Leaky Parking Brake Control Valve

[BrianE]

Am experiencing a parking brake control valve (under the yellow knob) that is hissing for the first 20 minutes or so after releasing, after which it becomes inaudible. It only hisses when energized, ie pushed down. Has anyone any experience with this valve? Is it rebuildable? Is it a common valve found on trucks? Is it a PIA to change? Thanks.

[JIM CHALOUPKA]

Brian, I thought you had the Prevost Catview?

From it I got, new valve part no., 641128 and valve repair kit, 641154.

Good luck on the fix, have not done it.

JIM:)

[truk4u]

Brian,

I'm sure it's just standard truck stuff and probably an "O" ring. Here's a link for Dash Control Valves:

http://velvac.thomasnet.com/viewitems/air-products-air-brake-valves/ontrol-valves-pp-i-pp-2-pp-3-pp-7-and-pp-8-styles-?&forward=1

PS - Order one with a red knob that Peter won't have..

[Orren Zook]

Heck Tom, you can buy the knobs separately in yellow, red, blue or black to compliment the interior of your coach.

[Orren Zook]

Am experiencing a parking brake control valve (under the yellow knob) that is hissing for the first 20 minutes or so after releasing, after which it becomes inaudible. It only hisses when energized, ie pushed down. Has anyone any experience with this valve? Is it rebuildable? Is it a common valve found on trucks? Is it a PIA to change? Thanks.

If you have the one Truk shows it is a PP1 usually available from a decent truck parts outlet for $15-20 dollars without a core. To remove and replace: push out the roll pin in the knob, place a socked over the nut, loosen and remove same, remove valve from dash then remove your air lines (marking them for re-installation). Reverse process for installation. I'd use new teflon tape on the fittings but that's your call. You can get a rebuild kit for a few dollars or the o-rings for even less but sometimes the spool will wear and you have to buy a rebuild kit with a spool which runs more than a new valve. You should be able to swap this valve out in less than one hour.

[BrianE]

Jim, I do have Catview, but why should I take the trouble to look it up when you'll do it for me? :D Many thanks buddy.

Tom, Thanks for the info. As to a different colored knob, judging from the color of his toad, I suspect Peter is colorblind.

Orren, Once again, thanks for the straight answer. It's on the schedule for tomorrow....with teflon tape.

[jonnie]

Brian.

Be carefull when you let the air out.

[Jon Wehrenberg]

Brian,

I have one if you want me to bring it to OKC.

Are you sure the hissing is in the valve and not a leaky diaphragm in the brake chamber?

[lloyd&pamela]

Sorry to poke in here, what is CatView? Does that mean catalog view? If so how do I get one for XL?

[JIM CHALOUPKA]

That's right Lloyd, It's the same catalog that the sales force at Prevost views when you order parts by phone.

Just call the sales office and ask for one, I believe it is FREE.

Good deal, no. Even if you don't buy much it is usefull to see the exploded views of many bus systems.

It is a small CD.

JIM

[lloyd&pamela]

Thanks Jim I will call them this morning and order one.

[BrianE]

Jon, The leak is coming from the valve shaft so can't figure how it could mean a leaky chamber. Thanks for the offer but I have it opened up now and will be repairing or replacing it in the next day or two.

[Orren Zook]

Jon, The leak is coming from the valve shaft so can't figure how it could mean a leaky chamber. Thanks for the offer but I have it opened up now and will be repairing or replacing it in the next day or two.

Brian, many times a leaking diaphram will bleed back through the control valve. I've seen do-it-yourself mechanics change several valves only to find a three dollar diaphragm be the problem. To diagnose this just pinch off the brake hoses (with a pair of vise grips) one by one to see if it eliminates the leak. Unfortunately you need to be able to get under the bus to do this procedure.

[Jon Wehrenberg]

Orren,

I have a spare combo brake unit that I rebuilt, but I am not sure anyone makes rebuildable combo brake chambers that can be fixed with a diaphragm. With the huge potential for serious injury if it is not properly caged before disassembly I am glad the new designs are throw aways.

[BrianE]

Orren, Figured there was more to Jon's question than I understood.........Am guilty of being a do-it-yourselfer. So far the leak is intermittent but will check the chambers, I've replaced one diaphram already so will go through the vice-grip procedure first. Thanks again.

[BrianE]

Jon, Actually, the one I replaced was a tag lift chamber. I replaced the entire brake chamber's on Tom's bus. Agree that with the brakes, new chambers are the way to go. From a truck parts store they're not that expensive and a whole lot easier to deal with. Also, new hoses are a part of the fix as far as I'm concerned. Very cheap insurance!

[rahangman]

Is this a fairly common malady ? If so, is this one of "those" that spares should be carried onboard and could/would an average Mechanical Owner be willing and able to do away from home pit?

[BrianE]

Rodger, It's pretty easy to go overboard buying spare parts. Considering the way we use our coaches, I would guess this is not a very common problem. Both parking brake valves and brake chambers are common to highway trucks as is the brake system itself. Most competent truck repair facilities should be able to cope with our brake problems. That said, Jon has taken the time to explain the parking brake deactivation process in one of his excellent tech papers: Prevost Owner Emergency Repairs which can be found in the articles section. Printing out these articles for use on the road is another very cheap insurance policy.

[Jon Wehrenberg]

My bad Brian for not doing a better job asking the question.

The only place it is going to be is in the spring brake diaphragm, and me being lazy would just release the emergency brake and listen outside the coach at the tag and drive. I have been able to hear air flow unaided and without getting under the coach.

When I had a diaphragm leak on the road one time I could have sworn it was coming from the valve, but the diaphragm was in fact the culprit. Hence the spare valve and knowledge.

I doubt if it is a diaphragm because they don't stop leaking once they start. You would likely have seen a very active air pressure gauge.

[Orren Zook]

Orren,

I have a spare combo brake unit that I rebuilt, but I am not sure anyone makes rebuildable combo brake chambers that can be fixed with a diaphragm. With the huge potential for serious injury if it is not properly caged before disassembly I am glad the new designs are throw aways.

All new parking/combination chamber are not servicable on the emergency side for this reason. The parking brake spring is caged at 2000 pounds per square inch, so on the type 36 chamber it's 72000 pounds of pressure on that spring, enough to do a lot of damage when released improperly. To get off the road to a service facility I've seen a coin inserted in the service side of the chamber or relay valve to block air flow to the service brake - certainly a temporary fix because you've eliminated that brake chamber but allowing you to drive at a safe speed to a garage for the correct repair.

[Orren Zook]

Every brake application causes some degree of chafing on the service side diaphragm - but they should last thousands of miles under normal service depending on the environment they are operated in. The vent holes in the chamber will allow outside contaminants into the housing if operated in harsh conditions. You should be able to buy a brake diaphragm at any HD parts store for $3 to $5 depending on the size. Service chambers should run around $20 and combination (service/parking) around $55 again depending on the size. Cheap to change on Jon's maintenance schedule and added peace of mind.

[Jon Wehrenberg]

To add to Orren's excellent info, think of your brake chamber diaphragms as you do the tires. They are rubber and with age they crack and fail if they have not worn a hole through themselves from use.

Fortunately, If you know how to cage a spring brake or plug the air supply to either spring or service brakes a failed diaphragm becomes an annoyance but not a disabling problem, unlike a blown tire that can be a serious issue.

If Skiffer can fit it in, if I remember to load it, and if enough are interested I will bring my brake teaching device to OKC so anyone that wants can learn how the brake chambers work. I do not have a complete system with relay valves and brake treadle, but I can show how our brakes work so anyone that wants can easily do a field fix to deal with brake problems.

[JIM CHALOUPKA]

You just bring it Jon, there are people here that never or rarely post and they will want to see your display.


JIM

[Jon Wehrenberg]

Done deal. I will have it for impromptu show and tell for anyone that wants to get a better understanding of how our brakes work.

For an overview of the entire system that involves a lot more than just the brake chambers Truk and Bill Jensen of Prevost will be doing that when we have our buses up on a lift at United.

[Ray Davis]

I think looking at the schedule, we've got lot's of free times that would be great to add this. I would like to see it again.

ray

[GDeen]

If Skiffer can fit it in, if I remember to load it, and if enough are interested I will bring my brake teaching device to OKC so anyone that wants can learn how the brake chambers work. I do not have a complete system with relay valves and brake treadle, but I can show how our brakes work so anyone that wants can easily do a field fix to deal with brake problems.

Definitely, please do. A number of us Noobs with lots of learning to do.

Muchas Gracias Jon!