55.2-59 1957 1/2 ton wheel cylinder bleed screw

[qbeanie]

Having difficulty locating replacement bleed screws. Napa sells individual screws but does not list the applications. Anyone know if these screws will fit?

[dsraven]

have you got the old one out? sometimes they are siezed so badly they won't budge and end up needing to be drilled out. that can be risky if you inadvertently drill too deep and damage the seat in the wheel cylinder. you can get backwards drill bits that may help you here because they turn backwards so if there is a chance the bleeder may start to turn the drill will start that motion as you work. if you have the old one out, one of the old ones out, you could take it for a match up. if you don't have it out yet then I would say pick up a few sizes and have them ready for when you try to remove the old bleeder. also pick up a new wheel cylinder for the appropriate side of the truck. if they have a new wheel cylinder in stock you may be able to get the correct sized bleeder from that as a sample. anyway, with a handfull of bleeder sizes, pick the bleeder that fits and take the other stuff back when done. if the bleeder is siezed beyond getting it out then you have the new wheel cylinder ready. check the brake lines as well because they may not wanna come out of the wheel cylinder either. in that case it is a good bet that all the lines need to be replaced for safety sake because they have rusted and are thinner walled in some spots. this could cause a rupture at the least convenient moment, like when somebody stops short in front of you. since the old brake systems are a single system, meaning the front and rear brakes run off the same circuit, then you would lose ALL your brakes at the same time. another good reason to update the master cylinder to a dual system master cylinder that separates the front and rear circuits for safety sake. I always advise guys to check the whole system from front to rear starting at the pedal and working down. check/repair the brake linkage from the pedal down to the master and ensure all the linkages and bump stops are in good working order, not rubbing on anything, adjusted correctly and the return spring is also in place. lube the pivot points, make sure the pedal pad is in good shape. check the master cylinder for leakage-pull back the rubber boot on the plunger and check, look in the reservoir and check for dirty fluid and deposits in the reservoir, a proper sealing and venting cap, brown fluid means it has been overheated or it has absorbed condensation. brake fluid likes condensation and absorbs it but that also turns the color of the fluid brown. this is why it is recommended to bleed the fluid yearly or at least at every brake job. more humid climates are harder on the brake fluid for the same reason. then look at the steel lines from front to rear especially under clamps and around connections where they tend to hold water, mud etc and end up with rust and get thin. then check the hoses for soft spots, bulges, cracking etc-bend the hoses and look for cracks in the rubber and around the crimped ends. next pull the drums off and check the wheel cylinders for leakage. you need to pull back the dust caps to see in there. a dry on the outside rubber boot doesn't mean the cylinder is not seeping. move the brake shoes so that the wheel cylinders also need to move the pistons to ensure they are not getting gummed up. check the adjusters and other related hardware as well as the remaining lining compared to the service limit. also, check the backing plates in the contact areas where the shoes rub. sometimes the shoes have worn a groove into the backing plate and that means the shoes can get hung up in that groove and not allow the brakes to be adjusted properly or operate properly. check the drums for ridges and service limit as well as the hub/axle seals. check the park brake for proper operation, proper adjuster operation, easy cable movement in the sheaves and for full return when released. check the brake lights to ensure they are operational. adjust the brakes when done. this needs to be done with the park brake backed off, adjust the brakes, then adjust the park brake. then bleed the whole system one wheel at a time until fresh clean fluid appears at each wheel-with no bubbles. start at the wheel that is furthest away from the master-usually the right rear, then left rear, then right front and finally left front. after that you should have no problem with the brakes for awhile.

as a safety hint, keep a hand sprayer of water close by so when you are removing the drums you can spray down the brakes and keep the airborne contaminants out of your lungs. the stuff is killer. also, brake fluid is harsh on the skin so a pair of rubber/nitrile gloves is a bonus as well as some safety glasses. parts are cheap but you only get one set of eyeballs.

here is a link to the master cylinder conversion

http://67-72chevytrucks.com/vboard/s...d.php?t=617103

a brothers video showing the process of updating the master cylinder to a dual system

https://www.youtube.com/watch?v=_eyhUseqNq8

a supplier with pics and prices-quick search. I just picked the first site that came up.

https://www.performanceonline.com/19...ders-and-kits/

hope that helps

[qbeanie]

Thanks

[dsraven]

Probably not stock wheel cylinders after all these years so a match up scenario is required. Buy a few and take back what you dont need. The alternative would be to simply replace the wheel cylinders as the internals are probably not far behind the external look of things. Unless you have a history.

[mr48chev]

In simple terms bleeders for pre 1975 or so American Usually had 5/16 or 3/8 Sae threads and the length and taper on the end would be the differences. If you have a thread gauge with your tap and die set check the thread pitch on the bleeder screw.

Best idea is still to take the wheel cylinder and or bleeder screw or what is left of it to a NAPA store and see if they can match it.
O'reilly's lists bleeder screws but may not stock them in most stores. Autozone also lists them but I expect the same, you have to know what you want to order it.

Dorman shows them and one thought is that if you have an independent parts house in the area with a large assortment of Dorman cabinets you might find bleeder screws there. One of my student's and his dad had a parts house and the whole front side of the conter below the counter was lined with Dorman cabinets. I scored odd ball items more than once in those cabinets but after they sold out the new outfit never restocked them and the last time I was there the pickings were slim.

I may have replaced one bleeder screw in all my years of working on brakes for a living and that was only because someone had rounded the head off using the wrong wrench.

All bets are off if you have a foreign made replacement wheel cylinder though. More likely than not they will have a metric thread on the bleeder screw.

[dsraven]

just to clarify your situation, is the bleeder screw removed or is it still in the wheel cylinder? front or rear? if it is still installed can you clarify why you need to replace? siezed, plugged, can't get a wrench to bite? if siezed you can try some penetrating oil and heat but then you may need to rebuild the internals since the rubber brake cups and the existing fluid are not gonna like the penetrating fluid. the heat, depending on how hot it gets, may bake the rubber cups inside.
with not knowing the circumstances and/or the tools you have available I will explain how I have dealt with siezed bleeders in the past. since that is the most common bleeder screw issue I find other then the stripped corners for the wrench.
assuming the wrench corners are ok, I will ensure the wrench fits on the screw well, then remove the wrench and keep it handy, like readily accessible and also have a hammer ready and clear the area to allow a hammer swing. then I heat JUST THE SCREW with a torch till it is starting to glow red. I use an acetylene torch for this because it heats just the screw mostly and not the surrounding brake cylinder area. it is a quick heat up with the acetylene welding tip torch, not the cuttting torch, to heat just the screw part but not melt or distort the screw part. that expands the screw at a different rate than surrounding parts so it seems to break the seal of the rust/corrosion between the parts. you can put the wrench on it quickly now and apply some torque but don't try to turn it out if it loosens as this sometimes causes distortion and stripping of threads OR simply twists the head of the screw off. then remove the wrench for a few secs to allow the screw to cool off without heating up the wrench. when it cools down, so it isn't glowing and is back to iron color, put the wrench on it and then give the end of the screw a hit with the hammer. I know, this is gonna distort the end of the bleeder because it is hollow. the bleeder is toast at this point anyway. now apply some torque to the wrench. not necessarily to turn the screw but to possibly break the seal on the corrosion. try both directions a bit but understand it is already tight so it may not move at all in that direction. keep at it with the wrench and the torque applied to the loosening direction, alternating between tightening and loosening, and when it cools enough so penetrating oil won't just burn off add a little to the area. keep going with the torque. if it doesn't let up, try the heat again. you will need to remove the wrench for this so do that but ensure you are able to get it back on the screw before you add more heat. repeat until it gives up and comes out or it breaks off. if it breaks off you might just as well replace the wheel cylinder because drilling it usually means it will leak after, even with a new bleeder screw installed. a new one is gonna run you about $10-20, depending on where you buy, and they are used on chevy products from 1950 up to the mid '70's so somebody should have one in stock for a decent price. it is just the inconvenience of changing it plus the possibility that the brake line also breaks off and it becomes a can of worms replacing more and more brake lines as you go. the good in that whole scenario is that those breaking lines were probably thin walled from corrosion, between the line and the line nut on the flared ends, so they probably needed replacing anyway from a safety standpoint and would likely not pass an inspection if the shop/inspector is worth his salt.
I know you didn't really wanna hear that. sorry man.
more info and pics would help us help you. or, maybe you got it figured out already.

[qbeanie]

The brake system has a leak. These are original wheel cylinders and are wet. I am in the process of removing for inspection/ overhaul to keep the truck movable until I can start on the upgrades. iIt is not to drive on the streets. I do not want to spend money on this system as a new brake system and rear axle will be installed. Your advice on taking the cylinder/bleed screw to a parts house to match is good advice. Both the bleed screw and mounting bolts are crusty and will require soaking and possibly heat to remove. Thanks.

[qbeanie]

Update - I was able to remove the wheel cylinder and bleed screw without much effort. Multiple applications of penetrating oil over several days, a little heat, and patience paid off. Again thanks for the advice.