Left rally park Friday noticed when I started engine front air pressure was slow getting to pressure.warning lights went off got to 100+.we left the campground 1/2 way home front warning light came on went to 25 lbs.still had rear air at 100 lbs .shifted into 3rd gear pressure rose to 50 lbs kept driving got it to to a storage area next to a mechanic who could fix it .got friends to drive us home.We went back picked up things needed at home .Have to take another trip to Tampa.next weekend maybe. (Frog Creek)
WHAT DO YOU THINK HAPPENED?
LENNY

My first impression is a leaking front air-bag.

quote:

Originally posted by Stratosurfer:
My first impression is a leaking front air-bag.

Same here... sounds like it could be a leaking airbag.

thanks I will soap it later lenny

Doesn't sound like an air bag. Usually the dual front/rear gauge indicates air pressure in the front/rear braking systems. Air bags generally don't have any sort of pressure indicator and are normally sourced off a separate partition in the main air tanks.

Unless you know how to deal with air brakes, get it to a mechanic to find the leak.

Mike

I agree with Mike - according to Gillig and my mechanic it is almost never the bags - it is usually the fittings on the air lines or other connected devices - FYI, I found the air operated wiper switch on the dash was leaking slowly and that deflated the bags, caused the accelerator pedal and transmission shift not stop working, and the step to not deploy. Once the engine started and the compressor was working it overcame the leak and things returned to normal. Sprague Devices made the air operated wipers and they have rebuild kits for the valves that replace a leather membrane inside the switch. To test this you can start the engine and just rock the wiper knob for each wiper slightly and see if you hear air leaks. If so you need the kit.
Good luck.

On a truck, when an airbag blows, we have a psi protection valve that keeps air psi up in the system to 60-70lbs. The psi protection valve is designed to allow one to limp off the road.

He did find out that it was not the airbag in another post.

Not the airbags.

Bill, This sounds a little weird to me. I was under the impression that the front brake system had its own chamber in the air supply tank(s), the rear brake system had its own chamber in the air supply tank(s) and the suspension air came from a separate, third system along with distribution for the air throttle and other air accessories, with each protected by one-way valves. On my coach, all four airbags could blow up and the pressure to the brakes will stay wherever they were before the blowouts - usually up to 120lbs.

The dual air gauge on my dash indicates pressure in the front and rear brake systems with separate needles that vary from 90 - 120 as I use the brakes.

I have no idea (I've never measured it) what the pressure is in the air bag system - only whether or not the coach is at the correct height and level and there's nothing hissing at me.

The brake chambers fill first, then the third chamber is allowed to take on air after the brake chambers hit 90 lbs.

I guess what I'm saying is that I have never seen a dash gauge vary because of airbag problems.

One more thing I'd like to comment on is if the airbags in any way affect the pressure in the brake system - that's a serious design defect.

quote:

Originally posted by Relative:
I was under the impression that the front brake system had its own chamber in the air supply tank(s), the rear brake system had its own chamber in the air supply tank(s) and the suspension air came from a separate, third system along with distribution for the air throttle and other air accessories, with each protected by one-way valves. On my coach, all four airbags could blow up and the pressure to the brakes will stay wherever they were before the blowouts - usually up to 120lbs.

100% correct!

quote:

Originally posted by Relative:
I guess what I'm saying is that I have never seen a dash gauge vary because of airbag problems.

You psi cutoff valve is designed to at least maintain around 70 psi.

Now, if the airbags are blown out the brake system will stay at 100-120 but only until you step on the brakes a couple of times. If the air escape rate exceeds the build rate, at this stage, the entire brake system will maintain 70psi. Still enough to limp off the road. Every time the foot brakes are depressed, the airpsi will go down in that side of the system to at least 70 psi. This is what the design of the low psi cutoff valve is for.

quote:

Originally posted by Relative:
One more thing I'd like to comment on is if the airbags in any way affect the pressure in the brake system - that's a serious design defect.

Here you go... the crux of the issue. If you know that your air system will at least maintain enough psi to allow your brakes to stay released, you'll...

A) Drive it down the road? Now at 70psi you have enough to release your brakes, you have enough to stop but at a longer distance because your psi is down.

B) Wait for road service or a tow truck? The buzzer and light are going off telling you not to move.

At this stage it becomes more of an operator defect as opposed to a design defect.

air system pdf

quote:

we left the campground 1/2 way home front warning light came on went to 25 lbs.still had rear air at 100 lbs .

That's the catch in the note at the start of this thread. Getting down to 25 lbs. should never have happened. That air protection valve that stops allowing air to enter that third chamber looks to have failed. Now, if Lenny has the air leak fixed, that valve is still bad waiting to bite him again. Agree?

I DON'T KNOW WHY THE GAUGE WENT TO 25LBS. .I thought front brakes would apply at 65 lbs .I also had a bad line going to the air bags and a small something that was loose in the air release switch
a wire was loose.Doesn't the front brakes apply when air hits 65 lbs?

quote:

Originally posted by lenny and judy:
Doesn't the front brakes apply when air hits 65 lbs?

The steer axle will not apply if you have low/no air psi. The ramifications of a locked up steer axle would force an accident to happen. Only the drives would lock up as those positions have maxi brake chambers on them.

quote:

Originally posted by Relative:
That air protection valve that stops allowing air to enter that third chamber looks to have failed. Now, if Lenny has the air leak fixed, that valve is still bad waiting to bite him again. Agree?

I agree, there are still other issues waiting to sneak up on him.

Lenny,

The best advice I could give in your situation is for you to get thoroughly familiar with the air system on your chassis - especially the brake portion. An excellent way to start is with the Florida CDL Handbook - pick one up at your local Dept. of Motor Vehicles or you can view Florida's online at

http://lowestpricetrafficschool.com/handbooks/cdl/en

Section 5 deals with brakes. (Every state has essentially the same info in their CDL handbooks.)

If you don't have the chassis manual for your coach, you might try Spartan and see if they can supply one for you based on your chassis number.

Now that you have your air bag leak fixed, carefully do the steps in chapter 5.3.3 of the CDL manual. (These should be done with some regularity by anyone with an air system.) You should also gain some better understanding of the operation by going through the steps.

The next is to have a qualified mechanic go over the air system to verify all the valves are working - and this is only because, right now, I really think you might have a problem with one or more of the check valves based on that 25 lb reading you got. Carefully explain it to him and get his opinion. The bad part is this could be an intermittent failure. However, those valves are cheap to replace.

One more note of caution, if you decide to get under the coach and fool with the air system, it can drop on you suddenly if you disconnect or damage the wrong thing - especially if you are just laying on the ground under the chassis. A pit or good jackstands are a necessity - especially for us amateurs.

Lenny,

Sorry, but one more step. In your case a final verification would be to leave the brakes alone and dump the air from the suspension. If that gauge again drops to 25 lbs doing this, get it fixed.

thanks guys took it to the mec today leaving in 10 days want it wright. lenny