Air pressure slow to build

[747guy]

When starting, front tank is lower than rear. I had a new air drier replaced last year. There was a leak in a shark bite type fittting on the air dryer which I had them reset in Pendleton OR on our way south.

now I am in Paso Robles and it is taking 5 minutes to get the low air alarm to go out and release the park brake.

while enroute, ii had the low air alarm come on for about 3-4 minutes, but the pressure on both tanks shoes above 75. Air gauge is badly calibrated and hard to figure out exactly what the pressure is.

no sounds of air leaking like I had with the loose shark bite fitting????

 

 

 

 

 

[96 EVO]

Yeah, 75psi isn't enough. You need to be up around 120psi!

Sounds like you have a bad air leak somewhere! Check the entire length of the airline from the compressor to the dryer, then from the dryer to the wet tank.

It's possible your compressor is failing, but unlikely.

Obviously, feel under the dryer ( the purge valve), for air releasing when it shouldn't be!

BTW... Are you regularly draining your air tanks? 

 

Edited April 12 by 96 EVO

[Frank Bergamo]

The air governor is probably your problem. They are not that expensive. Here is what you need, 

Bendix Or275491 - D-2 Air Brake Compressor Governor 

Hope this helps.

[96 EVO]

1 hour ago, Frank Bergamo said:

The air governor is probably your problem. They are not that expensive. Here is what you need, 

Bendix Or275491 - D-2 Air Brake Compressor Governor 

Hope this helps.

That wouldn't cause it to take 5min to build 65psi.

[Bar SR Ranch]

Check for a restriction on the inlet side of the compressor.

Pull the outlet line off the compressor and check for any oil in the line if there is oil in the discharge line the compressor is falling.

Not sure if Monaco used them but on the class 8 trucks they have one way check valves that can cause problems.

I have seen some air valves leak when there's less air pressure, may be try putting around 80psi and shutting off the engine and checking for leaks.

Also, probably not the case here but check your brake can diaphragm on the spring brake assembly these can leak when the brake is released.

If the spring brake assembly is leaking don't take it apart unless you know what you are doing you can lose your arm or head. 

[Frank Bergamo]

11 hours ago, 96 EVO said:

That wouldn't cause it to take 5min to build 65psi.

Yes it would. Had the exact same situation as stated in original post, replaced air governor, worked like a charm.

[96 EVO]

4 minutes ago, Frank Bergamo said:

Yes it would. Had the exact same situation as stated in original post, replaced air governor, worked like a charm.

Hmm, that's an odd one!

It would have to be loading / unloading the compressor, repeatedly.

[diplomat don]

23 hours ago, 96 EVO said:

Hmm, that's an odd one!

It would have to be loading / unloading the compressor, repeatedly.

Frank is correct as I have seen same or similar issues over my career. Ben I don't know where the air is going but the compressor can be working fine just doesn't build pressure. First thing to try is a hammer, hit the governor several times, not hard enough to break it but can knock some grit or whatever loose and the valve woks fine. Cheaper and easier than replacing the governor. Experience of 43 years and 4 million miles driving truck. 

[96 EVO]

I'll have to remember that one!

[747guy]

My service guy used his compressor to the front and rear access points. That seemed to make a difference as the compressor performance picked up noticeably. He also blew out the line to the governor.

when my dryer was changed a year ago the tech indicated the compressor was starting to push oil to the old dryer.

The Coach has been sitting during our visit in rainy Paso Robles. I have started it daily and the pressure seems to build much faster than before. Will be on I 5 Monday to Red Bluff CA so will see how she behaves.

cummins wants $2,300 for a reman. I found others on the web much cheaper.

Firsttruckparts.com has them for 1,349. However they will not accept CC and asked for a wire transfer. No reviews on the website. Set off alarm bells in my head.

[Ivan K]

Yeah, lot of fake scam sites on the net, I would not even consider such irreversible payment method. ISC/ISL compressor rebuild kit from Cummins is like $400.

[Ivylog]

Like EVO ^^^, check the SS braided line from compressor to air dryer… can’t hear it leaking when engine running. That was my issue for slow to fill… leak at the Adel clamp.

[Happycarz]

I couldn’t build air and I tried a governor first. No joy.

So I followed the Cummins QuickServe repair manual to diagnose it.  In the compressor head is a spool valve the shuttles back and forth. Cummins has a process to feed the head ATF to free it up. It probably would work better on a gummy valve rather than my stuck valve.  As I was on the way out of town, with friends waiting on me, I bought a new compressor head. 

Replacing it was a challenge with the compressor still in place. Fortunately, I have a side radiator. Otherwise the compressor would have to be removed to replace the head. Once the head was off, I verified that the valve was stuck, firmly. (When I returned home, I was able to free the valve with carb cleaner and a lot of work. Cummins procedure would not have help mine.) The new head fixed my issue.

This is not your issue. I bring it up so others will know that the compressor head valve can get stuck.

Governors, air driers, check valves, air leaks and now compressor head valves all can cause low air. Take your choice. 

But, share your story.