Changing the rear bags now

[Chopper Scott]

I had gotten 3 of the rear rolling lobe bags from Mohawk last month as well as the fronts that I have replaced but 1 was on backorder. It arrived yesterday!!!  Looks like I'll be busy this weekend. Tonight I got the bus jacked up and blocked and went about getting the rear wheels off. The right side was a bear. I have a 3/4 " impact that easily surpasses the 500 ft lb rating according to my torque wrench when I check the wheels after tightening. A trick I learned when loosening nuts is to hit the socket with a hammer while nailing it with the impact generally does the trick. Not this time. I ended up borrowing a 1" impact and got the outers off without incident but the inners!!! Holding  the 1 " impact with my legs, pulling the trigger and hitting the socket with a hammer finally broke em loose. One side done, one to go. Just because it was easier I tried the 3/4" on the street side and the outers came off way to easy. Generally the inners are the hardest and they also came off way to easy. I noticed the inners looked pretty new. After pulling the wheel I noticed the inside of the wheel was a caked on mess! Not fresh oil. Caked on crap! Also some fairly new blue goo on the axle cover. Someone replaced an inner seal and was probably not too educated about the procedure or didn't bother cleaning up the mess. I'm thinking the torque rating was something like a poor 1/2 drive would equal. The good news is it isn't leaking anyways but as I age and have gotten anal I have to knock the drum off and check the pads. Then get them bags changed!!! I may need some therapy down the road however. I'm starting to enjoy working on the ole girl!!!

[John316]

Good for you, Scott. Keep up the good work, and keep on doing things right.

God bless,

John

[jackhartjr]

Makes me wonder if the brake with the caked on crap was not working.  Otherwise the heat should have burnt the stuff off!
What do ya'll think guys?
Jack

[JackConrad]

Before you put thje wheels back on, take time to adjust the brakes. Much easier with the wheels off and you know they are adjusted. Don't forget 90 degree angle between slack adjuster and push rod with brake applied when properly adjusted. Jack

[DaveG]

Before you put thje wheels back on, take time to adjust the brakes. Much easier with the wheels off and you know they are adjusted. Don't forget 90 degree angle between slack adjuster and push rod with brake applied when properly adjusted. Jack

Just a reminder that the pushrod to slack adjuster angle should not go less that 90 degrees, otherwise you lose some of the leverage...you don't want it to go 'over center' kinda...you get the idea. The goal is not to be at 90 degrees, but to to go beyond center (which is actually less than 90 degrees).

This either cleared that up or stirred the murky waters.

[buswarrior]

The angle between pushrod and slack adjuster is a function of how long/short the installer cut the pushrod/screwed the yoke onto the pushrod when it was first put on there.

The goal, as noted, for good leverage of the mechanical bits is that the angle is close to 90 degrees when applied and brakes are within adjustment.

You can't do anything/shouldn't do anything about the angle via brake adjustment.
Only disassembly/replacement of the chamber/yoke adjustment on the pushrod will change what the angle is when the brakes are properly adjusted.

This is the big danger in unknowingly cutting the new chamber pushrods the same as what was on there...
If the last guy cut them too short or too long for that application, you copy him!

Properly adjusted brakes is about the distance between the linings and the drum when released being as close as possible without touching, the amount of mechanical movement to close the distance, and whether the mechanical movement has enough travel left before it comes up against its stops, to compensate for the heat induced expansion of the drum, and some wear of the lining material before the next time it is checked.

The mechanical bits end up where they end up?

Or something like that.

happy coaching!
buswarrior

[bevans6]

Pretty much clear as mud, I'm afraid.    You get maximum force transfer when the angle is exactly 90 degrees.  the loss of leverage is the same whether the angle is greater or less than 90 degrees.  But if the angle is greater than 90 degrees ( the slack adjuster is leaning towards the brake can, not away from the brake can) as the brakes wear, the force transferred will be come greater.  Also, as the can presses harder and moves the slack oh so marginally farther, the force transferred becomes greater.  If the angle goes past 90 degrees, as the  brakes wear or the can presses harder, the percentage of transfer reduces.

why would you not simply measure the applied stroke, the way they teach you to do?  Obviously if the angle is wrong, then something was installed wrong and you should always be aware of it, but why wouldn't you either adjust the brakes (if manual slacks) or check the auto slacks, and measure the applied stroke?  

For that matter, how the heck do you measure applied stroke at the rear with the wheels on?  I can't even see my slacks clearly with the wheels on, I have to take the wheels off to inspect and measure stroke.  There has to be an easier way...

Brian

[Chopper Scott]

Got em in! The rears are harder to replace than the fronts. More tires, more bolts holding the old bags in etc. I had a slow leak in one tire and ran it down to get fixed this morning. Just a valve stem. Tomorrow will be maintanance, setting the brakes etc while the rears are off. If all goes well I may plumb in the tranny cooler while I have it jacked up. As of now I'm tired! That was a long day!

[buswarrior]

What I tried to say:

Properly adjusted has nothing to do with the angle of the mechanicals, because the angle is determined by whoever assembled/cut the mechanicals on their installation.

If the rod was cut short...and you fix it to stroke 90 degrees...you'll have trouble stopping!

As Brian posts, adjustment is best checked by measuring applied pushrod stroke.

We must take care to discard the misinformation that has been fed to the road going transportation industry over the years.

happy coaching!
buswarrior

[dickegler]

Guys,

Here is a prime example of INCORRECT brake geometry.  Notice the angle is already past 90 degrees, with the brake at rest.  Very limited braking and dangerous to drive.  

Someone has replaced the brake cans and adjusters, and didn't shorten the threaded rods.  The tags were the same way.

If you don't understand the geometry involved, or not willing to learn, take it to a professional.   Remember: safety first!!

After cutting the rods to the correct length, installing new shoes and slack adjusters,  WOW, now I have great brakes.  YEA!!   Pucker factor greatly reduced.

Hope it helps understanding the brake system.

Happy Bussn    Dick Egler