The Stovebolt Site Forums The Shop Area General Truck Talk Bleeding brakes question....

Is bench bleeding the master cylinder required and, if so, can it be done without taking it off of the truck??? I have the order/technique down: Left rear, left front, right rear, right front as the manual says and everything else so that when I receive my wheel cylinders and shoes I can go ahead and get it done quickly, I don't want to be out in the cold longer than I need to. But, back to my question, is it needed? I filled it with some brake fluid when I took the old lines off and pumped the pedal a few times. Fluid came out and that was enough to tell me that it works. So, now the only reasoning that I can tell for bleeding it before doing the rest is to get all air out???? Thanks!

Yes you can bleed in the vehicle, and I would. Take an old (if you have it) brake line. Attach to the ports and bend it so it goes into the master cylinder and pump pedal till you get no more bubbles when preeing pedal.
Woodbutcher

Yes it is important to bench bleed the master cyl. but if you have pressure at the lines then you already have bled it.

Which wheel is this? LOL,
Scott

Okay okay, so you caught me on a typo. I'll correct this! LOL

Ummm, I saved the old lines and I'll do this. Thanks for the info, I had thought of some ways to do it but not quite that easy.

There's an even simpler way, if you still have the plastic plugs that the replacement cylinder had when you bought it. Leave the plugs in the cylinder, fill the reservoir with fluid, and work the pedal up and down just enough to make the M/C piston move about 1/2" or less. Air will be displaced from the cylinder and bubble up into the reservoir. When the bubbles stop, the M/C is purged of all the air inside it. Connect the lines and bleed as usual at the wheels.
Jerry

Well Jordan you've been hanging around the old guys here for a year now and I can tell you've learned a lot. Congratulations on your persistence.

Thank you.

I'm having problems... Got everything put on and tightened up, got my brake bleeder and loosened one of the bleeder screws...... Nothing, at least nothing that can compare to anything. Today a little more came out of the lines, but not enough. The only one that amounted to anything was the front left wheel cylinder which I had to put an old bleeder screw in(didn't come with one for some reason) and I guess I didn't have it in tight enough because it was leaking out. So, anyone know what is wrong? Do I need to re-bleed the master cylinder or what?

Did you end up bench bleeding your master cylinder? I just did my first full brake job on a '51 GMC and that was pretty crucial to getting the brakes to bleed without any problems. Did you replace your brake lines?

David Bush

I did bench bleed the master cylinder, and that was the only thing I didn't replace. I bled it about a week before I got the cylinders and shoes though. I'm hoping that that is the problem or fluid is not getting pulled up the MC to RH frame rail line yet.

Maybe that was the problem after all. I did the bleeding again, and it was like it was never bled. Of course, my brother(17) tried to get my truck started because I couldn't(battery was way low when the charger said it wasn't) and pumped the pedal waiting on it to charge so that probably messed it up some. Also sucked a bit of dirt out that I didn't know was in there. After that, I was putting on the lines again and the fluid was dripping down and covering me. Talk about Chinese water torture, maybe it was the redneck version! So, now I'm waiting on my helper(mom) to get done with supper so she can keep an eye on the level why I use the pump. Hope that was it.

JDL: since you have already seen some fluid you should be able to bleed two of the wheels without running the mastercylinder dry. Be sure to keep a top on it while bleeding it.

A simply way to bleed brakes is. Take a 16 oz water/pepsi bottle and drill a hole in the lid just big enough to stick a piece of vacuum hose in it. Then put about 1" of brake fluid in it......make sure hte vacuum hose is long enough to reach from teh bottom of the bottle to the bleeder screw while the bottle is sitting on the ground.
Fill master cylinder....then open the bleeder valve where you have slipped the end of the vacuum hose over it. Have your mom slowly pump the pedal. You will see the air bubbles as the air comes out.....when you see there is no more air tighten the bleeder screw and pull the hose off......check the master cylinder and be sure to refill if needed....move to the next wheel, hook up the hose, pump brakes....repeat on all wheels.

Do not reuse the brake fluid that goes into the bottle. This is simply and easy. Let me know how you do.

Note: when finished the brake pedal should remain in the same location......to check, wait a few minutes and then press the brake down....if the pedal goes down then you still have some air in it....if it stays where it was you are good to go.

NOTE: ....be sure the brakes are adjusted up are you may not get a pedal.

Alvin, thanks for that, and the brakes are adjusted as tight as they could be without locking up the wheels(they spin freely, I backed it off until I could fit the drum over them and turn it after I adjusted them up to where it would barely fit) so that should be fine. So, when we do this, do I need to close the bleeder screw when she returns the pedal to the top? And I thought that if the MC was full no air could get in...

Hey Alvin, I made what you told me to do! I just didn't realize that I shouldn't have tightened the cap! I think I answered my own question about the bleeder screw, but does anyone know if there is a standard substitute for 10mm bleeder screws? The new wheel cylinders' bleeders are metric, but the old one that I had to use in the one that didn't come with one is standard, so that is the only one I can close while the lines are on it.

If I understand this right you haven't adjusted your brakes. They need to be adjusted after the drums are installed. The shoes need to be seated on the drums then backed off.

Hmmm, didn't think about that, but there's still the issue of being a lot of air still in the lines. Thanks Cletis.

Jordan Check your pm.
Jim

I have always been told that you should have whoever is pumping your brakes hold the pedal to the floor as you tighten the bleeder. It take more pumping the brakes than you would think to fill the lines in a dry system. I would get a lot of brake fluid and two other folks one to watch the level and one to pump like crazy. It seems to work better if they don't pump to fast though. Make sure all four brakes are adjusted first. It is better to over do the bleeding. If you don't get all of the air forced out it will move in the line uphill as it sits for awhile. That means depending on how it is sitting any air in the line could move back towards the master cylinder as it sits. The next time you try to bleed you will have to force all of the fluid ahead of the air bubble out before you get to the air.

I figured that with the pump it wasn't necessary to have someone pump the brakes. I tried it again and both front wheels seem to have less air in them but the rear wheels improved very little. It is just about worthless trying right now because the only thing that will fit on them is a 10mm socket and for that I can't use the pump. So, I guess I'll just have to do it the old fashioned way if I try it again. Thanks farmer51 for the offer, hoping it will get better soon so I can give you a call.

Good new!!! The pop bottle thing worked, and it's automatic!!! I just put the line on the bleeder after I loosened it, loosened the cap on the bottle, squeezed the bottle, tightened the cap, and now it is bleeding itself! It is slow, but works good. Maybe I'll have brakes soon after all.

right smart of ya JD to automate Alvins technique by using the vacuum principle on a pressure system tell yer shop & physics teachers we give you an A+ for the semester!

just remember to check the master frequently so ya don't pick up more air

Bill

Thanks Bill, I am.

Hey JDL,

After reading about your adjustment technique, I'm not sure you've got the brakes adjusted properly. That needs to be done, and correct toeboard clearance set, before you bleed them. Check out this site. It's got free access to the shop manual for '54 Chevy trucks. It'll be a big help to you if you don't have one.

http://chevy.oldcarmanualproject.com/shop/1954truck/index.html

When I did the brakes on my '51 GMC I followed the manual exactly and ended up with solid brakes. If I were you I'd probably go for what they call a "major adjustment." As you'll see from the manual, this involves loosening the nut (just a little) that holds the pin at the top of the backing plate that the shoe return springs hook to. Put the drum on and turn the adjuster out until you can turn the wheel, but not easily. Bang (gently) on the nut of the pin and the backing plate. I used a 4lb. hammer for this, but GENTLY. This helps seat the shoes in the middle of the drum.

When you do this, you'll find the wheel will mysteriously turn much more easily. Tighten it up and do it again until the banging (tapping?) doesn't result in any difference in the drag on the wheel. Tighten the nut back up to 60-80 ft/lbs. At this point, my manual says to back off the adjuster 14 notches, don't know what the '54 manuual says. I thought 14 notches was a pretty strange amount, but I did it and my brakes are good. Good luck with yours - you'll get them.

Take it from one who knows - good brakes are the most important thing to have on your truck.

David Bush

Jorden, just a thought; if at this point you still are having no luck, you may want to replace the rubber hoses of your brake lines (if you haven't already). After many years, these hoses are prone to deteriorate on the inside, like a plugged artery, literally, even though they may "look" o.k. from the out side.
I have replaced many of these. If you disconnect the metal line from the rubber hose, have someone push down on the brake pedal, if you get a full powerful stream out of the metal line, chances are that your problem, besides air, is plugged rubber hoses. Be sure to catch the fluid coming out of the line in something!
Good Luck! Like David said, "from one who knows"

Thanks again. I've replaced the hoses. It seems that it is sucking in air somewhere... Or, maybe I'm just underestimating how much air is in the lines but...

Jordan, something is not tight if you are still sucking air. Did you adjust the brakes first prior to bleeding?

I know, think it is one of the rear wheel fittings, it is leaking even though I've used new washers and tightened it as tight as I can... So I guess this will be put off for a week or two so I can get new fittings, unless they are available somewhere closer??? Oh, and no, I didn't adjust them as they should have been but I did about a half hour ago and preceded with bleeding with little improvement. Oh, it can't be the master cylinder if any of you are thinking that, or else the front driver's side wheel wouldn't bleed correctly, right?

Opinions needed again. I've fixed the fitting problem but it still isn't doing very well. I've checked everything I can think of and it is all tight, so could the master cylinder once again need to be bled. I have asked my brother to see if he can get someone that he helps look at it. If not, I have more than enough money to have a local mechanic do something on it.

Put the hose in the coke bottle with out the top on the bottle to let the air out. Put enough brake fluid in the bottle to cover the end of the hose. Put the hose on the bleeder. Loosen the bleeder. Have someone pump the brake if it bubbles pump until the bubbles stop. Tighten the bleeder with the peddle held to the floor. Make sure to keep the master cylinder from running dry. The master cylinder and a leg can pump a lot of fluid through the line fast. If you don't see bubbles in the bottle or the fluid level isn't rising you have a problem.

Ok neilroy, I'll do that tomorrow.

Neilroy gave you the absolutely correct way to do the job.