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Topic: Air Brake Slack Adjusters - Dangers of Ignoring  (Read 1886 times) previous topic - next topic

Air Brake Slack Adjusters - Dangers of Ignoring

Topic title updated for clarity - Michelle


A brake system out of adjustment may be unable to fully or quickly stop a coach, perhaps especially in backing up.  It may be infrequent that the system would be out of adjustment, but rarity does not diminish the potential very serious consequences - someone or thing can easily be injured or crushed.

As I understand our braking system:  There is a shaft with knobs, called cams.  As you apply the brake pedal, the shaft turns, the cam comes around and presses a rod which in turn extends and presses the slack adjuster arm into the brake to activate it.  If the overall length is not right in this system, you cannot apply sufficient pressure to the disk brake and will have difficulty stopping.   

At least that is my mental picture.  What is important, regardless of understanding that picture, is to know that IF the slack adjuster arm (or the rod) length is not set properly, you lose braking power. Professional truck drivers are required to inspect for this often.

The FT air brake slack adjustment arms are the most frequent means to set the length, and they adjust manually or automatically, depending on the FT model.  They should be inspected at least annually.  You may learn to do this or have it as part of an annual maintenance by a shop.  Some believe this may require experienced service technicians, especially to adjust.

The process to adjust the slack arm is discussed elsewhere in this forum and in the web site I have provided below.  It also carries some warning information.

Again, I gather such an event is rare.  But it is important to understand this process and maintain the adjustment.  The consequence of brake inefficiency or failure cannot be over-emphasized.  I have seen that.

Mike

Web site referenced

http://www.rvtechlibrary.com/chassis/airbrake_manual.pdf
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #1 –
And some older Foretravel models have air operated Wedge brakes.
1994 U225
build #4514

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #2 –
This may warrant its own thread but I learned something at FOT getting my last service. Whey you ask for a lube service, it does not include greasing the brakes. That is an individual service item at Foretravel and includes adjusting the brakes. You have to ask for it. They don't mention that unless you ask.

Foretravel, you might suggest that the service writers mention the brake service when a customer asks for a lube job. 
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #3 –
Not for me to say if needs a separate thread, but it is the topic I am putting on here.  Service the brakes.

For annual maintenance service at MOT as a matter of routine, as I understand it, there is a check list that they ask the customer what they want done.  Customers opt in or out of this inspection as well as other maintenance services.

I was out visiting with Mike P. (morninghill) and Keith Risch was in working on something in his coach.  I reviewed with Keith what I had posted, the high concern I had.

Keith Risch told me, to emphasize my concern, of two recent examples, the latest being a coach that came in with some screw or nut backed all the way out.  I understood to the point that the emergency brake could not fully function. Several brakes could not work.

I am raising this awareness the only way I know in a general way.  I hope it helps just one person avoid what I have seen happen due to brake adjustment need.

Mike
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #4 –
as I recall from my air brake course, it is best not to mess with automatic slack
adjusters (asa).  if an asa is out of adjustment it will most likely be a problem
elsewhere in the braking system.  asa's should only be adjusted on installation
or some other emergency, and by a qualified expert.

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #5 –
Shouldn't every owner be responsible for following FT's service recommendations?  FT has issued service schedule books with every new coach for many years.  If a subsequent owner doesn't have the book, they should ask FT Service.  They'll copy the correct schedule.  I think it goes out to 250,000 miles if I recall correctly.  Brake service is different than any other lubrication.  Brake lubrication is a very infrequent action like twice in the life of the pads.
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #6 –
Brett,
That was my understanding as well.  Back in 2004 while at FOT, I asked James about the slack adjusters and lubrication and he advised to not worry about the lube and the slack adjusters need to be looked at at every coach service interval.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #7 –
Think it is more important to know about the proper grease that should be used with Meritor brake systems, one especially needs to know about the clay based grease, just ask George Hatfield about that stuff!!! -

*  "Do not use lithium-based grease inside the caliper.
Lithium-based grease may not adequately lubricate the caliper. Damage to the caliper can result. Some lithium-based greases can be used in the automatic slack adjuster. Refer to Maintenance Manual No. 1, Lubrication, for the approved lithium-based greases for automatic slack adjusters."

Anti-Seize Compound
"Meritor lubricant specification O-637 (part number 2297-U-4571) is a corrosion control grease. DO NOT MIX THIS GREASE WITH OTHER GREASES.
This compound is also available from the Southwest Petro-Chemical Division of Witco Chemical Corporation, 1400 South Harrison, Olathe, KS 66061, as "Corrosion Control" (part number SA 8249496).
*  Use anti-seize compound on the clevis pins of all slack adjusters.
*  Also use anti-seize compound on the automatic slack adjuster and cam splines if the slack adjuster gear has no grease groove and holes around its inner diameter"

"Lubricate the Caliper
CAUTION
Do not use common chassis lube (lithium-based grease) inside of the caliper. Common chassis lube can deteriorate at the high temperatures that can exist in a disc-brake caliper.  Meritor air disc brakes have been manufactured in three different designs. Note that the location of the caliper grease fitting and pressure relief valve is different in brakes manufactured before 1985, from 1985 to 1991, and after 1992."

And you want to read the Meritor Maintenance Manual:
http://www.beamalarm.com/foretravel-links/PDF/brakes-maintenance-manual-mm4m.pdf. especially the section on grease types, Section 13 on page 54.

Personally, I think lots of this is best left to the pros!!!
1994 U225
build #4514

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #8 –
Quote from: Michael Jackie –
Topic title updated for clarity - Michelle


As I understand our braking system:  There is a shaft with knobs, called cams.  As you apply the brake pedal, the shaft turns, the cam comes around and presses a rod which in turn extends and presses the slack adjuster arm into the brake to activate it.  If the overall length is not right in this system, you cannot apply sufficient pressure to the disk brake and will have difficulty stopping.   

At least that is my mental picture.  What is important, regardless of understanding that picture, is to know that IF the slack adjuster arm (or the rod) length is not set properly, you lose braking power.



Mike,

Your mental picture is not quite correct about the cam and rod, but you are very correct about the fact that if the slack is not correct you could have trouble stopping.  Too much slack, less braking power; not enough slack, dragging brake.  That is a good article, but like most of that type, it is written for truckers, who mostly use drum brakes.  It did have a short section on disk brakes.  Disk brakes don't have any cams.  Our air brake system is about the same as any other air brake system up to the brakes themselves.  The brake chamber push rod is attached to the automatic slack adjuster, an arm that rotates a power screw that applies clamping power to the pads. 

I found that my brakes had too much slack, and it was my fault, for being too gentle with brake use.  The spring brake (parking brake) was not holding as much as it should.  With parking brakes set, the coach would move with only 1000 rpm. Should hold with a higher RPM like about 1300-1500 (depends on engine). I found out that the automatic slack adjusters really need a hard application in order to do the adjusting.  This does not have to be done while moving, in fact it is best done when stopped on level ground with the parking brake off.  A couple of full brake applications occasionally should do it.  I also turn the retarder off at the beginning of a drive just to make sure the brakes are working properly. 
Jerry Whiteaker former owner 96 U270  36' #4831 Austin,TX-Owner Mods LCD TV w/front cabinet rebuild - LCD TV bedroom - Dual Central AC, either can cool coach w 30 amp - Skylights at roof AC openings - Drop ceiling for ducting of AC - Shower skylight white gelcoat/wood/epoxy frame - Air Springs/Shocks replaced - 2014 CRV - 8K Home Solar - Chevy Volt

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #9 –
Thanks so much Jerry.  I figured I did not have this totally technically correct and someone would help.  Thanks.  But my plea to people, do not leave the brakes forgotten.  (I recall on my first car I could adjust the brakes with a screw driver....yes, I go back that far)

 I am told though that not all FTs have automatic adjusters.  And those that do can get to the point that they do not adjust.

If the senior technician backing up that coach had not thought, in the last instance, to push the tranny into D, the damage would have been huge rather than in the repairable range.  Neat trick, two coach owners can be glad he was driving, not someone like me!

Thanks again,  maybe we can save a life or extensive damage.  Mike
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #10 –
Both FOT and MOT have made the point in the past that with the retarder the disk brakes don't get exercised enough in many cases leading to problems down the line...
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #11 –
Mike, Some of us had a BRAKE SPOON to do brake adjustmenst on those old cars (  I still have one but I don't know why ), but I suppose that you could make do with a srewdriver. :) :)
Gary B

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #12 –
A good procedure I remember reading somewhere is: before starting out on a trip, air up, release the parking brake (important!) and then hit the brakes 5 times as hard as possible to adjust the ALS. 

It's important to release the parking brake first because I read that it's possible to overstress some rear slack adjusters with the force of the parking brake spring added to the full force of the service brakes.  Not sure whether that applies to our Meritor brakes or not, but better safe...
Dave and Nancy
1999/2013 U270 36' Xtreme
Motorcade # 16774
2013 Subaru Outback
KD0NIM

Re: Air Brake Slack Adjusters - Dangers of Ignoring

Reply #13 –
Dave, I really appreciate your input.  Glad you emphasize what we should do.  I think this may only work with automatic adjusting slackers and I have been told not all coaches have that.  I am thinking that I was told that mine does but I must confirm.  Nonetheless, need inspections.

I do run the brake test before going, but think that is really about air pressure only.  Even today I heard personal accounts from others about the danger of not servicing these systems.

And for Gary, I never knew the name.  I had a great for me but now historic 1953 Chevy.  Just putting in an FM radio was a technological advance back in the 60's. 
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches