The Stovebolt Site Forums The Parking Lot Big Bolts Need help with bleeding brakes

I replaced the entire brake system on my 1953 Model 6400. The rear end is out of an earlier truck, but I finally found the proper brake cylinders. I installed all new lines, wheel cylinders, master cylinder and Hydravac. For some reason I can not get the brakes to pump up. I can't find any leaks, so I assume there must be air in the system, but I have been around it a number of times, including the Hydravac, with no luck. What am I either not doing, or doing wrong? I do not have the motor back in the truck yet so I have not had any vacuum on the system. Could that be the problem?

I read a post a few months back where a guy suggested using gravity to bleed the lines.

I havent ever tried it, but the dude said he'd open up all the bleeder valves, fill up the master cylinder, and then let gravity pull the fluid from the master cylinder down thru all the brake lines.

I dunno how well that would work, since on all the trucks i've bled the brakes on, the lines were usually lower than the master cylinder and individual brake cylinders.

I've also read that "professionals" use some sort of vac system to pull fluid thru the lines.. but I haven't ever done that either.

When I have bone dry lines, from either a fresh install, or from just sitting, I fill the MC up, put the cap back on, then pump the crap out of the brakes.

In both my '46 and '50 this results in some pressure build up of both air and fluid.. not so much you really feel it in the pedal, but enough that if you have a vented MC cap, it'll start squirting like a lawn sprinkler.

Then I have a helper hold the pedal to the floor, and I go to the wheel furthest away from the MC and open the bleeder.. which usually sighs a little air and a dribble or two of fluid.

Then I start standard brake bleeding procedure.. have the helper pump three times then hold to the floor, then I open the bleeder till all I get out of it is clean fluid.

Brakes work in my '46 2 ton with vac assist with or without the engine running, so fluid should be able to pass thru it regardless of the engine ever having been installed or run.. but thats just a guess.

I use one of those cheapie one man bleeders. Its a little plastic bottle with clear hoses (about $5.95)... ya put the hose on the bleeder screw with it open..and the hose runs to the bottom of the bottle. the vent on the bottle is open to air.. Its worked real good for me..start at farthest wheel..open bleeder,,attach bottle and pump till the bottle is almost full..close and move to next closest wheel...... Its worked good on three different old brake jobs.....PS.. did you bench bleed that master cylinder before ya put it on..??? in your case..id make sure the master cyl is bleed then go to wheels to bleed...Thats whith a completely empty system...it actually takes quite abit of fluid to fill everything on a truck...... completely empty with MC,,,hydrovac..and wheel cyl takes almost a quart....

You definitely need to bench bleed the master. If you don't want to remove it again, it needs to be perfectly level (use jack & stands) Also speed bleeders really do the trick for a one man show. Got a little spring loaded, one way valve in em. About $15 for 4 at Autozone. Good luck with it.

Here is how I do it and it works really well for me. I use the two person method. I start at the first bleeder to be done, open it and put my finger lightly over the end. I then have my helper pump the pedal leasurely up and down. When the fluid starts to come out I have them stop while I tighten the bleeder. This procedure gets me about 99 % of the way done. After making the rounds once, I have my helper maintain pressure while I bleed a little from each one, watching for air.

I guess this shows how little I know about this, but I have never hear of bench bleeding a master cylinder. I don't mind taking it off again, that's not such a big deal, but what do I do then? Thanks for the help. Allen

Here's a article on bench bleeding master cyl. Hope it helps.
Bench bleeding

Yea.. I don't know what "bench bleed" is.. other than having your hand slip off a wrench and smacking your knuckles on the bench vice!

Years ago I put a new Master Cylinder on a '79 Oldsmobile (first new MC i'd ever put on) and the parts guy told me I needed to bleed the Cylinder.. it involved hooking up little rubber hoses to where the brake lines connect. The hoses loop back up into the fluid fill spot.

With the cap off, the MC full of fluid, and the little rubber lines below the fluid level, you slowly pumped the brake pedal till no more bubbles surfaced.

That was neat and all, but in the dozen or so Master Cylinders i've put on since I haven't ever had to do it.

Maybe somebody will come along and explain what this "bench bleed" procedure is?

Fumblin, you've just hit it. It should be done to any new MC - saves a lot of time once it's in place.

As you all know, the purpose of bleeding brakes is to remove air from the brake system. When you install a new or rebuilt MC, what is it full of? You guessed it, air. Rather than distribute all that air throughout the entire brake system, and then try to chase it out all the bleeder screws, you can "bench bleed" your MC and eliminate all that air instead of introducing it to the brake system. I know what you mean Fumblin', bench bleeding, floor bleeding, kitchen sink bleeding, not quite the same, but none the less, I know what you mean.

On a dry system you still have a lot of bleeding to do, but at least you have a place to start. I've replaced MC's on a full brake system, and haven't had to do any bleeding of the vehicle, simply because I "bench bled" the MC.

Hope this helps explain it a little bit.

These big old trucks are harder to bleed clean. I never bench bleed. But, the little holes better be open for the fluid return in MC. That includes adjusting the pedal link to allow the push rod to come all the way back, or it won't get new fluid to refill. Adjust the link first. I then start at master, loosen rear main fitting till it drips, go to next spot, probly the Booster, which may have two bleeders on it. then go to closest, shortest front wheel, open till starts to be wet, then other front, then back ones. I feel I am allowing the fluid to "follow" me and system around till mostly full. THEN, use book procedure with rears first and so on to final bleed. If you're rears have dual cyls, it is sometimes harder to get all air out.
On "Gravity Bleeding" all that is meant is leaving ports open and fluid flows down eventually from gravity pulling. Won't work if it has to go uphill, as at wheels. Works pretty good with higher Master Cyl in modern vehicles.
Mighty Vac bleeder tool is sometimes workable. I never had luck with "One-man" bottles, peices of junk. The speed-bleeders seem like good idea, BUT, most stores don't have the 7/16" ones needed for many big trucks. If you have 3/8", you are in luck.
ONe more note on "helper" pumping pedal. Only go down to floor, not let up till you have bleeders closed again, or you will just draw air back in the bleeder. After fluid is at site, you can have helper pump with bleeders shut till he gets "pedal", then hold it. You open bleeders, pedal goes down, you close bleeder, pedal comes up, and pumps up again. Best if you can close bleeder Before he gets pedal to floor actually.

Thanks for the suggestions. I will let you know how it all works out. With the help of a friend, I have started putting the engine back together. This is a first for me. The people at the machine shop are helping talk me through this. It seems to be going OK, but I'm afraid I will do something stupid and mess it up. Wish me luck. Allen

I saw a "one man" bleeder jar in an old truck service manual and thought, "Hey! Thats a cool idea!" So I made one.

It was a pain in the [censored], and didn't work very well.. not to mention, what do you do when the jar gets full?

The two man method has always worked well for me.. of course it works best when you actually have another person to man one of the two positions.

If I could teach one of the dogs to pump the brake pedal, i'd be set!

I knew a guy years ago who made this spring loaded contraption for just such a purpose. He'd pump the breaks, then wedge this thing between the seat and the brake pedal.

When the bleeder valve was opened, the spring would expand pressing the pedal to the floor.

Of course it involved going back and forth, back and forth.. resetting the "peg leg" every time you opened and closed a bleeder.

You know the tube that you attach to the bleeder so the brake fluid does not go everywhere? Just bend it into an inverted 'p' trap. When air comes out, it rises to the top of the trap and you are free to pump inside. The one man bleeder. You just have to pay attention to the fluid in the MC, because you will run it out quick.

Most newer cars have a one way check valve in their window washer lines. I've put one of these at the end of a piece of hose that fits snug over the bleeder and slowly pump the air out. Usually works good,
Scott

I thought that bench bleeding was something that happens when you miss with the hammer!

My 2 ton disappears it's brake fluid during extended periods of storage. I never find it either. I think it goes trough the hydrovac into the engine and gets burned up.
Last week the master cylinder was dry again. I used my one man bleeder valve which has a ball bearing and a spring. I can pump about 5 times before having to refill the tiny master cylinder resevoir. But 5 pumps was enough to bring clear fluid even to the further wheel. So, I refilled the master four times and the brakes are great again.

My 48 had the hydrovac go bad, same thing, sits awhile, no brakes. I finally bypassed the booster and haven't had brake problems since. Now I need to do some research and find myself a new hydrovac, feels alittle scary trying to stop that much weight without power brakes in traffic,
Scott

It was my understanding that the old truck brake systems are vented and that they'll always go low after awhile. My '46 2 ton needs a top off once every 30 days or so weither it's sitting or not.. and there isn't any leaks, and stops on a dime.

Dunno.

I was at AutoZone the other day and in their bargian bin I found one way bleeder valves.. they let fluid and air out, but won't let air suck back in.. they were made by the same outfit that sells general use door handle cranks and replacement cigarette lighters and such.. I don't recall the name, but i've seen their products in auto parts stores coast to coast.. i'd bet you can find 'em anywhere.

Just make sure you bring one of your old bleeder valves in to match up the diameter and thread.

Fumblin,
the fluid does not disappear by evaporation. Either you have a leak or it is being sucked into the intake through the hydrovac. The vent issue is the fact that there is an air hole in the reservoir and this is where moisture can enter. the more modern masters have a rubber bladder to seal it.

Well if it's a leak it isn't making it to the ground, so I guess it must be getting sucked into the intake.

Dosen't suck much tho.. level might drop a 1/4 inch every 30 days or so.

Apparently it was an issue 30 years ago, too.. because the previous owner kept a big bottle of brake fluid behind the seat.. I carry on the tradition.

Scott Ward: I bought a new Hydravac at the local NAPA store. It seems these things are pretty common. Just a thought about the dissappearing brake fluid some folks have refered to. I don't know if it would have anything to do with it, but the instructions that came with the new Hydravac called for some light oil being put in the unit before using it, and perodically after that. I didn't understand that and had the store owner call the supplier. It seems the one I have has leather seals in it, and the oil is to keep them soft. I'll bet no ever does that. I know I would not have thought of it. I still don't have my brakes working. I have been involved with getting the motor back together and have let the brake issue slide. Will have to get back to that soon. Thanks Allen

Hey Allen, thanks for the heads-up. I've got an ex-coworker that now runs a local NAPA. Sounds like he's about to get a phone call. I was going to either call them or Car Quest anyway, they both still have the old catalogs on hand for me.
Thanks,
Scott

Scott: Let me know how you get along with the brakes. I have a problem getting the air out of the lines. I had everything pumped up one time, and then found a leak in a line connection. I took it apart and fixed that, and now I can't get a hard pledal. I haven't worked on it for a while because I have been doing other things, but need to get back to it. I made a mistake and put DOT 5 fluid in it. I don't suppose there is anything wrong with using that fluid, but it costs a fortune to buy, and you can run through a bottle very fast when you are having problems. Allen

I think you want to go and get rid of that. Doesn't that stuff ruin the rubber in the old trucks?

Tony: I could be wrong. It certainly would not be the first time, but I think the problem comes when you mix types. I put everything new on the truck including all cylinders, lines, fittings etc., so I think I am ok, outside of the cost. I did this because it was recommended by someone whose opinion I usually respect. He said the silicone would not collect moisture and would not clog the cylinders, and so on. I wish I had not done it, but it is in there now, and I'm not sure I could get the system clean enough to go back to DOT 3. If anyone has any other thoughts on this, I would appreciate hearing them. Thanks Allen