Two Questions With Air System

[jeffl1107]

Hey guys,

This is two questions in 1 post. Have been doing alot of work on my truck and have now pretty much got it in good condition. Replaced all wheel seals, bearings and brakes. Some brake cans and slack adjuster and some other odds and ends.

Anyway, need your help as I cant seem to troubleshoot these two things.

First, my low air alarm stays on constantly, even after it has built up to operating pressure, around 125psi. The guy had it unplugged, so I plugged back in. Stays on all the time. Bought a new alarm and plugged it in and it still stays on. Not sure where to go from here with it.

Second, with my lift axle. The axle, when I pull the quick air release valve, goes down in under 10 seconds, but when I go to lift it up, it takes almost 90 seconds. It is a non steerable hendrickson axle. I replaced the in cab Velvac quick release air valve and still does it. The little valves mounted on top of each air bag release air but I guess not fast enough. If I go out after I push the valve to bring the axle up, while it is releasing, if I stick a screw driver in the end of valve above air bag and push in slightly, it releases with a vengeance and comes right up. Do you think it is as simple as needing to replace those valves with new.

Thanks for any help.

Jeff

[Rob]

Hey guys,

This is two questions in 1 post. Have been doing alot of work on my truck and have now pretty much got it in good condition. Replaced all wheel seals, bearings and brakes. Some brake cans and slack adjuster and some other odds and ends.

Anyway, need your help as I cant seem to troubleshoot these two things.

First, my low air alarm stays on constantly, even after it has built up to operating pressure, around 125psi. The guy had it unplugged, so I plugged back in. Stays on all the time. Bought a new alarm and plugged it in and it still stays on. Not sure where to go from here with it.

Second, with my lift axle. The axle, when I pull the quick air release valve, goes down in under 10 seconds, but when I go to lift it up, it takes almost 90 seconds. It is a non steerable hendrickson axle. I replaced the in cab Velvac quick release air valve and still does it. The little valves mounted on top of each air bag release air but I guess not fast enough. If I go out after I push the valve to bring the axle up, while it is releasing, if I stick a screw driver in the end of valve above air bag and push in slightly, it releases with a vengeance and comes right up. Do you think it is as simple as needing to replace those valves with new.

Thanks for any help.

Jeff

Hi Jeff, it does sound as if the quick release valve is slow to respond. These should get rid of the air just as soon as you push, or pull the control handle and not really delay as yours sounds to be doing. I'd go with a Bendix "QR" series valve.

Rob

[buddy]

Hey guys,

This is two questions in 1 post. Have been doing alot of work on my truck and have now pretty much got it in good condition. Replaced all wheel seals, bearings and brakes. Some brake cans and slack adjuster and some other odds and ends.

Anyway, need your help as I cant seem to troubleshoot these two things.

First, my low air alarm stays on constantly, even after it has built up to operating pressure, around 125psi. The guy had it unplugged, so I plugged back in. Stays on all the time. Bought a new alarm and plugged it in and it still stays on. Not sure where to go from here with it.

Second, with my lift axle. The axle, when I pull the quick air release valve, goes down in under 10 seconds, but when I go to lift it up, it takes almost 90 seconds. It is a non steerable hendrickson axle. I replaced the in cab Velvac quick release air valve and still does it. The little valves mounted on top of each air bag release air but I guess not fast enough. If I go out after I push the valve to bring the axle up, while it is releasing, if I stick a screw driver in the end of valve above air bag and push in slightly, it releases with a vengeance and comes right up. Do you think it is as simple as needing to replace those valves with new.

Thanks for any help.

Jeff

I would find the low air pressure switch and check it out,may be stuck. As far as the air bags ,check the springs see if 1 is not broke. Then i would spray some wd40 in the release valves on top of the bags. if no good clean those valves out or replace. just my 2 cents

[jeffl1107]

Yeah, both you guys make sense with regards to the lift axle. I have already taken each valve off, cleaned it good with brake cleaner and then shot in some WD40 and still the same. I know when I push the valve in, you instantly hear air and the axle goes right down. But when I push it in to raise it up, there is about a 6-10 second delay before you start hearing air and then it takes forever for it to go up. So I guess I will try and replace them. Only reason I asked is it seems impossible to find these things. I even called Hendrickson and they were having a problem figuring out what I needed. But a local parts store found what I needed and they are ordering them.

As regards to the low air alarm, finding the switch will be a challenge since I dont know where that would be.

Jeff

[joes mack]

the low air press switch prob is the problem with the alarm i would get a new pres switch ($8-12) at most parts stores for a pai bendix might be a little more. the low air press switch should be on the inside of fire wall just above brake pedal. it should have 2 wires. thats my 2cents worth joe

[jeffl1107]

thanks joe, I will check that out tomorrow.

[jeffl1107]

replaced the pressure switch and brake light is still on. I am at my wits end with this thing.

[joes mack]

some trucks have 2 of these switches they look sim but one of them will be for the brake lights on the rear of the truck one switch will be norm open and one norm closed the low air one should be the open one you can check this with a voltage meter. when the air pres builds up it should close it. someone could also have a wire crossed somewhere.you might want to check where the switch screws into the air line by starting the truck and see if air is coming out of the line it could be stoped up and not puting pres to the switch. this is all i can think of right now i hope this might help..joe