Jake Brakes Not Working

[buswarrior]

Stock, the two toe switches were for high beam and the optional fog lights.

The heel switch was either the plunger button for the optional air horn, or was a momentary switch wired to the electric bill horns, parallel to the steering wheel mounted buttons.

Not to be confused with floor mounted turn signals, that's a whole different animal...

Fog lights had interrupt circuitry with the headlights, one or the other, not independently operated.

Happy coaching!
Buswarrior

[Glennman]

I really like the signal tracer. I bought it from a recommendation on this board. It'll be very handy for many things.

[luvrbus]

LOL I hope you don't need these they have gotten expensive Van is still reeling this tiny box with 4 of the solenoids for $500.00 and are aftermarket too

[freds]

I have 1980 Prevost with a 8V71T and HT740 automatic transmission.

I found an operators manual that specified the Jake Brake switch as off, low and high.

A previous owner did a stalled drivers panel upgrade with a two position switch on/off. When you turn it on, it sort of hardheartedly slows the bus. Nowhere as strong as I think it should be. Operator manual has all sorts of warnings about slippery roads, etc. 

However looking at the electrical schematic in the Maintenance Manual; it shows a single control wire for the Jake Brake functionality from front to back.

How would have the low high functionally have worked?

[chessie4905]

Low operates half of the cylinders of the engine. High operates them all.

[freds]

Low operates half of the cylinders of the engine. High operates them all.

I was kind of asking how this could work over one wire. Now thinking the electrical diagram must be in error and that I should trace the actual wiring.

[luvrbus]

Single wire are 1 stage Jakes

[richard5933]

There might have been a few options available (two-stage & single-stage) and your books reference both, but in different places. Go with whichever is actually installed in your bus. I've found lots of things which are slightly different in the book than reality.

[luvrbus]

The 2 stage brakes will have a wire from each head back to the control switch,1 to power the buffer switch from the control switch up front and 1 to power the switch from the buffer switch (4 total) if you have a buffer switch,sorta a waste of good wire on a 2 stroke engine

[freds]

There might have been a few options available (two-stage & single-stage) and your books reference both, but in different places. Go with whichever is actually installed in your bus. I've found lots of things which are slightly different in the book than reality.

OK, with the dash conversion not really sure what I have. So I should determine this by:

1. Pulling a valve cover? Stage one will cover fewer cylinders ? I have a V8...
2. Checking if there is separate wires to each head that go to the junction box?
3. Look for the old switch hidden away under the dash?

Thanks everyone!!!

[richard5933]

OK, with the dash conversion not really sure what I have. So I should determine this by:

1. Pulling a valve cover? Stage one will cover fewer cylinders ? I have a V8...
2. Checking if there is separate wires to each head that go to the junction box?
3. Look for the old switch hidden away under the dash?

Thanks everyone!!!

I'd go with what Luvrbus suggested and start by looking at the wiring. It takes one wire front-to-back to power the single stage Jakes. There will likely be some unused wires if the system had a multi-stage setup at some point in the past.

Your bus may not have had factory installed Jakes, and when they were installed they were installed as a single-stage setup. That would make the information in the Operator's Manual a red herring.

[freds]

I'd go with what Luvrbus suggested and start by looking at the wiring. It takes one wire front-to-back to power the single stage Jakes. There will likely be some unused wires if the system had a multi-stage setup at some point in the past.

Your bus may not have had factory installed Jakes, and when they were installed they were installed as a single-stage setup. That would make the information in the Operator's Manual a red herring.

Thanks everyone!!!

OK it is looking more like I had stage one; but was operating at stage 0.5 in the picture below:



Looking from the back of the engine; yellow is a wire going to the left bank, red is a unused terminal and blue is a wire going to the right bank of the engine that isn't hooked to anything. Below is picture of the wire coming out of the right bank and there is similar one on the left bank.



Any electrical tests to perform before I hook it back up?  In case it was disconnect for a reason?

Thanks again...

[akroyaleagle]

Effectiveness of the Jake also depends on the setting.
Many are set at .065
Some are set to .060
Mine are set at .055 They work great!
Be advised that when setting them at close tolerances you could cause major damage. Be careful!

[chessie4905]

So far, that is unknown till someone measures piston to valve clearance at tdc. I would think that Clifford would have checked one out of curiosity, due to all the engines he's  rebuilt/ repaired.

[lostagain]

I set mine at .059". Works good.

Do not think that Jakes will put you through the windshield. That is fantasy. They slow you down and hold you back, in the right gear for the circumstance, but it is not like the service brakes. That is why I don't agree with wiring the brake lights to the Jakes. Mine in the bus feel about the same as the engine brake in a semi loaded at 80,000 lb GVW.

JC