need a bendix brake valve

David Anderson · February 05, 2021, 07:33:29 AM

Let's change gears here for a minute. With what I just posted above. It has always taken me at least 2 tries, sometimes a 3rd try to get the parking brake released. I would make a hard press on the E6 footbrake, pull the parking brake knob out and walla, no release. Try a repeat and walla, no release. Pump the E6 a couple of pumps and hold, walla, parking brake releases and on my way.

It has always been like this since 2001. That has always annoyed me, but I figured it always works so I move on.

I've seen other coaches that don't have to do that. One pull of the knob and away you go.

This is why I was thinking my PP1 valve my be going bad. I'm sort of guessing, however.

David

lostagain · February 05, 2021, 08:07:06 AM

Don't you push the knob to release the park brakes? Or is it backwards on Eagle buses?

buswarrior · February 05, 2021, 09:18:38 AM

Hang on...

There were Eagles that were plumbed with valving that required a strong service brake application, to release a spring brake parking system.

If that bit of trickery is not functioning correctly, that may be the story.

Spring chambers can most certainly self apply, if there isn't somewhere over 60 lbs of air right there in them, never mind what is anywhere else in the system, the big spring starts squeezing out.

A local leak of sufficient size can cause this to happen.

My bet at this moment is the first suspicion. Confirm or deny the parking brake plumbing on that coach.

Maybe a pp4 was the device? I'm trying to remember which old busnut had it, and he sent me the schematic, back when i used to be intelligent... Shepard perhaps?

Happy coaching!
Buswarrior

richard5933 · February 05, 2021, 09:29:46 AM

Quote from: buswarrior on February 05, 2021, 09:18:38 AM
Hang on...

There were Eagles that were plumbed with valving that required a strong service brake application, to release a spring brake parking system.

If that bit of trickery is not functioning correctly, that may be the story.

Spring chambers can most certainly self apply, if there isn't somewhere over 60 lbs of air right there in them, never mind what is anywhere else in the system, the big spring starts squeezing out.

A local leak of sufficient size can cause this to happen.

My bet at this moment is the first suspicion. Confirm or deny the parking brake plumbing on that coach.

Maybe a pp4 was the device? I'm trying to remember which old busnut had it, and he sent me the schematic, back when i used to be intelligent... Shepard perhaps?

Happy coaching!
Buswarrior

Not applying a strong enough service brake application might explain why it's been difficult for him to release the parking brakes, but it doesn't explain how/why they self applied while traveling at 70mph with 100psi showing on the gauge.

Jim Blackwood · February 05, 2021, 09:34:26 AM

So the air leaked out and let the spring brakes apply? (at 70) and when he reset the parking brake it put more air back in the chambers?

Jim

richard5933 · February 05, 2021, 11:13:11 AM

Quote from: Jim Blackwood on February 05, 2021, 09:34:26 AM
So the air leaked out and let the spring brakes apply? (at 70) and when he reset the parking brake it put more air back in the chambers?

Jim

The part that is still a mystery is why his gauge showed 100 psi while this was happening. If the pressure dropped low enough at the cans to apply the brakes it should have done so at the gauge as well.

buswarrior · February 05, 2021, 11:19:35 AM

Quote from: Jim Blackwood on February 05, 2021, 09:34:26 AM
So the air leaked out and let the spring brakes apply? (at 70) and when he reset the parking brake it put more air back in the chambers?

Jim

If this trick circuit is involved, and failing somehow, perhaps it is blocking the direct path from spring chamber to tank, which is supposed to be wide open, when the spring brake is released. Add in a leak at the chamber, blockage in the trick circuit, springs could apply while underway, and no control valve pop, since there's still pressure at the control valve, sufficient to keep it in the released position.

Richard, in a properly working spring brake system, if there was a steady leak, the bus will likely already be stopped before the parking control valve pops. The spring chambers start applying as the air pressure drops thru 60 lbs, the control valve won't pop until the pressure at the valve drops below 40, as low as 25 lbs, depending on the spring in the control valve. Dashboard readings are only acccurate for wherever the other end of the hose from the gauge is plumbed in.

Most everyone has not been properly taught these subtle differences, usually just the "fan the brake until the button pops" and assumptions that are wrong, go from there...

The springs were already applied before the button popped.

Happy coaching!
Buswarrior

richard5933 · February 05, 2021, 11:26:43 AM

Quote from: buswarrior on February 05, 2021, 11:19:35 AM
If this trick circuit is involved, and failing somehow, perhaps it is blocking the direct path from spring chamber to tank, which is supposed to be wide open, when the spring brake is released. Add in a leak at the chamber, blockage in the trick circuit, springs could apply while underway, and no control valve pop, since there's still pressure at the control valve, sufficient to keep it in the released position.

Richard, in a properly working spring brake system, if there was a steady leak, the bus will likely already be stopped before the parking control valve pops. The spring chambers start applying as the air pressure drops thru 60 lbs, the control valve won't pop until the pressure at the valve drops below 40, as low as 25 lbs, depending on the spring in the control valve. Dashboard readings are only acccurate for wherever the other end of the hose from the gauge is plumbed in.

Most everyone has not been properly taught these subtle differences, usually just the "fan the brake until the button pops" and assumptions that are wrong, go from there...

The springs were already applied before the button popped.

Happy coaching!
Buswarrior

Helpful clarification.

Sounds like there are at least a few points of inspection in order for this Eagle.

niles500 · February 05, 2021, 03:41:21 PM

Sounds like there's an errant check valve some where in the brake system - fwiw

chessie4905 · February 05, 2021, 05:13:27 PM

If he has a dual brake system, maybe gauge only has one needle instead of two. Maybe gauge is reading auxiliary system only because of incorrect plumbing.
Maybe the push-pull valve is defective.

buswarrior · February 05, 2021, 07:06:11 PM

That trick safety system, that requires a service brake application, to release a spring brake parking system, is a high probablity.

I wish i coukd remember who had the Eagle that was so equipped... municipal/regional transit background almost guarentees it is plumbed this way...

NIles, who is it that I can't remember has this Eagle similarly equipped?

Getting old is total crap... young people, make notes, your turn will come... my mother warned me... she was right... as the years pass, you won't remember $hit...

Happy coaching!
Buswarrior

David Anderson · February 06, 2021, 06:53:18 AM

Yes, I have the trick system. Jim Sheppard does too.

Both front and rear gauges showed 100psi when this happened. I agree that a harder longer E6 brake application may be needed to to release. I tried that a few times in the shop and it worked ok which pretty much eliminates a problem in the PP1 push valve (push to open).

Still puzzled about the errant spring brake application. If what Clifford said about the air charge is true, then most likely it is a leaking can. I am replacing the R8 parking brake valve and the spring brake cans. I'm not sure if the pawl is relaxed or under pressure when the parking brake is applied. The pins have to be removed to get the clevis to pass through the bracket as you remove the cans.

I removed the two front service brake cans. They both leaked on a held E6 application. They were easy to get out. I have them on the bench and new ones in hand ($41 each) and will replace them and the R8 valve and retest to see how things work.

Then I will get the big boys off and replace them. Ugh, it's hard working on my back under there.

David

niles500 · February 06, 2021, 02:13:52 PM

BW wrong guy to ask your memory is better than mine for names/busses 😗

sledhead · February 06, 2021, 02:30:06 PM

ya I remember I forgot something but I can't for the life of me remember what it was

dave

David Anderson · February 06, 2021, 03:21:50 PM

I got the 2 front brake cans and new hoses installed, readjusted the slacks back to Eagle book specs. Installed the new R8 parking brake valve and reinstalled the PP1 valve and knob on the dash. Checked all my work for leaks and found none

It is easier to release the parking brake, but I do need to give it about 2 more seconds of E6 footbrake to load the spring brake cans with air and it will release.

No more audible leak down under the coach with E6 pedal hold down. I held it down for 120 seconds and lost about 5psi on the gauges.

Oh and I determined the spring brake cans need to be loaded with air to relax the clevis to get the keeper rods out. I can then remove the can and slowly dump the air and let the threaded rod extend, then remove the air hose.

I will block the wheels and do this next week and replace both cans. I figure after 21 years, why not?

David