Soft brakes after changing wheel cylinders.

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nephlyte

nephlyte

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So, i blew out one of the rear brake cylinders a few days ago. I still have 4 wheel drum, so I decided to go ahead and swap out all 4, i'm sure they were old.

So, i changed out the rear 2. I bled the brakes until no more air came out. When i tightened them, the pedal was just as stiff as before i blew the cylinder.

NOW, i tried my luck and replaced my front wheel cylinders and i can't bleed them back to stiff again.

How tight should the adjusters be? I've bled thru a whole big bottle of fluid, so i think i got all the air out. Perhaps i didn't make the adjusters tight enough.

Right now, I can stop very slowly or if i pump 2 or 3 times, i can stop immediately. After pumping it, if i hold it, it stays stiff, but if i let it sit for a second, its just as soft again.

Suggestions before i take it to the shop tomorrow?
 
I would double check the front brakes for proper adjustment. Sounds like the shoes are to far from the drums. Did you do one brake at a time? Did you use new hardware?
 
If i hold the brake it does not sink slowly. The master cylinder is fine. I would've noticed the master cylinder before the wheel cylinder blew. Before that blew, the brakes were great.

I just replaced the wheel cylinders w/ new ones. the brake shows/hardware didn't need to be replaced.

So, what is the proper adjustment. i'm headed to the store now for the adjuster tool. Never had to mess with them before.
 
yepperz!!!! NOW that you have a NEWLY closed system again....and your MC is meeting with Proper and full hydraulic pressure...NOW the MC shows itself as yet another in a
"string " of problems.
Brakes for me are kinda like a game of domino's...you touch any part of them and you might as well just replace everything....ESPECIALLY if the parts are all over 20 years old...lines can last a wee bit longer like maybe up to 30 IF they do not see ANY weather or if they are stainless......stainless can go to 40 but after that it is best to replace everything wheel cyls, rubber lines, steel lines and MC......I may go a lil over board BUT I want to make sure the car I gave all that money building, STOPS when I tell it to...EVERYTIME. just my thought/2 cents
 
Tighten up the adjusters until you can NOT turn the wheels, then back them off until the drum just "scrapes" going 'round. Try to get them even
 
nephlyte said:
The master cylinder is fine. I would've noticed the master cylinder before the wheel cylinder blew.
Click to expand...

Don't bet on it! Remember, the master cylinder only sees a fraction of its full stroke length during normal brake operation. Miles and years of partial-stroke operation cause the unused portion of the cylinder to accumulate rust and scale. Now you go bleed the brakes with full strokes of the pedal, right down to the floor. That pushes the piston right into the rough, rusty, cruddy portion of the cylinder. Really does a job on the piston and seals. Very easy (and very common) to finish off a master cylinder this way.

A few other things to keep in mind: you will have much better results bleeding the brakes if you will tighten all four brake adjustors so the shoes are right up against the drums before you start the bleeding operation, and also you must bleed the whole system each and every time you open it. There's no such a thing as "I only replaced the front cylinders so I only need to bleed the front". And you need to follow the correct sequence, going from farthest to closest relative to the master cylinder: Right rear, left rear, right front, left front.
 
What year? Dan just gave good advice. If you have a valve, you may have locked out the front, while bleeding the rears. Read up on it. If you needed cylinders, you need a MC, and bench bleed it.
From an old timer brake and front end mechanic, here. Don't say it is "good". Read up and find how to center the valve, if it is there.
M/C bad, valve off-center, or air in system; and adjust brakes. What year? If self-adjusting, read up, as you can't back off if too tight, unless you know the trick. It takes a small screwdriver thro the adjuster hole, or if you have 2 holes, thru there; to push the auto tang off the adjuster, in order to back it off. And push the pedal, while adjusting, to center the shoes.
You seem to have a later than 68, brakes only self adjust when pedal pushed kinda hard while backing up.
 
Looks like a '66 to me (in pic and in text in .sig). Single-pot master cylinder unless it's been upgraded, no safety valve. And yes, Green1 is right, the pre-'69 self-adjusters are not as reliable as the '69-up type.
 
Master cylinder primary cup seal is leaking. As previously stated, you pushed the M/C right through the "muck" in the pressure chamber. This "hurt" the cup seal and now allows fluid to "by-pass" around the primary cup seal.
Yes a good brake adjustment is very important to bleeding.
Start at the farthest ending at the left front!
Nice looking car!
 
I sped read right through 66, sorry. Replace the M/C and another quart through the system.And don't push it to the floor; tighten bleeder halfway down on pedal.
 
slantsixdan said:
and also you must bleed the whole system each and every time you open it. There's no such a thing as "I only replaced the front cylinders so I only need to bleed the front".
Click to expand...

Don't worry over having to bleed all 4 wheels and using a quart or two of brake fluid. Many people don't know you are well-advised to refresh the brake fluid (bleed) every few years. That is to combat moisture absorption. Besides rusting everything internal, the moisture greatly decreases the boiling point, making it more likely your fluid will boil and lose all braking ability. A smart alternative is to use silicone fluid (DOT 5), which doesn't absorb water.

You might get away with 10 years if you live in the dry West. I was trying to bleed my Aries once which had spent 10 yrs in Georgia and nothing was coming out of one caliper. I had the assistant jam the pedal with both feet and a big slug of rust blew out the hole. I have since used silicone in all cars that don't have ABS. Since it is getting rare, I bought a gallon on ebay (military surplus). The only drawbacks are that it has a slightly lower boiling point than fresh DOT 3 & 4 (though they soon degrade) and it is slightly more compressible, which I think is why they say not to use in ABS systems.
 
Thanks for everyone's help. I just assumed the self adjusters were worth a ****. They are not.

After a little manual adjusting, the car is braking like a champ. I thought i knew how to bleed brakes. I never really thought about the 4 wheel drums needing adjustment.

I tightened it up all the way, then backed it off a little and now the pedal is supertight.

BTW, MC still working great.
 
BillGrissom said:
A smart alternative is to use silicone fluid (DOT 5), which doesn't absorb water.
Click to expand...

Strongly disagree that this is a smart idea. I recommend not using silicone-based fluid. Its lack of hygroscopic nature (i.e., its not absorbing water) sounds like a good thing, but in fact it's not. Moisture will get into the brake hydraulic system with normal usage and changes in ambient temperature and humidity. Ordinary brake fluid is designed to absorb and assimilate a fair amount of moisture without causing substantial corrosion problems; only once the amount of water in the fluid overwhelms the corrosion inhibitors (because the vehicle is long overdue for a proper and necessary brake fluid flushout) does corrosion become an issue. With silicone fluid, the water will not mix with the fluid, it will accumulate in slugs at the lowest points of the system...and stay there, where it will aggressively corrode whatever it's touching. This is not an improvement!

Furthermore, it is very difficult to get all the air out of silicone brake fluid, so it is very difficult to get a good, firm pedal.

There is an enormous range of conventional non-silicone brake fluids on the market. You can get whatever properties you want (e.g., high boiling point) without having to go to a silicone-based fluid.

And as if that weren't enough, the cost and effort difference between regular and silicone fluid is such that you can flush the system with conventional fluid every two years or so (which is about the right interval) for a long time before you equal the cost of just one silicone fluid changeover.

Shop carefully. All silicone fluid is "DOT 5". The highest spec category for non-silicone fluids is "DOT 5.1".

DOT 3, DOT 4, and DOT 5.1 fluids are all intermixable.

DOT 5 (silicone fluid) cannot safely be mixed with DOT 3, 4, or 5.1.

Really, it should not be necessary to spend money on exotic brake fluids. Use a good brand of DOT 3 or DOT 4 (I have tended to use Castrol LMA DOT 4 when I can find it) and flush the system every two years and you'll be in fine shape.
 
MC still working great.
Click to expand...

Keep a careful eye on it. Often the piston and seal abrasion from full-stroke bleeding as described above will not immediately fail the MC, but it will fail soon thereafter. With the pre-'67 single-pot master, your margin for "oops" on this is basically zero. Best go ahead and buy at least a new master cylinder (better: the parts to retrofit to dual master) now, so you will have them right at hand when, sooner than later, you need them.
 
Yep, on a brake system that is old, as soon as you replace one part, you have disturbed the way it it used to, i/e you just pushed the M/C further than it is used too. Buy a new one (more fresh fluid thru the lines, lol).
 
slantsixdan said:
... I recommend not using silicone-based fluid.

flush the system with conventional fluid every two years or so (which is about the right interval)

DOT 5 (silicone fluid) cannot safely be mixed with DOT 3, 4, or 5.1.
Click to expand...

There has long been much misinformation and half-truths about silicone brake fluid. I am hardly the expert, but can relate a few experiences and things I have read:

1. Many mechanics and guys at the parts counter claim you must remove every trace of conventional brake fluid before using silicone. However, I have read the only risk is that any spots where conventional fluid remains is a place where corrosion can occur. No exotic chemical reaction occurs. Regardless, I have only switched to it when rebuilding or replacing all calipers and MC, and blew alcohol thru all lines and dried.

2. Many (like Dan) claim moisture will get into silicone fluid and form lumps of water that cause even worse corrosion. I have bled my silicone fluid in a few cars after many years and the old fluid comes out clear with no hint of rust. I think moisture gets into regular brake fluid because it absorbs it, i.e. pulls it in from the air. You could get water into a silicone system if you let it drip in, so don't open the reservoir when it is raining (in fact, you may never need to open your reservoir again). If silicone was bad, I wonder why auto manufacturers started switching to it just before ABS came along. Also, why did the military spec it? They don't make any decision without detailed study.

3. I agree that regular brake fluid is fine if you bleed your system every 2 years, but most people don't. I maintain 6 cars and am busy enough with oil changes. Compare the value of your time to the one-time cost of DOT 5. I recall ~$10/qt at NAPA. I bought 1 gal mil surplus on ebay for ~$20.

4. I don't notice a more spongy pedal with silicone, and I use it in cars with both drums and disks. I am careful not to entrain bubbles, by pouring it slowly down the side of a funnel. I never have to let it sit for bubbles to settle out. Maybe if one shook the bottle. Don't pour it if you see bubbles. I don't dispute it is more compressible than glycol fluids, just nothing that noticeably affects a non-ABS car.
 
slantsixdan said:
Keep a careful eye on it. Often the piston and seal abrasion from full-stroke bleeding as described above will not immediately fail the MC, but it will fail soon thereafter. With the pre-'67 single-pot master, your margin for "oops" on this is basically zero. Best go ahead and buy at least a new master cylinder (better: the parts to retrofit to dual master) now, so you will have them right at hand when, sooner than later, you need them.
Click to expand...


Yes, absolutely agree here. I want to replace with a dual master, but i'm not sure where to start. Is there a good thread or walk thru so i know what i'll actually be getting myself into?
 
nephlyte said:
I want to replace with a dual master, but i'm not sure where to start.
Click to expand...

It's very easy.

Get a new master cylinder, don't futz around with "remanufactured" garbage. Use a Wagner MC71258, Bendix 11323 or Raybestos MC36221. It'll bolt right in place of your existing single-pot master, and your existing pushrod will work. You'll need a distribution (splitter) block; this can be had used from any A-body with 4-wheel drums, '67-up, but probably easiest to get it new from Inline Tube for $35. You'll need to run dual hardlines from the new master to the splitter block. Be sure to bend at least one fully-circular loop in each of them to let them flex. Steel line is standard and is a pain to work with; Cunifer is a lot easier (and better).

Decide whose opinion you agree with on brake fluid, bench-bleed the master cylinder before you install it, bleed the brakes when you're done, and you're all set.
 
slantsixdan said:
Strongly disagree that this is a smart idea. I recommend not using silicone-based fluid. Its lack of hygroscopic nature (i.e., its not absorbing water) sounds like a good thing, but in fact it's not. Moisture will get into the brake hydraulic system with normal usage and changes in ambient temperature and humidity. Ordinary brake fluid is designed to absorb and assimilate a fair amount of moisture without causing substantial corrosion problems; only once the amount of water in the fluid overwhelms the corrosion inhibitors (because the vehicle is long overdue for a proper and necessary brake fluid flushout) does corrosion become an issue. With silicone fluid, the water will not mix with the fluid, it will accumulate in slugs at the lowest points of the system...and stay there, where it will aggressively corrode whatever it's touching. This is not an improvement!

Furthermore, it is very difficult to get all the air out of silicone brake fluid, so it is very difficult to get a good, firm pedal.

There is an enormous range of conventional non-silicone brake fluids on the market. You can get whatever properties you want (e.g., high boiling point) without having to go to a silicone-based fluid.

And as if that weren't enough, the cost and effort difference between regular and silicone fluid is such that you can flush the system with conventional fluid every two years or so (which is about the right interval) for a long time before you equal the cost of just one silicone fluid changeover.

Shop carefully. All silicone fluid is "DOT 5". The highest spec category for non-silicone fluids is "DOT 5.1".

DOT 3, DOT 4, and DOT 5.1 fluids are all intermixable.

DOT 5 (silicone fluid) cannot safely be mixed with DOT 3, 4, or 5.1.

Really, it should not be necessary to spend money on exotic brake fluids. Use a good brand of DOT 3 or DOT 4 (I have tended to use Castrol LMA DOT 4 when I can find it) and flush the system every two years and you'll be in fine shape.
Click to expand...

x2 on the castrol lma dot 4, thats what I've had the best performance out of.
 
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