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Old December 26th, 2009, 11:54 AM   #1
1965aaron
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Default foaming brake lines??
Re:: when i bleed it   

ok so for the longest tiime, ive had a hell of a time trying to get good pressure in my brakes.
i bleed and bleed, and i get pressure for about a day, and then its out again.

so ive been at college, and i come back and am getting the bug ready to drive around while im here, and im bleeding the brakes and everything is good until i get to the driverside front. and i start getting almost a foam while bleeding.
just tons and tons of tiny bubbles.
i got most of them out, but there were still a couple really small ones. but i was fed up and decided to call it good.
i had pressure and i drove all over town. the next day i get in and drive a block and the brakes lose allpressure again.

could it be a bad line?

i replaced all the rubber lines when i first got it 2 years ago

help please
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Old December 26th, 2009, 12:01 PM   #2
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Default Re: foaming break lines??

the "foam" is air. go back and check all your connections. youre getting a slow air leak in the line somewhere. theres probably a loose fitting between the m/c and wheel cylinder on that corner of the car.
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Old December 26th, 2009, 12:11 PM   #3
1965aaron
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Default Re: foaming break lines??

k ill check that

is there anything i could put on the treads to tighten them up?
like plumbers tape?
[but not plumbers tape cause that would get fried]
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Old December 26th, 2009, 05:22 PM   #4
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Default Re: foaming break lines??

Quote:
Originally Posted by 1965aaron View Post
k ill check that

is there anything i could put on the treads to tighten them up?
like plumbers tape?
[but not plumbers tape cause that would get fried]

VW brake lines should have a bell on the ends. When they are tightened into the fittings, that is what seals the system. Putting anything on the threads, would not help.

Sounds like you have a loose connection, or a bad line.

My 2 cents
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Old December 26th, 2009, 05:41 PM   #5
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Default Re: foaming break lines??

check the rubber line between the reservoir and master cylinder
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Old December 27th, 2009, 12:00 AM   #6
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Default Re: foaming break lines??

if it was the line between the cylinder and reservoir, wouldnt all the lines have air?
cause only the one does


also. i just rememvered that i replaced the brake cylinder on that drum... could it be a garbage one??
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Old December 30th, 2009, 06:57 AM   #7
38Chevy454
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Default Re: foaming break lines??

You might be sucking air back in the wheel cyl. You may need a residual pressure valve, drum brakes use 10 lbs. What they do is keep 10 psi pressure so the wheel cyl cups stay flexed against the wall preventing air from entering.
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Old January 2nd, 2010, 02:42 AM   #8
1965aaron
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Default Re: foaming break lines??

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Originally Posted by 38Chevy454 View Post
You might be sucking air back in the wheel cyl. You may need a residual pressure valve, drum brakes use 10 lbs. What they do is keep 10 psi pressure so the wheel cyl cups stay flexed against the wall preventing air from entering.

wait what?

more info on this please.
never heard of putting a pressure valve in the brake lines.
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Old January 2nd, 2010, 04:01 AM   #9
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Default Re: foaming break lines??

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Originally Posted by 1965aaron View Post
wait what?

more info on this please.
never heard of putting a pressure valve in the brake lines.
that really shouldnt be a problem if youre using the correct stock parts. the valves are built into the master cylinder. if you were using an aftermarket master cylinder (like a wilwood or something) then it would be something to consider.

did you find your leak yet?
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Old January 2nd, 2010, 11:00 AM   #10
38Chevy454
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Default Re: foaming break lines??

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Originally Posted by 1965aaron View Post
wait what?

more info on this please.
never heard of putting a pressure valve in the brake lines.
Yes, a stock M/C has it built into the outlet port. I should have put better description. Here is the theory behind what I said.

If your M/C is below the wheel cyl, then gravity can cause the fluid to suck back towards the M/C. Remember that wheel cyl have the cups so they press outward when pressure from the fluid is against them. If they have no real small residual pressure in the lines, it can suck down by gravity, and the cups allow air to get in. The small 10 psi in the lines is overcome by the brake return springs so your brakes don't drag, but is enough to force the cup lips against the side and prevent sucking back.

A residual pressure valve can fail, or if a non-stock M/C it may not have one. Drum brakes use 10 psi and disc brakes use 2 psi. Almost all brake systems have the RPV, even if the M/C is above the wheel cyl, to help from any air entering the wheel cyl when you let off the brake pedal. It is just more of a potential problem when the M/C is lower then the wheel cyl.

Does the extra explanation help?
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