Pacbrake blows down the air tank w/o working.

[Tuesdak]

Looks like there are only 2 electrical devices other than the compressor. One pressure switch and one valve. Compressor runs and builds up air.

I can't get it to work with the engine off and doesn't work when running. I can move the brake valve assembly so it isn't frozen.

Manually putting power to the valve that goes to the air cylinder on the exhaust causes a hissing at the valve and blows down the air tank quickly. Air appears to be coming from the bottom of the valve hitting the radiator hose. I assume the air release to shut off the brake is stuck open. Is it possible to service this valve? (It's expensive enough to try.) Maybe I am missing something?

Pacbrake says need a new valve, P/N C11935, and it would be a rare failure.

 

[richardcoxid]

It sounds like the “O” rings are shot or a piece of dirt has locked the spool in the vent position.

WARNING- cleanliness is a MUST the clearances are small!

Remove the control valve, my valve has 4 screws holding the cover plate on, Remove the 4 screws and cover plate. Pull out the valve spool, remove the “O” rings and buy new Buna-N rings (available at Lowes, HD etc) Reassemble in reverse order using a small amount of grease compatible with Buna- N “O” rings. Make sure that the spool is free to move when you reassemble it.

 

[ScottLewis]

Apparently, PacBrake has used more than one type valve. Mine began sticking closed recently and I pulled the valve apart, cleaned, lubed and re-assembled and it has been fine since. The nut at the bottom can be loosened and removed with a 9/16 wrench The cylinder then lifts out of the coil unit to be dismantled on the bench. There is a rubber seal at each end of the plunger that seals against a small orifice, top and bottom. If air blows out the bottom of the valve it isn't sealing there when the valve is activated. If the rubber seals look ok there may just be some debris inside.

 

[Prairie Dog]

I'm beginning to think PB never made two compressor assemblies the same.. Mine doesn't look anything like that or any others I've seen.

 

[jelag]

Let me try and help... the compressor charges the air tank and when the switch is closed and the throttle is at idle the solenoid will open allowing air to the cylinder... At the cylinder is a valve to dump the air quickly when the switch is turned off or the throttle is opened... thus turning off the brake... the compressor want to see a key on... and power is applied to the compressor until the air pressure limit switch shuts down the compressor.. once the tank is charged it should cycle the brake 4-8 times before the compressor starts again...

If your truck is tied to the ECM it will not work with the engine not running or the key off.... and in some cases it won't when the truck is stopped based on how the ECM in the truck is programed ...

I've never seen the valve at the cylinder to dump the air... go bad... I sold and installed the product for almost 20 years before retirement... I've seen a lot of bad solenoids... and air cylinders with bad seals that leaked air...

If you have just one air line running to your exhaust brake than the air cylinder returns by spring pressure... so when the brake is applied it must overcome spring pressure to apply the brake... in most cases its not easy to turn the butterfly against the spring...

So I'd suggest you unplug the air from the cylinder and apply 50-60 lbs of air to the line going to the air cylinder with the engine off.... take a bottle of soap and water and look for leaks... if this portion of the system is good... than reconnect it back to the solenoid and apply 12 vdc to the solenoid and turn it on... If the ECM is part of this circuit.. you must isolate the solenoid and add power and a ground... again with the truck off... remember you must have air in the tank... now check again for leaks...

The ECM in the circuit supply's a ground to the solenoid to turn it on... and the switch supply's a ground to the ECM telling it that you want the brake on when the ECM deems its necessary...

The biggest problems is water in the tank from the air system.. its never drained... the tanks rust... the rust is pushed through the system and sticks closed or open the solenoid... and/or damages the seal on the cylinder where the rod goes through the cylinder...

And YES PacBrake has changed the compressor many times... each time to solve either a vendor problem or to improve the system.. I'm a fan of their products but often disagreed on how their wiring sorted out... there was several of these systems that real issues with the way the wiring was routed... and there was a lot of simpler/better ways to do this... and make it simpler to sort out...

In each case my guys who installed them... could diagnosis the system in 15 min and know what was wrong... but to do that you have to fully understand the theory of operation, which I've tried to share above...

 

[Tuesdak]

I have the 'old' style where there is simply a line to the air cylinder on the exhaust. There does not appear to be any way to release the air at the cylinder like the 'updated' designs appear to have. I think it is a quick release valve or something like that - mine doesn't have it best I can tell.

Should I retrofit or upgrade my system to include the quick release part(s)?

So the air appears to be coming out of the only solenoid in the system when I manually activate it with jumper wires. The rest of the ECM or 'switching' for the system I have not tested yet. It fails a basic function test now. It may have other issues after the basic system is 'fixed'.

 

[jelag]

so your solenoid had 3 air lines connected to it... one from the compressor/tank and the other two to the air cylinder...

If that is the case when the solenoid is at rest... air is supplied through a port on the cylinder from the compressor/tank to one side of the cylinder... this line supplies line pressure to the back side o the cylinder to hold it open... than your cylinder won't have a spring inside it... and you'd be able to swing the butterfly with the system down....

Once the switch comes on... a ground is supplied... power from the key on is supplied to the 12v+ side of the solenoid... so once the switch is closed AND the engine is at idle the solenoid switches... opens to the atmosphere back side of the cylinder and supplies air to the operational side of the cylinder..

I'd do this... I'd open the air line between the solenoid and the tank/compressor and install a tee... available at home depot... and supply air from a shop compressor... with air supplied by this compressor.. I'd use the soap water and look or leaks... than I'd supply 12+ and ground to the solenoid and turn the system on... and leak test and solve all the leaks...

These compressors have a duty cycle of about 18-25% which means they can't run more than that percentage of time or they will burn out... from all I've read from what you've said.... and again I'm trying to read between the lines as your not as definitive as I'd like to give you very solid information...

Solve all the leaks... if the solenoid leaks at any time replace it... if the air cylinder leaks replace it... either call PacBrake directly or try Grainger in your town... any solenoid with 1/4" npt ports will work if you carry your old one in ask or one with the same operation.... and its my impression most of your issues are leaks... once you have the solenoid working and the leaks solved than move on to the electrical...

you again didn't say if your truck ties into the ECM.. I mentioned earlier that I sold and installed these... also ran them on my own rigs... I often owned 4-5 trucks at a time and ran them for 400K miles before I sold them... We checked for leaks 2 times a year... in the fall when we checked for the trucks for winter and than in the spring... leaks would destroy the compressor and water would contaminate the solenoid and rust out the tank... but 2 services a year would often prevent any issues...

If you upgrade you need to replace the air cylinder and add the quick relief valve, and drop the line on the other side of the cylinder and add filters to each of those connections... again available at www.grainer.com or their local store... I WOULD NOT do this unless the air cylinder was bad.....

I've not seen a solenoid leaking excessive air... most of what they used could be torn down cleaned up and assembled.. a little Vaseline on the valve keeps it moving.... the ports can be cleaned... its spring loaded and will pop apart if your not careful... its like a spool valve in a transmission... some have a push button hidden in the center of a rubber grommet on one end... you can push it with a small allen wrench and switch the valve without power...

 

[Tuesdak]

Red arrow is where the air comes out when I power the valve above it. Some minor air leaks on the tree from the compressor that need attention. (Hmmmm... A lot of mass with that tree unsupported on a vibration prone diesel engine.) I will start by rebuilding the valve and fixing air leaks. I am not sure if this goes through the ECM or not as I haven't traced the wires. It has 2 relays on the driver's side firewall.

 

[jelag]

I'm sorry to maybe have miss led you.... yep your solenoid is bad... I'm guessing you'll need a new one... but you don't have a spool valve in this solenoid.. and I didn't see a second line to the air cylinder... if there is no second line and only 2 connections to the solenoid then there is a return spring in the cylinder to bring the butterfly back open... on the rod end of the cylinder there should be a muffler.... make sure its clean and you can blow through it...

 

[ScottLewis]

Your pump and solenoid is like mine. The solenoid directs air to the cylinder when activated and dumps air from the bottom when off. There are rubber seals at both ends of the plunger inside. A spring holds it against the top orifice, shutting off the air. When current flows through the coil, the plunger is pulled against the spring to seal at the bottom while the brake is activated, directing all the air to the cylinder. If the plunger isn't pulled all the way to seal at the bottom, air will escape from the bottom instead of expanding the cylinder. Inspect the plunger for damage to the rubber seals at the end and assure that it and the chamber are clean. Unfortunately I haven't been able to find a source for just the plunger so if it is damaged, You will probably have the buy a new solenoid valve. PacBrake [Doug Scott (dougscott@pacbrake.com)] quoted a price of $73.77 for one. I didn't verify that it was the correct one since mine is working OK now.

ps. The return spring for the brake is external, on the butterfly shaft, rather than in the cylinder. One of the reasons Pac Rx. using their lube on the PBRX as directed.

 

[Tuesdak]

Several designs out there looks like and that is what made it interesting to figure out. Will be a weekend project. Thanks, at least I have a better idea of how it should work.

Any tips to see if it is ECM controlled or not?

 

[jelag]

one wire from one of the relays will go to the ECM and one wire from the off/on switch will go to the ECM.. I can't remember if you have a throttle cable... if you have a throttle cable there is a mechanical switch on the injection pump close to where the throttle cable runs into the pump.... this is the switch that keeps the brake from coming on when the throttle is down... this switch will be in series with the switch on the dash/shifter...... the throttle switch closes... the dash switch closes and the brake works.... if either switch is open (off idle or turned off) than the break will not work...

If its tied to the ECM it might not run at idle not moving based on the programing of the ECM...

And if its connected to the ECM it will be 2 wires in a plastic wire loom not in the factory wire loom... that's the easiest way to tell... just look at the ECM looking for that extra loom....

 

[Prairie Dog]

I have a throttle cable and the PB is connected to the ECM. The ECM provides a "low" or ground for the relay on the PB when zero percentage throttle is seen.
A micro switch isn't needed in this configuration unless a person doesn't want to connect to the ECM (per PB instructions). All third gens (even autos) have the signal present for the EB. In the rare case that they don't, it's because there's a problem with it seeing zero throttle.

 

[ScottLewis]

JDoremire





JDoremire: Sent you a PM.

Dan

 

[Tuesdak]

Ok finally got it working. Thanks for the help. Mine is ECM controlled. Fixed the solenoid as per advice above and PM. Then fixed the massive air leak at the cylinder air line. Then the connector at the compressor for the solenoid was 'open' - likely from me putting in a probe to manually activate the system. Crimped a butt connector on the wire and eliminated the bad connection.

 

[Prairie Dog]

Great, thx for updating us.

Scott