Compressor for air brakes in 1995 U300

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Compressor for air brakes in 1995 U300

July 12, 2020, 01:03:55 pm

Does anyone know the model # of the compressor for air brakes used in 1995 U300? Ours is not working and the previous owner had tied the lines into the compressor for the air ride.
My husband took it out but the model number is worn off.
The brand name is GAST.
Thanks Susan

Re: Compressor for air brakes in 1995 U300

Reply #1 – July 12, 2020, 01:25:50 pm

First some clarifications and questions:

The engine-driven compressor supplies both air brakes and air suspension.

The 12VDC compressor supplies air suspension for leveling.

1995 U 300 is the only year that used several different engines, so if you are referring to the engine compressor, we need to know what engine you have:

Detroit Diesel 6V92 (early ones only in that model year)
Caterpillar 3176
Cummins M11 (mostly later ones in that model year)

Re: Compressor for air brakes in 1995 U300

Reply #2 – July 12, 2020, 02:03:24 pm

Brett,

I was thinking that smog took the Detroit out of any 1995 models with mostly CATs and a few M11 in the big engine door models in that year. Perhaps some Detroit 1995 models were built midway in 1994 and listed as 1995. Anyone here have a big engine door U300 with a Detroit? Also, 1995 U300s had the six speed. Don't recall any Detroits matched with 6 speeds.

The big rear door on top of the large front access hatch sure make the '95 a winner.

Pierce

Re: Compressor for air brakes in 1995 U300

Reply #3 – July 12, 2020, 02:15:23 pm

Ours has the CAT 3176. The compressor that's not working is under the hood in front.
We noticed it was an issue when sitting at a traffic light with the brakes depressed. When the light turned green we were unable to go right away because the levelers had to build up air before we could drive.

Re: Compressor for air brakes in 1995 U300

Reply #4 – July 12, 2020, 02:32:16 pm

No, the Gast VACUUM PUMP under the front is to provide vacuum to the dash HVAC system. If non-functional, air will come out the defrost vents only.

Nothing to do with the air suspension or air brake system.

Tell us what your dash air gauges read-- normally and when this happens.

Re: Compressor for air brakes in 1995 U300

Reply #5 – July 12, 2020, 02:45:28 pm

Quote from: Rocky1down – July 12, 2020, 02:15:23 pm

Ours has the CAT 3176. The compressor that's not working is under the hood in front.
We noticed it was an issue when sitting at a traffic light with the brakes depressed. When the light turned green we were unable to go right away because the levelers had to build up air before we could drive.

Without the engine compressor working properly you could not drive AT ALL. When you step on the brakes at the light some pressure will drop but you will be able to take off immediately. The pressure will not build higher until it is less than 90 lbs, so I'm (we're) not sure what you mean by "unable to go".

Re: Compressor for air brakes in 1995 U300

Reply #6 – July 12, 2020, 02:47:42 pm

Quote from: Rocky1down – July 12, 2020, 02:15:23 pm

Ours has the CAT 3176. The compressor that's not working is under the hood in front.
We noticed it was an issue when sitting at a traffic light with the brakes depressed. When the light turned green we were unable to go right away because the levelers had to build up air before we could drive.

The Ford control for the dash HVAC is notorious for developing a leak when the slider is in the far left position. If your 12V compressor up front runs a lot of the time, put a stop on the sliding lever so it stops about a quarter inch short of the left position.

If you have trouble with brake air pressure, you may have a leak that needs looking at. Driving on the flat with your foot off the brake pedal, the pressure should remain pretty constant and not cycle much. It's from about 80 to 110 psi on ours.

Pierce

Re: Compressor for air brakes in 1995 U300

Reply #7 – July 12, 2020, 03:01:19 pm

It's actually a 89-96 Dodge Dakota control unit if this is it, but Pierce makes a good point.

Re: Compressor for air brakes in 1995 U300

Reply #8 – July 12, 2020, 03:47:06 pm

Susan and Bob,

Do you have the B-2036 Air Schematic for your coach? It should be in among the Owners Manual paperwork somewhere.

If you do have the schematic, then it is easy to see the flow of air from the engine driven air compressor and from the HWH aux air compressor. But as stated by Brett, neither of these air compressors have any connection to the GAST vacuum pump under the front hood.

We will need a much more complete description of the low air pressure symptoms you are experiencing before we can provide any help.

Re: Compressor for air brakes in 1995 U300

Reply #9 – July 12, 2020, 09:58:00 pm

We were stuck at a long traffic light. The light came on that said leveling system and the alarm went off just like it does when you first start it.
When the alarm quit we were able to drive.
He experimented to night in the driveway by pressing the brake and then letting off.
Pressured dropped 10 lbs each time he stepped on the brakes until it was down to 60 at which point it dropped out of travel mode, leveling system light came on and and alarm started going off.

Re: Compressor for air brakes in 1995 U300

Reply #10 – July 12, 2020, 10:16:50 pm

Rocky1down wrote:

Quote

"Does anyone know the model # of the compressor for air brakes used in 1995 U300? Ours is not working and the previous owner had tied the lines into the compressor for the air ride.
My husband took it out but the model number is worn off.
The brand name is GAST."
Thanks Susan

"Ours has the CAT 3176. The compressor that's not working is under the hood in front.
We noticed it was an issue when sitting at a traffic light with the brakes depressed. When the light turned green we were unable to go right away because the levelers had to build up air before we could drive."

There's a lot to unpack here but are we to understand that the air brakes are being pressurized by the electric compressor for the HWH leveling system? And yes, I understand that the Gast is probably the vacuum pump for the automotive climate control system.

Art

Re: Compressor for air brakes in 1995 U300

Reply #11 – July 12, 2020, 10:27:48 pm

Quote from: Rocky1down – July 12, 2020, 09:58:00 pm

We were stuck at a long traffic light. The light came on that said leveling system and the alarm went off just like it does when you first start it.
When the alarm quit we were able to drive.
He experimented to night in the driveway by pressing the brake and then letting off.
Pressured dropped 10 lbs each time he stepped on the brakes until it was down to 60 at which point it dropped out of travel mode, leveling system light came on and and alarm started going off.

OK, questions:

What was air pressure on the dash gauges when this happened? And a long shot: What was voltage on the dash gauge when this happened?

Perhaps separate question: When doing this in the driveway was the engine running?

Re: Compressor for air brakes in 1995 U300

Reply #12 – July 12, 2020, 11:18:57 pm

Susan and Bob,

Do you have the B-2036 Air Schematic for your coach? It should be included with your Owners Manuals & paperwork.

If you do have the schematic, looking at it will help you to understand what is causing your problem, and what we may suggest to correct it.

Re: Compressor for air brakes in 1995 U300

Reply #13 – July 13, 2020, 06:18:54 am

The engine was running. Bob thinks the voltage stayed at 13.5 but will check it again tonight to be sure.
Unfortunately this U300 was purchased as a repossession so didn't come with any manuals at all.
Foretravel sent me a basic manual by pdf file but it didn't include schematics.
Our 1996 U280 on the other hand, came with all manuals and every receipt for anything the previous owner ever added or fixed.
We flew to California in February to pick up the 1995 U300 and drove it all the way back to Ohio so the motor runs great.
Bob wonders if it could be a bad regulator?

Re: Compressor for air brakes in 1995 U300

Reply #14 – July 13, 2020, 08:16:26 am

Quote from: Rocky1down – July 13, 2020, 06:18:54 am

Bob wonders if it could be a bad regulator?

I will hazard a guess, based on what you have told us. It seems you had one (or more?) episodes where your system air pressure got below 60 psi (travel light goes off and air system pressure alarm sounds) and was very slow to recover back to "normal" pressure. But, it did eventually come back up to normal, allowing you to continue driving.

These facts would point to a sluggish D2 governor. The D2 is the device that tells your engine driven air compressor when to add pressure to the air system. If it is acting correctly, your dash air pressure gauges will fall to around 80-90psi and then the D2 will tell the compressor to kick in. Your dash gauges will rise to around 110-120psi and stop when the D2 tells the compressor to kick out.

Replacing the D2 would be a good move at this point. They are cheap (around 20-25 bucks) and widely available at NAPA dealers, truck parts dealers, etc. Replacing them is either easy, or difficult, depending on where it is located on your coach. I do not know where it is located on the CAT 3176 engine. Another member with that engine will need to tell you that.

Links below show you what a D2 looks like. They are adjustable so you can set the desired pressure range after installation.

NOTE: In this case, a new or rebuilt D2 made by either BENDIX or HALDEX will work fine. They are equal in quality.

[BENDIX D-2 GOVERNOR MANUAL Pdf Download | ManualsLib

https://www.napaonline.com/en/p/MBIKN18530?partTypeName=Brake+Governor&keywordInput=governor

Re: Compressor for air brakes in 1995 U300

Reply #15 – July 13, 2020, 09:36:40 am

Yes, we are kind of shooting in the dark on this one.

It could also be a leak in the brake system-- line or can IF the major drop in air pressure only happens when you apply the brakes.

As asked above, please tell us what air pressure is normally and what it does when the brakes are applied.

Also, just for drill, open the wet tank drain (driver's side just in front of the rear wheels) and let us know what comes out: clean, dry air/water/oil/white powder.

Re: Compressor for air brakes in 1995 U300

Reply #16 – July 13, 2020, 10:07:01 am

If stationary, you could apply pressure to the brake pedal keeping it constant and then watch the air pressure to see if it goes down a few pounds and remains there or continues to decrease.

At 1000 rpm in neutral, pump the brakes until the pressure drops to about 80 psi and starts to build to the pop off pressure (about 110 psi or a little higher) and let us know how long it takes.

For schematics, go here https://www.foreforums.com/index.php?action=media;sa=album;in=165 and go down the right hand column until you come to "schematics" and you will find the 12V as well as 110V schematics for your U300.

Pierce

Re: Compressor for air brakes in 1995 U300

Reply #17 – July 13, 2020, 09:01:13 pm

Have someone outside and listen at each wheel while someone holds their foot on the brake for leaking air.

Re: Compressor for air brakes in 1995 U300

Reply #18 – July 13, 2020, 09:47:06 pm

Ok. On my U270. Holding pedal down I have sound of air escaping to my left. Sounds like inside coach. I discovered it with everything running. No troubleshooting conducted yet.

Thinking of using aux compressor to charge air system. That way I dont have high ambient noise level.

It was loud, not a whistle. Sounded like air exhaust.

Mark

Re: Compressor for air brakes in 1995 U300

Reply #19 – July 13, 2020, 10:23:00 pm

Quote from: Texhub – July 13, 2020, 09:47:06 pm

On my U270. Holding pedal down I have sound of air escaping to my left.

I assume you are talking about the brake pedal?

If the sound of air escaping seems connected to pushing down on the brake pedal, then it is possible you could have a leak at one of the air line connections, or in the valve itself. The brake valve is a rather complicated device. I have not (yet) had the pleasure of needing to work on that valve on our coach. I am not looking forward to the experience.

Link below to a post by Don (Don & Tys) on a different subject, but he just happened to include a very nice photo of the brake valve on his U270, showing all the associated air lines that attach to the valve under the floor.

I can offer no further help on this subject, but I wish you luck!

Bit by the Sheppard M100 bug

Re: Compressor for air brakes in 1995 U300

Reply #20 – July 14, 2020, 08:24:15 am

Quote from: Texhub – July 13, 2020, 09:47:06 pm

Ok. On my U270. Holding pedal down I have sound of air escaping to my left. Sounds like inside coach. I discovered it with everything running. No troubleshooting conducted yet.

Thinking of using aux compressor to charge air system. That way I dont have high ambient noise level.

It was loud, not a whistle. Sounded like air exhaust.

Mark

Have you tried listening near the left front air brake chamber?

Re: Compressor for air brakes in 1995 U300

Reply #21 – July 14, 2020, 10:35:23 am

I had this happen after replacing my dryer filters. It took me a while to find I had never closed the wet tank drain valve! That's a major leak, yet the pressure was slowly able to recover and I was able to drive the coach. Stupid,yes. But you(or your wife if her hearing is better) should be able to hear this magnitude leak with someone pressing the brake pedal with the engine off.

Re: Compressor for air brakes in 1995 U300

Reply #22 – July 14, 2020, 12:07:24 pm

Not yet. Will update when able to.

Re: Compressor for air brakes in 1995 U300

Reply #23 – July 14, 2020, 06:52:44 pm

We tried pressing the brake with the engine off. The gauge just kept dropping. No leak was heard by the drivers front tire.
Tried holding the brake with it running. It dropped down to 55 and the alarm for leveling sounded.
Just idling with the brakes not on, it stays at 108.
The voltage is right at 13.5
I called Foretravel to see if they had the air schematic and they said they'd have Rodney either email me with it or call me.
I'm still waiting on a call back from them from two weeks ago when we had an issue with the isolater not working.

Re: Compressor for air brakes in 1995 U300

Reply #24 – July 14, 2020, 07:01:24 pm

Without the engine running but with pressure, have someone put pressure on the brake pedal while you go under and listen for leaks. Spray solution or soapy rag also good but you should be able to hear a leak unless you are a bit hard of hearing. Check all hoses and cans. Make sure the coach is blocked up and wheel chocks in place before you go under. If the pressure is dropping, it's going somewhere. Just have to find where. Does not take too much of a leak to let the pressure drop.

Never try to take a rear brake can apart. Serious injury can occur unless the internal spring is caged.

Pierce

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