Jake break? Sometimes.

[adamdegraff]

My Jake has been acting up for a little while now. Started maybe a few weeks ago. Here are the symptoms:

Driving down the road, everything is great, jake is working in hi and lo. No problems. Then all of the sudden, I find myself picking up speed going down a hill and notice the Jake isn't kicking in. So I step on the accelerator and let it back up and wham, the Jake kicks back in.

Once, I stopped, and lubed up that little wheel under the pedal and blew the spring out with some compressed air. Seemed to make it work better.

Some variations on the same theme.... jake no go, step on accel. and jake turns on, then off, then on then off, etc. It is almost as if the sensor thinks I'm keeping my foot on it ever so slightly. Ya know, how you can keep the Jake from coming on by just laying a slight amount of weight on the pedal?

Tonight, all was well, other than an obscene amount of driving today. Then, late at night, all of the sudden, no Jake. This time, I couldn't get it to come back on at all. We were not in the mountains any more, so it didn't matter... other than that we will again be in the mountains... soon!

Any thoughts? The previous owner had replaced that little square sensor that hooks to the pedal. I'm wondering if he did it because his Jake wasn't working. Maybe I'll email him and ask.

Thanks for any help.

Best,

Adam

[Jon Wehrenberg]

Didn't know the Jake had any sensor at the gas pedal.

Always thought the Jake was controlled through DDEC, which sent a 12 volt signal to two terminals in the rear electric box which in turn energized the two solenoids in the head.

This is something a tech with a DDEC reader should check. I wouldn't be oiling or messing around under the pedal. The throttle position sensor is under there and that sends a signal to the DDEC computer.

[Gary & Peggy Stevens]

I just spoke with Ste & Ste about checking my Jake brake issues.

I was told the majority of issues with the jake working or not, are not computer controlled at all, but mechanical. He stated one of the two stage jakes may not be working, and it would have to be researched under the valve covers, NOT just by hooking up to a computer?

While there is some electrical issues involved, between the Jake and DDEC, it sounds to me like a lot of money involved to check why mine doesn't work as well as I believe it should work. CRAP Not what I wanted to hear.

Gary S.

[Ray Davis]

When I had a jake issue in my CC, I pulled out the schematics. At least in the case of my 93 CC, the jake required that there be a signal from the DDEC which indicated zero throttle.

This is a wild guess, but I'm thinking that if you have to jiggle the throttle position, then there is a sensor that that is either not calibrated, or is mal-functioning.


If you had a DDEC reader, I would think you could see if you're getting zero throttle?

Ray

[adamdegraff]

Didn't know the Jake had any sensor at the gas pedal.

Always thought the Jake was controlled through DDEC, which sent a 12 volt signal to two terminals in the rear electric box which in turn energized the two solenoids in the head.

This is something a tech with a DDEC reader should check. I wouldn't be oiling or messing around under the pedal. The throttle position sensor is under there and that sends a signal to the DDEC computer.

Jon, I guess what I meant was that the Jake comes on when the pedal is in the upmost position. Since, I can often times get my Jake to come back on by "flicking" the pedal and letting it spring back up, it makes me think that my Jake is not cutting on because it thinks the pedal is not in the upmost position. See what I mean?

As for the lubricant, I was only lubing the little roller which wasn't rolling smoothly. I was careful to confine the silicone spray to the the roller axel and only used a very little. It made a big difference though. And, all of the sudden, the jake worked again.

By the way, I'm really not a very big fan of intermittent problems. My Webasto was working perfectly the other day. Now it is back to its old tricks.

I'll talk to Prevost about the Jake.

thanks for the input!

Adam

[Jon Wehrenberg]

Adam, If you pedal is not "returning" you can tell. With the coach in neutral operate the pedal and release it as you would when driving. The tach should show it dropping down to idle speed every time. If it returns to the 600 or 650 idle speed every time the computer should work the Jake.

Your accelerator pedal is doing nothing more than sending an electrical signal through a sensor to the computer. You're going to love this: They call the sensor located under your pedal a throttle position sensor. If the normal idle is experienced every time then it is not a question of the pedal returning because it is returned when the engine RPM is the normal idle.

However, if operating the pedal occasionally causes the idle speed to remain above the normal idle speed, you are correct in that the bus does not know the foot is off the pedal and it will not engage the Jake until it thinks your foot is off the pedal.

[adamdegraff]

Talked to my Prevost rep. He said that he was almost positive that it was a faulty throtle position sensor. This was based on my description of the problem. I hope he's right. I have a new one on the way and will put it on before our huge upcoming trip through the mountains. Will post and let everybody know if that does the trick. Keep your fingers crossed.

~Adam

[jimshoen]

Adam,
I can confirm what the Prevost Rep told you. I had the exact same issue and screwed around flipping the throttle position sensor by hand. Get the new part and install it. It only takes a few long grades with no Jake to make someone a believer. What is happening is that the Jake will not come on until the computer is positive you are not on the gas pedal. The failure is the throttle position sensor is not coming all the way off. Simple to fix.

[rfoster]

Adam: Just curious if your bus is equipped with a Pro Driver? and if so did it indicate a TPS failure? Or it just hasn't failed completely yet?

I once had a failure of the TPS and for such a tiny gizmo, it stopped us from our merry way.

This too should probably be added to the list of items that can shut you down. You can start the engine but it will not accelerate therefore - no go.

[Gary & Peggy Stevens]

I wonder if this throtle position sensor could be my problem as well ?

Gary S.