air compressor

youngsamuel · Oct 28, 2009

I have an fl60 with an 8.3 cummins. The air compressor is working sporatically. When the truck is started pressure builds to normal but when the brakes are applied tanks do not regain pressure. Although when sitting still and the accelerator is pushed the pressure will build. I am in Ohio going to Carolina and my load picks up at 8 pm. If it is the governor is this an easy fix? Will it possibly make it home all I have for tools out here are wrenches. Any suggestions? Thank you

greg334 · Oct 28, 2009

It sound's like the compressor, not the governor but I am going to warn you right now - get it fixed NOW.

If it is shot there comes a time when you can't build up any air, and that may come suddenly. So you have no brakes with no air as you know and that is too dangerous to drive regardless how much money you may make on any run.

Many times the compressor piston and rings start to go but other times the valves wear out and won't seal, which may be the case guessing.

Replacing the compressor is a pain in the a**, it is cooled by the engine coolant and that means draining the system.

davekc · Oct 28, 2009

Could be a compressor, but not likely if it builds pressure. If it is a bad governor (easy fix), it will discharge continously
When was the last time you had the dryer cartridge changed?
How much water is in the tanks?
Too much water and the dryer valve won't open.
Lastly, if it fails to build pressure when brakes are applied but builds when not, it could be a cracked/leaking brake chamber.
Takes about a half hour to change one of those

Mdbtyhtr · Oct 28, 2009

If it is the brake chamber, change the whole thing, not just the diaphragm, they are very dangerous to cage and disassemble.

Greg, without air to release the brakes, you won't be moving anyway, the no air default is brakes applied via the springs in the brake chambers.

If the compressor is failing, you will often see oil in the air tanks when you bleed them, indicative of ring or piston seizure issues.

Scott

greg334 · Oct 28, 2009

Well sorry to be a smart a** but I spent some of yesterday and today replacing a compressor that had a cracked intake valve.

I understand what you are both saying, but the truck had the same symptoms as described by youngsamuel and the owner of that truck already had the lines, different valves and governor replaced. Pretty much a new air system now.

You could drop the air to 60 PSI by applying the brakes allowing the governor to load the compressor and then wait for a long long time to get it up to 100, let alone the governor unload the compressor. The faster the revs, the more it built up the air but no where near what it was supposed to.

The compressor wasn't the type that the head could be removed easily to replace it, so the owner bought a new one from the KW dealer and put it on. I took it apart, and discovered the hairline crack. I wedged a popsicle stick on the exaust valve, put it together then put 150psi on the outlet - it was hissing through the intake. The intake valve would fight the pressure and lose, releasing some of the pressure back though the intake.

youngsamuel, I would still follow the advice of all, starting with the brake chambers, just replace them first. Don't try to repair them, I wouldn't drive the truck but that's me.

youngsamuel · Oct 29, 2009

I appreciate all the info and while pleased I am a little embarassed to say the problem was water in the service tank. I changed the tank last spring because the previous tank had a pinhole leak and never held water. Needless to say it had plenty of water, but when drained the dryer valve functioned properly and all is well. Thanks again

Mdbtyhtr · Oct 29, 2009

Dave wins diagnostician of the year!

Scott

davekc · Nov 1, 2009

Mdbtyhtr said:
Dave wins diagnostician of the year!

Scott

Thanks for the plug. A tip to remember. Check for water in the air tanks!

Moot · Nov 1, 2009

davekc said:
Thanks for the plug. A tip to remember. Check for water in the air tanks!

Better yet: Drain your air tanks daily.

youngsamuel · Nov 2, 2009

It appears draining the tank is not the only problem. The brake system worked fine coming back from Ohio, but this morning the system would not build pressure. I intended to replace the governor anyway. Two questions
1) Where is the governor?
2) How do you diagnose the dryer to find out if it needs to be replaced?

youngsamuel · Nov 2, 2009

I spoke with two Freightliner dealers and both of them said there is no dryer on this model. Unless it was not included in the original spec sheet.

greg334 · Nov 2, 2009

The governor is either on the compressor or near it because what a governor does to unload the compressor is to shut cut off the intake or open it wide (depending on the compressor, some stationary ones open the intake).

The dryer doesn't show up on my build sheet for my truck, the build sheet actually followed the truck down the line and has almost ever part on it but it doesn't have two items, one is the Davco fuel filter and heater or the air dryer. Both of them are factory installed - it is mounted on the inner frame rail right next to the trans.

Most of the time the cartridge needs to be replaced, it should be every few years anyways. There isn't much to them to fix.

If you follow the air line, there should be a metal flexible line from the air compressor, you will either find the governor or the air dryer by following that line. Be very careful and don't grab it if the truck has been running, let it cool down for at least 15 minutes or better 30 minutes - compressed air is hot.

youngsamuel · Nov 2, 2009

Thanks Greg, from what everyone says when I get the governor in hand it should be self explanatory as to where it goes on the compressor. One dealer did say the dryer could have been left off of the build sheet so I came here. Even if I had the money to send it to the mechanic I want to know how to work on the truck for myself and what parts go where. Thanks again.

greg334 · Nov 2, 2009

Yea but having a mechanic takes the fun away from learning.

youngsamuel · Nov 5, 2009

Ok I am pretty sure this will be my last reply on this thread. I wanted to give a plug for a great mechanic. I got a load up here to Minnesota and had the money to fix the air problem. It was the governor as well as a leaking fitting behind the dash. I took the truck to Independant Diesel Repair in S. St. Paul. These guys were extremely helpful, courteous, and reasonably priced. Not only did they fix the air problem they fixed the ground post that was corroted and loose. The truck is running great and pumping fine. Also my tuck does not have an air dryer. One less thing to fix but not good for northern winters, but one fix at a time. So again a big thank you to Independant Diesel Repair, as well as those who responded to my question.