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I am completely lost with brake my brakes on my '46 2 ton chevy. The rear brakes keep locking up whenever i use the brakes. They aren't locked enough to keep the truck from driving under its own power, but just barely and you can not turn the wheel by hand at all. I have already rebuilt every wheel cylinder, put new return springs all the way around. I have blown air through the entire system multiple times to try to remove a potential particle. And i have bled everything so many times i have lost count. Is there anything i can do short of replace everything?? Someone help! Any ideas will be greatly appreciated.

Just guessing, do you have the brake shoes backed off enough. Maybe just a bit to tight? again just a guess. Someone will know, hang in there - take a break and do as your doing ask questions and then git back at it,where you at in Cali? southern, mid or northern? good luck.

did you do anything to the master cyclinder?

Its probably like 55 1st says or the master cyl. pushrod rod needs adjustment. There must be a tiny bit of play in it so the piston can come all the way back to open the port. There are 2 holes in the bottom of the master cyl. reservoir. One is very small. If one of these are stoped up can cause this also. Poke a tag wire through it.

I just adjusted the master cylinder to where it needs to be, all the shoes just barely drag to where you can hear it scrape, and that fixed it, they no longer stick. But now I now think there is an air pocket somewhere because if I pump the brakes it will build up pressure but then when i let off the brake pedal a lot of fluid flows and for about 2 seconds. Only problem is i have bled all the way around about 6 times with no improvment. I will try finding the holes you speak of and try to clear them. @Tom, I live in central cal in the San Joaquin valley in Hanford.

Cleaned out both holes and I could tell the smaller one was plugged but it didn't make any difference. I must have a large air bubble that's hiding somewhere. I already blew through a whole quart of fluid looking for it just this afternoon at school.

Drove it home from school and all of the drums were just warm, not hot and all the same temp roughly. The way i got the brakes to work as I was driving was to pump them just like you would to bleed it and then they worked fine, like normal, for awhile. So when i got home i took the cap of the master cylinder and pumped my brakes until they got hard and then held it, then let off and then held them again and they held fluid. So i just sat there watching the reservoir and about a minute later the fluid just started squirting back in. Not really sure what this means now. But I am putting all this up here so hopefully someone will see and be the answer to my prayers! Thank you all for the input.

Seeing as though you have a two ton do you have a hydro vac unit and are you starting your bleeding sequence there? The H V unit can have two to three bleeders on them and you need to start with those and then to the wheel cylinder farthest from the M C then the next closest then the next closet etc. Go by brake line routing not wheel location as to which wheel cylinder has the fluid travel the farthest to get to. On my 45 1.5 ton it is the driver side rear wheel not the passenger side which is different from any other truck I've owned. If I started at the other side I'd have a bubble I'd never get out! One other thing If the hydro vac is bad they can leak fluid internally and it will make it impossible to get the pedal pumped up.

-Mike-

I do have hydrovac but i have never started there, i actually ended there today because that was the last thing i could think of that would have air in it but it didn't fix it. But seeing as i need to start there i shall go out and buy some more fluid and try again.

And i can get the pedal pumped up so I don't think it is the hyrdovac unit. I just can't seem to keep a solid hydraulic system currently.

Jimmy,

I have a few thoughts/questions;

1... are you still using the original MC or has it been replaced? It should have an 1-1/4" bore with casting number 5450259.

2... pumping the pedal to make it hard can be caused by the shoes being to far away from the drums requiring more fluid at the wheel cylinders than one push can deliver. Jack the truck up one wheel at a time and see if you have resistance when turning the wheel by hand...you want some resistance. Now that you've driven the truck the shoes should be centered in the drums.

3... did you replace ALL of the rubber lines? If not they can swell up internally and act like a check valve delaying the flow of fluid back to the MC.

Mike B

When I got my truck it turned out it had multiple problems. First I could get the system pumped up but it would'nt stay that way....turns out it was the hydro vac leaking internally. When I got the h v replaced the pedal stayed up but after a few pumps the brakes would lock and stay locked. That turned out to be the plugged port in the master cylinder.

Just sayin........

@ Mike. I am still using the original mc because it is still working correctly, little spurt when you press on the peadal and a bigger one when you let off. I have not replaced any of the rubber lines because they look pretty new, not even a single crack (I was told by my grandfather the last time it had new brakes was in '84) And I have the shoes adjusted to where you can hear them drag. With the help of sleeve I am pretty sure that I have been bleeding it wrong since I was completely skipping the booster until I tried it last today. Oops haha! @ sleeve, The mc was completely out of alignment and had plugged holes, that was the only thing I resolved today. So now when I let off the brakes after pumping it up to get pressure they no longer stick and there is a steady flow a fluid spurting up into the mc reservoir. I think it might be air in the booster but i cant bleed anymore until I get more fluid tomorrow. BUT! with the help of everyone here i have a good feeling that I shall soon have good brakes!

Sounds like your getting it Jimmy, hope so. I have bleed my brakes many times too, don't feel bad ;-)Lots of times when I am working on my stuff and having trouble, usually after several trys and I am about to give up - that's when I git it right, finally. Good luck with yours.

If you can easly spin the wheels and you just hear a little friction the shoes are still to far from the drums. I've always adjusted mine to where it takes arm power to turn the wheel...as soon as you stop pushing the wheel it stops turning, no free-wheeling.

After each adjustment and with the wheel still off the ground push on the brake pedal a couple times to "center" the shoes and check that wheel again. Keep doing that until there is no change in the arm power it takes to spin the wheel. It could take a couple adjustments to get it right. As you move to the other wheels you should feel the pedal getting better.

To test the Hydrovac, put moderate pressure on the brake pedal and start the engine...you should feel the pedal fade away a little as the engine developes vacuum.

Also, rubber brake lines will look new on the outside and be trash on the inside, they swell up restricting flow. I'd replace them if they are 20 years old

Mike B

Thanks for the input Mike. I was just told previously to adjust my brakes that way otherwise I would run my drums hot. Seeing as I have yet to drive it farther than 10 miles I suppose it probably wouldn't happen anyway. For the brake lines, you're probably right, should replace them even though I don't think they are restricting anything because there is plenty of fluid returning and my brakes aren't sticking, but new parts never hurt! I did do a quick bleed around my truck, this time starting at the hv booster and while it did not fix the problem there was an improvement. I just ran out of usable day light so I shall take another crack at it tomorrow, and I have monday off of school so I'll be spending a good portion of that day with my truck as well. Thanks again everyone!

If you pump the pedal several times and each time it gets higher, and with steady preasure it stays at this point its not air in the system, the shoes need to be adjusted, also as was stated above hold pressure on pedal and start engine if pedal goes down a bit the hydrovac works, if all else fails you'll need to check the master for being the correct one, one size smaller and things don't work, it needs to be the correct size I believe some one stated its 1 1/4, when the brakes were done in 84 the wrong cylinder may have been installed, I've had that happen.

I finally graduated from high school on the 31st and started machining full time on the 1st so I have been very busy and tired, and before that had finals and other stuff to button up, so I just now got the time to fiddle with my truck a little more. The bleed screws on the brake booster are plugged so I either need to drill those out or buy new ones because unscrewing them enough to let fluid out doesn't work very well. And I tried the pumping up the brakes until I had pressure and then turned the truck on but the pedal didn't go down any further. Could this be because everything is so out of whack still? Or do I need a new mc or booster overhaul? Since I now have money I think I will get a new mc anyway because it is leaking out the back and new parts never hurt. I shall also be getting all new rubber lines as well.

If it's leaking out the back it's toast. Rebuild or replace. New bleeders are cheap at the auto parts store if the old ones are badly plugged and corroded throw them out and get new ones

You might consider a power bleeder, mines made by Motive Products. Looks like a pump up garden sprayer with an adapter that screws on the master cylinder, and has a pressure gauge so you can do a leak down test. I never could get the brakes on my COE bled until I bought one. Even with that I had to "surge" the brakes by stomping them with the engine running. Finally got a full solid pedal though so keep trying.
Scott

Next paycheck I shall buy a new mc as well as rubber lines. Would napa have the replacement for both or either? I'll also look for a power bleeder. Then I wont have to bother a little sister to pump brakes too haha!

On my '55 2nd 6500,the wheel cylinders were so corroded that there was no way honing was an option. My M.C. and Hydro-vac are in good operating condition,so i'd think if you need to replace your M.C., you may as well go ahead and find complete wheel cylinders. I got mine from a fellow "Bolter, Mr. Marvin Ribbich. He is well-informed and may be able to answer your questions better than I. Look under "Big Bolt" topic: "Need help installing auxiliary transmission,then send him a P.M.-Hope this helps. Good luck!! B.T.W.,He may also have M.C. rebuild kits available. His prices are fair, TRUE ORIGIONAL PARTS,and he ships promptly.

I rebuilt all my wheel cylinders and they were in surprisingly good shape, no pitting or rust but i still honed them and got kits and they worked great before the mc started leaking, but farther down the road I should replace those as well.

Hi,

Bleeding sequence should be...

As stated above you have to "Start" bleeding at the Hydro-vac unit first.

There should be 2 bleeder screws, one is just above the line coming in from the master cylinder, that is the first one to bleed, the other one, on top is the second one to bleed.

Then start with the left rear wheel. If the brake lines run down the right frame channel. Else, reverse procedure sequence. But Hydro-vac comes first and last.

Question: Does you truck have 2 brake cylinders per wheel? Are they mounted top and bottom or are they mounted one on each the side on the backing plate???.

If top and bottom do the top first then the bottom. If sides, then this is tricky do both at the same time very slowly, if you can.

Then do the right rear, then left front and last right front.

Then go back and do the Hydro-vac again.

Do not start the engine to bleed the brakes.

Also, Depending on which axles are in your truck. There may be a bolt with a lock nut in the backing plate, mid-way of the arc of the brake shoe. This is an adjustment to align the brake shoe to center of the brake drum. If this is out of adjustment it can cause the wheels to lock up or drag and not return to relaxed position.

Then again I may be all wrong.

Good Luck
GMCPic

By the way...

You will get some back surge to the master cylinder, it is the brake return springs squeezing the cups in the wheel cylinders, forcing the fluid back to the master cylinder.

Hope this is of some help

GMCPic

GMCpic, thanks for solidifying the sequence, and I only have one cylinder per wheel, never heard of two. As for the adjustment nut to keep the shoes in the middle....I have no idea, I'll have to go check that out.

After adjusting all the drums to where they turn under man power, they all work perfectly! Thank you all so much,I am extremely happy that I am now able to drive my truck to work

Now I have found that my booster is also leaking. When I use the brakes there is a lot of smoke coming out of the tail pipe. So somewhere my booster is letting fluid into the vacuum line and after looking at the diagram, that leak could be anywhere. Next is to find a rebuild kit and tear down the booster

There's a how to on this site for rebuilding hydro vacs but if you are not up to it there are rebuilt units available. I took the easy way out and got the rebuilt H V .

I don't think you'd see smoke unless the check valve for the H vac's vacuum line is missing and or a LOT of fluid made its way back into the intake. If it is missing get a check valve for it before you run it with the replacement.

I don't feel like shelling out 600 bucks to get it rebuilt. And there was definitely A LOT of fluid going back to the intake. That's probably another reason why it felt like I never had brakes, as soon add I had pressure it was leaking. And when I took off the h v booster there was a stream of fluid coming from the vacuum line going back to the engine. How I never saw the smoke before? I have no idea.

I got my rebuilt / exchange hydrovac from Alretta Truck for slightly under three bills. $600.00 sounds like a hose job to me!

That's how much Jim Carter charges

If that's what Jim Carter is charging, he's WAY out of line. I got my last two from NAPA and it only took them a day to get it and they were in the $250-270 range.

Mike B

Napa will rebuild hydrovac units?