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Air Compressor governor part#
Driving back last night we had the pleasure of loosing air pressure as brakes were applied. The pressure went down from 120 to 100 and instead of recovering to 120 kept dropping until it stayed at a steady 50PSI.
We pulled over as soon as it was apparent the pressure was not coming back up. Shut down and checked for sounds of leaks and found none.
We started back up and I hit the brakes a couple of times and the pressure stayed at 50PSI but did not build any.
I was able to release the parking brake and by then my son was there so he followed us home, luckily only 5 miles at 45 MPH, fearing the parking brake would release if the pressure dropped much more.
I am suspecting the compressor governor is the issue but not having much luck with a part number. Looks like it might be a Bendix model D-2 275491????
Just wondering if anyone is sure of the part number before I remove this one.
Thanks,
Robert
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15 Replies
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Robert,
You might want to talk to Prevost service to see if they recommend replacement of the air dryer. It could be the governor or the pressure relief valve or even something else. Whatever it is you are going to hear the leak so if you can hook it up to shop air and safely get beneath the coach you will know exactly where the problem is. Don’t rule out anything including a failed relay valve.
I mention the replacement of the air dryer only if it is the culprit because your particular type with the bottom snap ring has been replaced by dryers with spin on cartridges which are much easier to service.
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The Governor can be bought just about anywhere that has truck parts including Napa, they are cheap.
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This is kind of a strange thing. I posted on here a little while back about trying to gain access from the floor behind the bed, which would be right above this area and here we go that is exactly where this issue is.
Kicking myself again for not digging that pit.
I hate Karma !!
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I still think you can get at the governor from beneath the coach. I spend many an hour sitting up in the area near the rear of the engine. If you can get under there you can sit up near the tag axle and reach the compressor if in fact it is the governor.
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Robert,
He was younger then and skinnier!!
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Yea, weren’t we all. I know there is a flap that runs across between the transmission and engine so there is no room for me to get into that area from below.
I bit the bullet and removed the floor access cover and I won’t go into detail here since I did go into detail in my other post about the access cover.
I filled the system with 120 PSI before replacing the governor and found no leaks, it sat there for 2 hours and did drop about 5 PSI but I did not think that was enough to prevent the compressor from building pressure.
Then I replaced the governor and it did not build any air. Decided to fill the system until the governor unloaded and then pumped the brakes until the pressure dropped from 120 to 85 and it started building pressure all the way to 100 in about 2 minutes. My maint manual says it should build from 85 to 100 in less than 25 seconds. I do not understand why it started pumping unless there is an issue in the compressor head,,,, valves etc.
Based on no large leaks and the time to build 15 PSI I am going to have the compressor rebuilt unless someone has another idea.
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Robert, Are you sure there is not a leak going on elsewhere when the compressor is pumping? Anything coming out of the bottom of the dryer?
Compressors don’t quit delivering instantly unless something is wrong. If your compressor was wearing out you would be spitting a lot of oil out of your dryer.
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I can’t hear any leaks, but with the engine running it is hard to say. I do not see anything on the ground under the dryer.
The only line I can not see completely is from the compressor to the dryer. I guess that might be leaking and if so the check valve would keep the system air from coming out of it when not pumping. If the rain lets up tomorrow I will crawl under and check with the engine running. I know there is no leak when shut off, holds pressure like I said above.
I have the bus out in the yard since that is as far as we got last night.
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First let me follow up on the governor part #s. The governor I removed was a 284358 specs say 105 – 125. I replaced with a 275491 spec 100 – 120. Called Prevost Jax and they said that was the correct replacement and the 5 PSI difference was a current spec for my coach.
OK, now I am really confused,,, Went out this morning to check the dryer and lines for issues while the compressor was loaded.
The Aux gauge was still holding 60 PSI but the Brake gauge was 0. Started up and the air started building like I have never seen before. Went from 0 to120 and unloaded in 3 minutes. Usually it takes at least 5 minutes. Got under the coach and the dryer and lines were not leaking.
Although the new governor did help, I am not comfortable with the huge improvement in performance I see this morning without any changes from last night. I still think like Jon said earlier there must be some erratic issue with the dryer check valve or purge valve. So I am going to either rebuild the dryer or replace it with the spin-on type Wabco.
At least now I know the compressor is pumping fine.
Is the Wabco System Saver 1200 the one used on the newer coaches ? Or is there another dryer that is more popular or better ?
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Robert, On my three coaches I have had 3 different Prevost installed OEM dryers. The second coach had a Wabco with a spin on filter, with the compressor mounted governor. I think that is the one Prevost would likely recommend as an upgrade. The one you have however is easily rebuildable.
The current dryer is a Haldex, and it has the governor internal to the dryer. I don’t think that would be a suitable replacement.
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Thanks Jon,
I think I will rebuild this one, it looks like a substantial dryer and the plumbing is good.
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Thought I would post the “Final Fix” for our air system.
Found the compressor was not discharging any air at the discharge fitting. After removing the floor access panel I removed the compressor head and found the unloader sticking and not allowing the intake valves to close to make compression. Rebuilt the unloader actuators and cleaned the intake and exhaust valves and seats, checked for leakage and reassembled.
It is now pumping great and the gauges drop slightly when the brakes are applied and recover fast. Also rebuilt the Drier and purge valve.
Only leak found was one of the tank drain valves had a slight leak, replaced the valve.
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Another air problem solved, thanks for posting the results.
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my 91 Prevost take about 8 minutes to air up at fast idle(1100) and then only produces 95 lb. of pressure.
Will not go to 120psi until on the road at 1500 rpm.
Have no record of ever changing the dryer filter. Is this step one?
Is replacing the compressor governor step two?
Am I correct you can rebuild the top end without removing the compressor?
Any/all help appreciated.
Whiskeybill
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I would certainly change the dryer element. You brake system is taking too long to charge and it could be an issu with the dryer, or the compressor could be getting tired. Since it does reach 120 PSI at higher RPM the first reaction I had was that you have a leak somewhere.
Do you?
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