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75 R Model Slack Adjusters


WOLFWALKER
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I am use to the old mack slack adjusters with the hex head for adjustment, but the 1975 R model I just got does not have any thing there but a little stub that you cant get a wrench on it.

How do you adjust the slack adjusters on this model truck? She's alittle hard to stop with a load and I can't seem to figure out how to adjust them.

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I think you're talking about 1 of 2 style adjusters. My first guess would be the hex 9/16" with the collar around the head. If it is this style, you must depress the round collar in order to get a socket/wrench around the head. The 2nd style would be a 4 sided square head, and you need a 5/16" open-end wrench to turn it. Don't forget that if these are Rockwell self adjusters (however doubtful), you will need to release the pull-pawl to turn the adjuster!

Torque wrench? Can I put an air hose on it??

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Has anybody seen slack adjusters that were turned to the left to tighten the brakes? My 78 Mack does. When I got the truck the prior owner stated he had just adjusted the brakes up and when I drove it, no brakes!! Turning the adjusters to the left brought them right up against the drums. All my others turn to the right to tighten.

These have the hex head and one uses the box of the end wrench to depress the lock before turning the hex.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Has anybody seen slack adjusters that were turned to the left to tighten the brakes? My 78 Mack does. When I got the truck the prior owner stated he had just adjusted the brakes up and when I drove it, no brakes!! Turning the adjusters to the left brought them right up against the drums. All my others turn to the right to tighten.

These have the hex head and one uses the box of the end wrench to depress the lock before turning the hex.

Rob

Drove an LTL9000 Ford that had them-was interesting to say the least the first time I drove it after I thought I had adjusted the brakes

Russ

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Has anybody seen slack adjusters that were turned to the left to tighten the brakes? My 78 Mack does. When I got the truck the prior owner stated he had just adjusted the brakes up and when I drove it, no brakes!! Turning the adjusters to the left brought them right up against the drums. All my others turn to the right to tighten.

These have the hex head and one uses the box of the end wrench to depress the lock before turning the hex.

Rob

Mornin' Rob.

That's common on the front drive axle of some Mack tandems.

If in doubt, I watch the splined end of the cam while turning the adjuster, making sure it is rotating toward the direction of application until tight, then I back off 1/4 turn.

That prevents the "oops" of actually backing it all the way off by mistake.

.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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Hi Herb, I know now, only takes one "experience" to learn. I'd never seen that before and by figured it had to be a front drive axle thing as the rears rotated in what I thought was the correct direction. I had started to adjust with the rear rear and thought nothing about it being different and apparently never looked as the cam rotated. The truck has new shoes on the rears at all corners. Boy was I surprised when I applied the brakes in a gravel parking lot and was skidding the front tires and freewheeling the rears!

I later discovered the rear rear relay valve to be frozen and not passing air also so absolutely no brakes on the rear!

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Adjust them the wrong way?? Oh, never done that LOL!! Back after I got the truck and put new slacks on it...I did that and WWooooahhhh it don't stop for squat when it's turned all the way out! Only had one wheel that was right and it don't stop 26K lbs very easy. Learned a very good lesson that day........always watch the cam as it turns to make sure you don't unwind it. Then I still give it a yank to check the free play.

Mine has the spring loaded lock ring that you have to depress with 9/16" socket to adjust.

IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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2 Possable causes

<1> the slack adjuster is put on the spline the other way round ( turned 180 degrees )

<2> last time the brake twaz assembled they mixed up the 'S' cams from left n right

ButEyeDoSt&2BCorrected

cya

§wishy

HasBeen

If the S cams are mixed up from left to right, the brakes at the wheel positions where this has happened won't apply at all, no matter how they're adjusted.

.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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If the S cams are mixed up from left to right, the brakes at the wheel positions where this has happened won't apply at all, no matter how they're adjusted.

.

That was my take using the limited analytical skills I possess; and was from very deep in the cold storage locker.

Project R-12 has the same setup I discovered tonight with left hand slacks. I've never adjusted the brakes on that truck.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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