Brake pedal suddenly dropped very low

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kavesh
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Brake pedal suddenly dropped very low

Post by kavesh » Sun 08 Jan 2017, 09:43

Hi guys. 2 days ago I replaced the plungers on my rear brake cylinders. (1972 chev el camino). Bled the system from furthest wheel to the master first reaching the closest last. Brake pedal was hard and brakes were good. Took my el Camino for a short 20km drive this morning and after about 10km I noticed that my brake pedal was very low and braking effectiveness was really poor. Drove home slowly and checked the master cylinder for fluid loss but it's full.
Do you think there is air in the system or the master cylinder plungers have now gone bad. Should I try to rebleed first in case there is air in the system or is that a waste of time? (The pedal is not all the way to the floor)

Thanks in advance.
Kavesh

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RASSIE
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Re: Brake pedal suddenly dropped very low

Post by RASSIE » Sun 08 Jan 2017, 09:47

Re-bleed and look for a rusted brake pipe.
Rassie.
http://www.rassiesauto.co.za/
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kavesh
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Re: Brake pedal suddenly dropped very low

Post by kavesh » Mon 09 Jan 2017, 19:39

I tried to rebleed the system today. The wheels bled fine, however the front wheels proved impossible. With a helper pumping the brakes and me opening the bleeding nipple I found that very little fluid came out the nipple and the brake pedal did not move further to the floorboard. This was the same for both front wheels.

I went back to one of the rear wheels and rebled just to see what is going on and the rear was fine with the pedal going to the floor when the nipple was opened.

I was now convinced that the front line is blocked up. So to confirm that I removed the line from the master and was expecting to see fluid come out that opening when the pedal is depressed but there was nothing.

So my assumption is that there is a problem with the master so I removed it and stripped it down, hoping to find a blockage. There was a bit of a grease like substance inside but I don't think that it would cause a complete blockage.

Am I doing the correct thing or is there something that I missed along the way and removed the master in error.

In any event I have taken the opportunity to remove the brake proportioning valve to give it a clean and make replace the seals in there.

Would appreciate your advice as always.

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RASSIE
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Re: Brake pedal suddenly dropped very low

Post by RASSIE » Tue 10 Jan 2017, 07:39

Test them separate. First put the front plunger with brake fluid and push with a screwdriver. Then fit the second plunger and test again. This is a fast way to find the problem.
The front rubber pipes also like to collapse on the inside.
Rassie.
http://www.rassiesauto.co.za/
“Cowboys do not ride donkeys”
“I will die driving a V8”

Doug Hirkham
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Re: Brake pedal suddenly dropped very low

Post by Doug Hirkham » Wed 11 Jan 2017, 14:35

Hi Kavesh - to isolate the problem, same old story. Put a vice grip on each rubber brake pipe and nip it closed. If your master cylinder is okay your pedal will be rock hard, and right at the top. Whilst sitting behind the wheel with your foot on the pedal get someone to remove the vice grips, one at a time. Your problem wheel/s will show when the pedal drops.

Good luck,

Doug

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kavesh
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Re: Brake pedal suddenly dropped very low

Post by kavesh » Wed 11 Jan 2017, 19:00

Thanks for all the advice thus far.

The lack of braking while on the road has scared me a little. So forgive me for seeming a little paranoid now. So I am into a major job on the brakes. This is what I am doing and you are welcome to tell me if I should be doing something else as well.

1. Stripped master cylinder and had it assessed. Bore is fine and is sporting a shiny stainless steel tube. (Previous owner did that). Brake shop said a new kit in there and should be as good as new.
2. Removed and stripped the proportioning valve. Found the spring and shaft was stuck inside. Removed and cleaned and found 2 new O rings rubbers for it. Does move a lot more freely now.
3. Today after a bit of googling I decided that it was time to replace the rubber hoses on the brake lines. I suspect 2 of he 3 are the original flex hoses. I called around town today and the hydraulic places say that they can make it up while I wait. I asked about the quality of the hose and they all say they use standard brake hoses. Hopefully it's good quality

I am happy with the steel brake lines as they do not show any sign of rust anywhere.

The rear cylinder cup seals have been replaced recently.

Is there anything else that I should be doing?

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Johann65
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Re: Brake pedal suddenly dropped very low

Post by Johann65 » Sun 15 Jan 2017, 20:51

Hullo Kavesh,
The proportioning valve appears to be the root cause!
I must do the same on my Opel as the rear brakes needs to be set softer than the front brakes!
Pressure too high! I must however state that my brakes are deadly! :mrgreen:
I have a proportioning unit I received from Ridgeback!
Johann
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kavesh
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Re: Brake pedal suddenly dropped very low

Post by kavesh » Sat 21 Jan 2017, 09:05

Johann65 wrote:Hullo Kavesh,
The proportioning valve appears to be the root cause!
I must do the same on my Opel as the rear brakes needs to be set softer than the front brakes!
Pressure too high! I must however state that my brakes are deadly! :mrgreen:
I have a proportioning unit I received from Ridgeback!
Johann
Hi Johann

Hope you sort out your rear brakes.

Today I will bleed my brakes and hopefully report that all is good again. (Bench bled the master during the week)

Doug Hirkham
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Re: Brake pedal suddenly dropped very low

Post by Doug Hirkham » Sat 21 Jan 2017, 10:34

Extremely important that you bleed at the pipes on the master as you tighten the fittings, otherwise you trap some air.

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kavesh
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Re: Brake pedal suddenly dropped very low

Post by kavesh » Mon 23 Jan 2017, 10:01

Brakes sorted. :D
As it turned out the problem was in the master cylinder. I little washer was in the wrong place. I have no idea how the brakes worked for 5 years before like that.
While bleeding the system after assembly the front wheels lost all braking. After stripping the master and consulting with Doug, he advised what the problem was.

A big thank you to Doug for his kind advice and help on the phone.
Attachments
IMG_1551.JPG
The washer should not have been at the end near the big nut. Once the piston shaft went through the opening in the washer the front spring remained compressed
IMG_1551.JPG (41.26 KiB) Viewed 1704 times
IMG_1563.JPG
This little washer caused the master to malfunction. Was located in the wrong place
IMG_1563.JPG (20.8 KiB) Viewed 1704 times
Last edited by kavesh on Mon 23 Jan 2017, 14:45, edited 2 times in total.

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