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Brake Bleeing/ Master Cylinder issue?

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6 June 2005
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Location
Farmington Hills, MI
Brake Bleeding/ Master Cylinder issue?

So, I wanted to put Motul brake fluid into my car a few weeks ago. I bled all the old fluid out and the new in. I emptied the ABS as well and put new fluid in it. I've now bled the whole system 3 times. Once with a hand pump, once with 2 person system and last night I installed speed bleeders. I still have intermittent issues with the pedal going to the floor. Sometimes the pedal will feel really nice and hard as a rock and then the next time it will just slowly go to the floor.
Seems like from what I have searched that this is the Master dying, but it just seems strange that it happened at the same time as I bled the system as it wasn't doing this before. Do I need to bleed the ABS system? Would exersizing the solenoids be any help? Any other ideas?
I've bled the brakes on at least a dozen cars before and never have run into this.
Any thoughts?
 
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If you bled it with the two person method and the person stepping on the brake pedal pushes down more than the normal amount (since there is no pressure and this is very likely) than it is pushing the rod more than the normal travel and if the seals are week can make it worse. When I do a 2 person bleed, I specifically tell the person only to push 1/2 way.

Not saying this is the cause, but it might have been a contributing factor to why the master now is going out.
 
If you bled it with the two person method and the person stepping on the brake pedal pushes down more than the normal amount (since there is no pressure and this is very likely) than it is pushing the rod more than the normal travel and if the seals are week can make it worse. When I do a 2 person bleed, I specifically tell the person only to push 1/2 way.

Not saying this is the cause, but it might have been a contributing factor to why the master now is going out.

Thanks Capt'n. That makes a lot of sense. Before we did the 2 person method, the pedal didn't go all the way down like it does now, it just felt spongey.
Just ordered a new master.
 
If you bled it with the two person method and the person stepping on the brake pedal pushes down more than the normal :wink:amount (since there is no pressure and this is very likely) than it is pushing the :wink:rod more than the normal travel and if the seals are week can make it worse. When I do a 2 person bleed, I specifically tell the person only to push 1/2 way.

Not saying this is the cause, but it might have been a contributing factor to why the master now is going out.

Some things never change, when I was taught how to bleed brakes along time ago you had to put a piece of 2x4 under the brake pedal to restrict its movement on a used master cyl. Very few mechanics followed this and a few months later the car needed a master cylinder
 
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Some things never change, when I was taught how to bleed brakes along time ago you had to put a piece of 2x4 under the brake pedal to restrict its movement on a used master cyl. Very few mechanics followed this and a few months later the car needed a master cylinder

A couple of things... the pedal going to the end of the travel can damage a Master. This is a possibility.
changing brake fluid can have an effect. I have had this happen. The new fluid may have had an effect on the old rubber in the master. (compatibility issue)

either way. Replace the master.
 
I bought a Vacula vacuum bleeder about 12 years ago. Great tool. You don't need a second person as you never touch the pedal. They work on stubborn bleeds and make change out easy. They simply suck the fluid in and bubbles out. I just did a TM van. I did however still bench bleed the master and then again on the car briefly with a partner on the pedal. Then used the vacula for the wheels.
 
Some things never change, when I was taught how to bleed brakes along time ago you had to put a piece of 2x4 under the brake pedal to restrict its movement on a used master cyl. Very few mechanics followed this and a few months later the car needed a master cylinder

Completely agree, and I used to use the wood block method. Now I have a Vacula, full vacuum bleeding system that pulls the fluid from the bleeder valve, no movement of the pedal at all. The trick is to VERY lightly press on the brake pedal a few times after completion to make sure it will not go too far, and cause the same issue as pumping it up/down.

Regards,
LarryB
 
FYI, I changed the master. The pedal going to the floor has gone away. However, the pedal still feels a little spongy. I've bled the heck out of the system. Would the ABS need to be bled as well in this situation?
 
The ABS should not be an issue. I"m wondering if you bled the master. There are videos on line on how to do this, but you will need to remove the outlet lines, make up two 2" or so stubs of brake line with one fitting only, screw these into the outlets, put vinyl hoses on these looping the end of the hoses into the full reservoir of the master. Pump the pedal slowly about twenty times keeping the reservior full. When you pull the temp lines off, get the standard lines on quickly not letting the master drain down.

Thats the fullproof method. Often you can simply have a person work pedal and only loosen the outlet fittings one by one bleeding the master. I just did a toyota and i had to do the temp fittings method. FWI most do this master bleed on the "bench" but i don't see why you couldn't do it on the car.
 
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