bigragu

Ok, finally got around to changing out rear wheel cylinders to 1 1/8" and 3" shoes on my W250. Trying to flush system out and bleed at the 5 points. Cannot get the pedal to feel solid. When bleeding the abs valve bubble after bubble coming out. Already went thru 48 oz of fluid and pedal is soft and brake lite and ABS lite comes on. I've been under that truck bleeding the 5 points at least 12 times. For the last 4 attempts I bought a mighty vac hand pump brake bleeding tool. The earlier attempts was a tube from bleeder into a container half filled w/ fluid while my son built up his quads pumping the pedal. How long is this suppose to take, on average? Any of you use/like the mighty vac tool?

BHD

So you're still getting air at the ABS valve? Have you tried the single stroke method? (Open that bleeder push the pedal down, close the bleeder let the pedal up.) Then bleed the rear wheels the same way. I own a MightyVac, its great to evac a system but no luck to bleed the brakes. I bought a Phoenix reverse power bleeder and that works well. Also, I hate to ask, but are your shoes adjusted fairly tight? A lot of shoe movement can give you a soft feeling pedal.

Angry Johnny

OK, so all you have done was replace the rear wheel cylinders as far as the hydraulics are concerned? Did the master cylinder run dry? If it did you will need to bleed the master cylinder separately first, then the rest of the system.

I also like the single stroke method as pumping the pedal can create a lot of tiny air bubbles in the system.

NJTman

Mr. Terminator,

I've felt your pain, but since then, I've finally figured out how to do these rear wheel cylinders. Reality is that it should only take about 10 minutes, and maybe a 1/3rd of a pint of fluid.

My most recent bout with these rear brake parts was when I replaced my rear brake hose and steel lines on the axle, sometime about 3 weeks ago. I never bled the ABS unit, and I still have good brakes. I really don't think it's necessary, as it didn't make any difference is what I was doing so, I just don't bleed anything but the cylinders.

I have the Mighty vac, and I do not use it, as I found it wouldn't work properly, as it sucks too much air. I use the mighty vac tube end, the clear tube and a peanut butter jar with a hole in the top that fits the tube where it's tight and makes a good seal.. You don't even need to put any fluid in it. I've made this known before, but I'll repeat it again.

1. 10 mm wrench on the bleeder, making sure they're TIGHT. Once you know both sides are tight, then start on the passenger side.

2. Have the assistant pump the brakes slowly, and easily. Once a few pumps have been completed, they "stop and HOLD IT", and you crack the bleeder just barely enough to let some fluid / air out. DO NOT OPEN THE VALVE UP MORE THAN 5* of an arc. OPEN IT UP JUST A SMIDGE, then close it back up. Pump up again, and repeat.

3. MOST IMPORTANT: The bleeder has the mighty vac tube end and clear hose attached to it. Make sure the peanut butter jar is ELEVATED above center of the axle and backing plate (I put it on the leaf spring), and the tube points to 12 o'clock, loops UPWARDS towards the sky, and back down into the peanut butter jar. This creates the rising column of brake fluid, which eventually will crest over the peak of the arch, and drain into the jar.

You want that tube to be vertical at all times, IOW pointing up towards the sky. This allows you to visually see if you have bubbles, but more importantly, it allows you to see whether or not you're tightening the bleeder enough in between the bleeding sessions. If you're not tightening the bleeder enough, you will witness the fluid rising up and down as the assistant (my wife usually) is pumping the brakes in between your bleeding times. This is where most of my errors had previously occurred, as what I was doing was not closing the bleeder tight enough between openings. This allows air to be sucked into the bleeder at it's threads, and you never get a full / hard pedal because of the air that infiltrated into the wheel cylinder.

I cannot stress this enough. The Tube MUST BE VERTICAL and looped up under the wheel well, and back down into the jar. YOU MUST BE ABLE TO WITNESS the air bubbles in a "rising vertical tube of brake fluid", and know you're tightening the valve enough to seal it properly in between bleedings.

4. Go to the other side, and repeat.


5. Go back to the passenger side and repeat.

6. Go back to the drivers side and repeat

7. Feel the pedal for confirmed proper bleeding.

8.... Don't forget to periodically check the master as to not run out of fluid while you're doing this.. I never let the master go below 1/2 full, as I don't want to take the chance of sucking air in the master, and having to start all over again.



After struggling with these brake systems for what seemed like a lifetime, I'm confident in my techniques that ever time I do a brake bleeding, I end up with a pedal that works as it should....and it doesn't take more than a few minutes to achieve. And I don't bleed the ABS unit either unless it's completely dry from a removal or disconnect from the brake hose. I didn't do the bleeding of the ABS and it still bled properly. I really don't think it's necessary.

My problems were simply the fact that I was not doing the bleeding properly, and unfortunately, it's where most of us make the same mistakes.

bigragu

All great advise, all, and thanks a bunch. I will try all methods as a combination of the advice given . Will post up my results. Thanks again!

bigragu

Still working on this bleeding situation. Tried the single pump method and it got somewhat better but I know I am still short of 100 percent accomplishment. Tying this into my dilemma is the e brake. Do adjustments to the emergency brake cable have to be made upon installation of new shoes, cylinders, and spring hardware? No where in the shop manual does it state to adjust the e brake upon replacement of the rear brakes. Thanks

rrgrassi

That is a yes or no question. Was the e-brake adjusted before? If no, probably not. You do not want the ebrake adjusted too tight, as it can make brake shoes contact the drum which is not good when driving. Too loose, and the e-brake may not hold the truck.

Basically, test the e-brake before adjusting. IIRC, e-brake should engage betwenn 3-5 clicks on the e-brake pedal.

BHD

The parking brake is often affected by replacing shoes if you mess with the brake shoe adjusting screw. Are your shoes adjusted so you can hear them just begin to drag on the drum? Improperly adjusted shoes make bleeding the brakes a pain and make the parking brake ineffective.

bigragu

All right- update. Hopefully this tread will assist others to avoid my bafoon mistakes. Readjusted my shoes to achieve a slight drag on the inner drum. Swapped out my regular bleeder screws for speed bleeders to avoid pulling in air at pedal pump procedure. I had to tap my ABS Valve bleeder threads to 1/8" NPT so I could plug that thing. All the unscrewing/tightening over the years had stripped out the threads, and being a $200 part, I chose the route of plugging it up. I am able to bleed it still, just by pumping the pedal, holding, and cracking the plug till fluid drips out, then tighten. All 4 other bleeders are all speed bleeders with the one way check valve built in. So, here is where I'm at: After pumping and holding for each wheel a total of 10 times, each time cracking the bleeder screw open, allowing fluid to pass out, and re-tightening, I have a somewhat firm pedal with the truck off. At start up, the pedal slowly falls to the floor. There is pressure, though. I really have to push down to get it to the floor. Then the ABS and Brake warning lights come on. My O'Rileys Booster just turned 1 year old. I never let the Master Cylinder run dry. You think I still Have air in the lines? How often does the ABS valve go out, and if so, what are the signs? I do have a Cardon Brake booster remanufactured. Is 1 year all I am getting on that? I must rule out vacuum leak, cause along with new vac hoses my cruise works and all HVAC controls. In fact, all was good(cruise, HVAC, brake apply pressure) till I swapped out for the 1 Ton 3" shoes, the 1 1/8"wheel cylinders, and all spring hardware. At a standstill, pondering what else I need to check or do. Need assistance. Thanks to all who responded so far. Your advise has indeed been a guidance

rrgrassi

It sounds like there is air still trapped in the system.

maybe368

I think that the MC is bad, even the new ones can be bad out of the box, so 1 year is believable. I would try to warranty it, if not, get a new Bendix, I feel your pain ...Mark

bigragu

Can anyone explain to me what the vacuum is suppose to do when created by the vacuum pump at start up of the truck? This is as far as brakes are concerned. Is the pedal suppose to stay at one spot with foot pressure applied or is it fading in my case because I am starting the truck and letting it idle for 1 minute after start up? Maybe I am not building up vacuum tha is reqd to solidify that brake pedal? Can someone clear this up? I don't want to tear into a brake booster replacement if I don't need to. Got a sneakin suspicion that's it. I will keep bleeding after work tonite I suppose

maybe368

A bad booster causes a hard brake pedal. Mine started doing exactly the same as yours and a new bendix mc solved the problem...Mark

rrgrassi

If you get no more air after bleeding the brakes, I agree with Mark. Bad Master cylinder.

The brake pedal should stay in place when pressed. If it begins sinking, or if you hold the brake pedal in one spot and the truck begins to roll, it is a bad M/C. Brake fluid is bypassing the M/C seals.

NJTman

If this was true, you would have a line of fluid coming out the bottom back side of the master, or being pushed into the brake booster itself. Anytime a master had gone bad with me, It always leaked out the back and down onto the frame.

I agree with Mark to install the bendix MC and be done with it.

You're still getting air in the system, and simply to eliminate the possibility of the master being bad, I'd just replace it with the bendix. All the other MC's I bought all failed. New and old. Napa, autozone, Advance, Etc. All failed to keep the fluid in the master.