Air pack.

[Jeepsinker]

Bench bleed it before you install it, then gravity bleed it once you have it installed. Then let it sit overnight and you shouldn't have to do any active bleeding at all.

 

[kooldadd]

10-4 thanks

 

[porkysplace]

Porky, I agree that the truck needs all the drums to be gone through, and a flush is in order as well, that being said....
There is no reason to use a gallon of fluid to bleed the brakes on any of these trucks. Not unless the system is dry.
I have replaced master cylinder, all 6 wheel cylinders, and air pack on multiple trucks and never used more than two quarts of fluid.
Beyond that, I've also never needed to bleed at the air pack.

They wouldn't put a bleeder on the airpac if bleeding it was unnecessary . Will gravity get most of the air out probably , but cutting corners on a single circut brake system is never a good idea .

 

[chestypuller1371]

what is the method for gravity bleeding? i dont know how to do it.

 

[Jeepsinker]

I wouldn't call getting all the air out with less fluid loss cutting corners. And no, I'm not trying to pick a fight with you Porky. I just see so many people wasting tons of fluid, or even better, not being able to successfully bleed their brakes at all. Through all the work I've done on these trucks, I've found a few better ways to do things. And there is nothing unsafe at all about it either, the truck doesn't leave the yard unless it has a full, hard pedal.

 

[Jeepsinker]

Gravity bleeding is simple. Just an example: you just replaced a wheel cylinder, and it has no fluid in it, but there is fluid above it in the lines and master cylinder. All you do is open the bleed screw on the part you just replaced and wait for gravity to pull the fluid down and fill the wheel cylinder until fluid comes out of the bleeder, then close it.

 

[porkysplace]

I wouldn't call getting all the air out with less fluid loss cutting corners. And no, I'm not trying to pick a fight with you Porky. I just see so many people wasting tons of fluid, or even better, not being able to successfully bleed their brakes at all. Through all the work I've done on these trucks, I've found a few better ways to do things. And there is nothing unsafe at all about it either, the truck doesn't leave the yard unless it has a full, hard pedal.

Gravity bleeding dosen't compress the small air bubbles that get suspended in the fluid , they will eventually work their way to the wheel cylinder and cause spongy brakes , it is a band-aid method of bleeding breaks. I"ve been certified in heavy truck brakes since june of 1980 . Cutting corner to save a couple bucks on fluid is shade tree mechanics at best .

 

[rustystud]

Gravity bleeding dosen't compress the small air bubbles that get suspended in the fluid , they will eventually work their way to the wheel cylinder and cause spongy brakes , it is a band-aid method of bleeding breaks. I"ve been certified in heavy truck brakes since june of 1980 . Cutting corner to save a couple bucks on fluid is shade tree mechanics at best .

Actually gravity bleeding is a valid way of bleeding brakes. Many early shop manuals list this as a valid process. Shops don't do it this way due to time (time is money) but it will work. The small air bubbles will naturally work their way out to the highest place. This is usually the master cylinder not the wheel cylinders. I use gravity to bleed out my brake lines then after almost all the air is out I use the brakes (and power booster) themselves to finish the process.

 

[porkysplace]

Actually gravity bleeding is a valid way of bleeding brakes. Many early shop manuals list this as a valid process. Shops don't do it this way due to time (time is money) but it will work. The small air bubbles will naturally work their way out to the highest place. This is usually the master cylinder not the wheel cylinders. I use gravity to bleed out my brake lines then after almost all the air is out I use the brakes (and power booster) themselves to finish the process.

Back when those manuals were printed it was also common for brand new highway tractors to straight into the shop to have the front brakes completely removed before ever hitting the road . Just because it was done 70 years ago doesn't mean it was done right .

 

[Jeepsinker]

Porky, you are 100% correct. Gravity bleeding alone is not sufficient to remove all of the air. However, these systems move so much fluid that after you gravity bleed so that you have some kind of pedal, a bit of working the pedal, say one half push every 5 minutes over maybe an hour, then leaving it to sit overnight does get all of the air out. I have found that after doing that, the air will rise with the fluid returning to the master cylinder and drop the fluid level.
Now, when I am doing a repair that had to leave same day, then yes I pressure bleed it just like everyone else.
My method doesn't work if the truck has a clogged return port in the master cylinder though, which I have been seeing a lot lately. Actually that reminds me, I need to order some more rebuild kits.

 

[Jeepsinker]

And there is no reason to call names. I wasn't trying to start an argument.

 

[rustystud]

Back when those manuals were printed it was also common for brand new highway tractors to straight into the shop to have the front brakes completely removed before ever hitting the road . Just because it was done 70 years ago doesn't mean it was done right .

Actually the manuals I was referring to are from the 1980's. Not that old really. I still remember my training instructors from VoTec school saying "Gravity Bleeding" done right was a better way of bleeding brakes since air didn't get trapped in pockets by the force of pressure bleeding. So really there is no need to get all mad at those who choose to use this method.
I know you worked on brakes at a shop but I have also worked on a few in my time. Remember I am a "ASE Master" Certified Mechanic with 38 years of experience in medium and heavy duty trucks behind me. So I do know a few things about brakes also.

 

[rustystud]

View attachment Scan0100.pdf

This little blurb is from a modern brake manufacturer "HydraTechBraking" . Even today they say gravity bleeding is the best.

 

[TAKPAK]

And, while on the subject of the air pack, an old motor pool mechanic told me that once in a while one should put a little lubricating oil (air tool oil) in the air pack, through a plug on the housing? He said this is overlooked a lot, and it will keep the pack working better for a longer time. True, false, or??? I've looked in the tech manual and haven't seen anything regarding this. However, it does sort of make sense in some ways.....! Opinions?

 

[rustystud]

And, while on the subject of the air pack, an old motor pool mechanic told me that once in a while one should put a little lubricating oil (air tool oil) in the air pack, through a plug on the housing? He said this is overlooked a lot, and it will keep the pack working better for a longer time. True, false, or??? I've looked in the tech manual and haven't seen anything regarding this. However, it does sort of make sense in some ways.....! Opinions?

There is actually a special oil the military uses. It costs about $15.00 a quart and you must buy it in 5 gallon buckets. I tried to find a civilian equivalent but there is none available. In all mine I just use Synthetic grease. It works great. They also make the grease in a spray form.

 

[gimpyrobb]

And, while on the subject of the air pack, an old motor pool mechanic told me that once in a while one should put a little lubricating oil (air tool oil) in the air pack, through a plug on the housing? He said this is overlooked a lot, and it will keep the pack working better for a longer time. True, false, or??? I've looked in the tech manual and haven't seen anything regarding this. However, it does sort of make sense in some ways.....! Opinions?

It is not a bad practice as it protects against rust, but shouldn't be needed if you keep as much moisture out of your air system as possible(draining the air tanks often or installing an air drier).

The new style airpacks don't have that port to ad oil to.

 

[Floridianson]

Well the new style can have oil added to the pipe on the air pack it just leaves some oil your elbow when you stick the pipe back on. Just watch out for the O ring.
Also no matter how one would bleed the system I myself would still crack the air pack bleeder. Myself I use the Ace hardware one Gal. pump up sprayer and when the tip of the wand is removed the wand will screw right into the master cap and seal just fine.

 

[rustystud]

Well the new style can have oil added to the pipe on the air pack it just leaves some oil your elbow when you stick the pipe back on. Just watch out for the O ring.
Also no matter how one would bleed the system I myself would still crack the air pack bleeder. Myself I use the Ace hardware one Gal. pump up sprayer and when the tip of the wand is removed the wand will screw right into the master cap and seal just fine.

I bought this nice stainless steel sprayer and it works great to bleed the brakes. I usually let the brake fluid gravity bleed for a 1/2 hour then put the pressure can on to finish the job. Saves a ton of brake fluid this way.