Brake Fluid Fright - Impala Tech
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post #1 of 9 (permalink) Old 12-01-2018, 06:09 PM Thread Starter
Hal
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Brake Fluid Fright

During a recent "exercise" cruise in my '63 Impala I noticed an extra amount of travel in the brake pedal during normal braking. There was no "spongy" feel to it and the pedal never hit the floor, just the extra travel. My Impala's brakes are regular hydraulic but not power-assist, which means the master cylinder has only one reservoir for all the fluid and that my emergency/parking brake had better be in working order in an actual emergency.
Upon returning home I backed the car into the garage without incident and the brakes did not fail. I made a mental note to check the fluid level before taking her out again. So, a couple of weeks later I was preparing to take her out again on a bright sunny day, remembering to check the brake fluid level first. When I popped off the master cylinder cap and looked inside it was bone dry! That's when I started wondering; is it possible to have a small enough leak somewhere in the brake system, perhaps at one of the wheel cylinders, that will let out just enough fluid but not suck back in too much air during low speed braking? Thereby avoiding complete brake failure because no air bubbles make it all the way back to the master cylinder?
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post #2 of 9 (permalink) Old 12-01-2018, 06:46 PM
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When is the last time you checked the reservoir?

A pinhole leak is possible, but it would leave evidence. Is there any residual brake fluid on the lines or at each wheel cylinder? Or even some rust underneath the master cylinder where it may be dripping on to the car's firewall?

I would think there would be some evidence even with a small leak.
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post #3 of 9 (permalink) Old 12-01-2018, 07:49 PM
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As said above a pin hole in the line would squirt pretty far as the brake pedal produces 1,500 psi of pressure. It could be pumping fluid into the lane next to you as you stop.

By the way you have a single reservoir because your car was built before 1967 when the factory went to mandated dual master cylinder reservoirs for safety reasons. Congress mandated these changes because their boss and owner the insurance industry said so.

You could upgrade to dual master cylinder brakes with a manual master cylinder if you wanted to tomorrow as the parts all inter change.

Big Dave
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post #4 of 9 (permalink) Old 12-02-2018, 12:53 PM
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You almost certainly have a leaking wheel cylinder. Get the wheels and drums off immediately. Consider swapping the master for the 67 Impala dual master, and modify the lines.

Two doors, four doors, wagons, and ragtops.
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post #5 of 9 (permalink) Old 12-02-2018, 02:11 PM Thread Starter
Hal
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Thank you gentlemen! I'll be towing her into the shop very soon and will likely switch to that '67 dual master cylinder.
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post #6 of 9 (permalink) Old 12-02-2018, 04:22 PM
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With a dual master cylinder you will need dual brake lines off of a 1967 and up to '81/'84 full size (when GM switched over to aluminum master cylinders with plastic reservoirs). You can buy this aluminum body stainless steel sleeved one inch bore master cylinder as it works with manual or power brakes.

https://www.speedwaymotors.com/Alumi...ore,50598.html

The manual master cylinder had a 7/8th inch bore to build pressure with less foot effort. This was possible because drum brakes are self activating. Those big strong springs inside are to pry the brake shoe off the drum, not to push them into it. As such it didn't need a lot of brake line pressure to operate drum brakes.

The power assist brakes has a 1-1/8th inch bore master cylinder used with disc brakes that have larger wheel cylinder volume (with nearly double the brake line pressure to clamp the smaller area friction pads against the rotors). You have to press the pad to the rotor to keep a car from moving forward at a stop light. That is why almost all disc brakes are power assist (little old ladies legs would tire if they had to stand on the brakes to prevent forward creep).

It is not just a mater of buying one single part; the other parts have to match what you have now, or soon may install, since money doesn't grow on trees. Plan ahead to buy fewer parts.

Big Dave

Last edited by Big Dave; 12-02-2018 at 04:54 PM. Reason: updated production dates
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post #7 of 9 (permalink) Old 12-02-2018, 05:27 PM
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Any parts store can get you an inexpensive 67 Impala drum/drum non-power master. Likewise, any competent shop can bend up a couple lines for you. Remember on this car, the FRONT port goes to the front drums. Not like on modern cars. Don't let them tell you the front goes to the rears. It doesn't. If you want pre-bent lines and a distribution block, they come pre-made.


This one's for my 65, I happened to have it bookmarked.


https://www.ebay.com/itm/65-66-Impal...e/190782419218

Two doors, four doors, wagons, and ragtops.
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post #8 of 9 (permalink) Old 07-20-2019, 06:47 AM
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Garage
They do make a power assist for drum bakes front and rear. I just put this on my 67, works great. check out Advance Auto & Rockauto.com.
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post #9 of 9 (permalink) Old 07-20-2019, 10:25 AM
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Quote:
Originally Posted by Hal View Post
During a recent "exercise" cruise in my '63 Impala I noticed an extra amount of travel in the brake pedal during normal braking. There was no "spongy" feel to it and the pedal never hit the floor, just the extra travel. My Impala's brakes are regular hydraulic but not power-assist, which means the master cylinder has only one reservoir for all the fluid and that my emergency/parking brake had better be in working order in an actual emergency.
Upon returning home I backed the car into the garage without incident and the brakes did not fail. I made a mental note to check the fluid level before taking her out again. So, a couple of weeks later I was preparing to take her out again on a bright sunny day, remembering to check the brake fluid level first. When I popped off the master cylinder cap and looked inside it was bone dry! That's when I started wondering; is it possible to have a small enough leak somewhere in the brake system, perhaps at one of the wheel cylinders, that will let out just enough fluid but not suck back in too much air during low speed braking? Thereby avoiding complete brake failure because no air bubbles make it all the way back to the master cylinder?

Your brake system's condition is not due to any systemic design flaw that requires part/system changes. It's due to lack of proper maintenance/attention. The system gives 'notice' of problem(s), typically thru the feel of the pedal, grabbing/pulling to one side, and/or 'puddles' of fluid . Waiting for symptoms to occur to inspect the brakes is not something I would do.

Even with no sign of problem, I check the fluid when I check the oil. I pull a drum (a different one each time) about every six months as part of a periodic brake system check. I did that back in the '60s and have continued the process with my current '63.

Such a routine is recommended regardless of the master cylinder. Surprisingly losing approx 60% (if front brakes fail in a dual system) of braking capacity and relying on the remaining 40% is quit risky.

Is having 40% better than what the mechanical brake supplies? Likely yes (I never did any sort of test). But performing proper periodic preventive maintenance has proven (by all the safe miles driven prior to 1967) to provide safe driving.

I'm NOT anti dual master cylinder; just PRO preventive maintenance.

To the specific question:

"... is it possible to have a small enough leak somewhere in the brake system, perhaps at one of the wheel cylinders, that will let out just enough fluid but not suck back in too much air during low speed braking? Thereby avoiding complete brake failure because no air bubbles make it all the way back to the master cylinder?"

Yes. The seals and springs within the wheel cylinders can 'leak' as they begin to fail. Also, within the master cylinder there is a check valve that keeps some pressure on the wheel cylinders to help maintain the 'seal'. Dirt and other contaminants can cause 'leaks' and changing fluid periodically is essential.

Pete
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