Air Brake issues M1079

[Mike Robo]

Blue glad hands front and back leaking air when i press the brake pedal. I removed the glade hands and plugged them up with a brass fitting, i don't use them. Now when i apply the brakes, the whole truck locks up. The reason i'm trouble shooting the brakes is thier was very little braking power to the rear wheels. I adjusted the rear brakes they are operating as they should. Checked the weight sensing valve and air is passing throw it. Im not sure what valve is acting up. If i loosen the plugs in the glad hands the truck will move but air will leak out and very little braking power to the rear wheels. Any thoughts are appreciated

 

[coachgeo]

replace the valve behind the washer bottle that is closest to top front of truck. It has a sensor screwed to it... other two do not. (probably best to replace all three and get rebuild kit for each for future)

You reach the valves under there with cab up. they are above driver wheel well on the wall of washer bottle box/step driver side

ps...
. if you have not already; download the technical manuals (TM's) if you have an A0 truck (3116 engine). Well even if you have A1 they still help a ton.*
. see the threads pinned to top of this forum. the parts spreadsheet in particular

*TM section for downloading is the top most forum on this discussion board.... back on the first page with menu of forums on this site.

 

[Suprman]

The rear ones can be the tractor valve under the back rear. There are 3 diaphragm valves under the drivers side when you fold the cab. I would replace or rebuild them all. Not good to block off gladhands. The brakes will not function properly like that.

 

[Ronmar]

You must block/cap the rear gladhands unless you are connected to a towed vehicle/trailer.

the front gladhands are vented and air coming out of those indicate a bad 2way check valve under the drivers floor behind grill. Top one is for park/emer brake, the lower two valves are for primary and secondary brakes. If you are leaking air out of the blue service gladhand up front it is one of the lower two valves. Yes, capping the front gladhands will cause a lockup if the 2way checks are leaking past...

 

[Mike Robo]

replace the valve behind the washer bottle that is closest to top front of truck. It has a sensor screwed to it... other two do not. (probably best to replace all three and get rebuild kit for each for future)

You reach the valves under there with cab up. they are above driver wheel well on the wall of washer bottle box/step driver side

ps...
. if you have not already; download the technical manuals (TM's) if you have an A0 truck (3116 engine). Well even if you have A1 they still help a ton.*
. see the threads pinned to top of this forum. the parts spreadsheet in particular

*TM section for downloading is the top most forum on this discussion board.... back on the first page with menu of forums on this site.

 

[Mike Robo]

I was leaning towards those valves but wanted to double check before i started throwing money out the window. Thanks for the reply.

 

[Third From Texas]

You must block/cap the rear gladhands unless you are connected to a towed vehicle/trailer.

the front gladhands are vented and air coming out of those indicate a bad 2way check valve under the drivers floor behind grill. Top one is for park/emer brake, the lower two valves are for primary and secondary brakes. If you are leaking air out of the blue service gladhand up front it is one of the lower two valves. Yes, capping the front gladhands will cause a lockup if the 2way checks are leaking past...

^This is what I've always read.

Don't cap the front or it can't vent (and thus lock up the brakes). There is a way to do it, but it involves dome tinkering and re-routing.