Question about brake master cylinder
11-10-2012, 09:14 AM
#1
Racer
Thread Starter
Question about brake master cylinder
Will or does a worn out master cylinder cause a spongy brake pedal?
Just asking because my brake pedal doesn't seem to be as firm as when it was new. 50k on car and the brakes have been bleed also have SS brake lines. I also just put on new rotors and pads.
If I stand on the pedal it sinks just a little but doesn't bottom out.
Thanks.
Just asking because my brake pedal doesn't seem to be as firm as when it was new. 50k on car and the brakes have been bleed also have SS brake lines. I also just put on new rotors and pads.
If I stand on the pedal it sinks just a little but doesn't bottom out.
Thanks.
11-10-2012, 12:15 PM
#2
Melting Slicks
Member Since: Jul 2010
Location: Tacoma, Wa/Surprise, Az
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At 50k miles, my first guess would be trapped air somewhere in the brake system. I think if the master cylinder had a problem, it would leak brake fluid around the seals and the pedal would slowly sink to the floor -just a guess though.
You didn't say what car you have, does it have abs? If so, was the abs module also bled? If not, you might have to take it to a dealer or someone that has a device to open the abs unit during the bleed process.
If you bled the brakes yourself, look very closely at the brake fluid to see if you can see tiny bubbles - about the size of high quality champagne bubbles. I used a drop light behind clear tubing attached to the brake bleed screw to see them, but they were there.
What I hate about brake fluid is its ability to remove paint.
You didn't say what car you have, does it have abs? If so, was the abs module also bled? If not, you might have to take it to a dealer or someone that has a device to open the abs unit during the bleed process.
If you bled the brakes yourself, look very closely at the brake fluid to see if you can see tiny bubbles - about the size of high quality champagne bubbles. I used a drop light behind clear tubing attached to the brake bleed screw to see them, but they were there.
What I hate about brake fluid is its ability to remove paint.
11-10-2012, 12:53 PM
#3
Racer
Thread Starter
At 50k miles, my first guess would be trapped air somewhere in the brake system. I think if the master cylinder had a problem, it would leak brake fluid around the seals and the pedal would slowly sink to the floor -just a guess though.
You didn't say what car you have, does it have abs? If so, was the abs module also bled? If not, you might have to take it to a dealer or someone that has a device to open the abs unit during the bleed process.
If you bled the brakes yourself, look very closely at the brake fluid to see if you can see tiny bubbles - about the size of high quality champagne bubbles. I used a drop light behind clear tubing attached to the brake bleed screw to see them, but they were there.
What I hate about brake fluid is its ability to remove paint.
You didn't say what car you have, does it have abs? If so, was the abs module also bled? If not, you might have to take it to a dealer or someone that has a device to open the abs unit during the bleed process.
If you bled the brakes yourself, look very closely at the brake fluid to see if you can see tiny bubbles - about the size of high quality champagne bubbles. I used a drop light behind clear tubing attached to the brake bleed screw to see them, but they were there.
What I hate about brake fluid is its ability to remove paint.
I wish there was a simple way to bleed the abs module in place.
Last edited by V4kerker; 11-11-2012 at 01:55 PM.
11-10-2012, 06:11 PM
#4
i get mushy when the rears are half worn ... threw them out and al good..
also tap on the calipers with a socket wrench to dislodge the microbubbles in the calipers
that has helped my weak pedle
are u using a master bleeder or a human..
also tap on the calipers with a socket wrench to dislodge the microbubbles in the calipers
that has helped my weak pedle
are u using a master bleeder or a human..
11-11-2012, 01:58 PM
#5
Racer
Thread Starter
11-11-2012, 09:03 PM
#6
Melting Slicks
Member Since: Jul 2010
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There is a product called speed bleeders. They are bleed screws with a built in check valve that actuate with a 1/4 turn of the bleed screw so you could actually do this job without the aid of a helper. I was able to buy a set from Napa autoparts though I don't know if Napa sells them in Maryland.
Brake fluid really doesn't move much or circulate through your system, just back and forth when you actuate the brake pedal. So when you activate the anti-lock brake system, you are not moving any brake fluid in and out of the ABS module. That is why you need a special tool to open the abs module to run fluid through it. I have a feeling a lot of shops don't take the extra step in actuating the abs module too, it may be a consideration in your quest for a harder brake pedal.
Power bleeders are another issue too. From what I understand, the cheaper power bleeders for home use have a tendency to introduce pressurized air into the brake fluid.
The type used by dealers separate air and brake fluid and consequently are much more costly to buy.
I tried to use one of those reverse brake bleeders where you bleed from the caliper up to the master cylinder and ran into problems introducing air into the system in the form of micro bubbles. The kit comes with some specialty fittings I found interesting to use with other brake bleeding methods but that is about the only use I could find for the 150 bucks I spent - in other words it was a total waste of money.
There are vacuum bleeders, the idea is to try to draw a vacuum from the caliper. The problem is there is too much resistance in the system to make this work efficiently.
Another way to bleed brakes is to just open the bleed screws and let the system self bleed. You probably noticed that when you replaced the factory brake lines.
I have a lot of experience trying to bleed air out of diesel fuel systems, with a clear fuel filter, you could see air become trapped in the filter - and stay there. The pump would pull the fuel through the filter but the air bubble would remain. I think this is much the same with brake systems, though the brake fluid is under pressure, the air bubble will remain or compress giving you the soft pedal as you actuate the brake pedal. Air wants to rise with the system - hence the reverse bleed method, but like mentioned I could not get it to work properly without introducing micro bubbles.
In the end, I did what you are doing and that is a manual bleed. Any rises in the tubing and brake lines will hold air and not bleed out no matter how many times you try. My SS lines had to rise up - form a loop - for the front wheels to turn without binding the brake lines. This could be where your air pockets are if you did not let the SS lines dangle down while bleeding them.
Hopefully, this will help nail down the problem. Speed bleeders are pretty inexpensive and can be quite helpful especially if there is a lack of communication between you and your helper.
Brake fluid really doesn't move much or circulate through your system, just back and forth when you actuate the brake pedal. So when you activate the anti-lock brake system, you are not moving any brake fluid in and out of the ABS module. That is why you need a special tool to open the abs module to run fluid through it. I have a feeling a lot of shops don't take the extra step in actuating the abs module too, it may be a consideration in your quest for a harder brake pedal.
Power bleeders are another issue too. From what I understand, the cheaper power bleeders for home use have a tendency to introduce pressurized air into the brake fluid.
The type used by dealers separate air and brake fluid and consequently are much more costly to buy.
I tried to use one of those reverse brake bleeders where you bleed from the caliper up to the master cylinder and ran into problems introducing air into the system in the form of micro bubbles. The kit comes with some specialty fittings I found interesting to use with other brake bleeding methods but that is about the only use I could find for the 150 bucks I spent - in other words it was a total waste of money.
There are vacuum bleeders, the idea is to try to draw a vacuum from the caliper. The problem is there is too much resistance in the system to make this work efficiently.
Another way to bleed brakes is to just open the bleed screws and let the system self bleed. You probably noticed that when you replaced the factory brake lines.
I have a lot of experience trying to bleed air out of diesel fuel systems, with a clear fuel filter, you could see air become trapped in the filter - and stay there. The pump would pull the fuel through the filter but the air bubble would remain. I think this is much the same with brake systems, though the brake fluid is under pressure, the air bubble will remain or compress giving you the soft pedal as you actuate the brake pedal. Air wants to rise with the system - hence the reverse bleed method, but like mentioned I could not get it to work properly without introducing micro bubbles.
In the end, I did what you are doing and that is a manual bleed. Any rises in the tubing and brake lines will hold air and not bleed out no matter how many times you try. My SS lines had to rise up - form a loop - for the front wheels to turn without binding the brake lines. This could be where your air pockets are if you did not let the SS lines dangle down while bleeding them.
Hopefully, this will help nail down the problem. Speed bleeders are pretty inexpensive and can be quite helpful especially if there is a lack of communication between you and your helper.
11-12-2012, 04:05 PM
#7
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Bill
11-12-2012, 08:15 PM
#8
Melting Slicks
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Hi Bill,
I've tried to use a Mity-Vac which has worked well for other jobs, one of which is drawing brake fluid out of the master cylinder reservoir but doesn't have the power for wheel calipers. Does the Vacula use compressed air to create the vacuum?
I'm going to have to get a set of Speed Bleeders for the GS, I had them on the '08 and worked great for solo operation. Come to think of it, would Vacula work with Speed-Bleeders?
I've tried to use a Mity-Vac which has worked well for other jobs, one of which is drawing brake fluid out of the master cylinder reservoir but doesn't have the power for wheel calipers. Does the Vacula use compressed air to create the vacuum?
I'm going to have to get a set of Speed Bleeders for the GS, I had them on the '08 and worked great for solo operation. Come to think of it, would Vacula work with Speed-Bleeders?
11-12-2012, 08:44 PM
#9
Burning Brakes
Will or does a worn out master cylinder cause a spongy brake pedal?
Just asking because my brake pedal doesn't seem to be as firm as when it was new. 50k on car and the brakes have been bleed also have SS brake lines. I also just put on new rotors and pads.
If I stand on the pedal it sinks just a little but doesn't bottom out.
Thanks.
Just asking because my brake pedal doesn't seem to be as firm as when it was new. 50k on car and the brakes have been bleed also have SS brake lines. I also just put on new rotors and pads.
If I stand on the pedal it sinks just a little but doesn't bottom out.
Thanks.
11-13-2012, 10:35 AM
#10
Racer
Thread Starter
I'm not sure how the master cylinder works during padel travel? I guess the front brakes get pressure first than the rears come into play(F/R Bias?). Will the brake bias change as the seals wearout? Last month when I changed rotors My rear brake pads were almost gone but the fronts looked like I could've done one my HPDE weekend.I have brake ducts on the front.
This off season I'm going to change out the master cylinder and rebuild the old one for a backup spare. Just to be on the safe side.
11-13-2012, 10:52 AM
#11
Racer
Thread Starter
MikeCsix and Bill Dearborn, I have a set of speed bleeders but haven't put them on yet. I think thats what I'm going to do to get a better/faster flush on the brake lines to make sure the air is out.
I thought about getting a motive brake bleeder just don't feel like spending the money on one. I heard pros and cons on some of these systems. I think I'll try the speed bleeders and a long enough hose to run from the bleeder back to the master cylinder and pump on the brake padel like I'm going into turn 1 at VIR without any brake pedal.
Does anybody know how to bleed the abs unit/module their self without having to buy a special tool or going to the dealer/shop?
I thought about getting a motive brake bleeder just don't feel like spending the money on one. I heard pros and cons on some of these systems. I think I'll try the speed bleeders and a long enough hose to run from the bleeder back to the master cylinder and pump on the brake padel like I'm going into turn 1 at VIR without any brake pedal.
Does anybody know how to bleed the abs unit/module their self without having to buy a special tool or going to the dealer/shop?
11-13-2012, 11:56 AM
#12
Melting Slicks
Member Since: Jul 2010
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If the seals in the master cylinder are leaking, the brake fluid leaks around the seal and won't hold pressure when you apply the brake pedal. I don't think you will introduce are into the system.
The motive types (bleed under pressure from the master cylinder) can introduce microbubbles. The type Bill uses would be best.
On the C-6's, the brakes are cross linked, ie, left front - right rear and right front - left rear. That way if you were to lose one of the circuits, you would still retain a front and rear brake.
For your next attempt, look at your brake lines to the wheels. Air will settle in the upper part of the brake line if there is an arc in the line and it won't bleed out. I would think about removing the brake line from the caliper and letting it dangle down into a drip pan and just let the fluid run for a bit. Then re-attach to the caliper and try to bleed the caliper again. Try the tapping method on the caliper as suggested.
With all of this time and energy invested though, you may want to take it to either a high performance shop or a dealer and tell them the problem. The dealer will have a tool to open the abs so it can be bled also.
I've been using Motul 600 and at $20 a pint, it doesn't take many pints to make this an expensive exercise. Your best bet might be to pick up a couple of pints and have the dealer do a flush. At least you'll be good for next season and have a hard pedal.
You have to have absolute faith in your brakes - your life rides on them.
The motive types (bleed under pressure from the master cylinder) can introduce microbubbles. The type Bill uses would be best.
On the C-6's, the brakes are cross linked, ie, left front - right rear and right front - left rear. That way if you were to lose one of the circuits, you would still retain a front and rear brake.
For your next attempt, look at your brake lines to the wheels. Air will settle in the upper part of the brake line if there is an arc in the line and it won't bleed out. I would think about removing the brake line from the caliper and letting it dangle down into a drip pan and just let the fluid run for a bit. Then re-attach to the caliper and try to bleed the caliper again. Try the tapping method on the caliper as suggested.
With all of this time and energy invested though, you may want to take it to either a high performance shop or a dealer and tell them the problem. The dealer will have a tool to open the abs so it can be bled also.
I've been using Motul 600 and at $20 a pint, it doesn't take many pints to make this an expensive exercise. Your best bet might be to pick up a couple of pints and have the dealer do a flush. At least you'll be good for next season and have a hard pedal.
You have to have absolute faith in your brakes - your life rides on them.