I've been reading some of the replies and some info needs clarifying.
Spongy brakes are USUALLY a result of air in the brake fluid, and
occasionally brake lines that are swelling. Usually brake lines that swell,
don't last long before they burst. If they have expanded a lot, the rubber
will sometimes have a permanent stretch to the rubber, enough to see or
feel. Quite often the fluid leaks through to the rubber via very small
holes because of the pressure generated during braking. Once off the brakes
the fluid pressure drops, and only the expansion of the rubber pushes the
fluid back through and it doesn't return quickly. You may be able to see
the bulges immediately after a firm brake application.
The flexing firewall will feel similar to spongy brakes too.
When you have a firm or hard pedal one cause is excess heat transferring to
the brake fluid getting close to the boiling point. Old fluid or moisture
contaminated fluid causes this. As soon as brake fluid is opened in the
bottle and is exposed to the atmosphere, it begins to absorb moisture. Even
in that half full bottle of new fluid you've had for several years. When I
buy a new bottle of fluid" I buy enough for what I need, and I write the
opening date on it with a Sharpie. After 2 years it doesn't get used for
brakes anymore, but I keep it to soak small parts in to remove paint. after
3 years it's disposed of . DO NOT USE BRAKE FLUID FROM OPEN CONTAINERS if
you don't know how long it's been open.
Check to see if both front and back brakes are working. If either isn't,
the dual master cylinder compensates, allowing braking by the other. It
gets a bit more complicated.
To find if the brakes are working, find a gravel or dusty rod, and try to
lock them up. If you do, get out and see which ones skidded.
Good luck.
Bob Winslade
1966-1600 Missy
1967-1600 Bender
1972-510 Daisy
1972-510 Spare Change
----- Original Message -----
From: "Dave Cooke" <cookefam314@gmail.com>
To: <datsun-roadsters@autox.team.net>
Sent: Monday, June 08, 2009 10:33 AM
Subject: [Roadsters] my Brakes don't feel right
> My 68 1600 has the original style brakes, my mechanic checked the brakes &
> says there's still plenty of pad & rotor left & they look fine. But, when
> I
> brake hard, like coming to a quick stop when I get a yellow traffic light
> from 55mph, the pedal seems like it's firm enough, but it also feels like
> the pedal bottoms out. I checked the firewall & it seems very solid, so I
> don't know if the "Stan Chernoff firewall brace" would help or what. The
> brake fluid levels are fine, maybe I'm just used to how modern disc brakes
> feel compared to 40 year old technology...any thoughts what to check next?
>
> --
> Dave Cooke
> 68 1600
> Lake in the Hills, IL
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