Braking Quality - Luxury Coach Lifestyles
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Old 06-22-2008, 03:15 PM   #1
Aragona
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Default Braking Quality

I had to make an aggressive stop from 45 MPH on a 3% downhill grade asphalt road the other day. I jumped on the brake pedal as hard as I could and to my surprise none of the tires locked up and the stopping distance was greater than I had estimated. Is this normal, or is something wrong with the braking system? I have a 1994 45" with the 8V92 and the jake brake was on.
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Old 06-22-2008, 04:39 PM   #2
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You have discovered the mass of a Newell. Stopping a 45,000+ pound vehicle takes a lot of space, especially on a downhill grade. The jake on a two-stroke Detroit doesn't have the braking force of a jake on a four-stroke Detroit and as soon as the rpms drop, it loses effectiveness quickly. As to locking up the wheels, I have never had a wheel lock up on me when stopping aggressively other than on gravel. As a matter of fact, the newer coaches have anti-lock brakes to make sure that they don't lock up. However, the brakes should be on the verge of locking up when you are standing on the brake pedal.

Since different people have different perceptions of stopping distances, I would suggest that if you haven't have the slack adjusters checked, this would be a good time to do so. I had Newell adjust mine about a year and a half ago and they all needed some tightening. You can adjust them yourself if you know how and have a way to block up the coach so it doesn't come down on you while you are under it. While you (or a mechanic) are down their, you can also check the thickness of the brake linings. It takes a long time to wear out the brake linings but it is a good idea to check (or have them checked) about once a year.

I presume that your air pressure was good (brake air pressure gauges in the 110-125 range) prior to the stop and that the pressure was still above 95-110 after the stop. Some people used to car hydraulic brakes make the mistake of pumping their brakes (although it certainly doesn't sound like you did) and find they run out of air very quickly. An air leak in the brake can ruin your entire day. Do you do the air brake test recommended for commercial trucks periodically? If you don't (or are not familar with the procedure) download a CDL manual from your state and go through the air brake testing procedure. It will give you confidence that the air is staying up and that the emergency spring brake will work if needed. Also, verify that the brake air pressure isn't dropping with the supply air pressure when you are not using the brakes. Tom and I have both had to replace the air check valves that were allowing air pressure from the twin brake tanks to bleed back into the supply tank. That is an easy test. Start the engine and get your air system up to the compressor's shutoff point (typically around 125-130 psi). Shut the engine down and without touching the brakes, see how fast the supply system drops. If no air is used (air doors, genset slide out, etc, the supply pressure should not drop more than 20 psi in about 40 minutes. HOWEVER, in that 40 minutes, the brake air pressure needles should have stayed virtually unchanged. When the check valves start malfunctioning, one or both brake pressure needles (there is a white one and a red one) will follow the supply gauge down and that is a very dangerous situation.

Since you are concerned about the stopping distance, I would suggest you have the wheels and drums pulled and see if the linings are glazed or the drums badly scored. New linings are cheap compared to not being able to stop in time.

I believe it is a good idea for everyone to find a safe location where they can get up to 50 mph or so and get down HARD on the brakes. You may be surprised who long it takes to stop 45,000+ pounds. You will also benefit from knowing what to expect and what it feels like to do a panic stop in a massive vehicle with air brakes.

This is a great topic and I really appreciate you bringing it up. I see many heavy coaches disregard the reduced truck speed limits on downhill grades. I personally think that is a bad decision. A Newell's weight and brakes are very similar to a large truck and if it isn't safe for them to go down a long 6% grade at more than 35-40 mph it isn't safe from us either.

I have found that manually downshifting when trying to stop quickly helps reduce stopping distances. The older HT-740 transmissions did not downshift quickly enough to keep the engine speed up for the jake to help out very much. You want to downshift as soon as the engine drops to about 1600 rpms. That will maximize the engine braking with breaking the engine.
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Old 06-23-2008, 01:28 AM   #3
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Very interesting topic indeed. I just finished 3000 miles, and truthfully scared myself a couple of times in stop and go traffic thinking I was going to hit the car in front of me.

It really made me aware of just how hard I have to press the pedal to stop. It's too hard in my opinion. Much harder than other coaches I have driven. I am wondering why I have to press the pedal so hard.

Michael, your comment on the slack adjusters made me wonder if that could be part of the problem. Did you notice any difference in pedal effort after the slack adjusters were adjusted?

Does anyone have any experience with the "other" style of brake pedal? Mine is a firewall mounted pedal. The "other" style looks like the accelerator pedal. I have driven coaches with this style pedal and it was not nearly as hard to press.
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Old 06-23-2008, 05:13 AM   #4
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This is an interesting subject. Prior to owning my 1982 Newell I had never operated a rig this big with air brakes. I really didn't know what to expect, or what would be normal operation. In general I have found that just as I had to anticipate the need to stop suddenly with my class "c", I must also do that even more so with the Newell. The difference is that with air brakes I have never thought I wouldn't stop. I have also found that with only a little extra pressure on the fireweall mounted brake that the stopping power increases exponentially, unlike the class "c". It may be that my brakes and all the associated adjustments are perfect right now, but I have no complaints about the stopping power. I always start out thinking "this thing weighs 36,000 pounds...it's not a 1968 VW".....I have to have a different driving mentality in the coach than I do in our 2002 T-Bird, which, comparatively, stops on a dime.

By the way, when I had the 4 rear tires replaced last week my mechanic checked the brake linings on all wheels and they are in great shape with many thousands of pleasure filled miles remaining on them.
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Old 04-10-2010, 01:36 PM   #5
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OK, so what is the difference between the two air brake gauge needles?

"When the check valves start malfunctioning, one or both brake pressure needles (there is a white one and a red one) will follow the supply gauge down and that is a very dangerous situation."
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Old 04-10-2010, 02:10 PM   #6
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make sure all you stuff is tied down for the test , or it will end up by the drivers seat
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Old 04-10-2010, 03:18 PM   #7
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Forest, you have two air pressure gauges, a Supply and a Brake. The Brake has twin needles. The supply gauge shows the air pressure in the wet/auxiliary/main tank. This tank gets air from the air compressors, both the engine mounted compressor and the 120 volt compressor. From the wet/auxiliary/main air tank, air flows through a check valve into two brake tanks. The two needles on the Brake tank show the air pressure in each of the two brake air tanks. One of these tanks feeds air to the front brakes while the other tank feeds air to the rear brakes and tag brakes. Since it takes more air to activate the four chambers on the rear/tag brakes than the two on the front brakes, the rear gauge will typically drop a little faster. However, if the adjustment is off on the slack adjusters, that might not be the case as more air would have to be used to push the rod before some of the brakes start to activate.
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Old 04-10-2010, 03:26 PM   #8
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Thanks Michael. That really helps in my understanding of air brakes. Never could figure out why it had two needles. I didn't realize the front and rear were separate.
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Old 04-10-2010, 04:08 PM   #9
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My thanks also Michael. Some additional clarification would be appreciated. what all does the supply tank feed when parked and leveled with the auto leveling system? Also, I'm assuming the 12v air pump located in my water heater compartment will supply air to these same items when I'm parked and not connected to power. I have four tanks, 2 large in the front, one large in the rear and a small one in front of the pass. side rear drive axle. Can you clarify the usage of each? I'm sure looking forward to the day I can get to one of the mini rallies and get a good education from some of you experts. I've driven over 200,000 miles and am still shocked at the things I don't know. This forum has been a gift from above!
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Old 04-10-2010, 06:06 PM   #10
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Larry, the wet tank and the front brake tank are the two at the front. Typically the wet tank, the one that receives air from the air compressors, is closer to the front and mounted lower (at least on the early 1990's models). The large tank in the rear is the rear brake tank. The small tank near the drive axle is the auxiliary tank for the air toilet if the coach is configured such that the toilet is not located directly over the waste holding tank and in later models with air-pocket doors supplies air to operate them. Additionally there are rectangular air tanks that feed the leveling system.

What does each tank feed? The front brake tank ONLY supplies the front air brakes. The rear brake tank ONLY supplies the drive axle and the tag axle brakes. At least on your coach, the small tank ahead of the drive axle typically feeds the air toilet and if equipped air-operated pocket doors. That tank is filled by the 12 volt air compressor and likely has a line from the wet/supply tank as a secondary feed with a check valve in the line. The supply tank feeds everything, the brake tanks, the leveling system tanks, the air-powered slides for the generator and slides in any of the bays, air-sealed slide-out bladders in coaches with slide-outs, the air powered slide over the steps and air-toilet if so equipped, the air-ride drivers seat, air-operated pocket doors in coach after about 1993, and in later models (some as early as 2000 year models) the Bode air-powered entry door.

The smaller tanks are all filled from the wet/supply tank. It is frequently referred to as the wet tank because it gets most of the moisture settling out in it and needs to be drained the most frequently since the engine air compressor and 120 volt air compressor feed directly into it. Air dryers maintained in good condition will help eliminate much of the moisture getting into the wet tank. If you have the 12 volt auxilary pump, you also need to maintain the drier on it as well as those for the engine compressor and the 120 volt compressor.

Since my coach doesn't have the air-toilet or air-pocket doors, I am sure that Richard can add to this discussion. The 12 volt pump and tank allow you to operate the toilet and air-pocket doors without having to keep the 120 volt pump operating. The supply tank will leak down due to the large number of fittings and connectors in the complex air system on a Newell. Wally is one of the few Newell owners that has spent the time and money to keep his tight enough to go for several days without the wet tank bleeding down significantly.

Once you are parked and leveled, assuming you don't have an air toilet or air pocket doors, slide bladders or air-entry door, you will likely not need to run the 120 volt pump unless you want to access the genset, move the step slide cover, re-level the coach or operate a bay air-powered slide.

Most of the air-operated items on the coach require 60 psi or more to operate. The air-toilet and air-operated pocket doors may be set to operate at about 45 psi but I will let those with more experience in their operation than I go into that.
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Old 04-10-2010, 11:05 PM   #11
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Thanks again Michael. You are most helpful and this clears up a lot of my air tank related questions , except for one: When are you opening your service center? I would be a good customer.
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Old 04-11-2010, 01:19 AM   #12
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Larry, the small tank in the rear well for the toilet should be set at 60#s. You should have preasure guage and preasure control valve in the bay with you heater. I removed my tank from the wheel well because it developed leaks in the welds of the tank from using it in the north with salt on the roads in the winter. I installed it in the bay next to the water heater and it works great. When I used green breat methods to elimimate air leaks I discovered that my main (wet) air tank and the toilet both had leaks in the weld seams and had to replace them both.
I also replaced all of the check valves, air preasure control valves, air operated wiper motors and air wiper switches, air switches for the step cover, generator slide out, cheater dump valve, etc, etc,.
As Michael said we are fulltimers and with full use of the vehicle with an air operated toilet our 110 pump does not go on more that 2 times in 24 hours.
As our coaches get older air equipment fails and it is my opinion that the less a coach us used the more likley that air systems will dry up from moisture settleing and clogging up check valves and other items in the system.
I like all things on the coach to operated as designed and at the present time the only thing on my coach that does not work is satilite dish that automaticly goes up. It failed and until i'm ready to bite the bullet for a new one that is the one flaw I living with.

Sorry for the long reply.
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Old 04-11-2010, 02:29 PM   #13
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Michael:
Where is the 12v air pump located? I found the small tank by the passenger side drive axle.
Thanks,
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Old 04-11-2010, 04:09 PM   #14
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Typically, the air pump is located in one of the bays. If you have an aqua-hot, it may be in that bay. I have seen them in the wet bay by the water heater (non-aqua-hot units).
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Old 04-12-2010, 02:17 PM   #15
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Mine is in the passenger side bay with the outdoor faucet. It is concealed behind a panel.

Here is how to find it.

Park the coach. Don't run any compressors. Flush operate some air device until the supply pressure is depleted. Turn on the red switch in the toilet. Go outside and listen, you should be able to hear it run.

One of the coach to coach differences is that on some coaches the 12v pump supplies pressure to the toilet and the air pocket door. On mine, it only supplies pressure to the toilet. It's on my list to replumb the air supply for the door to run off the 12V pump.
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Old 04-12-2010, 04:05 PM   #16
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Interesting, mine has a "straight dump" toilet and an air door to the bedroom. I've never found or heard another compressor. It must be plumbed to the main air supply. (of course I never did find a safe also, so I put one in)
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