Brake pedal valve

[Coco620]

(09-16-2018 )Chamberpains Wrote:  Which valve is it thats leaking?

The one that the brake pedal mounts to under the cab. 2-3 days after replacing the stock one that was leaking

[Coco620]

(09-16-2018 )snailexpress Wrote:  Is valve leaking from exhaust port or where?

Yes the exhaust port right at bottom of it

[Coco620]

(09-16-2018 )snailexpress Wrote:  I guess treadle valve.

Yes right under brake pedal under cab

[Coco620]

(09-16-2018 )dhirocz Wrote:  How does it act bobtail vs with a trailer?

Air pressure with the foot brake applied lower when this happens?

You could have a bad chamber backfeeding out the exhaust. For me, it only did it when I was bobtail...my tractor protection valve was at fault.

I also noticed when I started replacing valves the other ones in the circuit started acting up...I said the hell with it and replaced them all.

Also, you aren't using aftermarket valves, are you?

Seems to be the same bobtail, Yes I used an aftermarket valve

[Chamberpains]

Aftermarket makes me cringe. Bendix makes good reman stuff and hell new ain't that expensive. Almost any price is better than having to contort yourself up to get at that SOB more than once.

Well at least you say your working with a KW W900. They aren't the worst treadle valves to get to. Sounds like you got a faulty one. But also check that you have it plumbed correctly. Its a spider web of air lines but they all need to go exactly where they need to go or the valve will not send air where it needs to go. Sometimes causing your exact problem.

[Coco620]

Thanks much to all of you for helping, I think I have to ger under that cab again & go to work! Not fat guy friendly under there Lol.

[snailexpress]

Some words about weak brakes as I was dealing with this recently.
Weak tractor brakes and good trailer brakes could have many roots.
1. Greasy brakes on the tractor. I.m not kidding. Quick lube bay monkey never watching grease coming out from S-cam bracket inside the brake. Then grease got heated and dropped on the drum. Brake shoe is done.
2. If truck equipped with advanced ABC the ABS module sensing truck load from rear air suspension air pressure sensor. So ABS is determine is truck loaded or bobtail. If sensor reading wrong or intermittent ABS thinks you are bobtail and weakened brakes. On my truck it was like locking trailer brakes up to trailer ABS release and truck was rolling without brakes till ABS is reset. Replaced the air suspension sensor and brakes are back to normal.