New master cylinder wont work??

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zcook13

zcook13

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Brazil, Indiana
Need some help again.. I have a 70 dart with drum all the way around. Manual brakes also. My old master cylinder was bad so I went down to Napa and got a new one. Wasn't a reman. Took it home and bench bleed it and it worked perfect. Put the new master cylinder on the car and now I'm only getting fluid out the rear reservoir, which is to the front brakes, the pedal sags and now the brakes lights stay on all the time. Has anyone ever had or heard of this problem? :banghead:
 
I was having gremlin in my master cylinder. I placed it on the bench and operated it manually until I could get it flowing properly. I used a can of brake cleaner and put the tube into the ports and used that to clean out the gunk.

I ended up having to replace everything between the master cylinder and the wheel cylinders. It was scary how tight I had to make every connection so the tubes would "crush" to make a good seal.
 
Well being a new master cylinder it shouldn't have the problem of being dirty or rusted. but I could try that on the old one and put it back on the car and see if it starts working again?
 
I had ordered a new cylinder and took the old one in as a core. The cylinder they had was wrong. As I was standing there I forced the plunger down and it spit out everything gumming it up. Made quite a mess, also.
So I took it home and cleaned it as I stated above.
I think my problem was severely corroded lines inside and out. So I R/R'ed them
 
Did you bleed it when you put it on the car?

If the master cylinder installs in the car at an angle, it must be straight to bleed correctly on the car or you'll never get all the air out. You will need to jack up the rear to level the master cylinder out if it is not level.
 
If you are bleeding it on the car by pumping the pedal, you will have to lift the pedal back up after every pump, to expose the compensating port ,so that fluid can exit the m/c and enter the lines
 
I've surprised myself, thinking I had an adequate "bench" bleed, when installed on car had same symptoms you describe. Took MC off and re-bench bled and could tell the difference the second time around!

Do you get any out of the wheel cylinders by gravity bleeding?

Also, just because it came out of a box doesn't mean it is immune to failure..
 
The correct way is to bench bleed. Put it on the car. Put the lines on. Then get someone in the car to press the pedal down and hold it. Break the lines loose to bleed the air out, close the lines and repeat. Do NOT let the person in the car lift the pedal until the lines are closed after each SINGLE pump. It will not take long at all doing it this way.
 
I would check the rubber line connection at the rear axle. They can collapse/restrict with age and still look good from the outside. I had a friend with the same problem. Replaced, fixed!
 
If you have done no other brake work on the car and are replacing ONLY the master cylinder, it is not necessary to bleed the entire system. The air is RIGHT AT the master cylinder in the lines. All you have to do is bleed like I described and you will get all the air out. There is no need to bleed anything else.
 
Rusty's posts,both dead on.Small details, make all the difference.
 
Rusty is correct. But, if you haven't refreshed the brake fluid in 3 years, you should flush thru new fluid anyway since glycol absorbs moisture and rusts the innards once it absorbs too much. Oops, make that every 2 years since you live in IN. You can go a little longer if you use DOT 4, or forever if you use DOT 5 (silicone) like me.
 
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