Suspected brake master issue

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cbez
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Re: Suspected brake master issue

Post by cbez »

An all 4 corners + master bleed is in the works tomorrow. I'll see if I can recruit someone to watch for bubbles.

I wonder how much air you would need in the system to really need 4+ full pumps to pressurize it though. Seems like it would take a lot (and therefore I would have a big leak somewhere that didn't want to hold pressure in the first place).
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Re: Suspected brake master issue

Post by JT68 »

cbez wrote: Sat Nov 27, 2021 7:46 pm I wonder how much air you would need in the system to really need 4+ full pumps to pressurize it though. Seems like it would take a lot (and therefore I would have a big leak somewhere that didn't want to hold pressure in the first place).
it only takes a bubble-air is highly compressible right?.

Bleed the master first, a lot, and pump the pedal very SLOWLY always.

I don't remember if you have speed bleeders or not, but if ANY air gets past the threads, you will never get the system fully bled.

You may need to use the old method:

open bleed screw, depress pedal SLOWLY to floor, close bleed screw, return pedal SLOWLY, repeat

If the master ever gets too low and takes in a gulp of air, start over.
If you ever return the pedal with the bleeder open, start over.
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Re: Suspected brake master issue

Post by redroadster »

Aaahhhh thats your brake master cyl in the picture ?
a single cyl , what year spl ?
I would definitely go to a double cyl mc system
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Re: Suspected brake master issue

Post by DAC21 »

redroadster wrote: Sat Nov 27, 2021 9:11 pm Aaahhhh thats your brake master cyl in the picture ?
a single cyl , what year spl ?
I would definitely go to a double cyl mc system

Major undertaking to modify the firewall to accommodate a dual MC.
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Re: Suspected brake master issue

Post by Curtis »

redroadster wrote: Sat Nov 27, 2021 9:11 pm Aaahhhh thats your brake master cyl in the picture ?
a single cyl , what year spl ?
I would definitely go to a double cyl mc system
He could but it requires the following.

Get a brake pocket from another car.
Cut up firewall to install pocket.
Change brake lines and put in split manifold.
Put in electric brake switch and change wiring.
And probably other stuff I wouldn't know about.

Ask Spreadbury how much work it is. I'd like a double master but I'm not qualified to do that much work.
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Re: Suspected brake master issue

Post by JT68 »

redroadster wrote: Sat Nov 27, 2021 9:11 pm Aaahhhh thats your brake master cyl in the picture ?
a single cyl , what year spl ?
I would definitely go to a double cyl mc system
Probably would not be the first choice....
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Re: Suspected brake master issue

Post by redroadster »

Bypass the brake safety swt. with a double cyl its kinda a 1950s thing
+ Never going to work with dot 5
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Re: Suspected brake master issue

Post by JT68 »

Not sure what is being suggested above….the tandem master won’t fit the firewall of a 63-67 car…the master would be in the AF/carburetors unless you do a massive firewall modification- not recommended and certainly not necessary.

There is no differential brake pressure switch in a 63-67. Only a simple brake light switch, so again no modification is necessary.

65-67 disc brake cars stop just as well or better than later tandem master cars, again no firewall or master modification is needed(or desirable)

Dot5 fluid will work fine in any roadster if the system doesn’t have dot3-4 in the lines. It just requires more/careful/extensive bleeding.

Plenty of cars are running dot5 with no issues-it's not the fluid. Dot5 has been around for decades, if it didn't work, it would have been recalled and discontinued years ago. Thousands of auto restorations use it to avoid damage to expensive paint.
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Re: Suspected brake master issue

Post by C.Costine »

I love my DOT 5 fluid in my '67! Installed three years ago after flushing the old DOT four through. No way I was putting old DOT 4 on my new paint! I like it mainly though because I hate water and rust in my wheel cylinders. I topped my clutch cylinder off last spring after finding out that four and five are compatible. Four thousand miles since then with no issues. I also really like the purple color, LOL!!!
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Re: Suspected brake master issue

Post by Curtis »

I have dot 5 in mine because of the new paint. Took a couple times bleeding it with speed bleeders.
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Re: Suspected brake master issue

Post by spyder »

Dot 5 since the mid ninetys.............always worked fine.

viewtopic.php?p=16111&hilit=dot#p16111
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Re: Suspected brake master issue

Post by GeoffM »

Pretty sure most of us already know the drawback to DOT 5 is that it's hydrophobic and also lighter than water, meaning any moisture that gets into your brake system condenses into water and settles in the low points like your calipers and wheel cylinders, where corrosion can occur if not bled regularly.

DOT 3 and DOT4 are hydroscopic, which means it absorbs moisture, but the moisture stays widely dispersed. That can also cause general corrosion if not bled regularly
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Re: Suspected brake master issue

Post by redroadster »

Someone fo a test
In a jar 5 tabledpoons dot 5 & half a spoon of dot 3, heat to 130-140 degrees for a hour lets see , really need to do it 2 or 3 times
mine in the new mc and slave cyl took 3 weeks to have a problem. Then it was cooked
My 123gt had a single cyl mc but still a 2 sided safety swt. ... which cant be emptied or cleaned out ...if you say it can, explain the operation in detail ,how it comes new
Id do the clutch system and see how it performs
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cbez
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Re: Suspected brake master issue

Post by cbez »

the 66 switch is literally just a brass union with a switch that screws on top. mine had the lines off and acid dipped, calipers rebuilt, new rear pistons and a nos master used. if any dot 3 survived all that it earned the right to stay there lol.

sorry no update been under the weather and didn't bleed them.
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cbez
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Re: Suspected brake master issue

Post by cbez »

Bled a bunch through the master (couple tiny bubbles) and all 4 sides (couldn't see cuz doing it solo). Next morning, two pumps to get firm again.

I tried bleeding the master more at various angles (up driveway, down driveway, various corners lifted). Still just solid brake fluid.

I tried this morning (to coincide with a soft pedal) and got some more very small bubbles. Current working theory is air in or near the master that collects overnight /at cold temps to a spot where I can get some out.

So I guess I will just keep bleeding it in the morning to see how it behaves.
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