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I am ready to bleed my brakes, is there anything to be done different just because i have a hydrovac booster installed ?

Bruce

With a hydrovac it may bleed easier with the vehicle running -start with the furthest wheel cylinder and work your way thru each wheel then to the hydrovac itself which should also have a bleeder on it.
Gary

Bleed the air off at the booster first, then move to the wheel cylinders.

Charles is right on this one! Until you bleed the booster, you'll be compressing air on every stroke of the pedal and it will take forever to bleed the air out of the lines. You can bleed the lines first, but it will take longer and be more frustrating because your pedal will still be "squishy" until you bleed the booster.

Yesterday i was about to commence bleeding of the booster, until i noticed it has two bleeders on it.
In a nutshell, i have broken the top bleeder, but the one where the brake hose attatches is fine, my question is did i really need to bleed both, or can i just cap of the broken one and just bleed of the one good one.

Bruce

SydneyM37 wrote:Yesterday i was about to commence bleeding of the booster, until i noticed it has two bleeders on it.
In a nutshell, i have broken the top bleeder, but the one where the brake hose attatches is fine, my question is did i really need to bleed both, or can i just cap of the broken one and just bleed of the one good one.

Bruce

I would pick up a new bleeder valve and replace the broken one, then proceed with the procedure.

Thanks Charles,
Going of yourearlier post, i will bleed the booster first before the wheel cylinders.
With the booster having two bleed screws, is there a particular order i should bleed those ?

Hello Sydney,
This should answer those questions for you. From another truck forum but the same issue.

Bleeding A Hydrovac Brake System, Manual
Manual bleeding requires filling the master cylinder reservoir and pumping the brake pedal to force the fluid through the lines to expel air from the system. This operation must be done with the engine shut off and no vacuum in the power brake system.

With the master cylinder reservoir filled, open No.1 bleed screw on the Hydrovac and depress the brake pedal to expel air. When the brake pedal has reached the toe board, close the bleed screw before returning pedal to release position. Repeat this procedure until soild fluid, free from bubbles, comes from the bleed screw. Check the master cylinder frequently to insure an ample supply of fluid.

Using this method, bleed No.1 and No.2 bleed screws on the Hydrovac and then proceed to the vehicle wheel cylinders. Then start with the wheel cylinder farthest from the master cyl and work your way to the wheel that's closest; typically Rr, Lr, Rf, Lf.

SydneyM37 wrote:Thanks Charles,
Going of yourearlier post, i will bleed the booster first before the wheel cylinders.
With the booster having two bleed screws, is there a particular order i should bleed those ?

Whomever wrote the post from the other site has included some instruction that is 100% WRONG, and will cause you problems. He says "push the pedal to the toe board" during the bleeding procedure, NEVER PUSH THE PEDAL ALL THE WAY TO THE FLOOR. Doing this will extend the M/C piston farther than its normal range of travel within the cylinder bore which will screw up the piston cups every time in a master cylinder that is worn in, ruining the unit. It is not as likely to damage the piston cups in a new cylinder as it is a worn one, however I have seen new ones ruined from the same thing. A good rule of thumb is to never push the pedal farther than 3/4 of its total travel distance when bleeding the system. Closing the bleeder each time the pedal returns is not the proper way either. You need to put about 2 inches of clean brake fluid in a small container, glass or plastic that you can see through. Connect a short length of hose that is a snug fit onto the bleeder valve. Place the hose in the container of fluid so the end is submerged in the fluid at all times. Open the bleeder valve, have your assistant pump the pedal slowly and repeatedly until all the air bubbles are expelled, close the bleeder and proceed to the next bleeder in the sequence. Be sure to never let the master cylinder reservoir run dry during bleeding. By having the hose submerged in fluid, no air will be drawn back into the system when the pedal returns. This procedure eliminates having to close the bleeder each time the pedal returns, and it cuts fluid waste to "0" as the collected fluid from bleeding can be poured right back into the master cylinder.

After you get air free fluid flow at the booster bleeders, proceed next to the wheel cylinder bleeder that is the fartherest away from the booster, verify by checking the line routing. Bleed out the longest line first following through to the shortest line last. This guys bleeding sequence is also incorrect for a M37. The fartherest wheel cylinder by line length is the left rear, next is right rear, then left front, and finally right front.

Thanks guys, I am getting the busted bleeder fixed, then proceeding with the job

Bruce

The article was introduced for information only and was not directive in nature and did not specify vehicle make/model/type. The toe board issue depends on the equipment you are working on. The orginal question concerned the hydrovac unit itself. The writer's reference very clearly states

Then start with the wheel cylinder farthest from the master cyl and work your way to the wheel that's closest; typically Rr, Lr, Rf, Lf.

Not wrong enough to beat him up for it.

We keep articles like that posted in the files area of our web sites so readers can access this data anytime. It also helps to do away with those constant repeat questions every 3 or 4 months and the time wasted re-replying and re-explaining.

We have articles submitted by jnowlegable folks and load them to the files section permanently with proper credits.

It would be nice to see folks like Charles publish a few of these replies as short articles and then permanently install them to the web site for reference. In the long run these articles will save hours of typing repeats.

Cuz, incorrect, undetailed, poorly written, generalized, or what ever terms you use simply does not give good solid information to someone who is searching the CORRECT procedure. It's great that you are willing to offer help, however simply posting an article written by God knows who with incorrect information in it is not the kind of help I would be looking for in solving a problem. One would assume you must have agreed with the information this guy put up or you would not have passed it on as quality info. My suggestion to you would be to read this stuff carefully and completely before you post it as the best way or even a way in general. No doubt that posting has caused some people on the other forum to ruin their master cylinder during the bleeding process because of the issue I described. Is this the kind of information you would like to take to the garage? Would you appreciate someone offering a procedure to you that will cause further issues with your brake system in addition to the one you are already attempting to correct? No telling how many times I've heard the story when trucks come in here for brake service, "I replaced the shoes and wheel cylinders, but could never get the system to build pressure like it should." A quick tear down of the master cylinder most always reveals the piston cup turned inside out from piston over travel during bleeding. The most common reply when you tell them what the problem was, "I never thought about that." Here you are posting an article that gives instruction for bleeding a system that will cause further damage in the name of generalization. I just don't get it.

An answer to your question, why don't I offer some articles to help people. I have done that many times. I have also been challenged many times by people who's procedures leave a lot to be desired. This situation many times results in rediculous confrontations that should never be on a forum. Simple straight forward, factual, information that is correct and to the point is the only needed end product when a person ask a question. Quite honestly, I would much rather a person just call me if they would like my input on an issue. That way I am free to ask further questions about the particular issue, thus I'm able to offer a much better, more direct answer to that specific situation. Long story short, if I know the answer to a question, I can give it, straight forward. 10 different answers with varying degrees of accuracy isn't what I look for when I ask a SPECIFIC question. A general analysis that may not even apply directly to my issue, well that just don't get it either. I don't have the time to get into hours of writing trying to find out all the particulate details of a situation necessary for me to give the needed answer in many cases. With that said,I simply pass up offering info on many issues I read about here. My case is different from most folks here, I'm not a person who just sits in the office watching things run at M Series Rebuild, I'm also a person turning nuts and bolts on M-series trucks on a daily basis at least 5 days a week, sometimes more. You can rest assured my answers to questions have come as a result of actual hands on experience. If I offer an answer, you can count on that answer being based on just that, and not from someone's poorly written and inaccurate article on some forum. I really don't know whether that person even knows what a M37 looks like, much less whether they have real world experience on which to base their answer. If I don't know the answer, I'll tell you that I don't. If there are several possibilities, I may offer my preferred sequence of troubleshooting to check things out. My preferences for troubleshooting are based on real shop experience; in other words I have solid reasoning behind suggesting a compression test before looking at accessory items sometimes, even though some may feel that is rediculous, but that is a story for another day.

That was a lot of rhetoric for a fellow who tells us how busy he is. This is a public forum and I don't recall the use bylaws stating it was Charles way or the highway. I disgaree with you completely. The article was not a M37 article and as such would have been percieved by anyone above the 8th grade reading level as not directly applicable to the M37. Yes I have a M37. Yes I am the guy who maintains it. And yes I have been bending wrenches since 1955. And no I do not spend a lot of time on forums talking down my nose at folks. And no I do not profit from my posts on this web site.

Have a nice day!

cuz wrote:That was a lot of rhetoric for a fellow who tells us how busy he is. This is a public forum and I don't recall the use bylaws stating it was Charles way or the highway. I disgaree with you completely. The article was not a M37 article and as such would have been percieved by anyone above the 8th grade reading level as not directly applicable to the M37. Yes I have a M37. Yes I am the guy who maintains it. And yes I have been bending wrenches since 1955. And no I do not spend a lot of time on forums talking down my nose at folks. And no I do not profit from my posts on this web site.

Have a nice day!

Whatever, today is Saturday, so I had a little more time to type. Nobody said it was my way solely, those are however the facts as they are relative to the M37. I do believe it is more beneficial to all here on this forum if things remain relative to the M37 since the questions asked were concerning that system, my thoughts solely. We could give "general" comments all day, may help someone, may confuse someone, that's why I try to keep on subject with such issues, just my opinion.

As far as my education, I did graduate from high school way back when, so now you know I did make it past the 8th grade, virtually everything since then has been hands on for me. I will readily admit that I have always learned better using the hands on method. Any comments made such as yours about the 8th grade reading level just rolls off like water on a duck. I've received more help along life's way from folks who had learned by doing and from their years of experience than I ever have from the ones who claim to be scholars. Some that I learned the most from were not priviledged to have any formal education at all, and I must admit they were some of the smartest people I've ever known. Maybe it has been different for you, and hey it is whatever works.

If you took my comments about the wrong stuff in the article as you having made them, you need to read again. Those comments were directed at the author of the article, not you. What I really wondered about from your comments was why you would not clarify statements in the article that were wrong info and info that will cause M/C failure such as pressing the pedal to the toe board during bleeding, in fact if you check, you will find the piston travel is at its end before the pedal hits the toe board in a M37. Once again, I'm sticking to the relative facts. I don't feel you would be one to intentionally pass along info that will cause further problems. Nothing wrong with using the cut away illustration and it was a good general description of a vacuum booster other than these certain points described in the text just being flat wrong. You had a lot to say about the fact the article was not M37 specific, what do you have to say about the wrong pumping procedure? I mean it will cause the same damage on a '49 Buick or a '55 Ford master cylinder just the same as the cylinder on a M37, was it not relative in those models either? Even in a general context, it is still wrong and bad information to convey. Were you aware that pumping as described in the article would ruin the M/C internals? I noticed you have made no comment on that subject in all you have shared. Come to think of it, sounds like you were just willing to take the article contents at face value assuming its correctness, but I could be wrong. Now in my case, as I wrote previously in this post, I've got much of my education by hands on, thus I learned years ago not to use the "to the toe board" pumping method in the bleeding process. Yes, after screwing up a couple of good master cylinders as a result of using the very steps the article author described, I learned the procedure of "to the toe board" was WRONG. I reckon things such as this that I learned the hard way might qualify me as a graduate of the School of hard knocks also. Anyhow, that thought has stuck with me since that hands on education that I received concernig a correct pumping procedure, I share it with everyone who ask me anything about rebuilding a brake system in order to help them steer clear of further complications. That is really all I intended to do by making these comments here.

What I have found over the years is to put a block under the brake pedal as it is hard to drop the pedal 3/4 the way then hold it without drawing air back in.
J.B.