M35a2 AIR BRAKES ...... YEEEEEP!

[jamasonodom]

 

[jamasonodom]

Alright here are some pictures finally. I had to call in my little bro (computer programmer) to figure it out. Sorry they r not in order. Will give a play by play later on to help explain anything. And just remember all these parts came off a oh mighty cheese wagon (school bus). Any questions i will try to answer. Thanks

 

[jamasonodom]

As u can tell i cut the brake pans off the rockwell. I took out the brake bolt and cut the rivets off. I then removed the whole brake assembly off the front axle of the bus. Once u drop the hub it aint but eight bolts and undo the air line. I took off the slack adjuster and removed the s-cam housing which the can is attached which leaves just the ring. Now u need to decide where u want the cans to ride. On ours i wanted it a little higher which will restrict articulation of the axle. I have about 6 inches of travel. I horse shoed the ring and then burned out the center to about 6 3/4 inches. By doing this it will fit behind the axle flange and ride on the flanges ridge. Important to cut that ring as true as u can so it rides centered in the drum!! Why in back because the buses shoe will scrub the deuces inner dust sheild. The shoe will stick out the back about 3/4 of an inch but no problem. Clamp the ring out check for centeredness and weld it on. No junk welds either!! Install the bus brake shoes and reinstall the original rockwells hub and drum unit. Reinstall s-cam housing, slack adjuster, etc. Adjust slack adjuster. I ran the air line to a cross member triangle. If u grab the front brake airlines off the bus it has a divider with a pop off in between the two. Install the lines. Next is the foot valve. I cut the fire wall out and used that as a base to build the foot value bracket. Remove master cylinder and air booster. Build ur foot valve bracket. I removed the arm out of the foot valve cut it and threaded it and used a clevis off the door. Fit perfect. I plumbed the main air line coming from tank to the lower foot valve. One line going out to brakes. And one side for brake switch. The lower valve is just for front brakes. I will later plumb the upper half for the rear that will have parking brakes. But for right now i left blank. The trucks two tanks have enough air capacity for the front but i will add another tank to help support the rear. As for now i have brakes and it will s t o p too!! I will put brakes on the front to later but it will require cutting down the s-cam shaft and housing so a machine shop will b needed.

 

[F18hornetM]

I will say you have certainly put some effort in that. What was the need?? Or just something you wanted to do? Interesting looking with the brake shoe sticking out the back of the drum 3/4".

 

[m16ty]

I will say you have certainly put some effort in that. What was the need?? Or just something you wanted to do? Interesting looking with the brake shoe sticking out the back of the drum 3/4".

Air brakes are miles ahead of the stock air-assisted hyd system. The main thing is no more brake fluid leaks. You can still have air leaks but it's not as messy as fluid leaks and you're not as likely to run out of air because the compressor is always making more. Adjustment is much easier for s-cam brakes (the same can't be said for the 5-ton wedge brakes). Also, no more leaking, malfunctioning master cylinder or airpack.

If set up right and you loose air pressure or a line blows, the brakes will lock up. It's not the ideal situation for your brakes to lock going down the road but it sure beats loosing all brakes when something fails (which is a possibility with the stock system). Air brakes are just safer all the way around on bigger trucks.

About the only drawback of air brakes is you don't have the feel in the pedal you do with hyd brakes and there is a short lag time (very short but it's there) from when you press the pedal and the brakes apply.

 

[jamasonodom]

The school bought this deuce at an auction about 5 years ago just to pull out buses. The brakes never really worked right since they owned it. I came into the shop this year and was told to work on it. I found the whole system full of water and muck. I flushed the system and tried to patch it. The school system said they couldnt afford to fix it but yet they cant afford a wrecker bill either. So i looked in to converting because i still can buy "bus parts" and not "extra parts". Long story short we had a scrap bus and i went to town striping it.

 

[m16ty]

A couple of things need mentioning about converting to air-brakes. One, you will need more and larger air tanks (at least 2 ). Two, you will need R-14 valves for each axle. Three, you will need several one-way check valves in the system. Four, you will need an air dryer like the Bendix AD-9 or the Haldex PureAir . Five, you will need an application valve ( brake valve) and it will need to be sized to the rig. Six, you will need a new air-compressor. One that has a higher CFM rating and longer duty cycle . These are just the start of what you will need to convert to an all air-brake system. The cost will be considerable.

While a air drier would be nice, it's not a necessity. There are plenty of air brake trucks on the road without air dryers and they do just fine (you just have to drain your tanks every day).

I also think you could probably get by ok with the stock air compressor. Only testing of the system would tell for sure but the stock compressor is comparable to what older civilian air brake trucks use.

Good points on all the rest.


I would also caution the OP on making these kits for resell. Designing complete brake systems from the ground up and selling them has lawsuit written all over it. I'm not saying don't do it and I may be interested in a kit myself but just know what kind of liability your exposing yourself to.

 

[gimpyrobb]

Is there a defined CFM requirement for air brakes? If you know the size of the chamber, you should be able to calculate it. I'm pretty sure our air compressors are rated at 7.5cfm.

 

[m16ty]

Gimpy, there probably are some specs somewhere on what is required when building a system but I'd have no idea where to find it.

You could get a rough estimate by calculating the chamber volume but it would be a rough estimate at best. The volume of air is going to change depending on how hard the pedal is pressed (remember, air can be compressed, unlike fluid, and more pressure requires more volume). Also you're going to have to figure in how often the pedal would be pressed in a given amount of time.

If I were the OP I would just get the brakes installed and do extensive testing in all types of braking situations and make sure the gauge doesn't get too close to the 60psi mark. It would be different if you didn't have a compressor already and was trying to figure which size to install.

If the compressor was having trouble keeping up, installing more or bigger air tanks would probably solve your problems. More air storage would give you more reserve to use for braking when needed.

 

[gimpyrobb]

Thats what I figured, I was just throwing out food for thought if someone else cared to look up specs.

 

[Birdman]

Air brake design

FMVSS-121 covers air brakes, I believe. There are specific design requirements for enough air to capacity to provide x # of full brake applications and to replenish the air in a set time limit. You need a wet tank, dry tank and a tank for each axle all protected by check valves. Also relay/quick release valves for each axle to limit response time.
Dual circuits are required, you probably have that or not?
Rear axles would need spring brakes for emergency.
With no air dryer you need a methanol injector. Tanks will not drain in freezing weather and any ice in a valve means no brakes.

Manufacturer catalogues like Bendix etc. often have design info and tables to help you meet the spec with their components.

 

[rustystud]

While a air drier would be nice, it's not a necessity. There are plenty of air brake trucks on the road without air dryers and they do just fine (you just have to drain your tanks every day).

I also think you could probably get by ok with the stock air compressor. Only testing of the system would tell for sure but the stock compressor is comparable to what older civilian air brake trucks use.

Good points on all the rest.


I would also caution the OP on making these kits for resell. Designing complete brake systems from the ground up and selling them has lawsuit written all over it. I'm not saying don't do it and I may be interested in a kit myself but just know what kind of liability your exposing yourself to.

As far as the air-dryer goes, according to Federal regulations you either have an air-dryer or as "Birdman" mentioned an "methanol injection" system. As far as the air compressor goes, it probably does meet the minimum CFM requirement but it does not have the "duty cycle" needed for a total air system. Bendix has copious amounts of documents for download explaining all this. Personally I would love it if the deuce came with air-brakes. I have worked on these systems for decades, and have quite a lot of spare parts squirreled away, ie: R-14 rebuild kits, one-way check valves, dump valves, AD-9 rebuild kits etc. I know though what it would take to make a deuce into a complete air-brake system and the money needed to make it Federally compliant. These last few years at Metro Transit I have been the Inspector for the busses. Every 6 months I had to go to class and recertify to be compliant with Federal Law. I have manuals on what is legal and what is not. Brakes are the number "1" issue that the Feds are most anal about, and if you mess with them and they no longer meet requirements then your truck is booted off the road period. So saying all that, if anyone wants to go ahead with converting to an all air brake system I say "go for it" . I would love to see ! Then maybe in the future I will attempt it.

 

[jamasonodom]

My next step in this process will be the rear most axle. This axle will receive the spring brake cans. I will also install an extra tank off the bus and also its air dryer. I will also re-plumb everything with plastic air line hose just because it is so easy to fix. I'm going to install a much bigger tank in the rear with a ball valve to have working air. Flat tires, tools, jacks, etc. So when we first get in truck it will b closed to set running down the road and when we get their i can open the valve and fill the tank. Now my goal is to install a wrecker lift arm in the rear of the truck. It will look like one of those wrecker lift that attach to a fifth wheel. I want this truck to just assist and rescue buses.

 

[m16ty]

As far as the air-dryer goes, according to Federal regulations you either have an air-dryer or as "Birdman" mentioned an "methanol injection" system.

I would love to see the regulation that says a air dryer or methanol injector is required. There are thousands of civilian trucks on the road than never came with either system from the factory. I've personally got a 1983 Freightliner that doesn't have a dryer or injector and has been federally inspected and there was no mention of a brake violation. I've also looked through the federal standards (FMVSS 121) and see no mention of a air dryer or methanol injector being required.

I'm not saying I'm 100% right on this but just going by the shear numbers of trucks on the road today without air dryers (most all older trucks unless one has been retrofitted) and the fact that I haven't been able to find it in the regs, I tend to think, although a air dyer is a good addition to any system, it's not a requirement.

 

[rustystud]

I would love to see the regulation that says a air dryer or methanol injector is required. There are thousands of civilian trucks on the road than never came with either system from the factory. I've personally got a 1983 Freightliner that doesn't have a dryer or injector and has been federally inspected and there was no mention of a brake violation. I've also looked through the federal standards (FMVSS 121) and see no mention of a air dryer or methanol injector being required.

I'm not saying I'm 100% right on this but just going by the shear numbers of trucks on the road today without air dryers (most all older trucks unless one has been retrofitted) and the fact that I haven't been able to find it in the regs, I tend to think, although a air dyer is a good addition to any system, it's not a requirement.

I'm talking about 2014 not early models grandfathered in. If you complete this project in 2014 you will be required to meet 2014 standards. Go and talk with any State Patrol inspection station, you will soon find out what is required.

 

[rustystud]

View attachment Scan0002.pdf The regulation went into effect in 1998. According to the "Federal Motor Vehicle Safety Standards and Regulations" Standard No. 121 paragraph S5.1.2 "manufactures are required to provide either an automatic condensate drain valve for each service reservoir or have a means of moisture/contaminant removal (air-dryer) adequate to maintain the safety of such systems"