Should I hear air leaking from brakes with brakes applied?

belfert · August 27, 2011, 09:10:38 AM

I pushed my brake pedal down with a 2x4 to check my brake lights. When I walked by the right front and rear I hear a small amount of air leaking from somewhere. Is this normal with the service brakes engaged?

If it is not normal I guess I better see if I can get the bus in to be repaired Monday or Tuesday. I can't imagine it would anything more than a brake canister, air line, or a valve. At least spring brake chambers are reasonably priced to replace if necessary.

Edit: I went out and chocked the wheels and tested without parking brake applied and it still does it. Front right also leaking.

bobofthenorth · August 27, 2011, 09:47:17 AM

No, you shouldn't hear air leaks. But this doesn't have to be a trip to a shop. Get it up on blocks and go under with a spray bottle of soapy water. Most of the time its just a fitting that needs tightening. At least if you do the soapy water thing you will know what to ask the shop to fix when you take it to them. IMHO looking for air leaks and greasing your coach are two excellent ways to do a thorough chassis inspection and should be mandatory before you go to the shop. By the time you get done crawling around looking at air fittings and searching for grease zerks you will have had a good look at everything under there. Sometimes you will be surprised what you find - no surprises is good.

trucktramp · August 27, 2011, 09:48:30 AM

You should not hear air leaking when you apply your brakes with or without the park brake applied. It could be something as simple as a bad pancake but if it leaks in two spots I would suspect something else...maybe a valve. Time to get the soapy water out.

oldmansax · August 27, 2011, 09:49:02 AM

NO!!! It is NOT normal!

You have a leak somewhere.... Guess you knew that already.. LOL

You already have everything in place to find it, just find it.

TOM

prevosman · August 27, 2011, 10:08:49 AM

No need for soapy water if you can hear the air. Your ear will lead you to the source of the noise.

You should pull up a commercial driver brake test procedure and before driving do a brake check. You are experiencing what that test would have revealed.

My gut tells me you have a leak in a hose, or depending on the age of your brake chambers a leak in the brake chamber diaphragm. Neither is a big deal to repair or replace but until that repair is made you should not be driving the coach. If the leak is in the diaphragm the diaphragm itself is replaceable but if you opt to go that route rather than just replacing the brake chamber as an assembly pay attention to the surface condition of the metal disc the diaphragm pushes against. If it is corroded and has a nasty surface it should be cleaned, smooth and protected against corrosion otherwise that rough surface is going to wear the diaphragm prematurely and you will be replacing it soon.

belfert · August 27, 2011, 11:23:10 AM

I was pretty sure it shouldn't be leaking, but I had to ask. I have performed the full air brake check from the article by RJ Long over on BNO. The bus passes these checks.

I guess I can crawl under there and see what I can find. Time is my enemy as I'm heading out Wednesday.

Just Dallas · August 27, 2011, 11:36:06 AM

Brian, it passes because your dash gauge is on an accessory tank, not on the brake tank. The accessory tank has a check valve to keep it separate from the brake tank, so it won't show a leak when you step down on the pedal.

Shouldn't you have found this leak weeks or months ago instead of looking for other stuff?

Just askin'.

Quote from: belfert on August 27, 2011, 11:23:10 AM
I was pretty sure it shouldn't be leaking, but I had to ask. I have performed the full air brake check from the article by RJ Long over on BNO. The bus passes these checks.

I guess I can crawl under there and see what I can find. Time is my enemy as I'm heading out Wednesday.

belfert · August 27, 2011, 11:44:54 AM

Quote from: Just Dallas on August 27, 2011, 11:36:06 AM
Brian, it passes because your dash gauge is on an accessory tank, not on the brake tank. The accessory tank has a check valve to keep it separate from the brake tank, so it won't show a leak when you step down on the pedal.

Shouldn't you have found this leak weeks or months ago instead of looking for other stuff?

Give me a break. I pay others to check out the brakes since I'm not an expert on these things. I had C&J Bus Repair check the brakes back in May and they didn't find any issues. I've driven maybe 100 miles since then. C&J redid the brake shoes and drums back in 2006 and they have checked the brakes at least annually since then. It was dumb luck I noticed a couple of minor leaks. It isn't exactly normal to force the service brakes on and walk around the bus.

I have both a front and rear air gauge and both read fine. The bus still passes R.J.'s air brake checks.

bobofthenorth · August 27, 2011, 12:07:04 PM

Probably 99% of the air brake systems on the road have some level of air leaks - maybe 100%. Its a matter of degree when they become serious enough to impair your/public safety. That's what the air brake tests are set up to determine but its still a continuum - its safer if it passes the test but its not "100% safe" just because it passed the test. Similarly its not a death trap just because it has an air leak. I understand the reluctance to inspect something when you don't feel confident in your knowledge - I face that myself all the time. But I repeat, crawling around under there with a squirt bottle and a grease gun is a great way to inspect the system and you'll be surprised how much of it you understand. Its not rocket surgery after all - it can't be that hard - just look at all the cowboys on this BBS who DIY all the time.

belfert · August 27, 2011, 12:54:13 PM

I think the QR-1 valve is bad up front. I don't think it should be letting air out when the brakes are applied and not being released at all. It is cheap enough to replace.

I talked to the Freightliner dealer parts guy and he said it is probably bad, but he doesn't have one. The Peterbilt dealer does have one though.

belfert · August 27, 2011, 03:05:48 PM

I replaced the QR-1 valve up front and all seems well now. It took about as long to locate and go get the part as to replace the valve. No idea what is happening in the rear yet.

DMoedave · August 27, 2011, 04:31:22 PM

Way to go Brian, the same thing happened to me moving the coach recently. heard air applying brake, it was the hose front curb side, replaced both while i was at it.

jbnewman · August 27, 2011, 06:45:43 PM

Quote from: Just Dallas on August 27, 2011, 11:36:06 AM
Brian, it passes because your dash gauge is on an accessory tank, not on the brake tank. The accessory tank has a check valve to keep it separate from the brake tank, so it won't show a leak when you step down on the pedal.

It was my (perhaps inaccurate) understanding that by the mid-80's, gauges reflected dry tank, rather than accessory tank. Is this something folks likely have "mucked with", or did some manufacturers continue the accessory tank nonsense lots longer?

-jbn