get to the underside of the three foot switches? If you can, it should be pretty obvious which are connected to what, or at least give you a starting point for tracing things forward.

I believe you are correct about the purpose of the terminals. That post #56 would have had another wire on coming from the front of the bus. On my GM, the power feed goes from the power source, through a relay, a clutch switch, and the dash switch before going to the terminal in the driver's electrical panel. Then it rides the harness till it emerges at a terminal in the engine compartment electrical panel.

[chessie4905]

While you are tracing wires, might as well determine what the extra foot controls are supposed to do. How do you like the signal tracer? I really like mine. Makes tracing a wire easier for me.