braking issue - bad master cylinder out of the box?

[hedz]

i just installed a remanned master cylinder from autozone on the 72f100. i installed a brand new one on the truck a year and a half ago. the problem with it is that noone made a replacement gasket or a replacement lid for it. it started leaking at the lid and so i replaced it with a remanned. the remanned has a small front resevoir and a large rear. the one that had all the leaks was probably meant for another vehicle and boxed in the incorrect box and just so happened to fit. it had equal sized chambers on the front and back. the leaky MC actually stopped better than this one does. the pedal softly goes to the floor. the brakes still engage.

i had decent brake pressure the first day and now it's going to the floor. i bled the brakes properly.

is there a adjustment on the powerbooster that changes the length of the rod that engages the back of the MC?

i've never thought to look until now.

rpms do not go high when i press the pedal so i'm thinking power booster is fine with no vacuum leaks.

ever got a bad master cylinder out of the box? i'm reading this can happen but want some second opinions before get another one.

this is a front drum rear drum 72 f100. if someone needs a pic of the mc to properly answer my question i'll throw it up here. thought it was strange that the same mc that autozone tried to sell me for a drum/drum is the same a disc/drum

[ultraranger]

Assuming all the air is bled from the brake system, if you press down and hold pressure on the brake pedal and it slowly creeps down towards the floor, the MC is likely bypassing internally (the compensating port inside the bore is not sealing off which would let the fluid leak right back into the MC's reservoir).

Any replacement part can be defective right out of the box. A re-manufactured MC has an even greater chance, than a new MC, of being bad right out of the box or shortly after it's installed.


The following link explains how to adjust the boosters output rod to the bore depth of the back of the MC.

http://www.maximummotorsports.com/asset ... AK-1r1.pdf

A booster output rod that's adjusted too short will make for a very long pedal travel. An output rod that's adjusted out too far will push in on the MC pistons and keep the brakes partially applied, even when you don't have your foot on the brake pedal. This would cause the brakes to drag.

[tqwrench]

Been there done that recently. Got a bad bendix m/c brand new out of the box, did the exact same thing, pedal slowly fell out from under my foot. Got a new one from AZ, but before installing it, I knew from previous experience, they typically have debris (pieces of shot) left in them from the manufacturing process. I disassembled it and flushed it with clean brake fluid before putting it on. The QC on this stuff is garbage. That one is working fine now.

[hedz]

i rebled the rear drums with a friend just now in the pouring rain. that was fun. the brakes stiffened alot but not satisfactory.

i'm going to unbolt the MC and do a measurement as per instructions on that link. great link by the way. i'd recommend that link to anyone doing brakes.

if that adjustment does not fix this than i'm returning the MC. it's a good thing it has a lifetime warranty.

thank you folks. yall always get me on the right track

[ultraranger]

Before you start bleeding the brakes, lift the wheels off the ground and run the adjusters up until you can no longer turn the wheels by hand. Once they are too tight to turn by hand, back the adjusters off 10 clicks.

The brake pedal will not be firm and will have a long travel length if the brakes are not adjusted up, prior to the brake bleeding process.

[motzingg]

yeah i'd second the 'reman the reman' comment. The MC that i got from o'riely was pretty nicely rebuilt, although i did take it all apart, the one that was on my truck when i got it was terrible... i have no idea where it came from, but there was nasty pitting in the bottom of the bore that had been epoxied over, then bored out. they had actually sandblasted the rust out (i hope) and skimmed the inner surface with epoxy, then machined that out... the epoxy was coming out and had tore up the cup seal and the valves were all clogged with rusty debris... woof.

the new one leaks like crazy from the top mating surface... its rough, either as-cast or coarse sandblasted, and the gasket is pretty hard. I painted the thing and it has eaten all the paint off.

I'm going to try to find a new one, maybe rock auto, take it all apart, powdercoat it, reassemble, even though my old one is good still... its leaking and looks like crap. maybe even chuck it in a mill and machine that mating surface clean with a flycutter.

also nice to paint or p-coat the cast iron while it is clean, once that brake juice gets in there paint will never stick. I used VHT engine enamel last time but i didn't bake it afterwards so the brake juice just ate it up... that stuff is pretty bombproof once you bake it properly.

[hedz]

well i adjusted the rod to the MC. i got that right and then the rear left wheel cylinder decided to blow out. keep in mind that my wheel cylinders have less than 10k miles on them and i purchased them from oreillys.

my negative history with oreillys is as follows

bad master cylinder out of the box - check
bad torque converter out of the box - check (this one raised my blood pressure quite a bit)
bad alternator ouf of the box - check
and now bad wheel cylinder - check

that being said i got 1 wheel cylinder from napa for $15. my buddy told me i should just invest in a wheel cylinder honing kit and rebuild my own and i know i should be replacing all of them if this is the case but frankly i'm starting to feel lazy from all the broken crap. i'm going to do one at a time as they go kapoop

i'll replace the wheel cylinder this weekend and get ol booger back on the road.

[ultraranger]

well i adjusted the rod to the MC. i got that right and then the rear left wheel cylinder decided to blow out. keep in mind that my wheel cylinders have less than 10k miles on them and i purchased them from oreillys.

Is this ~10,000 miles in 1 year, 2 years, 3 years or more? Does the truck get used regularly or, only occasionally?

Brake fluid is hygroscopic (it absorbs moisture). Even in a sealed brake system, moisture will accumulate. DOT 3, 4 or 5.1 should be changed out no longer than every 24 months. If the fluid remains in the system, unchanged, and especially if the truck gets little use where the fluid sits stagnant for long periods, moisture accumulation in the system will settle out in the brake components.

Cast iron MC's and wheel cylinders begin to rust or pit when moisture settles in their bores. This can easily damage the seals and cause them to blow out.

If the ~10,000 miles accumulated in less than a 2 year period, then it's a good probability the wheel cylinder was less than stellar, in the quality department.

[hedz]

well i adjusted the rod to the MC. i got that right and then the rear left wheel cylinder decided to blow out. keep in mind that my wheel cylinders have less than 10k miles on them and i purchased them from oreillys.

Is this ~10,000 miles in 1 year, 2 years, 3 years or more? Does the truck get used regularly or, only occasionally?

Brake fluid is hygroscopic (it absorbs moisture). Even in a sealed brake system, moisture will accumulate. DOT 3, 4 or 5.1 should be changed out no longer than every 24 months. If the fluid remains in the system, unchanged, and especially if the truck gets little use where the fluid sits stagnant for long periods, moisture accumulation in the system will settle out in the brake components.

Cast iron MC's and wheel cylinders begin to rust or pit when moisture settles in their bores. This can easily damage the seals and cause them to blow out.

If the ~10,000 miles accumulated in less than a 2 year period, then it's a good probability the wheel cylinder was less than stellar, in the quality department.

truck is used to drive to work which is a very short distance and gets used regularly. i change brake fluid when it changes color or about every 8 months. i run military grade dot 5 always. less rust problems. i run steel braided lines on the front.

[guhfluh]

Sounds like my story with all the crappy parts I've been getting for my truck. All the Chiwanese reman and even new parts available for these trucks have been junk. New, USA made parts are hard to find though. As you've found, NAPA is the best gamble for quality parts, but try to buy a new, name brand brake part from whomever you get it from when you do.

[motzingg]

i've had the best luck with Rock Auto, it looks like they are buying out dead stock and often times it is coming in old USA boxes. Its like christmas every time i see something in an old ratty box.

its pretty sad that is what its coming to, the good stuff is actually getting closed out in favor of garbage. oh well.

anyone see 'tommy boy?' ... "I can $#it in a box and slap a guarantee on it!"

[hedz]

i took the truck to a shop handed them the wheel cylinders and some spare drum hardware and the rest of my dot 5 and told them to have at it. they have a vacuum bleeder which is better than what i can do and i just don't have the time. it was enough doing a power steering pump 3 times this weekend. next i'll change the timing cover myself and throw those granatelli wires in the garbage. i'm buying the dui hei plug wires reccomended for the ford fe. ol booger will be back on the road soon.

[BobbyFord]

I generally look up premium, new parts online, make a list and take it to my local parts house. That is, if Summit doesn't have what I need.
I find that paying a little more money for the good stuff is less frustrating than getting poorly made parts that don't last.

[hedz]

I generally look up premium, new parts online, make a list and take it to my local parts house. That is, if Summit doesn't have what I need.
I find that paying a little more money for the good stuff is less frustrating than getting poorly made parts that don't last.

you have much wisdom. i'm worried that the front cylinders are going to go out now. i don't want the f100 to be a hazard to anyone else. going to pay the same guys to rebuild my front drums with some napa wheel cylinders. i can't risk the fronts going out too. i would do it but i don't have time. while the truck is at the shop next week getting the fronts rebuilt i'll be doing door hinges on my friends jeep and door hinges on the f250.

i got the f100 back by the way. cost me $180. all drums adjusted, vacuum bled, and rear wheel cylinders replaced. stops so hard i could break my nose on the glass.

[motzingg]

yeah, this was being discussed on that drums vs. disc thread, i said the same thing... a set of properly adjusted and trued drum brakes stop a lightweight truck as fast as you care to stop. people just don't keep up on them, adjusters freeze up, etc. Amongst the vintage motorcycles i work on, better than 80% of them come in with one or both drums out of adjustment, glazed, or totally shot.

I got the 'pronto' brand wheel cylinders from Rock Auto and they seem to be pretty good, taiwan instead of china i think.