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Master Cylinder?

Frankensteineken

NAXJA Forum User
Location
MN
I was in need of some better pads, so I put new pads on the front and turned the rotors. I also pulled the drums in the rear and inspected and adjusted. Figuring it was time for new brake fluid, I sucked the brake fluid out of the master, put in new fluid, and bled all the brakes using gravity and the buddy method. I started with the furthest corner first, and made my way around, not really getting much air, keeping my eye on the master and topping it off.

To get to the point, when the engine is off, the brake pedal is rock solid, but when started, the pedal is mushy and too low. A quick drive around the block confirmed that the brakes suck and barely work. I have never had a pedal problem, and it really seems like there is air in the system. But I am wondering if the master is leaking internally. A quick search turned up the dreaded o ring problem, and the first time I hit the pedal, it went way lower than normal, so it is entirely possible I messed up the o ring.

I am going out to get a vacuum bleeder tomorrow, should I pick up a master cylinder as well?
 
I would try and bleed again before buying the MC.

I haven't seen Oceanside since 1979.
 
If master cyl is leaking internally, it would steadily go down when you hold your foot firmly on the pedal. You have already adjusted the rears, but could they still be a little loose? Sometimes using the self adjusters by backing up slowly and pumping the brakes helps adjust them up tighter and takes some of the required stroke out of the rear cyls, which brings the pedal up.
 
Definately sounds like air in the system. Don't waste your money on a MC just yet.
 
Alright, thanks for the replies. I think I'm gonna go pick up one of those Mi-T-Vac's or whatever they're called from Harbor Freight and try it again.

This is really frustrating me, I am leaving on a cross country trip tomorrow and this is the last thing I need.

The first thing I thought of were the rears, I jacked it up and tightened them even more. At this point they are tighter than they were before, and I didn't have a low pedal before. Now, along with a low pedal, there is very low braking power. It does feel like air in the system, but I am curious how so much got in and why everything looks good coming out.

And Joe, Oceanside is still here, and it's still over run by boot Marines.
 
I'm not a big fan of using vacuum to bleed brakes. Yes, the hand vacuum pump has its place. I use it to pull fluid through the system before I start "really" bleeding the system.
Problem with the vacuum method is it's very hard to stop air from being sucked in around the bleed screw threads. That makes it very difficult to know if you have actually removed all air from the brake system, itself.
Also, I firmly believe it's necessary to the bleed process to "shock" the system using the tried and true "buddy" approach. Some systems will bleed find by other methods, and some wont.
Just remember, pump slowly 4-5 times, hold pressure and open the bleed screw quickly; this pressure "shock" helps dislodge "sticky" air bubbles. As you appear to know, don't let the pedal go to the floor--place a piece of wood underneath the pedal to stop its travel.
I occasionally "buddy bleed" by myself. I hand pump the brake pedal, then place a stick between something like the seat frame and the pedal. It must be difficult to get the stick in-place, otherwise this method won't work.

Not sure how air got into your system by just sucking the fluid out of the reservoirs. However, if someone pressed on the brake pedal after having removed the fluid, then, yes, you have lots of air in the system. Hopefully, you won't have to re-start by "bench bleeding" the master cylinder--something that should be done when installing a new master cylinder.
If the MC has air in it, it can get trapped so that normal bleeding won't remove it. The MC should be level in order to properly bleed it; hence "bench bleeding". When installed, generally there is an upward slope to the MC, which makes bleeding it difficult. I have read that it's possible to jack the back of the vehicle up to level an already installed MC.
 
If you emptied the MC by sucking the fluid out of the reservoir and didn't open any lines, any air would stay near the MC. First, watch the fluid in the reservoir while a buddy pumps up the brakes, holds the pressure for a bit, and then releases it. Watch for bubbles returning to the reservoir with the fluid. If bubbles are returning, probably most of the air can be removed that way.

If that doesn't work, remember that to get air from near the MC to go out a brake bleeder, you have to pump all the fluid between the MC and the bleeder out. In order to get the air past any high points in the lines, you have to move it pretty fast. Use a piece of vacuum line to direct the fluid to the bottom of a clear bottle or jar. Open the bleeder and pump the pedal fairly fast. Make sure the end of the hose stays at the bottom of the container to keep air from being sucked back in.

Another idea would be to have a brake shop fllush the lines. They would use a power flushing tool that pumps fluid fast enough to move all the air out. Keep in mind they may try to sell you parts... From your description, you probably don't need any.

Good luck.
 
Update:

Here's where I am now. Bought the vaccuum bleeder, hooked it up, and found an incredible amount of air in the rear lines. Three complete bottle of brake fluid later, it is still there. I checked the whole system, there are no leaks, but it appears air is getting in somehow. I even went back to the buddy method and clear new fluid is coming out of the rears.

When the engine is off, three pumps makes the pedal rock hard, and it stays that way and does not bleed off. Engine running, the pedal feels ok, a little mushy maybe, but goes about halfway and stays. I drove it, and it is driveable, but I can't lock the tires up or even come close.

I am at a loss. Can one of the seals be sucking air and not leaking? Could a wheel cylinder be the culprit? Or can the master be sucking air somehow and not leaking?

ETA: I cracked the lines at the master, and the fluid looks ok coming out. Hard to tell with out a hose or bleeder.
 
I'm not a big fan of using vacuum to bleed brakes. Yes, the hand vacuum pump has its place. I use it to pull fluid through the system before I start "really" bleeding the system.
Problem with the vacuum method is it's very hard to stop air from being sucked in around the bleed screw threads. That makes it very difficult to know if you have actually removed all air from the brake system, itself.
---.

Don't think you read my post, or you thought I was making the above comment up.
You still have air in your system--again, it's quite possible you have an air bubble in your MC, which may require you to "bench bleed" the MC; especially if the MC is not level. What I mean by level, is put bubble-level on it, and be sure that it is level.
 
I have NEVER found gravity bleeding to fail. Pumping is not required.

Bleeding brakes: The best way is the GRAVITY method. The only problem is it takes a lot of beer and you don't want to drive right after. (CAUTION: YOU MUST BE 21 TO BLEED YOUR BRAKES THIS WAY!) I use it whenever I replace brake cylinders or calipers, but mostly it's just to change the brake fluid, which I do whenever I change shoes or pads. Ideally you change brake fluid at least every other year. If you worked on old cars and saw rusty pistons, you'd know why, but people also say that old brake fluid boils and won't stop you right.

1.) Get the car in a position where you can open up the bleeders. I always like to break them loose with a 6 point socket being careful not to break them off. If you can, spray them with breakaway or similar a day before.)
2) Starting with the bleeder futhest away from the master (pass. rear), open it about 1 turn. You can put a little hose and cup on it if you want to keep the old fluid from running all over. Make SURE to keep the master cylinder topped off with fluid and DON'T let it get down to where air gets back into the master cyl. Let it flow this way until the fluid comes out of the bleeder clean. This will take at least 2 cups or so of brake fluid. Using gravity alone, you can drink 2 beers while topping off the master cylinder for the first corner. (CAUTION: Do not store brake fluid in beer cans or put beer into master cyinder. Drinking a little brake fluid however will probably not kill you. Beer in your brake lines might.) Snug up bleeder good when you're done.
3.) Proceed to drivers rear and repeat. It won't take as long because the long brake line has already been purged of the old fluid. So you have to drink your beer faster.
4.) Pass front. Drink even faster.
5.) Drivers front. Etc.

Patience can be substituted for beers, but that's no fun.

This prevents the rubber pieces from going any further than they are used to and self destructing.
"
 
I have NEVER found gravity bleeding to fail. Pumping is not required.

Bleeding brakes: The best way is the GRAVITY method. ----"

You change MC's without bench bleeding first, and gravity bleed will not work.
You inadvertently pump air into the MC while it's still in the car, and it's doubtful gravity bleed will work.
You replace rear calipers with built-in e-brake (not the brake-shoe type) and it's extremely probable they won't gravity bleed.
The point is, different circumstances and different system configurations require different approaches to bleeding.
 
You need to make certain there is no leaks in the system. I think there isin't since the breaks will hold pressure after it have been pumped a few times.

There is the possibility that air is still in the system. Did the MC run out of fluid during the bleeding process? I do not use the buddy process, the gravity process or the vacumn pump process although I would use the buddy process if I had a buddy available. I use the russel speed bleeder. I put a clear hose on the bleeder, put the end of the hose in a clear jar with fluid in it, loosen the bleeder 1/2 a turn, start the engine and stroke the break pedal a few times. After a few strokes, I would top up the MC and chcek the hose to see if air is present. If I am satisfied with what I see, I re-tighten the bleeder and move to the next wheel. I have been using this method for many years with 100% satisfaction. I also always bleed the breaks with the engine running. I think it work better that way.

Then there is the question of the rear being out of adjustment. I do that by jacking the rear wheels off the ground and turning the adjusters until the wheel could not be turned by hand then I back off the adjuster until the wheel turns. I repeat the process for the other wheel.
 
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