Bad regulator?

[John Banks]

The other day while driving the Freightliner, I noticed that the dryer kept purging the secondary tank. I also noticed that the primary air tank was a bit above normal or 125 psi, it's usually right on 125 psi. It was raining so I thought it was obviously just the moisture. Today while I was out I noticed the same thing, the secondary tank keeps purging (via the dryer) just below 125 psi, then within a minute or so, the pressure creeps back up and it purges again. It does this constantly every minute or so. If I pump the brake, I can get the primary pressur ebelow 125, but it too creeps back up just over. I've drained both tanks a number of times manually. I spoke with another guy who has a similar truck and he said his does it all the time and he's never had a problem. I'm thinking maybe the regulator is bad...any thoughts?

[Jeff D.]

John,

There's a small air line that runs from your air dryer to your govenor(on the compressor).If this line(I think it's referred to as an impulse line),has a leak in it anywhere it will cause this type of behaivor,cycling before the air pressure in the tanks drop's to the "normal cut in pressure",although there may be other causes too.This lines function is to tell the govenor when to start the compressor building pressure.The govenor can be adjusted to change the air pressure max.There's usually a black plastic cover that can be threaded off.Under that there's and adjustment screw,and lock nut.Loosen the locknut,and turn the screw to change the pressure.I can't remember if in,or out,increases pressure.The change will only be noticed after the next cycle.

Good luck,

[John Banks]

Thanks very much Jeff. Funny you mention the leak. After shutting the truck down and looking at this more closely, I did hear a slight leak. I haven't been able to find it yet, but I can hear it. I'll keep looking. Thanks again!

[John Banks]

I did find a leak. It was one of the air-lines that run to the selector switch. I replaced it today, all of literally $1.86 for the new line and a sleeve.

However, it's still cycling. About once every 10 seconds, the pressure rises in the secondary tank, the valve on the dryer opens up and purges. Once I shut the trucks down, it holds pressure, therefore leading me to believe there are no more leaks, none that I can hear or feel anyway.

I have looked at all the air lines and everything looks ok.

Would running the a/c have any affect on this type of condition? I wouldn't think so, but it's the only thing different in running the truck since this started.

[Jeff D.]

Have you checked the air compressor govenor,make sure that it isn't loose on the compressor?I've seen where they can loosen up causing this behaivor.It has two bolts holding it too the compressor.I won't leak air when shut off if it happens,but it won't control the compressor correctly.

Othewise,the air dryer may have some issues,internally,too.

[Ford LT-9000]

Was there any white snot come out of the air tanks ?

When has the last time the air dryer been serviced ?

[John Banks]

This sounds dumb, but how hard should it be to find the compressor? I'm probably looking right at it, but don't see it...I can follow the lines all around, but nothing looks like a compressor with a regulator to me. On the firewall there is a distribution block/manifold where the lines appear to enter and exit, green ,red, yellow, blue colored lines.

The dryer has never been serviced, truck is only 1 1/2 years old. No white snot coming from the tanks, all clear.

[digger242j]

Did you try following the belts? The thing that's not the fan, alternator, power sterering pump, or crankshaft, might be the compressor...

[Jeff D.]

The compressor is mounted to the engine.It'll look similiar to an air compressor on a garage style air compressor.They usually have two cylinders.On the compressor there is an aluminum small cylinder looking device mounted too the head.This is the air govenor.There is one small plastic air line going to it,from the air dryer.This is what controls the compressors air building cycles.The air govenor has two bolts holding it too the compressor.The comprssor also has one large air line going too it.This is the line that feeds your air system.

[Jeff D.]

Most compressors are driven via gears internal too the engine,although some are belt driven.

The air govenor is an inexpensive part.About $15.00,and easy too change.On the end of the cylider part of the govenor,is a round black cap,that is threaded too a screw.If you thread that cap off,under there is a locknut for the screw.This screw and nut are the air pressure adjustments.

Very rarely they'll mount this air govenor away from the compressor,on the firewall.But usually only when there's no room for it on the compressor.

What kind of motor do you have?I might be able to tell you which side of the block too look for it.

[digger242j]

Most compressors are driven via gears internal too the engine,although some are belt driven.


Yeah, that's why I said "might". Although in my experience, most of the ones I've seen have been belt driven. (But I've never owned a new truck either.)

[John Banks]

It's the MBE900 motor, built by DT, although not a 60 series, badged by Mercedes. That's what's throwing me, I've been looking at that serp belt and everything coming off of it and still don't see it. I'll look at it again tomorrow. Thanks again guys, I sincerely appreciate it!

[Jeff D.]

John,

That engines compressor is on the left side of the engine(sitting in the drivers seat)and is driven from the rear of the engine(mounted backwards).The Govenor may be mounted remotely on that one due to the frame rail interferance.

Digger,I hope I didn't sound like I was being sarcastic with my reply.That's not what I intended.I apoligize if it did.You are right many are driven by belts.Usually on the V-8's.Most of the bigger 6 cylinder diesel engines are by gears though.

[digger242j]

Jeff, as long as you don't start writing any more poetry, you can say whatever you want to... :wink2

[Jeff D.]

Jeff, as long as you don't start writing any more poetry, you can say whatever you want to... :wink2

Notice I didn't say "You're Momma!!" either.:rolleyes:

I guess "Ode to Dryer McSpitsalot" or the child's version "Lenny the dumptruck get's the hiccup's" are out then,huh??:cool:

Good luck John finding the problem.

[Ford LT-9000]

Nothing can be as bad as a old truck with 2 stroke V series detroit where the compressor runs off the back of the engines gear train. What a SOB place to get at.

Its pretty rare to see belt driven compessors usually they were on old gas pots and engines like the 3208.

If its a newer truck there probably is so much wiring and hoses etc all over the side of the engine its probably hiding the compressor. The newer trucks with engine shoved under the cab worse than a Louis Ford its hard to see anything.

You should beable to follow some cooling lines look like heater hoses to the air compressor aswell its water cooled.

Also watch out with the plastic air line its not that strong it kinks easy worse yet breaks. When tightening the plastic air line fittings don't over tighten them. Some fittings just have a brass furrel some have a sleeve on the inside to keep it from colaspsing.

Good Luck :bouncegri