brake survey

[DaveG]

I am putting something together for the magazine and would like some input from you regarding two things-brake chamber size (24/30/36) and automatic slack adjusters.

I am assuming most of you have type 30 on drive and tag/bogie, but what about steer?

Regarding automatic slack adjusters, which years/models/makes etc came with them?

Thanks in advance.

[DaveG]

Okay, let me help us out here...automatics were not required until late 1994, so you guys with the GMs and Eagles don't need to crawl underneath and check that for me!

[luvrbus]

Dave,automatic slack adjusters were optional with the model 10 Eagle in 1984, then came the dual air system with spring brakes.

good luck

[Iceni John]

For my bus's 37,400 lbs GVWR on two axles:
Front brakes - Rockwell 16.5 x 6", with 24" chambers.
Rear brakes - Rockwell 16.5 x 10", with 30"/30" dual chambers.
Haldex ASAs all round.
Bendix Tu-Flo 700 direct-driven off the back (the front?) of the engine.
And a Jake.

John

[TomC]

When doing a brake job, one of the most important things is the choice of brake linings.  There are probably close to 20 different choices with a few that could come close to your choice.  Linings are made for line haul trucks that work best when cold (after being on the highway for more then a couple of hours and the brakes have cooled down), transit linings that work best when hot, linings for dumps that don't mind dust and dirt, standard gray block that is used on new trucks, linings for over the road buses that provide smooth braking and don't squeak, etc.  Good Luck, TomC

[bevans6]

My MCI MC-5C manual shows automatic slack adjusters as optional in 1980.  Mine has;

Front - Bendix manual slack adjuster, 20" chamber
Rear - automatic slack adjuster, make unknown, 30" DD3 chamber,

I had thought that most tags would have had 24" chambers?

Edit to correct front chamber size - manual says it's 20 square inches, not 24 square inches!

Brian

[belfert]

I have a 1995 Dina Viaggio 1000 and it has automatic slack adjusters.

[robertglines1]

98 prevost....front  30 BW.....Drive  Anchorlock divison...30 as service-36 as emergency....Tag 16 as service BW....Slack Adjuster.front Rockwell...same for drive and tag all different part numbers for location

[rv_safetyman]

Dave, I hope you cover the subject of checking brake adjustment.  That always comes up and there is quite a bit of controversy about how you do it.  There are good sources on the Internet you can cite.

Also, I hope you emphasize the fact that auto adjusters are quite a mixed bag.  Given the age of some of our buses, the slack adjusters are probably getting towards the end of their useful life.  If a person relies on the fact that they have auto adjusters and never check their brake adjustment, they could be in serious danger.  One of mine was locked up when I drove my bus home and the brake cam was trying to go over center.  The bogey was locking up and I could have had a brake fire!

Jim

Update.  I did a bit of searching and your best reference site is:  http://www.bendix.com/en-us/service/library/Pages/Home.aspx  From that page you can download the BW handbook (BW5057 - the bible).

[DaveG]

Okay, thanks for the replies folks. I will try to cover all the brake chamber sizes in my article. I am only going to cover slack adjusters, and along with that would be brake stroke...which is determined by the chamber size.

[JackConrad]

Per MC-8 manual Front axle Type 24, Drive axle Type 30 (both service & emergency), tag alxe Type 12.  Slack adjusters were manual.  Jack

[DaveG]

Thanks Jack and all who replied. Anyone know what year autoslacks were installed at the factory...either as an option or mandated? Thanks again guys.

[bevans6]

the DOT spec for measuring brake stroke is a full brake application with the tank pressures between 90 and 100 psi.  For an OTR trucker that can be important - you could pass with a legal pressure, yet fail with a full 120 psi.  A 30 inch brake canister will develop a push of 3,000 lbs at 100 psi, and that is well able to find all of the play, twist, bearing clearance and everything else that needs to be accounted for when checking brake adjustment.  I'm curious about why there is controversy about how to check adjustment, since there is only one way to do it - brake stroke with a 90 - 100 psi application. 

One thing that does bear explanation and discussion - how much stroke is legal?  There are long stroke and normal stroke versions of most canisters, how do you tell them apart? 

Brian

[DaveG]

Thanks Brian. I am working on a piece for BCM and the slack adjuster is what they've asked me to address. You are correct in your statements, other than a couple of publications I've read state the application pressure as 80-90. Regarding long stroke chambers, generally there will be a tag indicating so...otherwise you as the owner of the vehicle need to advise the inspector of same. If you'd like I can post the brake chamber sizing and stroke, which I planned to do in the article anyway.

[JackConrad]

We added a brake application pressure gauge when we put in the new dash. This gauge is tied into the line from the brake application valve to the front brakes.  A normal "Ok, I see brakes lights coming on ahead of us, so we need to apply a little slow down" application uses about 10 PSI. A " the light just changed and we need to stop now rarely exceeds 20-25 PSI. An "Oh S*&T" application is about 35-45 PSI.  The emergency air tank that operates the DD3 parking brakes applies 85 PSI.  All these numbers are with properly adjusted brakes. I have noted that as the brakes get out of adjustment, it requires more pressure for the same amount of whoa. 
Disclaimer: This is my experience on our bus, YMMV. No animals were used and all electrons used in generating this message were recycled.  Jack