Brake issue - MasterCylinder packed it in?
04-28-2002, 05:34 AM
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Brake issue - MasterCylinder packed it in?
Hi Guys,
I would like some advice regarding a brake issue. I and my mechanic have just rebuilt all four brake calipers as they were sticking and had a lot of gunk in them (not sure the last time they were rebuilt I just bought the car).
We put the calipers back on, put the brake lines back in, bled the brake system, and put fresh brake fluid in and repeated the process to make sure all the air was out. This is on a 1977 911.
However, what is happening now is when you depress the brakes the pedal goes straight to the floor the first time, and if I press it again it firms up, then again and its as it should be. Leave it a few seconds and it goes spongy again.
My mechanic reckons that the MasterCylinder has decided to pack it in after 20 years of service and isn't holding the fluid in the chamber properly.
Intuitively, I tend to think that the issue may lay at the rebuilt brakes but we checked for leaks and problems, and nothing seems to be wrong.
I got under the car, pulled the pan that protects the master cylinder and it had a lot of brake fluid on it, but I assume thats from the brake resivior overflow tube.
One last thing, if you pump the brake pedal and have a look at the brake line that runs into the resivior you can see a few bubbles coming back up as brake fluid comes back up the line.
Any suggestions, does it sound like its a MasterCylinder or is there some way I can isolate the problem? Thank you.
I would like some advice regarding a brake issue. I and my mechanic have just rebuilt all four brake calipers as they were sticking and had a lot of gunk in them (not sure the last time they were rebuilt I just bought the car).
We put the calipers back on, put the brake lines back in, bled the brake system, and put fresh brake fluid in and repeated the process to make sure all the air was out. This is on a 1977 911.
However, what is happening now is when you depress the brakes the pedal goes straight to the floor the first time, and if I press it again it firms up, then again and its as it should be. Leave it a few seconds and it goes spongy again.
My mechanic reckons that the MasterCylinder has decided to pack it in after 20 years of service and isn't holding the fluid in the chamber properly.
Intuitively, I tend to think that the issue may lay at the rebuilt brakes but we checked for leaks and problems, and nothing seems to be wrong.
I got under the car, pulled the pan that protects the master cylinder and it had a lot of brake fluid on it, but I assume thats from the brake resivior overflow tube.
One last thing, if you pump the brake pedal and have a look at the brake line that runs into the resivior you can see a few bubbles coming back up as brake fluid comes back up the line.
Any suggestions, does it sound like its a MasterCylinder or is there some way I can isolate the problem? Thank you.
04-28-2002, 08:44 AM
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If you brake calipers don't leak my bet is they are fine.
Now the master, when you bleed brakes you probably push master to floor when you pump up to brakes. If you use the "pump it" " hold it" for the brake bleed then you putting the master piston in places it has not been for 20 years and probably detroyed the rubber. If the master had corrosion, in the chamber where when you push it to the floor, the rubber is gone.
I use a MITI-vac , no need to touch master for the reason I just expanded on.
Hell these Are porsche brakes, get a new master and do it right! Don't rebuild it.
Now the master, when you bleed brakes you probably push master to floor when you pump up to brakes. If you use the "pump it" " hold it" for the brake bleed then you putting the master piston in places it has not been for 20 years and probably detroyed the rubber. If the master had corrosion, in the chamber where when you push it to the floor, the rubber is gone.
I use a MITI-vac , no need to touch master for the reason I just expanded on.
Hell these Are porsche brakes, get a new master and do it right! Don't rebuild it.
04-28-2002, 06:07 PM
#3
Pull up your driver floorboad and have a look at the end of master cylinder where the brake pedal push rod goes into it. If this area is wet, time to replace the MC.
If the MC is OK, I recall having my front calipers rebuilt last year, and experienced a somewhat similar problem immedately after the rebuild, which my mechanic informed would go away after driving it a few days.....which it did.
Drive cautiously for a few days and see if it improves by itself.
If the MC is OK, I recall having my front calipers rebuilt last year, and experienced a somewhat similar problem immedately after the rebuild, which my mechanic informed would go away after driving it a few days.....which it did.
Drive cautiously for a few days and see if it improves by itself.
04-28-2002, 07:13 PM
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Dana,
After rebuilding calipers, if you put the old pads back in, and the pistons were depressed flat into the caliper, it can take around 120 miles for the pistons to work their way out to where they contact the pads and retract they way they are supposed to. In the meantime, a long pedal is a bit disconcerting. When I rebuild a caliper, I position the piston so I have to still push it in a little to get the pad in.
The way to check if your MC is bad, asides from brake fluid dripping on the carpet above the pedals, is to step on the pedal and put consistent hard pressure on the pedal. If it slowly goes to the floor, it's new master cylinder time. This is due to the fluid moving past the interior seals. This is one reason why power bleeding, especially on a high mileage vehicle, is a good idea. As bds1 pointed out, bleeding by stepping on the brakes pushes the seals into areas that are rough and corroded, ie, where the seals don't normally go, and it rips the seals.
After rebuilding calipers, if you put the old pads back in, and the pistons were depressed flat into the caliper, it can take around 120 miles for the pistons to work their way out to where they contact the pads and retract they way they are supposed to. In the meantime, a long pedal is a bit disconcerting. When I rebuild a caliper, I position the piston so I have to still push it in a little to get the pad in.
The way to check if your MC is bad, asides from brake fluid dripping on the carpet above the pedals, is to step on the pedal and put consistent hard pressure on the pedal. If it slowly goes to the floor, it's new master cylinder time. This is due to the fluid moving past the interior seals. This is one reason why power bleeding, especially on a high mileage vehicle, is a good idea. As bds1 pointed out, bleeding by stepping on the brakes pushes the seals into areas that are rough and corroded, ie, where the seals don't normally go, and it rips the seals.
04-28-2002, 11:16 PM
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Hi Bill,
Thanks for taking the time to write back. I will purchase a new master cylinder today, and its probably a good idea anyway considering the age of the original one.
If you held your foot on the pedal eventually it would lose pressure so I suspect that and the fluid moving back up the line indicate that its not holding it properly.
I am not too worried about the Calipers as such, it will take a while for them to settle in, I just wanted to narrow down what the problem might be.
Thanks for all your help guys.
Thanks for taking the time to write back. I will purchase a new master cylinder today, and its probably a good idea anyway considering the age of the original one.
If you held your foot on the pedal eventually it would lose pressure so I suspect that and the fluid moving back up the line indicate that its not holding it properly.
I am not too worried about the Calipers as such, it will take a while for them to settle in, I just wanted to narrow down what the problem might be.
Thanks for all your help guys.
04-29-2002, 12:50 AM
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I have had a dragging caliper and the cause was the brake line, after 20 or so years in service often the lines get clogged and prevent the fluid from returning to the master. So after all you have done I would also replace atleast the flexible lines as well, Then you have a complete restoration at least as far as most people go. the hard line are a bit more work to replase.
Jim
Jim
04-29-2002, 10:45 AM
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Like Bill says, this is typical of the caliper pucks being too far into the body of the caliper. What you and your mech. need to do is to simply pull one pad at a time, put in a thinner shim, push the puck out via brake pedal pressure, then push it back in just enough to let the new pad in.
Typically folks rebuild their calipers and put in new pads. This way you bleed the car with the old pads in, then pull the resevoir down to 1/2 full. Start anywhere, removing the older, thinner pad, and push the puck in slightly to accept the new pad. The backflow of fluid is very little and you have already pulled fluid from the resevoir, letting the backflow not turn into overflow.
Really common problem. I am surprised your mech didn't recommend this. Of course a new master cylinder is not a bad idea at all, but be sure to follow this procedure new master cylinder or old.
Jw
Typically folks rebuild their calipers and put in new pads. This way you bleed the car with the old pads in, then pull the resevoir down to 1/2 full. Start anywhere, removing the older, thinner pad, and push the puck in slightly to accept the new pad. The backflow of fluid is very little and you have already pulled fluid from the resevoir, letting the backflow not turn into overflow.
Really common problem. I am surprised your mech didn't recommend this. Of course a new master cylinder is not a bad idea at all, but be sure to follow this procedure new master cylinder or old.
Jw
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04-30-2002, 01:05 PM
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I just replaced my master cylinder in my 76 euro.Actually my pedal felt fine but I was loosing fluid.When I lifted my carpet and pedal board there was a small flood of brake fluid around the pedal cluster.I used a turkey baster to get most of it up.The problem is where the master is located.The plate that covers it doesn't really keep out 26 yrs
of rust and corrosion.By soaking all the nuts with WD-40 I was able to save a few but had to order two new lines and a fitting from Porsche via Germany.So it turned into a couple of weekends job.Just bled the brakes this past weekend and they feel great.
By the way I got my master from Vertex for $96,good prices and fast delivery and the lines and fitting came to $32/two day delivery from Germany from the local Porsche dealer with my PCA discount.Now I just have to figure out why my alt. light goes on and off occasionly?????
Good Luck,
Steve
of rust and corrosion.By soaking all the nuts with WD-40 I was able to save a few but had to order two new lines and a fitting from Porsche via Germany.So it turned into a couple of weekends job.Just bled the brakes this past weekend and they feel great.
By the way I got my master from Vertex for $96,good prices and fast delivery and the lines and fitting came to $32/two day delivery from Germany from the local Porsche dealer with my PCA discount.Now I just have to figure out why my alt. light goes on and off occasionly?????
Good Luck,
Steve