Reply
 
Thread Tools Display Modes
 
Old 12-11-2004, 11:27 AM   #1
Skoolie
 
pangaia's Avatar
 
Join Date: Nov 2004
Location: Low Desert Mountains, So. California
Posts: 111
Air vs. Hydraulic

So.... from what I've read on the posts, air is better than hydraulic due to the more reliable fail safe system? Or is it?

I'm afraid my high school automotive is dated. I am looking at three buses and two of them have 4 disk hydraulic the other regular air brakes. My problem is I don't know enough about EITHER to choose the right bus.

Can we do a quick "What is" on both braking systems and opinions/thoughts on both systems? I know this newbie will appreciated it!

pm
__________________
'Before you go out seeking revenge you must first dig two holes'--Chinese Proverb
-------------------
Bright Blessings of the Mother upon you ;)
----------------
1990 International Ward Volunteer "Fantastic Voyage"
pangaia is offline   Reply With Quote
Old 12-11-2004, 04:06 PM   #2
Bus Geek
 
lapeer20m's Avatar
 
Join Date: Nov 2003
Location: near flint michigan
Posts: 2,653
There are lots of skoolies with hydraulic brakes, however, I think most people will agree that air brakes are superior technology when it comes to buses and other large vehicles. Will having one or the other keep you from buying a bus? I think it's something to consider, but if you found the ideal engine/trans setup, or a really good deal on a decent bus, i don't think hydraulic brakes should be a disqualifier

From a safety standpoint, air is better.

here's a short comparison

Hydraulic brakes:

If they fail, the bus doesn't stop very well. Isn't that what emergency brakes are for?? Even better if you ahve a manual trans.

You can "feel" that the brakes need adjustment/replacement/or more fluid.

No special training or certification required to drive

Provides a more controlled feel in slippery conditions.

umm.....i'll let other people add to the list.

Air brakes:

Simple to adjust, but require regular inspection

More stopping power than hydraulic brakes

If they fail, the bus stops

Difficult to use in slippery conditions....increased time between pushing/releasing pedal and the response of the brakes.

Unable to "feel" that the brakes need adjustment by pushing on the pedal

air lines can freeze up in extremely cold weather

parts are easily found just about anywhere, since air brakes are pretty much standard. There's only a couple different vairieties, available from nearly any truck stop or napa store.

You can use the air system to run air tools, fill tires, and actuate pnumatic cylinders (perhaps for a door that opens and closes with remote keyless entry?)


this post is biased! I'm a big fan of air brakes
__________________
Quis custodiet ipsos custodes (who will watch the watchmen?)
lapeer20m is offline   Reply With Quote
Old 12-12-2004, 12:29 AM   #3
Bus Nut
 
Join Date: Feb 2004
Location: Idaho
Posts: 448
Get the bus with air brakes if it is in good shape. I would not feel comfortable driving something that big without them. If you are planning on converting the bus to a motorhome and titling as such you should not have to worry about special licensing requirements. If the bus you are looking at has an air dryer you should not have an ice problem with the air lines. This mostly happened many years ago before air dryers. If you decide to get one of the buses with the hydraulic brakes be sure and check all the lines before driving it far. You don't want a line breaking while you are on the road.
busone is offline   Reply With Quote
Old 12-12-2004, 01:26 AM   #4
Skoolie
 
pangaia's Avatar
 
Join Date: Nov 2004
Location: Low Desert Mountains, So. California
Posts: 111
Quote:
Originally Posted by lapeer20m
Will having one or the other keep you from buying a bus?
Dunno. Guess I'll see when everyone has posted their know-how/opinions.

pg
__________________
'Before you go out seeking revenge you must first dig two holes'--Chinese Proverb
-------------------
Bright Blessings of the Mother upon you ;)
----------------
1990 International Ward Volunteer "Fantastic Voyage"
pangaia is offline   Reply With Quote
Old 12-12-2004, 10:40 AM   #5
Ron
Mini-Skoolie
 
Ron's Avatar
 
Join Date: Jun 2004
Location: Ontario, Canada
Posts: 14
Well folks, I'm probably in the minority in this crowd but I'm not a big fan of air brakes. True, it's a proven technology and widely used in the trucking industry, but with my terms of reference with heavy off road haulers and loaders, air brakes have been virtually abandoned completely over the last 20 years. 25 years ago, all heavy equipment was equiped with air brakes that were the same as found on today's trucks and in this case buses. Performance and maintenance were the reasons the industry changed. Hydraulically actuated brakes perform better, particularly the fully enclosed wet discs and they don't require nearly as much maintenance. I remember years ago having to do complete brake jobs on loaders at 1000 hrs. Today's machines routinely go 20,000 hrs and more between brake jobs, and the stopping power of these systems is simply awesome.

I believe the reason air brakes are still with us today is simply $$'s. Air brakes are adequate for today's over the road haulers and inexpensive to boot. However, they are not the best sytem available.

My own bus has 4 wheel hydraulic discs. Neat, simple and easy to maintain although I must admit I was a little mystified by the electric booster on the master cylinder and needed some assistance in finding out how to properly bleed the system. When I bought this bus I was looking for one without air brakes for simplicity. I had expected to find a hydra booster instead of this electric pump, but it works well and I'm pleased with it so far. It does have the advantage of providing power brakes even with the engine not running. I'll let you know if I change my mind.
Ron is offline   Reply With Quote
Old 12-12-2004, 11:19 AM   #6
Bus Nut
 
Les Lampman's Avatar
 
Join Date: Nov 2003
Location: Whidbey Island, Washington (USA)
Posts: 465
Air or Hydraulic...in the real world I don't think it matters. If you find a 15 to 20 year old bus to purchase (that hasn't been wrecked) it means the brake system on that bus has been reliably stopping it for its entire life. And you know after that many miles of driving almost everyday that some "I gotta stop now!" situations have popped up.

Either system requires routine maintenance and given the size and weight of a most buses you don't want to mess around with just an 'OK' system...air or hydraulic. Keep either system in good repair and it will do its job.

I think the air system is less "forgiving", rather than just the once-in-awhile maintenance that hydraulic brakes need, air brakes should receive rather continuous looking after. It's really a commercial system designed to be inspected by trained commercial drivers and maintained by professional mechanics. That absolutely does not mean you can not maintain the system yourself but it does mean the system wasn't designed to make it as easy as possible on the operator. That's precisely why a CDL (Commercial Drivers License) requires an Air Brake endorsement and why some states (not all) require an Air Brake endorsement on your regular (personal) drivers license for air brake equipped vehicles (of any kind). While the air brakes system is realiable and easily understood there are lots of important parts that are typically unfamiliar to the average non-commercial driver (like...where's the master cylinder?) and keeping the brakes adjusted (individual pots at each wheel) is vitally important as it's an honest to goodness life or death maintence item. Air brakes have no capability of being "pumped up" like hydraulic brakes that are a bit too worn or out of adjustment; when an air brake pot reaches the end of it's throw that's it and no amount of pumping the brake pedal will result in more braking action. [As an aside...adustment requires that the 'parking' brake be released so you need to be on a level suface with the wheels chocked. Then you crawl under the bus and adjust each of the four brake's actuators. If they're too tight you'll have partially applied brakes all the time (not a good thing!); if too loose you don't have full braking capability (that's a really bad thing!).]

So, here's where I'd leave it...if you're a person inclined to maintain things and you're fussy about details you'll coexist with air brakes just fine if you're willing to learn the system and crawl under the bus for maintenance routinely (even checking belts is important since one of them runs the all important air compressor). If you'd rather just drive and not spend time under the bus and just have the system serviced periodicaly (I suppose every couple years or so depending on mileage) you'll be happier (and definitely safer) with a hydraulic system. In the end a "so so" hydraulic system is better than a "so so" air system; the air system needs to be "right on" and when it is it works really well. [Obviously I'm not advocating not having a hydruaulic system "right on" too; my point is that a hydraulic system is more tolerant than the air system. You just don't crawl under the bus with hydraulic brakes to adjust things on a routine basis; something that should be done on an air brake vehicle fairly often.]

FYI...I have air brakes on my bus. That happens to be what was on the bus I found that met all my other criteria. I drove semi's for a number of years and I'm quite comfortable with air bakes so it's wasn't an "issue" for me. Had I found the exact same bus with hydraulic brakes (especially discs!) I would have still purchased it.
__________________
Les Lampman
1982 Thomas Saf-T-Liner Pusher "Illusion"

Skoolie.net Gallery
Illusion's SmugMug site
Les Lampman is offline   Reply With Quote
Old 12-12-2004, 06:04 PM   #7
Skoolie
 
pangaia's Avatar
 
Join Date: Nov 2004
Location: Low Desert Mountains, So. California
Posts: 111
ugh....so much information!
All of it makes sense but its only served to confuse me more, thus delaying my decision.

To answer your question, I have no interest in crawling around messing with braking systems if I don't have to. I'm only comfortable checking auto brakes which is only what's required for maintance with normal wear and tear. Air brakes sound like they are a lot more work than I care to fuss with but are stable. While hydraulics sounds less stable (correct PLEASE if I'm wrong!) than air brakes in cases of mass failure but aren't as maintience heavy like air brakes.

ya know, I'm propably making this more complicated that it really is, but safety is safety. Besides I and I alone shall make the trip back to california from Florida thus I want as few/no worries as possible.

Thanks folks!
pg
__________________
'Before you go out seeking revenge you must first dig two holes'--Chinese Proverb
-------------------
Bright Blessings of the Mother upon you ;)
----------------
1990 International Ward Volunteer "Fantastic Voyage"
pangaia is offline   Reply With Quote
Old 12-13-2004, 01:42 PM   #8
Bus Nut
 
Les Lampman's Avatar
 
Join Date: Nov 2003
Location: Whidbey Island, Washington (USA)
Posts: 465
Quote:
Originally Posted by pangaia
ugh....so much information!
All of it makes sense but its only served to confuse me more, thus delaying my decision.

To answer your question, I have no interest in crawling around messing with braking systems if I don't have to. I'm only comfortable checking auto brakes which is only what's required for maintance with normal wear and tear. Air brakes sound like they are a lot more work than I care to fuss with but are stable. While hydraulics sounds less stable (correct PLEASE if I'm wrong!) than air brakes in cases of mass failure but aren't as maintience heavy like air brakes.

ya know, I'm propably making this more complicated that it really is, but safety is safety. Besides I and I alone shall make the trip back to california from Florida thus I want as few/no worries as possible.

Thanks folks!
pg
I do think we're making it more complicated than it really is...

I would not characterize Air Brakes as "maintenance heavy", rather that they require more 'routine' (but easy) maintenance (really checking) then hydraulic brakes.

Let me try another angle...if the air brake acuators are not adjusted properly and they reach the end of their (finite and definite) stroke before the brakes are fully applied you've got a problem; one that isn't solved by 'pumping' the brake pedal. What that means, quite simply, is that you *must* check the adjustment on each actuator often enough for you to feel comfortable that they're right. Depending on how many miles you're driving that could be once a year or every day (and realistically the frequency is probably in the middle somewhere). You can not wait with air brakes until the brakes get 'spongy' or something as there is no advance warning; they work or they don't. To take the edge off this...once you've checked the brake adjustment a few times you'll know how often you need to do it (just like your oil, if you've got a car that uses 'a little' oil, soon enough you'll know how often you've got to top it off). This might come down to getting under there twice a year and making adjustments (maybe more, maybe less); certainly not heavy maintenance. But you can't just drive an Air Brake system for the next 5 years and do nothing; for your peace-of-mind you've got to know those brakes adjustments are correct (and they're easy to make).

The likelihood of a failure of either system is remote. Hydraulic systems are always (to the best of my knowledge) double-circuited; meaning the left front & right rear brakes are on one circuit and the right front and left rear are on a seperate circuit. If one circuit fails the other still works.

If you lose air in an air brake system the 'parking' (emergency) brakes are applied. In practice that means the two rear brakes come on since it's usually only the rear brake cannisters that are spring equipped (YMMV). This only works if the brakes are adjusted properly; the spring in the emergency/park brake system can't make the actuator throw any greater than its limit (any more than you 'pumping' the brakes can). Another reason to not ignore your air brake adjustment!

Both systems are safe, both are reliable, and both have been used for millions of miles with success. Choice is either taking whatever comes with an otherwise acceptable bus or making the determintaion that one system or the other is a "must have" and then finding the bus with that system.

Do not use Class 8 semis as an indication of saftey or level of desirability; they have completely different needs than does a school bus (like stopping 80,000 or more pounds). It's a rarity that semis "lose their brakes"; over 99% of the time it's operator error. Speed has not been keep down, the brakes have been used too heavily and the brake shoes have been heated beyond usefulness (literally smoking sometimes). You can overheat hydraulic brakes too but you don't see it as often since they're not used on semi trucks and most other vehicles aren't heavy enough to really push the limits (obviously there are exceptions but I'm working with generalities here).

On school buses both systems are designed for the safety of children and for heavy stop-n-go use; either will get the job done just fine for our typical conversions.
__________________
Les Lampman
1982 Thomas Saf-T-Liner Pusher "Illusion"

Skoolie.net Gallery
Illusion's SmugMug site
Les Lampman is offline   Reply With Quote
Old 12-13-2004, 08:34 PM   #9
Bus Geek
 
lapeer20m's Avatar
 
Join Date: Nov 2003
Location: near flint michigan
Posts: 2,653
keep in mind that even though air brakes need adjustment, it's not tedious or complicted. It takes me about 5 minutes or less to adjust all 4 wheels on my bus. I took a 7,000 mile trip cross country from michigan to LA and back. I checked my brakes a total of four times, which is probably more excessive than necessary. ONce before i left., Once at the top of the continental divide, once while in cali, and again when i reached the top of the continental divide coming home. The brakes really were not out of adjustment at all, except the first time i checked them.

Here at home, i check my brakes about 3 or 4 times a year. They are usually slightly out of adjustment, but not much.

When i get time, i'll try to put a tutorial on here about how to adjust air brakes. It's so incredibly easy.
__________________
Quis custodiet ipsos custodes (who will watch the watchmen?)
lapeer20m is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
tractor hydraulic fluid, can I use it? jlhollowx13 Mechanical and Drivetrains 6 08-04-2013 09:46 AM
86 International Hydraulic Brakes hmacris International | Navistar Drivetrain 2 07-26-2011 01:13 PM
1991 BlueBird TC2000 Hydraulic/Hydraulic Brakes Sticking C00LR Mechanical and Drivetrains 0 10-15-2009 11:11 AM
hydraulic to air brakes adamanderr Conversion General Discussions 2 01-03-2008 11:35 PM
Hydraulic brake maintaince busone Conversion General Discussions 0 09-24-2006 01:26 AM

» Virginia Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 05:56 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.