Master cylinder leaking

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6pkScamp

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I upgraded master cyl. to an 80's truck when I changed to disc brakes. Now when you drive the car it pushes fluid out thru the breather hole in the caps. Never had this happen before. Am I missing something?

Help
 
I recall reading of a similar complaint some months ago, but I forgot the answer. It could be as simple as the rod adjustment. Do you have a booster?
 
If you've still got air in the brakes,, it can cause a violent return of fluid to the reservoir when you release the brakes..

To check for air, set the emergency, and with the M/C cap on,, have someone pump the brakes twice,, and hold,, remove the M/C cover,, and have the brakes released..
If you have a fountain of fluid returned,, that's trapped compressed air "springing" fluid back at you.., and that system needs more bleeding..

Brake fluid is excellent paint remover,, avoid getting any on the paint,, if you do,, rinse with lotsa water IMMEDIATELY..

hope it helps
 
If you've still got air in the brakes,, it can couse a violent return of fluid to the reservoir when you release the brakes..

To check for air, set the emergency, and with the M/C cap on,, have someone pump the brakes twice,, and hold,, remove the M/C cover,, and have the brakes released..
If you have a fountain of fluid returned,, that's trapped compressed air "springing" fluid back at you.., and that system needs more bleeding..

Brake fluid is excellent paint remover,, avoid getting any on the paint,, if you do,, rinse with lotsa water IMMEDIATELY..

hope it helps

Got a good stiff pedal, I don't think there is air in the system. At this point I'll try anything. I was wondering if the bore was to large for the system...
 
Got a good stiff pedal, I don't think there is air in the system. At this point I'll try anything. I was wondering if the bore was to large for the system...

My mentor taught me the difference between "thinking" you got all the air out,, and "knowing" you got all the air out,, is that test.... lol

On my first brake job as apprentice,, while bleeding, he asked me if I knew how to tell if all the air was out.. He took me to 3 vehicles parked on the lot and pumped the brakes, had me remove the cover and watch, very little fluid movement on release.. We went back and did test to car I was working on,.. lol,, had about a 3 inch fountain,, and I "knew".....

That was the final test on every brake job..

We'd find air in cars that never lost fluid...

I've passed that on to all my apprentices, and everyone who worked for me..

hope it helps
 
My mentor taught me the difference between "thinking" you got all the air out,, and "knowing" you got all the air out,, is that test.... lol

On my first brake job as apprentice,, while bleeding, he asked me if I knew how to tell if all the air was out.. He took me to 3 vehicles parked on the lot and pumped the brakes, had me remove the cover and watch, very little fluid movement on release.. We went back and did test to car I was working on,.. lol,, had about a 3 inch fountain,, and I "knew".....

That was the final test on every brake job..

We'd find air in cars that never lost fluid...

I've passed that on to all my apprentices, and everyone who worked for me..

hope it helps

I performed the test that you described. I saw very little movement in the front part of the master cylinder and none in the back. I had the wife push on the brake pedal with both caps off the master cylinder and as she was depressing the pedal I saw an eruption of brake fluid splashing up
 
That's why you pump it with the cap on,, but if you had little to no return,, then you "know" it's not air,,
 
I upgraded master cyl. to an 80's truck when I changed to disc brakes. Now when you drive the car it pushes fluid out thru the breather hole in the caps. Never had this happen before. Am I missing something?

Help
mine does same. I replaced the caps this year and leaking was gone for a couple months, but now is leaking again. the plastic caps don't fit right. if their was a metal cap available I think it would fix our issue.
 
mine does same. I replaced the caps this year and leaking was gone for a couple months, but now is leaking again. the plastic caps don't fit right. if their was a metal cap available I think it would fix our issue.

Blue, for what it's worth. I did a little reading and found a forum that mentioned that if the piston is to far out on the stroke, the initial push causes a flood to the reservoir. I toyed with mine a bit and so far no more leak
 
... if the piston is to far out on the stroke, the initial push causes a flood to the reservoir....
That is what I was thinking when I mentioned the rod adjustment. I think the way the MC works is that with the piston back, it exposes a side feed hole for the cylinder. As the piston strokes forward, it soon closes the feed hole, allowing pressure to build up in the cylinder. Until the feed hole is passed, the fluid would be squirting up into the reservoir. I don't think there are check valves in an MC (other than "residual valve" on outlet of old drum MC's). However, I don't think you can adjust how far back the piston retracts in a manual MC, since it stops against the retainer. If you are using a power MC in a manual brake application, the piston might retract too far.
 
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