68 brake master cylinder
Thread Starter
Instructor
Joined: Aug 2009
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From: Demotte In
68 brake master cylinder
Hello
What are the symptoms of the master brake cylinder going bad?
My break peddle is firm and high 1 time and the next time I press the break it goes half the way to the floor and spongy?
IF I press it a few times it comes back firm and high?
It is not consistant.
No break fluid leaking I checked that.
Thanks
Ed
What are the symptoms of the master brake cylinder going bad?
My break peddle is firm and high 1 time and the next time I press the break it goes half the way to the floor and spongy?
IF I press it a few times it comes back firm and high?
It is not consistant.
No break fluid leaking I checked that.
Thanks
Ed
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From: Muskegon MI
Le Mans Master
Joined: Mar 2001
Posts: 6,640
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From: Ann Arbor Michigan
Press lightly on the pedal and see if the pedal goes down. If the seals in the M/C are shot, the pedal will drift to the floor at this low pressure, but will seal at high pressure. I assume there are no exturnal leaks, correct?
Gary
Gary
Team Owner
Joined: Jun 2000
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From: Southbound
Cruise-In II Veteran
Have you changed the master cylinder? If it's the old original '68, it probably needed to be rebuilt/replaced a long time ago. Pull the cap off and look at the fluid. Clear or crudded up?
Thread Starter
Instructor
Joined: Aug 2009
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From: Demotte In
Hello
There is no fluid on the floor and the pedal is hard the first hit then the second hit it goes down twice as far, master cylinder fluid is pretty clean and a full brake job with new calipers was done abour 8K miles ago. I do not know any history on the master cylinder.
If I pump it 2 or 3 times it comes back up to the original height when pressed. The pedal is still hard and the breaks work even when it travels farther towards the floor.
Thanks
Ed
There is no fluid on the floor and the pedal is hard the first hit then the second hit it goes down twice as far, master cylinder fluid is pretty clean and a full brake job with new calipers was done abour 8K miles ago. I do not know any history on the master cylinder.
If I pump it 2 or 3 times it comes back up to the original height when pressed. The pedal is still hard and the breaks work even when it travels farther towards the floor.
Thanks
Ed
Melting Slicks
Joined: Mar 2007
Posts: 2,520
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From: Hinckley OH
If you have power brakes, it might be the power brake booster. When the booster has no vacuum, the pedal is hard. The resevoir gets it's vacuum from the engine and normally saves enough for two or three stops after the engine stops running. Pumping the brake uses vacuum from the resevoir so the brake pedal gets hard if it doesn't have/retain enough vacuum.
You can try this on any car that has power brakes that run from vacuum. With the engine shut off, press the brake a few times. The pedal will get hard and high. Then start the engine. This will apply vacuum to the power brake booster and the pedal will fall and become softer. Shut off the engine and press the brake pedal a few times. As the vacuum is used up, the pedal will once again become hard and high.
Does this sound like what your car is doing?
You can try this on any car that has power brakes that run from vacuum. With the engine shut off, press the brake a few times. The pedal will get hard and high. Then start the engine. This will apply vacuum to the power brake booster and the pedal will fall and become softer. Shut off the engine and press the brake pedal a few times. As the vacuum is used up, the pedal will once again become hard and high.
Does this sound like what your car is doing?
Thread Starter
Instructor
Joined: Aug 2009
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From: Demotte In
Hello again
The break pedal is hard and when the car runs it may travel % 30 down- never to the floor. There are no leaks onto the floor.
When the car is shut off and if you press the break pedal it gets very firm on the second press.
The master cylinder maybe ok. I just thought that was alot of pedal travel.
Thanks
Ed
The break pedal is hard and when the car runs it may travel % 30 down- never to the floor. There are no leaks onto the floor.
When the car is shut off and if you press the break pedal it gets very firm on the second press.
The master cylinder maybe ok. I just thought that was alot of pedal travel.
Thanks
Ed
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Le Mans Master
Joined: Mar 2001
Posts: 6,640
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From: Ann Arbor Michigan
Hello again
The break pedal is hard and when the car runs it may travel % 30 down- never to the floor. There are no leaks onto the floor.
When the car is shut off and if you press the break pedal it gets very firm on the second press.
The master cylinder maybe ok. I just thought that was alot of pedal travel.
Thanks
Ed
The break pedal is hard and when the car runs it may travel % 30 down- never to the floor. There are no leaks onto the floor.
When the car is shut off and if you press the break pedal it gets very firm on the second press.
The master cylinder maybe ok. I just thought that was alot of pedal travel.
Thanks
Ed
Gary
