Air Pressure build slowly

Topic: Air Pressure build slowly (Read 1669 times) previous topic - next topic

Air Pressure build slowly

May 20, 2020, 12:47:06 pm

First trip out in a while, and the air pressure builds real slow. It will make it to 120psi from 20psi in about 10 minutes. Useing the brakes in the RV park to back in will cause the Air guage to fall below 60psi and spring brake will kick in. High RPM will increase speed with which air pressure will build up. I do no hear any air leaks. After 2 days in RV parks air guage show 30psi. 185K miles on my 95 U240 Cat 3116 no air bags. Can the air compressor be in need of overhaul? Cruise and throttle work fine. At 60 MPH air guage show steady at 110-120psi all the time. It does seam like the white needle on air guage will go down futher than red needle some times.

Re: Air Pressure build slowly

Reply #1 – May 20, 2020, 01:35:24 pm

Have someone listen for air leaks while you are applying the brakes. What you are describing is a leak after the treadle valve.

Re: Air Pressure build slowly

Reply #2 – May 20, 2020, 01:42:01 pm

Since you hear no obvious air leaks I would replace the D2 governor about 17.00 Always carry a spare if you don't already.. Air compressor last cheap part first. In conjunction to what Chuck said.

Re: Air Pressure build slowly

Reply #3 – May 20, 2020, 01:45:34 pm

Or you could have a leak in one of the cans. If it's in the back, you would never hear it with the engine running. Pustefix Amazon.com: Pustefix Premium Bubbles Refill 8.3 fl.0z.: Toys & Games solution sprayed on with a Dollar Tree spray bottle will find the leak. The bubbles don't pop for a long time, they just get bigger and bigger when there is a leak.

Pierce

Re: Air Pressure build slowly

Reply #4 – May 20, 2020, 02:09:06 pm

Like P said.. a canister won't blow air until you mash the brake. Get someone to listen for you.

Re: Air Pressure build slowly

Reply #5 – May 20, 2020, 02:51:08 pm

We had the same issue you described, recently. Taking Foreforum advice....

We listened but didn't hear any leaks.
Replaced the D2 with no change.
Replaced the air hose from the compressor to the air dryer, no change.
Replaced the compressor, all fixed.

I was due for an air dryer service so we replaced it with a reman air dryer

Re: Air Pressure build slowly

Reply #6 – May 20, 2020, 02:58:22 pm

Yes, ASSUME you have a leak "downstream" of the brake pedal. Run engine at 1,100 RPM or so to build pressure to cut out PSI. Turn off engine. Have someone step on the brake pedal while you do a "walk around/crawl around and listen".

But, it that isn't the issue, here is the order I would do a "diagnosis by parts replacement" (which I really hate to do):

Replace the D2 (governor) under $20.

If the air dryer is over 3 years old, replace with a FACTORY REMAN-- count this as preventive maintenance.

After that, back to basic diagnostic work.

The good news is with no air suspension/leveling systems your air system is VERY simplified.

Re: Air Pressure build slowly

Reply #7 – May 20, 2020, 05:04:24 pm

When I was coming back from New Mexico last year, it took a long time to build the air. I changed the air dryer cartridge and now she comes up to pressure quickly. My next move would have been the D2, but it was new the year before. The air dryer system was new in 2018.

Larry

Re: Air Pressure build slowly

Reply #8 – May 20, 2020, 05:07:46 pm

Thanks for all of the responses.
I made this topic at least 4 hrs ago, and I still have the 30psi from 2 days ago. I want to know why the air pressure builds up so slowly. It has never took so long to get to 120psi. Once at 120psi in the past, the air pressure would never go down much unless you pumped the brakes. Even at idle now, holding pressure on brake peddle, the air pressure gauge will stay at one number(it does not fall down). Just now as a test, engine dead, 30psi, press and hold brake peddle down for several seconds, red needle jumps down and then back up with white needle, after a couple of applies and release after few seconds, I still have 20psi both needles.

Re: Air Pressure build slowly

Reply #9 – May 20, 2020, 05:19:43 pm

This last test you did eliminated the brake system from your problem. Now you have the air compressor, line from the air compressor to the dryer and the dryer itself as the problem. The line from the compressor to the dryer will only have air pressure when the engine is running because of the check valve at the dryer. Do a good visual check of it as it has been posted before as the culprit with your symptoms. If the dryer hasn't been replaced in the last 3 years change it out. The air compressor would be the last thing I would throw parts at.

Re: Air Pressure build slowly

Reply #10 – May 20, 2020, 05:23:57 pm

is this black Haldex filter the air dryer cartridge ya'll are talking about?

Buy one at O'Reilys?

Pat and Thanks a lot

Re: Air Pressure build slowly

Reply #11 – May 20, 2020, 05:25:52 pm

Yes, that is the filter. But, from the looks of the dryer itself, it (valves and heater) have not been serviced in a long time.

Again, a Factory (i.e. Haldex) reman replaces not just filters, but valves, heater, etc. Basically only the metal case is reused.

Re: Air Pressure build slowly

Reply #12 – May 20, 2020, 05:32:02 pm

Brett, your thinking replace the whole thing that the filter is screwed onto?

what is a number and where do I get one?

I am out of town now.

Pat

Re: Air Pressure build slowly

Reply #13 – May 20, 2020, 05:33:24 pm

Pat,

Yes, "the whole thing" would be replaced by a reman Haldex dryer.

There will be a PN on the dryer itself. Most any parts house that deals with OTR trucks will have the reman units in stock.

Again, think of this as preventive maintenance. As several of us have said, if all you are trying to do is get back on the road, replace the governor first. But a parts house that has one will likely have the other as well.

Re: Air Pressure build slowly

Reply #14 – May 20, 2020, 07:48:12 pm

When my air dryer went bad after sitting in storage, I could get to 30 PSI and no more. Replaced the dryer assembly, like Brett said, worked perfect till coming back from NM. It would slooooowwwwly build air pressure to 110-120 and hold no problem going down the highway. Changed the cartridge out and pressure builds perfect now at fast idle. Haldex has a 2# and a 3# cartridge. I went with the bigger one. It wasn't cheap at Transwest. Seems like it was just south of $200, just for the cartridge. I could have gotten much better online.

Larry

Re: Air Pressure build slowly

Reply #15 – May 21, 2020, 09:30:22 pm

I get them at NAPA part number DA33100X Haldex

Re: Air Pressure build slowly

Reply #16 – May 22, 2020, 10:44:19 am

Thanks Red for that part number and source.

pat,

Re: Air Pressure build slowly

Reply #17 – May 22, 2020, 10:57:03 am

When you unscrew the filter, spray the basin with WD 40 or ATF and toothbrush out the goo that settles at the purge port.

Re: Air Pressure build slowly

Reply #18 – May 22, 2020, 11:04:57 am

Hi Mike,
I have made it to Gunsmoke Rv Park, Dodge City Kansas. Going down the road, no problem, gauge stays at 110-120psi. Going to try for home in the morning. I will do as Brett suggested and change the whole air dryer. i will update when I do that. I really appreciate all the help from everyone here.

Pat,

Re: Air Pressure build slowly

Reply #19 – May 26, 2020, 07:55:03 pm

I made it home with no problems, other that a patio awning deploy at 60MPH. I replaced the air dryer today with a napa da33100x. It is the same a my old one. I had to change 3 fittings from old to new. Hooked up the heater. I can tell no difference. The air pressure still builds real slow. It will make it to 120psi after 1300RPM for too long. Kill engine and check for leaks with windex glass cleaner, no leaks and I cannot hear any leaks. Gauge falls to 60 psi after 4 hrs. How long should it take to build air pressure from 30psi to 70psi??

Pat,

Re: Air Pressure build slowly

Reply #20 – May 26, 2020, 08:06:50 pm

60 psi to 110 psi is fairly fast but 0 to 60 psi takes about 4 or 5 minutes on ours. Windex is not good for bubbles. You need a soapy mixture so bubbles will show leaks. Lots of places for a leak to be so it takes time to find the leak. Any water in wet tank?

Pierce

Re: Air Pressure build slowly

Reply #21 – May 26, 2020, 09:43:13 pm

I use a product called Super Miracle Bubbles which is a bubble maker for kids to make bubbles.

Re: Air Pressure build slowly

Reply #22 – May 26, 2020, 10:04:44 pm

I will look more tomorrow with dish soap and water. I was check my work today on the install of the air dryer. BTW the napa dryer was $275 with exchange of old unit.

Pierce are you talking about idle RPM(,ine is 700) on the 0-60psi

Pat

Re: Air Pressure build slowly

Reply #23 – May 26, 2020, 10:13:35 pm

I usually build air at about 900-1000 rpm. Idle is 600.

P

Re: Air Pressure build slowly

Reply #24 – May 26, 2020, 10:30:47 pm

Pat,

Gauge falls to 60 psi after 4 hrs. This indicates a pretty good-sized leak, as your only air is the brakes, air horn and "tire fill hose", not the complex suspension of other coaches.

Be sure to check the gate valve to the hose to fill tires. If leaking, replace with a DOT approved ball valve. Much better. Though I have not heard of it leaking, probably wouldn't hurt to check the air horn valve.

BUT, I don't think your leak accounts for that slow build. At under $25, I would sure change it and check hoses back there very carefully.

I know it has been mentioned many times, but have you replaced the governor?

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