I just bought a 97 Freightliner FL70 with a 8.3 cummins and 6 speed manual single axle stake truck. The truck sat most of its life, has just over 180k on it. Awesome shape, even the a/c works great. Anyway, It has a weird issue with building air pressure. Dont jump to conclusions, read this first. It takes FOREVER to build pressure from 0-60 psi at an idle, if at all. Bring her up to 1500 rpms or so, it will build within reason, maybe 30-45 seconds. ONCE IT HITS 60 PSI, it will climb to 125 at idle very quickly. It will also hold pressure for days. I can leave it parked for 2 days and get in and still be at or over 80 psi. My concern is the slow build to 60. It has a cummins/holset 3558052rx pump in it, with a NEW governor on it. Heck, even if its at 60 psi and I release the parking brakes, by the time it rolls 50 feet at just over idle in 1st gear, I am at 125 psi.

Is this normal or something wrong somewhere, the guy at the truck parts shop said something about a low pressure valve, blah blah and did not say anything else. I am just worried I wont pass a level 2 inspection.

 

If the system won't build ANY air at idle, I would assume the compressor is shot, however...

Once it hits 60 psi the system really skyrockets?

What compressor and governor are you running? I am assuming it is a Bendix D2 governor which should have been pre-set from the factory.

With the symptoms, it sounds like the governor cut-in is grossly misadjusted.

Does your truck have a reciever/dryer? I know the two FL70 trucks we have do not have one.

One thing I find funny I'll pass on, one truck will sometimes have a hard time building air, until you pump the brakes (pressure is @ 0) and then all of a sudden it builds air.

Go figure.

Josh

 

If you don't get a good answer here, you can go to the American Truck Historical Society (ATHS) forums board, those guys are really sharp and can probably give you a good solution to your problem. Heres a link Road Kill Cafe and Coffee Shop

 

I just found this and don't know if you have found a solution yet but here's a couple things to try. First find the primary air tank ( often called the wet tank ). This will be the first tank after the compresser. You didn't mention if your truck has an air dryer if it does the primary tank will be the first one after the dryer. Next open the drain and let any moisture drain out. Now you'll need a known good test gauge with a rating of at least 150 psi. Tap into the tank ( most tanks have at least one unused port that is plugged off). Start the truck and compare gauge readings. Don't worry about the secondary side. It sounds as if it's okay. I suspect you'll find that the test gauge rises at a normal rate while the dash gauge lags far behind. If this is the case you'll need to replace the dash gauge. Also take a look at the main air line. This is the one that comes from the compresser. Leaks, kinks, or holes from chafing can cause similar problems. On your Freightliner this line should be covered in braided stainless. Be careful because they break the outer covering and leave razor sharp strands sticking out.

The problem that you're describing does not sound like a compresser or governer issue. In all of the Holset compresser failures I've seen the compresser just stops pumping.

 

you could have a bad purge valve, a bad protection valve to the secondary tank or a defective air governor

 

Sure sounds like this guy has a bad foot application valve.... as in the foot pedal valve is stuck open... $200 something from the dealer

 

I would suspect that the o rings in the compressor unloader valve are shot, and you need to Kit/Rebuild the compressors unloader valve/valves, behind the D2 Gov, on the comp.
at the bottom of this page shows the comp, and a unloader kit, or have a truck shop do the repair, it wont be that expensive, fairly easy job.hope that helps, Chellie

http://www.newlifeparts.com/nl/catal..._section_1.pdf

 

also, if the air drier has not been rebuilt in a while, have it rebuilt and drain your air tanks daily, to prevent problems with you air valves, leave the drain valves open on the air tanks, so any water can drain out, when not in use.