Parking Brake Leak?

[Wryly Blithe]

Originally Posted by D Lindy

When you PUSH-IN the knob to release the parking brakes you will get a drop in air pressure because the valve is sending air to the rear spring brake to release the parking brake so the drop in pressure when releasing it is normal.

Yeah, I understand. What's not normal is how long the hissing lasts. It used to hiss for just a second or so... now it hisses for 10, maybe 15 seconds. It all ends up working normally - eventually - but there is a definite change it how it's operating.

I really appreciate your input!

[twinboat]

Check the yellow knob, some are held on with pins and crack. That causes it to not completely push the rod it's pinned to, all the way in, causing your hissing, until the pressure builds in the valve to hold it in..


If the knob screws on, loosen it a turn or two and see what happens. Check for a lock nut that has run down the threads. Also make sure the valve is not loose behind the dash, causing it to move away when pushing it.


I have seen all of these things happen.

[docj]

Originally Posted by Wryly Blithe

@Docj - I hear ya, and you may very well be right, but I gotta start somewhere and the plunger valve is the logical place. I hope it doesn't turn out to be what you went through, I got places to go!

I'm not saying you are wrong, only that I wouldn't be surprised if it is something else. I replaced the valve on mine first, also. It only took another ~$500 to get it finally fixed.

[Wryly Blithe]

Originally Posted by twinboat

Check the yellow knob, some are held on with pins and crack. That causes it to not completely push the rod it's pinned to, all the way in, causing your hissing, until the pressure builds in the valve to hold it in..


If the knob screws on, loosen it a turn or two and see what happens. Check for a lock nut that has run down the threads. Also make sure the valve is not loose behind the dash, causing it to move away when pushing it.


I have seen all of these things happen.

Wow, I hope it's this simple! Definitely gonna check. Thanks!

[Wryly Blithe]

Originally Posted by docj

I'm not saying you are wrong, only that I wouldn't be surprised if it is something else. I replaced the valve on mine first, also. It only took another ~$500 to get it finally fixed.

Yeah, that's my biggest worry, too. I don't mind fixin' stuff, but I do mind fixin' stuff and something else is still broken. I'll chase it down and let ya know... thanks!!!

[twinboat]

Keep us posted

[Dtwallace]

Originally Posted by Wryly Blithe

Hmmm... that's an interesting idea, and you're right - I should check it out. But let me ask: If this were the problem, would I hear the longer-than-normal hissing in the cab right behind plunger in the dash? That's definitely where the hissing sound is coming from, so just curious. But thanks for the info - I love learning new stuff everyday!

It sounds the same because part of the air will back up into the control valve, that's why I suggest to at least to check it. (the relay valve)

With some of the other comments you've made referencing turning the knob and the leak rate change, you'll more than likely be replacing the push pull control valve. The (O) rings inside of the valve do go bad.

And at least that's an easier and cleaner job also.

[Wryly Blithe]

Originally Posted by Dtwallace

It sounds the same because part of the air will back up into the control valve, that's why I suggest to at least to check it. (the relay valve)

With some of the other comments you've made referencing turning the knob and the leak rate change, you'll more than likely be replacing the push pull control valve. The (O) rings inside of the valve do go bad.

And at least that's an easier and cleaner job also.

Thanks for the info! I'm still going to check on that relay valve you mentioned - might as well, if I'm checking on everything else