Just got home from a weekend air brake course as it is mandatory in canada.Air over was discussed but not reccomended because if either system fails you dont have any brakes Wally Vancouver island.

Air over hydraulic is fairly common and used widely for braking systems.

I can not understand the comment, "either system fails", In most air over systems there is separate master cylinders for front and rear brakes. Yes if you loose air you have no brakes front or rear but the "E"brake will come on! If you have air only,what is the difference??? you loose air----??

If you loose hydraulics, you probably will not loose front or rear at this same time.

Sounds to me it is a personal opinion of the instructor.

Fear of the unknown...

Air over hydraulics, while not a personal favorite of mine, is perfectly safe and would be fine in a Motorhome Setting. I agree with Ed, it sounds like you might have heard his opinion as opposed to a stated fact.

It's true, the heavier you go with an "over the road" vehicle, the more likely it is you'll see that the system has air brakes.

Based on your statement, He went over the "Air Over Juice" systems.

Did he go over hydraulic over juice. AKA a hydroboost system?

What about a "Vacuum over Juice" brakes. AKA Vacuum Assist.

All of these have in common the same thing - they are juice (Brake Fluid) brakes. The only difference is the boost part. You know, what the driver feels on his little foot.

My 72 Chevy Nova had full juice brake. I added a vacuum assist unit to it. Several years later the vacuum diaphragm failed and I had a harder time stopping. Why? Because it required more psi on my part to obtain the same results.

I had a K10 Chevy pickup with a hydroboost - the belt broke and I had a harder time stopping. Why? Because it required more psi on my part to obtain the same results.

I've worked on big trucks for all of my adult life. I've seen and repaired each of the various systems just described. Air over hydraulics, while not a personal favorite of mine, is perfectly fine.

My biggest issue has always been availability of parts. My job is to get someone on the road ASAP. If I have to order parts, it takes longer to do a job. Here lies my only frustration... the immediate gratification of fixing a vehicle by running down to the parts house and getting my supplies.

Do not be turned off with an "Air Over Hydraulic" system on a Breakaway. On the other hand, if you have an MCC... then the availability of parts "could/might" pose a challenge.

So, at great risk of disagreeing with two highly respected gear-heads (Ed and Bill) I think there is still something to the instructor's warning even if it wasn't fully explained out.

Here's my logic, admittedly with no experience with these systems. Please point out if I'm off base as I'm making some assumptions that could be wrong.

1) A over H is used on diesels as a less expensive overall braking system because full air systems are more costly to manufacture.
2) The air is used on diesels because they do not have consistent vacuum like a gas motor (?)
3) As diesels are typically bigger, heavier rigs - the hydraulic part of the A over H is pushing the limits of safety.
4) Any liquid in a braking system that has the ability to boil can ruin a perfectly good day in the mountains

Number 4 I will stand by as a very good reason to stay away from hydraulic brakes of any variety in a heavy unit. This is why trains, big rigs, buses use full air brakes exclusively.

I know what you're thinking, but Corey, ocean liners use hydraulic brakes...........

quote:

Originally posted by Moonbeam-Express:
1) A over H is used on diesels as a less expensive overall braking system because full air systems are more costly to manufacture.
2) The air is used on diesels because they do not have consistent vacuum like a gas motor (?)
3) As diesels are typically bigger, heavier rigs - the hydraulic part of the A over H is pushing the limits of safety.
4) Any liquid in a braking system that has the ability to boil can ruin a perfectly good day in the mountains

1) The real reasons that air is used on big rigs is because a little leak in the system will only produce a hiss - a little leak in hydraulics will cause the vehicle to have a much harder time stopping. Also, how would you get the average truck driver to hook up to a trailer with hydraulics? Air is the safer way to go for those reasons alone.
2) True
3) You can design any braking system to work off of hydraulics in ANY WEIGHT classification. I've seen em - they work.
4) DOT5 Fluid, while not available back in the 90's, have minimized this today.

>>> Dry boiling point ----- Wet boiling point <<<
. DOT 3 205 °C (401 °F) -- 140 °C (284 °F)
. DOT 4 230 °C (446 °F) -- 155 °C (311 °F)
. DOT 5 260 °C (500 °F) -- 180 °C (356 °F)
.DOT 5.1 270 °C (518 °F) -- 190 °C (374 °F)

Wet boiling point defined as 3.7% water by volume.

This is why Bill H constantly reminds everyone to bleed out your brakes on a regular basis - the addition of water will cause a lower boiling point and you'll suffer from a loss of braking.

Now, this can also happen in a bigger rig - however, this is called brake fading. The overuse of brakes in a mountain setting because you're driving faster than the conditions in which you should be for the terrain.

This is why there are still runaway ramps in the mountains - the overuse of brakes to the point that they either fail from overheating of the pads or the brake fluid boils causing air pockets.

What would I rather have? I would rather have a full airbrake system.

There is another thing to consider and that is on the breakaways the brakes are disk and if you should need them they will not fade like drum brakes. my last experience was with a 55 GMC bus motor-home and it was truly press and pray, the breakaway is like heaven- it will stop.

quote:

Now, this can also happen in a bigger rig - however, this is called brake fading. The overuse of brakes in a mountain setting because you're driving faster than the conditions in which you should be for the terrain.

This is why there are still runaway ramps in the mountains - the overuse of brakes to the point that they either fail from overheating of the pads or the brake fluid boils causing air pockets.

What would I rather have? I would rather have a full airbrake system.

Yup, air brakes are hard to beat. A real Jake Brake with the air brakes is even harder to beat. I use my 3 stage Jake more than I ever use the brakes and nothing is wearing down. I typically only hit the brakes at the very end to get fully stopped.

quote:

Originally posted by john canning:
There is another thing to consider and that is on the breakaways the brakes are disk and if you should need them they will not fade like drum brakes.

Disc brakes will and do fade in situations where brake management is not followed. I have put on nearly 100K miles on my Breakaway and have had two instances where the brake fade was severe, requiring me to stop and let them cool before proceeding onward. Both situations were coming down a VERY steep incline, even though I was moving slow.

Brake management while driving and Brake maintenance are the two biggest factors in having a safe reliable system.

Just one more thing, that has been mentioned before (but worth reminding), diesels do not have the compression of a gas motor. No throttle plate to shut! Therefore, they pretty much free-wheel down steep grades. This can catch a new diesel owner by surprise and cause overuse of brakes. Although you can sometimes use the tranny to slow things down, I know I was always worried about the RPM levels and tranny heat on my old Barth. This was in what would be considered hills compared to the Rockies or Sierra Nevada ranges!

So for general knowledge, do all Barth diesels have air brakes? Do any gassers have air brakes?

When lurking through listings I always wonder why most do not post "air brakes" if that is the fact. Maybe I should know that automaticallly.

Good question Stick.

I'm pretty sure no gasser ever got air brakes in modern times anyway. Certainly no Barth.

This thread started around the concept of air over hydraulic brakes that some Barths are equipped with. Strictly speaking, these are not full air brake systems. I think it is generally agreed that full air is the higher end approach, but may be overkill to some. I was hoping someone would confirm or negate my guess that full air was a more expensive approach and that is why some RVs have the hybrid setup.

Corey - I'm assuming then that only diesels would have full air or air over hydraulic. If this is correct then which model has what?

I know this is sort of like asking a generalized question about a Bluebird. No two were alike.

From what I can gather, some Breakaways have AoH as well as some or all MCCs leaving all other diesels to full air. I think one of the Bills or Rusty/Nick could verify more definitively.

In regard to Wanderlodges, the mechanics are very similar throughout the lineups with interiors being the most unique parts. Unlike a conversion Prevost or a custom ordered Newell, Wanderlodges were built from a catalog of options (like automobiles) and the base components were usually identical through many machines. For instance, every LXi has the same engine/trans/chassis throughout the years. Barths were far more "custom", often depending on what the factory had hanging around for chassis. A good example was my 97 Monarch built on a 95 Spartan chassis

Just thought I would throw in my "two cents".

The full air systems seem to be a better and safer way of stopping then the others on larger
vehicles.
This may be the reason that most school busses have full air brakes.

My Regency has the A/H system and while it will stop in an emergency it does require a good amount of pressure. I know this for a fact when a car on the right side of me lost control on the interstate and went across in front of me. I locked up the brakes to prevent hitting her and thought I was going to pull the steering wheel off. She was so close I could only see the top of her car roof go by.

Jim

Corey, re: engine 'braking'.
If 17.0:1 is not high compression, what is?
http://www.cumminsdieselspecs.com/12v.html

Can any over-the-road gasoline powered vehicle engines maintain compression that high?

As for intake manifold back pressure, you're right.
As for compression, you're wrong, IMHO.