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brakes won't release


Ronbo

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2000 kenworth t2000. I was running around and stopped. Ready to go and brake won't release. Air leaking from yellow know. Replaced. No go. Air blowing from bottom of lt abs module. Replaced. No go. Air blowing out bottom of relaym replaced. Still no go. What next?

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Ronbo, are you building good pressure in your air system ? If so, how much ? A bad compressor, a blown line or a bad air governor could keep you from building air pressure. A ruptured diaphraghm in a brake can could prevent brake release. Will any of the brakes release or do they all stay locked ? I have seen ice and/or rust keep them from releasing but that was usually after they had been sitting for a long time....a big hammer may release them if that were the case. Current air brake systems are not simple. Please post what you find. Maybe someone with more air brake knowledge will post and be more helpful. I hope you are rolling by now. Charlie

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Guest Lostinaz

If it's blowing out your ABS valve,it's coming out a service line.

That would tell me to check that side brake chamber.

Like it's blowing from the emergency side of the brake chamber through to the service side.

If you pull the service line off the brake chamber on that side, try to put air to that brake chamber to release that brake,and air comes out the service port, you have a bad brake chamber.

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Guest Lostinaz

No, push in the yellow button which puts air to the brake chamber to release it.(it pushes back the spring)

If air is coming out the service port, you have a bad brake chamber.

The air is supposed to stay on the emergency side and hold the spring back to release the brake.

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Guest Lostinaz

When you go to replace the brake chamber, about 40 bucks, run the clevis lock nut way down the pushrod, then cut the pushrod EXACTLY the same length as the old chamber and unscrew the nut to chase the threads so the clevis will go back on.

You said air was blowing out the ABS valve exhaust, which goes to the service side of the spring brake chamber on that side of the axle-should be pretty easy to find which chamber is bad.

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See the little black hole in the chamber? Any air leaking from those holes is not good.

If you have that big a leak when you push in the yellow knob that the pressure just drops constantly, turn off the truck and listen. That big of a leak should be VERY obvious.

rearpushrodslackadjuster.jpg

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It sure sounds like one brake can is bad. Lets see you cannot cage them if you cannot build enough air to release it. So only solution is to back of the push rod to release that brake can. You can drive that way but will not have brakes on the location. I know some who have driven a pretty long way that way but me personally would not very far. I would consider changing all the brake cans as if one is bad the others my happen in a short time but maybe not who knows. I changed all my brake cans after I purchased for my piece of mind. :)

 

On edit: I am not sure what I was thinking but you can cage the brakes with no or little air pressure which will unlock basically the parking brakes. Now it something else is holding the brakes you need find and correct that!!1 :(

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Guest Lostinaz

The service port is where the service air line goes into the brake chamber.

The service port is closer to the bracket, the emergency port is closer to the spring chamber.

If you look closely, it should say service and emergency on the chamber ports.

If air was leaking from a blown rubber diaphragm out the vent holes Phil mentioned, it wouldn't be coming out the ABS valve exhaust port as you mentioned earlier.

On a KW there is an ABS valve on each side of the frame. If it is leaking out there, at the bottom of the ABS valve, it is probably a bad pushrod seal between the two brake chambers, in the brake chamber on that side.

If it is leaking out the vent holes in the chamber,(when air is applied to release the brakes) it is probably just a blown diaphragm.

Either way, you need a new spring brake chamber. They will be called a 30-30 chamber, and stamped on the chamber somewhere which refers to the 30 square inches in the diaphragm area.

If they look old and run in salt, Bob Cochran's suggestion of replacing both is not a bad idea.

Just use Teflon tape on the fittings you clean and re-use, and cut the pushrod length the same as original.

 

You can run with a caged brake, but block the emergency air to the disabled chamber. No need to lose all that air and overwork your compressor.

 

You can kink the line and zip tie it, clamp something padded across the line gently, or put a dime inside the fitting and tighten the line back down. Rub the dime on the pavement until it fits inside the swivel fitting on the air line. Your service brake will still work, but fix it ASAP because that's half your parking brakes disabled.

 

With both caged you have no parking brake at all!

 

Let us know how it goes...if you were nearby I would have you come over and show you how to fix it.

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I caged both rear brakes and didn't push in yellow knob. Worked great.

As Lostinaz said if you caged both rear brakes you have no parking brake at all. Hopefully you figured this out. Doing this is only meant to get you from where you break down to a place where you can get repaired, be it the farmers field next to the highway or the dealer in the next town. Not to drive until its convenient to fix. EMERGENCY USE ONLY.

 

Not to be a **** but this is yet another example of why there should be a air brake endorsement requirement. I am not talking a CDL of any sorts but proper air brake training.

 

Here in Alberta you can drive a "personal" HDT with a regular "car" drivers licence but are required to obtain your 'Q' endorsement (air brakes) to be legal, which is an 8hr course that teaches the basic operation, plumbing, and adjustments/maintenance of the air system, using a wall mounted functional mini air system. It teaches you enough information to eliminate probably 75% of the air questions on here. Plus when you properly understand how it is designed to function you will be able to use the system better.

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I know most pilots know how to fly and operate a plane but don't know jack about fixing them. Heck if they place too big a drink in their cup holder they call on a mechanic to remove the holder from the coffee cup and place it back in the tray for them!

 

Everyone has to learn sometime that they have something new to learn! The most dangerous person out on the road or shop is the person that is afraid to ask the questions and just tries to figure out on their own. Driving or working on these things can kill you fast if you are too proud to ask.

 

So thanks for posting this thread because ALL of us don't know everything there is to know about these HDT's or Life in general!

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That's a good one. :lol: But, a pilot is unlikely to stop, get out, and fix an issue, unless it's something on/in the instrument panel.

 

Sorta like apples v. oranges.

 

But, a class on air systems as a presentation at a rally might be a good idea. I've owned/driven air brake vehicles since 1963 (well, technically, Dad owned that one) and I'm still learning.

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Rick,

 

Great idea! Honestly, it's a good refresher course even if you know about the systems.

 

I'm 50 and it's funny when you run into a problem 20 years apart the second time you end up learning all over again until at the very end you're like, "SOB, I remember now that this happened 20 years ago and if I could rememberred that early I could been out a here 3 hours ago!"

 

For example, I have this race car that you can remove the 5/7 SBC spark plugs fairly easily but you'll never get them started into the threads again UNLESS you remove the valve covers! How do I know, me and 3 friends spent 7 hours trying! The header tube goes right overy those plugs and until I remembered that the first time I put the engine together that the valve covers were off when I the plugs in I was screwed!

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Went to th e truck today and released the parking brakes just like they are supposed to. Disconnected the service line and did not hear any air at port. I did hear air coming from vent holes on both sides. More on left than right. Replaced both cans and it works great. I believe the seal between the chambers was leaking intermittently and the problem would have returned at the most inopportune time

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