Adjusting auto slacks

[lostagain]

Being under the bus yesterday greasing and such, I pull on the adjuster and find almost 2 inches of slack on the front axle. So I get a wrench and tighten it and loosen it by a quarter turn. It tightens smoothly and slackens with the click-click of the rachet. The drive axle only had about 3/4" play, but I did the same to it. Seems like the right thing to do, but then I think: these are automatic slacks and I shouldn't have to do that.

What do you guys say? Should auto slacks be left alone, or is taking up the slack OK?

JC

[belfert]

If I remember right BW talked about brakes at Bussin' 11.  I seem to recall that if you start manually adjusting auto slack adjusters they will no longer be auto slack adjusters.  The answer seemed to be replace the auto slacks if they are going wonky.

[luvrbus]

If you were that far off they are not working they will adjust right if proper maintenance is done one thing I noticed they don't work good on the older splines (6) s -cams if memory serves me the Feds required at least 10 spline count starting in 1994 for use with auto adjusters.
My guy in my truck shop always had a tool he would back the auto adjusters all the way off then set the auto adjusters seem to work we never got a ticket on a truck or trailer for brake adjustments


good luck

[lostagain]

I can see new slack adjusters in my near future, LOL.

Can you still buy manual slack adjusters? I liked them.

JC

[belfert]

I also seem recall that BW liked manual slack adjusters better for bus conversions because our vehicles usually sit still much of the time.  An auto slack adjuster that isn't lubed and such won't stay working.

Auto slack adjusters have been required on new vehicles in the USA since October 20, 1994.  You would certainly want to keep auto slacks on anything manufactured after that date which isn't too many of us.  If you have a vehicle that came OEM with auto slacks before October 94 I would probably keep them for liability reasons.  If they were added later there would be no reason you couldn't go back to manual.

[skihor]

Auto slack adjusters work by brake applications. If you do a "brake test" every time you drive they will stay adjusted, provided they work. Do 4 HARD apps. several times and they should tighten up like they are supposed to. By hard app. I mean like 90 LBS of pedal pressure, (gauge/air pressure). In your "bleed down" test use hard pedal apps. and they should stay proper. Remember older car drum brakes ? They adjusted by stopping in reverse. That is what worked the self adjuster. If one never had firm braking, in reverse, the auto adjusters wouldn't work properly. Kinda the same deal here... if you don't have any FIRM braking on a regular basis then the auto slack adjusters won't keep up. All the more reason to do a 7 point brake check each, and, EVERY day you get in to drive.

Don & Sheila

[buswarrior]

An auto slack that is found "out of adjustment" cannot be trusted.

They should not need anything other than grease and inspection, once installed according to the particular manufacturer's procedures.

Auto slacks are well regarded in those fleets in which everyone has been trained and supervised to treat them properly.

It is shocking how many technicians out there do not follow the procedures for the auto slack in hand. The procedures are not one size fits all. They differ by manufacturer and vintage.

How did it get out of adjustment? The busnut is best to find out.

internal failure, incorrect install procedures, abuse by unwitting wrench turners, other worn parts in the assembly manifesting themselves as bad adjustment, the adjusting mechanism in some can be damaged by using the wrench in the wrong way.

The challenge for a busnut is our low mileage and our unknown vintage inherited auto slacks. Add in a set of Jakes or a Retarder, we may go a year or more before the mechanism reaches the adjustment point, and then, will it adjust?

Again, a component that is thrust into an operating environment for which the designing engineers never imagined - sitting still most of the time.

Best practice would be to establish a written record of measuring the applied pushrod stroke at each wheel location in order to establish your particular trends in brake wear.

Pulling on the pushrod to check free play is not very accurate, and limited by your strength and the accessibility of the linkage to pry on. The air pressure will be able to push it further, and you'd really like to know that, wouldn't you?

happy coaching!
buswarrior

[lostagain]

Thank you all.

I will keep a close eye on them. And replace them if necessary.

The coach is a '77. So I don't see a liability issue with going back to manual slacks if I can buy them.

JC

[John316]

Thank you all.

I will keep a close eye on them. And replace them if necessary.

The coach is a '77. So I don't see a liability issue with going back to manual slacks if I can buy them.

JC

JC,

You can go back to manual, if you want. I know Bendix sells them. I assume the other names sell them too. If your bus was made before they required auto slacks (I think 1996 and later, but I don't remember), you can revert to manual.

And when you have to adjust your slacks, they are junk (from what I have learned).

HTH

John

[Lee Bradley]

You might check the air can. I have an air can with a broken return spring (it will be replaced before the bus sees the road again) so it doesn't return to the zero position for the auto slack to adjust.

[TomC]

Personally like the manual slack adjusters.  You should only have to adjust them every 5,000 miles or so depending on whether you're in mountains or not.  So that would be about once a years for most of us.  I like it because you have to get underneath to grease up the brake fittings anyway, so adjusting them gives you built in chance to inspect the linings and drums for any types of failures.  1/4 to 1/3 turn out is the right amount to adjust the brakes.  If you're in doubt-hit the drum with your wrench to see if it rings like a bell. If it just clunks, it is too tight and the brakes will be dragging creating unnecessary heat.  Good Luck, TomC

[Joe Camper]

Auto slack adjusters are inherently self destructive. All slacks, even the manual ones correctly adjusted are too.

Let me try to explan and help some.

A correctly adjusted slack adjuster should have less than 1 inch of travel. After many repeated braking cycles the short travel forms a "dam" of grease in the slack at that point where the travel ends. Eventually is gets so thick and sludged up at that point that the "ratchet" in it does not have the ability to overcome that rezistance and they quit auto ratchiting. Left unchecked it will even strip itself.

Something I have learned and you all can also do to eliminate the situation is when you grease or at minimum once a year manually back the slack adjuster ALL THE WAY OFF. That turns the s-cam almost an entire 180 degree and then when you grease it you will be shooting grease on the backside of it where it normally is not seeing it there. It will bust the dam of crud and built up old grease by greasing the bakside of the s-cams like this too.

This works really really well and will extend the service life of those components exponentially.

[Joe Camper]

Another good idea is to take the pin that goes thru the clevace and the hole in the slack adjuster and replace it with a 3 or 4 in grade 8 bolt. That creates a handle that you can get a good grip on to pull to check slack.

I have seen these for sale specifically for this purpose i do not remember where but a 4 in grade 8 bolt will do the same thing.

Another thing I do is after greasing I get all the excess grease that has pushed out cleaned off. That stuff is a dirt magnet and creates a whole nother set of issues.