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Old 09-18-2019, 11:56 AM   #1
Mini-Skoolie
 
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Air brakes bizzarity

Hi, the air brakes on my '77 Gillig are the first ones I have ever seen or dealt with. I consider the brakes to be the most important system on this bus and I insist on understanding them but there is something very bizarre with the S cams. All the pictures of S cams I see show the rollers sitting relatively inside the S cam "pockets". At all four corners on my bus the rollers are sitting up on top of the S cam. This was clearly done on purpose. They have also clearly been that way for a LONG time. These are pictures of one each front and rear S cam with the system not aired up. Everything moves as it should it's just the position of the S cams on the rollers seems completely wrong. Any thoughts? 001.jpg002.jpg
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Old 09-20-2019, 09:26 PM   #2
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OK, I figured it out. Problem solved. Had to discover the slack adjusters, where they were and what they did. S cams set correctly at all 4 corners now.
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Old 09-20-2019, 10:20 PM   #3
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Thank you for these good pictures.


Later Johan
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Old 09-21-2019, 03:28 AM   #4
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You'll find as the brake shoes wear down, the rollers will "ride" further out the S-cams to compensate for this wear. That's what the slack adjusters are for. These days most slack adjusters are automatic (many older vehicles had them retrofitted).


At some point if/when the brakes wear enough, and you press the pedal hard enough, they can "cam over" (A Bad Thing), you have no brakes after this. Can also happen when you apply parking brakes too. This is why wear limits are so important.
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Old 09-21-2019, 08:46 AM   #5
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what brad says!! you definitely dont want an S-cam to flip!.. also dont wantthe slack adjusters too tight
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Old 09-22-2019, 07:16 AM   #6
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I know this post is old, but i have some experience that might be over all helpful for this topic. I use to work as a mechanic maintenance connex chassis and they were all air break systems, from what i can tell the air brake system on buses is exactly on the rear axel. I had to to routinely preform annual federal DOT inspections of chassis for being safe to be used on the road.

DOT standard on the brakes pas is 1/4 of an inch minimum, and if below, it got red flagged for repair or approval for repair. So it would be good to look at the pads and if they are less than a 1/4 inch thick, think about changing them, also it would be wise to look at the drum for any grease in the the brake housing which would indicate a bad seal which would need be replaced. and is important because you do not want to burn out an axel. which is a very costly repair, usually they replace the bearings when they replace the seals, also the brakes are fairly cheap a brake kit runs 40$ per side of an axel. and if you have the tools to change it yourself you save money on labor, but even then labor should not be much.

also the gap between the brake shoes and the drum, standard was a heavy 1/16th to 1/8th

Things that can effect your brakes:

the cam shaft can sieze up ( though usually when they are pretty rusty) you can attempt to fix this by using a 5 pound hand sledge and heating it up with a torch and hitting it, can take a few tries, it can break up the rust bulid up,

The spring break chamber: if the rod from the chamber that connects to the slack adjuster is bent. it need to be replace ( also not horribly expensive about 25 - 30$, a bent rod will effect your spacing of the amount of pressure you have when breaking and can cause you breaks to slip.

if you have been sitting rust can sieve the break pad to the drum a quick hit with a hand sledge or pupping up with a pr bar can help.

your hose connections from the air valve to the chamber could have a hole, extra hose and fittings make it an easy fix, you air valve could also be corroded, you can get lucky trying to clean it out, but its mostly just wrench work and some time to swap it out a new one

I hope you find this info informative and helpful
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Old 09-22-2019, 09:41 AM   #7
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Air brakes

The shoes look pretty new. The drums look like they have been recently turned. I am pulling the rear oil bath hubs and changing the seals. I will examine the bearings and S cams and bushings at that time and replace as needed.

Another oddity. The oil in the hubs is red and is much lighter viscosity than what one would expect for gear oil. Maybe 30 weight. I am still not sure but suspect the hub bearings get oiled from the rear end through the axle. I will drain the pumpkin to find out. If I discover the rear end is filled with this way too light lubricant.......... gulp.
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Old 09-22-2019, 11:23 AM   #8
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if your axel uses oil, it might be the same for refilling as the oil axel hubs i had on the some of hte chassi i worked on, there should be a round rubber cap on the end of the axle hub, if so you can pup it off using a flat head screw driver, I know when i did my DOT inspections for the Chassis we would replace them early cause they can get dmged over time, so have a few extra in case is never a bad idea, i would look up manufacture speculations on the recommended oil, but if you are through in alot of highway miles it might be a better idea to use an oil that is to help with the decrease of wear at high temps. due to the difference in city/vs highway conditions, more and faster rpm =more friction and higher temps. I know our specs required the oil to filled to the brim of the hole where that rubber cap is.

Now i will say this is just me speculating, given off my own experience working on trailer chassis that hauled 40 - 60+ pounds on them, so I could be slightly off and I'm still currently in research mode and haven't bought my own or looked at a bus to buy just yet. So either way, please keep us inform I think this is an important information for anyone. and hopefully the info I have gave you has helped you in some way.
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Old 09-22-2019, 02:35 PM   #9
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Differential lubricant

After a 1 1/2 hour struggle to get the 3/4 pipe plug out, finally using heat, I did remove it. The fluid in there is bright red so as I expected the axle bearings are lubricated by the differential lubricant flowing in through the axle housings. I'm thinking this must be Lucas gear oil. There is some sparkle in the oil drained from the hubs so we will see after the 4" hub nut socket gets here and I get the hubs off.
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Old 09-23-2019, 04:24 AM   #10
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Sparkle, as in metal filings?
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Old 09-23-2019, 08:47 AM   #11
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I would call it metal dust. The condition of the bearings and races will determine how bad it is or isn't. I will lean toward just replacing them.
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Old 09-23-2019, 10:51 AM   #12
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You need to find someone competent about air brake adjustments to have a look at your bus before you take it on the road. Adjusting the slack adjusters because the rollers aren't were you think they should be is a recipe for disaster.

If you don't understand what you're doing regarding brakes, please don't mess with them. Pay someone who is competent to do them because doing it wrong can cause death. It's not an area to fool around with.

Normally, if the rollers are riding on the s cam that far out it's because the shoes or drums are worn out. The spec is 120 degrees of s-cam movement. Anything beyond that indicates something is worn beyond spec and needs serviced.

As far as the adjustment is concerned, it depends on the brake chamber stroke. I usually aim for 1/3 the stroke while moving the slack adjuster by hand, or half stroke with your foot on the brake. If whoever installed the brake chamber cut the pushrod to the correct length, half stroke should have the pushrod and slack adjuster at a 90 degree angle.

Automatic slack adjusters will keep them in adjustment, but you should always do an initial adjustment after brake service.
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Old 09-23-2019, 01:25 PM   #13
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It took a week of frustration and anguish trying to pry the information out of the internet and while I may not have years of experience under my belt I do now fundamentally understand what is going on there. It was my understanding of how mechanical things work that led me to believe that what I was seeing was completely wrong in the first place. My personality is that I will NOT take a piece of equipment like this out on the road until I understand how the brakes work and have them properly adjusted. Whoever the last idiot who worked on the brakes was simply cranked the cams around until they were 180 degrees from their normal resting positions, resting meaning the system is under full pressure or spring brakes caged. Once I understood the slack adjusters I simply cranked the S cams into their nominal correct positions.

After I have dealt with the wheel bearings and S cams I will tighten the slack adjusters until the brakes are tight to the drums, then back them off until I have .020 to.030 clearance.
The shoes and drums look fresh (almost 3/4 inch of shoe) so that isn't an issue. I am more concerned with the condition of the wheel bearings and S cam shafts now. I have a 4" socket for the wheel bearing nuts on the way and that is when I will get a good look at the bearings and races and pull the S cams and inspect them and their bushings.
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Old 09-23-2019, 04:00 PM   #14
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Quote:
Originally Posted by wireguy View Post
It took a week of frustration and anguish trying to pry the information out of the internet and while I may not have years of experience under my belt I do now fundamentally understand what is going on there. It was my understanding of how mechanical things work that led me to believe that what I was seeing was completely wrong in the first place. My personality is that I will NOT take a piece of equipment like this out on the road until I understand how the brakes work and have them properly adjusted. Whoever the last idiot who worked on the brakes was simply cranked the cams around until they were 180 degrees from their normal resting positions, resting meaning the system is under full pressure or spring brakes caged. Once I understood the slack adjusters I simply cranked the S cams into their nominal correct positions.

After I have dealt with the wheel bearings and S cams I will tighten the slack adjusters until the brakes are tight to the drums, then back them off until I have .020 to.030 clearance.
The shoes and drums look fresh (almost 3/4 inch of shoe) so that isn't an issue. I am more concerned with the condition of the wheel bearings and S cam shafts now. I have a 4" socket for the wheel bearing nuts on the way and that is when I will get a good look at the bearings and races and pull the S cams and inspect them and their bushings.
You don't have an understanding of what's going on in there.

First off, they couldn't have had the s cams cranked 180 from their normal resting position, because 180 is half a rotation, and you'd be in the same exact position that you started at if you moved them a true 180, just on the opposite side of the s-cam.

Based off of your picture, your s-cams are 90 off of 0 meaning you have 30 left before you're out of adjustment and needing to replace parts. The nominal or "correct" location of the s cam is anywhere between 0 and 120. Whatever location of the s-cam that puts the stroke of the chamber pushrod into the correct distance is the correct spot for the s-cam.

The only time you should crank those back to 0, is if you need to do so to remove the drums, or you want to check the amount of wear on the shoe/drum.

In service, they'll never be sitting all the way back to 0, unless that is the correct location for pushrod stroke, which is highly unlikely.
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Old 09-23-2019, 04:15 PM   #15
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Quote:
Originally Posted by wireguy View Post
After I have dealt with the wheel bearings and S cams I will tighten the slack adjusters until the brakes are tight to the drums, then back them off until I have .020 to.030 clearance.
The shoes and drums look fresh (almost 3/4 inch of shoe) so that isn't an issue. I am more concerned with the condition of the wheel bearings and S cam shafts now. I have a 4" socket for the wheel bearing nuts on the way and that is when I will get a good look at the bearings and races and pull the S cams and inspect them and their bushings.
You don't adjust brakes that way.

If your bushings, rollers, etc. are all in good order, you adjust the slack adjuster until you get the recommended amount of stroke from the brake chamber pushrod while the brakes are applied. Most of the time it's around 1.5 inches. The correct # should be half the total push rod stroke. So with a type 30 chamber, your total rated stroke is 2.5", so you set the slack adjuster between 1.25" and 1.5". There isn't really a measurement of shoe to drum clearance that you check, because it would be nearly impossible to do so.
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Old 09-23-2019, 07:46 PM   #16
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My 4" hub nut socket arrived today so I got the hubs off. The bearings and races look good but the lock tab that lies just behind the outer nut is missing on both sides. The last guy into these brakes must be an even bigger menace to society than me. I got a number off the gigantic seals and it crosses over so I'm hoping they are readily available.

Tomorrow I will remove the S cams and check those and their bushings.
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Old 09-23-2019, 11:01 PM   #17
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Measure the internal diameter of the brake drums while they are off, max diameter should be stamped on the drum somewhere
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Old 09-24-2019, 09:26 AM   #18
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Been thinking about how to get an accurate measurement on those. It isn't tape measure work.
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Old 09-24-2019, 09:40 AM   #19
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https://www.amazon.com/Brake-Drum-Ro.../dp/B000XQ0YF2
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Old 09-24-2019, 10:46 AM   #20
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I have bought my share of expensive specialty tools for this bus but this is where I draw the line. There has to be a way to measure them that doesn't cost $75.00 I'm thinking something like a piece of steel rod, rounded on one end, cut to a specific length that is 2" or so shy and then measure the difference with my dial caliper.
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