avalanche66

Howdy people, I have a brake problem I can't solve.

Last summer I had a brake problem start. I can't remember much of the circumstances that occurred when the problem started but what was happening, was the pedal was firm, but the braking power was weak. So I would be standing on the pedal and taking a dangerously long distance to stop.

First thing I did was check the fluid. It was dark and appeared to have sediment floating in it. Not sure what that was.

Fast forward to this spring. I went to Advance Auto and picked up a new Cardone Select master cylinder, hoping that would fix the issue. Swapped that in, flushed and bled the brakes with DOT 5 silicone fluid. I still have the same issue. I also noticed the car makes a brake grinding noise and kind of lurches when it finally does stop. No tires are locking up and the pedal doesn't sink.

Also, I thought that booster might be an issue, but a smoke test showed it had no leaks.

The calipers were bought quite some time ago but they're all the high end stainless ones so I would hope they're not the problem. This car doesn't get driven in the winter to rust them up.

Someone suggested a brake hose could be broken and expanding and compressing and absorbing the hydraulic pressure but we didn't observe anything when bleeding the brakes.

Maybe something with the proportioning valve? I'm at my wits end here. The next step I was going to take would be to find a brake caliper pressure gauge and see if the issue can be localized, but even with 1 or 2 calipers not working right I would think the car could stop faster than it does.

So any help is much appreciated. Thanks.

Mike Ward

Your first sentence rules out the 'absorbing pressure' theory.

You may have done a smoke test on the booster, but that won't confirm that it actually works. Start there.

I'd have a look at the condition of the pads if you've got a grinding noise.

Gale Banks 80'

If you have one or more bad Calipers then the Car should pull in the oposite direction. Kinda sounds to me You went from a Power assist Car to a none Power assist Car as mentioned above. You might be up agaist the dreaded Power Booster replacement. Booster Dewey in Portland Oregon did mine and the Guys who have gone to Hydra Boost seem to like it. I'd shy away from local Auto Parts stores.

...Roger...

One thing you might try. Since your brakes produce heat to stop ,go out and drive around ,then stop and see if you can feel differences in the heat of each wheel. If you have calipers that are noticeably cooler I would start looking into why they aren't helping in the braking. Just a thought.

Timsride

Mine worked like that when I first started driving the car after a frame off. The only thing that wasn't new on the brakes was the power booster and pedal. I played with vacum trying to increase as much as possible, re-bled the brakes. Nothing worked. I changed the check valve and brakes started working normally. Simple fix that can maybe help You out too? By the sounds of it it is either vacum related or booster itself. My brakes had almost no play in them but had no stopping power, now work great. Worth a try?

my 76 ray

I was also thinking the booster is not working. I was going to suggest disconnecting and plugging the vacuum line to the booster to see if it changed the braking at all. If no change it would seem to point to the booster not working.

batmedic

Just another quick and silly thought. I had similar issues, but only on the cool mornings. I found that my choke was hooked up wrong. I would warm the car up, head out and have the issue you describe. I found out that the car was jumping back into high idle while driving. This decreased the vacuum to the booster and causing the problem. Goes along with what has been said here, but just something else to think about.

NassyVette

I think this is a simple problem, you used dot 5 silicone. Not recommended for a number of reasons. Compressibility and it is not hygroscopic by nature, so any moisture introduced into your system will both corrode the lines and further add to compressibility and lower wet boiling point. Not to mention it is not compatible with the rubber seals used in our cars. Drain and flush with a quality dot 3/4 fluid and I'm sure your issues will go away.

terry82

when you bleed the brakes do you get much fluid out ?i would take a line off hit the brake and see if you get the fluid out that you should be getting ,your rubber hoses may be bad inside .the sediment in the master clyinder came from somewhere.

markdtn

good suggestion as a starting point

noonie

Easy test for a booster.
Press the brake pedal with engine not running.
Then start engine, if the pedal pressure needed is much less, then the booster/vacuum is ok.

Dot5 isn't the best for street driving.

avalanche66

Can you elaborate on that?

Thanks for the suggestions guys keep em coming.

SIXFOOTER

Bad Booster, DOT5 is good stuff if you flush the lines clean. That means disassembling the calipers and cleaning them too. replace if necessary.
You said it in the beginning of your post, Pedal was firm but you had to stand on the pedal....Booster

SanDiegoPaul

You used silicone fluid in an old brake system? Bad idea.

Will's'74VetteL-82

I have no experience with DOT5 but ive heard mixed "reviews" of it for street driving in an old system. From what you said though, your pedal is firm, try the booster test as said before. Turn car off and it should still have some vacuum held to pump 2 to 3 times you can hear the booster working too. Deplete the held vacuum by pumping with car off, (thats one test there, if theres no held vacuum its bad) and start with your foot on the pedal, it should move in towards the floor. If this works then the booster is good.

Will

pauldana

may be a good path to follow..... I was told this by my friends and several others, "Buy a Hydro Boost" I finally did and it is GREAT, i screwed with my brakes on and off for 20 years.. Go HB and never look back

the silicon absorbs water and thus compresses... just don't use it is what i have been told...

also, my proportioning valve was full of crud changed it and it too was a world of difference..

good luck.. p

avalanche66

Do you have any links to this hydro boost you speak of? Thanks.

pewter-FRC

get rid of the dot 5 fluid, your problem will go away

NassyVette

It's actually quite compressible all on it's own, it has no place in a performance/racing environment.

...Roger...

You can boil a lot of that compressibility out before you put it in the car.