End of my rope!

[pctrans]

Been trying to resolve the braking issue on my 816. It all started when I attempted to adjust the brake shoes. Found that the adjusting cams were frozen; ended up replacing all of them. Next, rebuilt the master cylinder, still mushy pedal. Also determined the airpack wasn't operating properly, air blowing through exhaust tube when applying brakes. So, replaced it with a spare one I had, stopped the air escape, but still mushy. Had a good hard pedal UNTIL the air built up in the system, then pedal goes to the floor. Ordered a NEW airpack, installed, bled system again, SAME PROBLEM! Got great pedal until the air builds up. Surely someone on here has a cure for me. Thanks in advance.

 

[doghead]

When you say "air builds up", do you mean the air pressure in the truck, or air in the brake fluid until the pedal goes away?

How long does it take to get bad?

 

[pctrans]

Air builds up in the truck air system.

 

[gimpyrobb]

With the added pressure of the air pack, couldn't it be a bad rubber line?

 

[doghead]

Are you sure you have no BFS loss, after you do this a few times?

 

[Recovry4x4]

It sounds like there is copious amounts of air hiding somewhere. Maybe 939 axles???

 

[pctrans]

BFS?? Brake fluid loss? No leaks.

"Copious amount of air?" ALL lines have been bled multiple times, can't remember how much fluid I've bought.....
939 axles....you suggesting I switch them out??

If a rubber line was swelling, the pedal would also slowly go soft with no air. The pedal stays hard, until I start it up.

 

[Recovry4x4]

Was teasing about the air brakes. I know this is very very elementary but did you bleed at the air pack bleeder? I don't know how much bleeding you have done today but there have been many times I struggled to get a firm pedal only to give up and go to bed. Come out ina day or so to be good brake pedal. Agitation of bleeding sometimes causes BFS to entrain air bubbles in the fluid itself. I would walk away and give it another gentle bleeding tomorrow. Are you using a pressure bleeder or Soldier B? All 5 rubber lines are OK? No swelling? A rubber line that looks good can swell and remember, once air builds up you are increasing your brake pressure in the lines 3 fold.

 

[73m819]

this sounds real dumb, but could ypu have air lines switch, since the hard-no air/soft with air all started AFTER the air pack change, this is where I would look, at the change.

 

[halftrack]

Had the same problem with a M35. For the longest time I thought it was a bad air pack and all kind of other stuff. It turned out to be simple shoe adjustments on each wheel using the cam on the back side of the wheel hub/back plate. The shoes just had too much travel in them and the pedal would bottom before the shoes could make proper contact with the wheel hubs. You should adjust them until they just start to drag a little. I had to jack up each individual wheel in order to do this properly and spin them by hand. I dont know if this is the problem but is just a suggestion. Good luck, I feel your pain.

 

[doghead]

BFS / Brake Fluid Silicone

 

[pctrans]

Was teasing about the air brakes. I know this is very very elementary but did you bleed at the air pack bleeder? I don't know how much bleeding you have done today but there have been many times I struggled to get a firm pedal only to give up and go to bed. Come out ina day or so to be good brake pedal. Agitation of bleeding sometimes causes BFS to entrain air bubbles in the fluid itself. I would walk away and give it another gentle bleeding tomorrow. Are you using a pressure bleeder or Soldier B? All 5 rubber lines are OK? No swelling? A rubber line that looks good can swell and remember, once air builds up you are increasing your brake pressure in the lines 3 fold.

Used both bleeding methods. Will check rubber lines tomorrow, with pressure on. Bled both ports on airpack. As to the lines getting switched, would be hard to do as they are solid lines; BUT, will double-check them anyway.

 

[doghead]

Kenny is very correct about air entrapment. That is why DOT5 is not used in anti-lock brake systems.

 

[AMGeneral]

I had the same problem in my 816,I switched from silicone brake fluid to DOT3(after flushing the system of course) and the problems disappeared.

The current owner switched it back to silicone,and the problems came back,definetly a dissolved air in the brake fluid issue I think on mine.

I have switched ALL my MVs to DOT 3 as of now,and have had good sucess with it.

 

[Stretch44875]

Yep, DOT 3 hear also... Works well.

I've got a mushy pedal on the M108 at the moment. Have a new master and rebuilt airpack to go on, I know both of the old ones are not the best. And adjusting the brakes really helps on pedal height. My M35 has a great pedal and brakes.

Hey kenny, I even made a flat plate with a rubber gasket to use on other vehicles for the power bleeder. Works great.

 

[augiedoggy]

Hey pctrans, just a little trick I use sometimes on cars, using needle nose vice grips, pinch off each of the brake hoses at the wheels (one at a time) and see if pedal quality improves. Don't mash the pedal real hard! If it does that would indicate a problem in that wheel (axle) ie. excessive brake shoe travel, wheel cylinder ect. This is not really good for the hoses but for diagnostic purposes can be helpful.

best of luck!

 

[pctrans]

Worth a shot....just need to find a "soldier B"

 

[renovate7]

What Halftrack said.

 

[halftrack]

Hey pctrans, just a little trick I use sometimes on cars, using needle nose vice grips, pinch off each of the brake hoses at the wheels (one at a time) and see if pedal quality improves. Don't mash the pedal real hard! If it does that would indicate a problem in that wheel (axle) ie. excessive brake shoe travel, wheel cylinder ect. This is not really good for the hoses but for diagnostic purposes can be helpful.

best of luck!

I need to remember that.

 

[papercu]

I vote for the DOT 5 as at least some of the problem, just filling the MC will let air in the system. You have to take it very slow while pouring. DOT 5 is only helpful for moisture and even then lines can still rust out. Good luck, Wayne