Brake pedal close to hitting floor board..

[jims427400]

Last week I had the 67 out for a very short drive when I felt like the brake pedal was very close if not touching the floor board. Checked the master cylinder and it was full and clear. No leaks anywhere. No idea when it was last replaced cause I've only had it about 3 yrs.
Need new fluid and bleeding??
Need a new master cylinder ??
Both ??


Jim

 

[67HEAVEN]

Jim,

The first thing I would do is replace the fluid and check that you get a good bleed. It may be that simple. Let's hope.

 

[jims427400]

Heaven,
That was my 1st guess but my machanic thought it was my master cylinder..
Gotta get her running cuase this fall weather is the only time I can drive it with/out baking. Need to get some speed bleeders. Thanks

 

[67HEAVEN]

Jim,

It could easily be plain "old" brake fluid with bubbles in it.

See here - http://www.canadiandriver.com/articles/jk/060531.htm

 

[jims427400]

Sounds like a plan.. Still have plenty of synthetic fluid left from the 68 job. Do you agree that synthetics are better??

 

[67HEAVEN]

Sounds like a plan.. Still have plenty of synthetic fluid left from the 68 job. Do you agree that synthetics are better??

That's what I'm using.

 

[JohnZ]

Sounds like a plan.. Still have plenty of synthetic fluid left from the 68 job. Do you agree that synthetics are better??

ALL brake fluids are "synthetic"; if you mean DOT5 silicone-based fluid vs. conventional DOT3/4 fluid, that's a matter of personal choice; just DON'T try to mix them in the same system - they're NOT miscible/compatible.

Bleed your brakes to make sure air isn't your problem first. If you still have a sinking pedal afterwards and no visible leaks, it's the master cylinder bypassing internally - time for a rebuild.

 

[jims427400]

What I planned on doing is to drain the master cylinder and keep filling w/dot 5, eventually whatever was in there before should be flushed out.
Would'nt that be rite.

 

[Hib Halverson]

A number of questions have been raised here about the 65-82 disc brakes.

First, DOT5 fluid...the only thing DOT 5 fluid is good for is show cars which are seldom driven and which seldom receive brake maintenance. It is true that DOT5 is non-hydroscopic, which is an excellent hedge against the 65-82 system's problem with corrosion, but from a performance standpoint, DOT5 fluids offer no clear advantage and, in fact, in some racing applications are a problem because of their slight compressibility at high temperature.

DOT5 fluid is not always a good choice for cars which get driven regularly and certainly is not a good choice for a car whch is driven hard. I think a better strategy to use against corrosion is stainless-steel sleeved calipers along with periodic maintenance and a DOT4 or DOT5.1 fluid. But....DOT5 fluid can't hurt anything.

Now, as far as a low pedal. Typically, that's because of one or more of four problems

1) air in the system
2) problematic master cylinder
3) expanding brake hoses or brake pipes.

As for "synthetic", some brake fluids are synthetic and some are not.
DOT3 fluid usually are not
DOT4 fluid...some are and some aren't
DOT5.0 is silicone-based and synthetic by nature.
DOT5.1 fluids may or may not be (but probably are) synthetic

 

[jims427400]

Just an update, started bleeding lines today and everything looked good until I got to the drivers front and found a 3 inch worn area on the flexible rubber line down to the fibers. Luckily I had one in my stash. Replaced it and finished remaining lines and ended up with a hard pedal. Problem solved, thanks all cause I was going to replace the master cylinder too.. Thanks 67..

 

[67HEAVEN]

Excellent. I'm glad that it worked out that well.

 

[Kid_Again]

Hmmmmm....a bit off topic but here's one definition of the word "synthetic":

"A substance that is formulated or manufactured by a chemical process or by a process that chemically changes a substance extracted from naturally occurring plant, animal, or mineral sources, except that such term shall not apply to substances created by naturally occurring biological processes."


Got it off of some webapedia.

A few years ago, I was involved in a case before the government about the definition of "natural" (the opposite of synthetic) and I'm OK with the above referenced definition of synthetic, based on that experience (the government agreed with our definition of natural). So, by that definition, ANY brake fluid is synthetic, no?

 

[jims427400]

So why does one type eat my paint and the other does not...
Went to Wallmart today and bought two more bottles of DOT 3 "synthetic" for $3.50ea. Do you suppose its truly synthetic ? If so why does"nt it cost 10 times more????
All I know is that it worked..

 

[JohnZ]

So why does one type eat my paint and the other does not...
Went to Wallmart today and bought two more bottles of DOT 3 "synthetic" for $3.50ea. Do you suppose its truly synthetic ? If so why does"nt it cost 10 times more????
All I know is that it worked..

"Synthetic" is a marketing hype word to make you think it's the latest high-tech product, made with a secret process in a multi-billion-dollar factory; ALL brake fluid is "synthetic" - they're just made from a different base chemical (glycol for DOT3/4, silicone for DOT5).