View Full Version : Brake Saftey

Joe Camper
04-28-2013, 08:09 AM
Are the slack adjusters on your bus automatic or manual?

If U are not sure thats bad EVERYBODY and ANYBODY who drives and owns something with air brake should know this.

Im in Peoria this weekend helping another POGer with an early 90s XL.

There are many of our campers with MANUAL slack adjusters and many arent aware. Right up to the mid 90s (newer stuff normally are automatily adjusting brakes but if U bought used whos to say someplace other parts were installed) SO we all need verify at some point.

This CC has all 3 axles with manual adjusters. Other years the drive axle had automatic adjusters but manuall on the stear and tag. He was unaware as I know many others hence this post.

Please learn what is on yours. If U do have manual thats not nessessarily bad they are easy to adjust U do it when greasing. I would never assume they are checking them with oil change and service so specify for your mechanics. Heck for a grease monkey they are BETTER because my slack is always "right there" every time the camper rolls.

Be careful out there boys and girls.

Additionally up untill APROXIMETLY 93 The buses are being held by ONLY 1 AXLE when the parking brakes are applied, the drive axle.

If an owner with one of these chassis with parking brakes on the drives only AND manual slack adjusters AND unaware or neglegent with periotic brake adjustments

THAT IS DANGEROUS. At some point the maxi runs out of travel and the parking brakes will allow the bus to roll after they are applied.

That is what happens in a worst case senerio for the "emergency air". The other half of the senerio is unadjusted manuall adjusters also drasticly diminish the preformance of the "service air" and braking as well too or it will be stopping dangerously bad.

Happy to share.

Joe Camper
04-28-2013, 09:04 AM
Truckers often have an additional gauge and it is application air pressure. It will be 0 and only register the amount of pressure on the brake pedal when u step on it. Harder U push higher the psi goes. Never saw a bus with one would be a great upgrade nobody else has. lLts of trucks have um, lots.

This is a great tool especially for when U have manual slack adjusters on your brakes. When your brakes are adjusted tight U only see 15 or 20psi of application air to stop quick. As the adjustment gets old and loose you watch that pressure go up until your needing 60 psi of application air to do the same thing 20psi used to get U and can gauge it. Without a gauge U can still feel it if U get enough miles behind ya.

04-28-2013, 01:11 PM
Joe how do you tell the differences? What looks difference on the Axles.

Joe Camper
04-28-2013, 05:59 PM
Greg are U asking how to tell if your slack adjusters for your brakes are manual or are U asking how to tell if they are correctly adjusted?

04-29-2013, 01:18 AM
Both sound like good questions, but the first one was my question.

Joe Camper
04-29-2013, 07:47 AM
OK Greg U have a 92 and even if the chassis is a 92 as well yours would be a chassis with parking or emergency brakes on 1 axle only. On the drive axle the only way U will know is if U support the bus and go under for that drive axle, only way.

Otherwise next time U have service done ask the mechanic to verify if U have manuall or automatic adjusters on the drive axle. Also ask him to "check slack" regardless of what type they are and also if they are manual ask him to adjust them.

Steer axle is easier. Turn the wheels all the way left and look in drivers side.


If yours look like this, this is a manual slack adjuster. The collar around the bolt is a lock there is spring pressure behind it pushing it up and locking in the adjustment. When U put a 9/16 wrench on the bolt and depress the locking ring down it allows U to turn it.

To see if your adjusted correctly. With minimum 100 psi in the brake tanks have someone step on the brakes while U are looking at the slack. The most movement U want to see is 2 inches NO MORE even 2 inches is boardering on unacceptable. If they are tight 1/2 to 1 in max movement when brakes are applied that is good. The less movement or travel of the slack the tighter and better the brakes.

The tag axle can be viewed by looking in from behind the tag tire U will need to lay on the ground to scoot in behind the tag wheel to see that axle. Same thing have someone step on the brake pedal. U do not have to release the emergency brake to check this.

Unless someone upgraded the drive axle to auto whatever U have on the steer and tag is probably what is on the drive axle too. HOWEVER I have seen auto slack adjusters on drive axles on buses that had manuall on the other 2 axles.

In order to see the adjustment on the drive axle or any hub with a "maxi" or emergency brake, the emergency brake needs to be released to do it and I DO NOT SUGGEST U TRY CHECKING THAT AXLE YOURSELF unless U absolutly know what U are doing.

If your camper is 92 or older unless someone upgraded the brake slack adjusters the brakes on your bus DONT automaticly stay in adjustment as the pads wear down like in a car or probably every other thing U have ever owned and drove.

They require periotic adjustment to stay in adjustment and safe. Depending on how U drive and where U live will dictate that.

On my Peterbuilt brake preformance would become noticably less by 2500 miles but I was a local hauler 90% non freeway. Under those conditions the slack would require 1/2 turn in to get it back where it was 2500 miles prior.

Joe Camper
04-29-2013, 08:27 AM
If U got coveralls and have been seen from time to time under the bus this procedure is something U definatly want to learn how to do. Best feeling in the world for a driver

Not going to actually explain the procedure. Only a qualified mechanic in person shold be showing someone else whos wanting to learn and doing it for the first time.

I should come out to a rally with my X12 and my coveralls. Someone could donate their bus for a seminar I could show everyone all my secrets. It would be fun. We could pull the drives on the patio side quick and quiet.

We could seminar 1 chassis with all drum brake and manual adjusters, we could seminar another chassis that had drum drive axle and disc on steer and tag and I could seminar a 3rd chassis with knorr-bremmis disc all around.

04-29-2013, 10:29 AM

I seem to recall the DoT mandated all DoT inspected vehicles to have auto slack adjusters. If true, I assume it shouldn't be too hard or expensive to convert. Of course and again if true, we would not be required to have the conversion done given most of us register our Prevost's and personal RVs.

BTW, my 98 chassis appears to air over hydraulic on the drives; make sense?

Joe Camper
04-29-2013, 10:40 AM
I wont bother with who says what. There is still plenty of equipment on the road with manually adjused brakes. My bus was not required to be DOT inspected in Illilois for example.

Assume NOTHING if U can not say for SURE what slack adjusters are on all 6 hubs U need to Verify that.

Gill the air over hyd your refering to is that 2 large additional inboard shocks forward of the drive axle, that are in addition tothe 6 normal rear shocks?

Joe Camper
04-29-2013, 10:58 AM
When a cop DOTs a truck at the scale he blocks the wheels has U release the emergency brakes and rolls under your stuff on a creeper. He goes to the slack with a little tape measure and has U step on the brake and hold it. he goes around to every hub and notes the travel of each one.

2 inches of travel of the slack adjuster is max allowable. IMO on most vehicals if 2 in all around although deemed safe by big brother preformance of the brakes like that is crummy.

A well adjusted slack adjuster will be much tighter 1/2 in travel or slightly less.

Ya know automatic slack adjusters can and do go bad too. They may quit ratcheting and only way to know is your a very aware opporator or U gotta check slack with service Id be sure to ask for it.

The Knorr Bremis dont have slack adjusters BUT Service mechanics should be cheking the calipers to be sure no slides are sticking anytime oil and lube is done. U need to release the emergency brakes just the same to check that too. Similar but different.

05-02-2013, 01:10 AM
I have to thank Joe for this post, as much as Jon W use to mention polishing your Slack Adjusters I never though much of it. I mentioned once I blew through a red light, I hit the brakes at the first turn of the yellow blew right through the red. I always wondered about my brakes so when Joe brought up the subject I checked my adjusters I had at least 2 inches of travel on the front axle. So I fixed the front axles and worked on the Tag. I can't get the tag brakes to work, either with the tag up, tag down, or with the emergency brake off. So it looks like no brakes there. Tomorrow I will work on the Drive axle before troubleshooting the tags. With any luck I will have brakes on the drives. No wonder I blew through that stop light.
So Thanks to Joe and POG my hundred dollar fee saved me thousands in an accident payout.

05-02-2013, 01:25 AM
I would like to add something to this post. Joe said to have them checked. I have had my coach in for service three times once for a brake line recall, once for a lube and again to have the front air bags replaced. I brought up a noise in the right front brake when doing a hard stop. Once they even told me I still had good brake lining. Even with all this the Slack Adjuster were never adjusted. So it doesn't hear to check them yourself or bring the subject up at your next lube or service.

Joe Camper
05-02-2013, 07:28 AM
So Greg when U check the service brakes nothing happens at the slacks on the tag Axle.

Holy cow batman. Thats a new failure for me. SHould not be difficult to get to the bottom of it.

Greg although U do not need to release the emergency brakes to view tag brake opporation the tag air bags do need to be inflated or the brakes are turned off I hope this was the case.


Couple questions. If U have the Pnewmatic schematic on the inside of the engine bay doors take some time deciphering it.
See if your chassis have the tag brakes that are being controled by a r-12 brake relay that gets a signal from the tag bag air pressure. If not possibly U have a chassis with an inversion valve doing it. Newer years they used additional norgrens. I think 92 tag brakes were controled by the r-12s

Those relays are there to shut off the brakes with tag lift up and may be the cause. There is also another r12 in there that gets signal from the brake pedal that is the relay that will signal brake application when u r actually stepping on the brake. The service air going to all 4 rear hubs will be fed thru. IMO your failure whill be in one of those components.

Thats where Id go first if it turns out U still see no brakes with air in the tag suspension.