Why is brake fluid puking out the resevoir cap??

[68basket]

I put this truck together and have been driving it for 4 months. Put about 3000 miles on it and today the brake pedal went to the floor. The front resevoir was empty so i filled it and reinstalled the cap. checked and no leaks at lines, hoses, or calipers. Pump the brakes and fluid leaks out around the resevoir cap. why does it spit out and how did it run it dry? this is the setup i have, should i ditch it and buy a whole cpp unit?

http://www.ebay.com/itm/1967-1972-ch...0c5284&vxp=mtr

[Willys47]

check the brake drums the cylinders may have faild

[68basket]

There are no leaks, and the reservoir for the rear brakes was still full. I have worked on cars for a long time and never seen one spit all the fluid out of the cap

[mgchevyparts]

The cap is vented, 1 or 2 little holes, probably at the bail wire passage thru the metal cap. Check if they're plugged. Or the cap is a loose fit. You can bend the L tang slightly to tighten the cap

[litew8]

Sounds like you are positive there are no leaks, anywhere. How did bleeding the lines go after you installed? Did you remember to bleed the MC too?

[68basket]

the brakes bleed out fine, there are no leaks anywhere else. I guess i need to try to bend the cap or the hold downs to get it to fit tighter. The seal on the cap looks ok. After bleeding the brakes and putting the cap back on when i pump the pedal it pushes fluid out of the cap.

[Steeveedee]

You need to bleed the brakes, there is air in the lines. Then you need to check for where the leak is, even if you don't believe you have one. If you have front drums, you for sure have a leak. If you have disc brakes, it is possible that the pads are so worn that the cylinder got that low. If you don't see fluid leaks at the flexible brake lines or wheel cylinders, pull the master away from the booster and see if there is fluid leaking out the back of the master.

[leddzepp]

Lightly sanding the mating surface of the master cylinder has worked for me in the past when I had this same problem. If not perfectly smooth they will leak.

[litew8]

You keep saying the 'brakes' bled out fine. Did you bleed the master cylinder?

[68basket]

I bleed out of the calipers and wheel cylinders till there was no air coming out. ALso i just built the truck. Literally every brake component was new in 2013, hoses, calipers, wheel cylinders, master, prop valve, booster. I have driven approx 3000 miles with no problems untill today. I will mess with it tomorrow to try to get the cap to seal, i think that is my main problem.

[imjeff]

Since ran the master down you should probably bleed it. I believe that is what 68 (Mr. Basket?) is asking.

Jeff

[litew8]

You MUST bleed a new Master Cylinder. That could possibly (?) be causing your issue (I've never not bled a new master cylinder so I don't know first hand). Air in the Master Cylinder finally displaced (or escaped) and your pedal hits the floor. After bleeding the Master Cylinder, you'll need to go back and re-bleed the lines again. Since you've already got the Master Cylinder and booster installed on the truck, no need to remove it. Remove the lines and bleed the master cylinder as shown in this video - only you'll use your brake pedal instead. It'd help if you had another person. The process shown in this video applies.

Bleeding the New Master Cylinder - YouTube

[truckdude239]

I dont bench bled mine anymore specialy since the last one i bought didnot come with plugs or bleeders bled mine o the truck no issuses.


Is it oppable the master cylinder has a leak internally you push brakes it blews fuild out the oother chamber

[truckdude239]

I dont bench bled mine anymore specialy since the last one i bought didnot come with plugs or bleeders bled mine o the truck no issuses.


Is it oppable the master cylinder has a leak internally you push brakes it blews fuild out the oother chamber

[litew8]

Either way, if he didn't bleed the master cylinder it needs to be done (always for new, and or if it emptied). The master cylinder itself could be defective, but he needs to bleed it, then all four wheels before being able to determine if the master cylinder is faulty. To the OP, buying a new master cylinder, think about it - there's no fluid - just air all up in it, which needs removed before installing. Not doing so will allow pockets of air to remain in the chamber. The video mentions it briefly - what happens when it isn't removed.

[midniteblues]

heres my 2 cents
i think with that much air in the lines would've been noticed right away not 4 months 3k mi. later.
air bubbles allways travel up unless forced down. 3k mi. bounceing down the road any air would've made it up too the mc and the rubber in the cap would displace the escaped air in the system.

i would fill the master and bleed the entire system and be positive there is no leaks ANYWHERE!(if its non power be sure too check in the cab behind the pedal).

if there is no leaks...
i would replace the master and be absolutely sure the brake push rod is adjusted too the proper length. it could be a lil' long and pushing the piston a lil' too far over the past few months eventually blowing or hanging up the last in line seal on the piston hence the reason fluid is presureizeing the resivior instead of the lines.

also be sure the valve on the prop valve is centered

again just my 2 cents

[litew8]

Bleeding the lines and bleeding the master cylinder are two different things. The master cylinder will not be bled properly by be bleeding the lines only. The air is trapped differently in the master cylinder and needs to be removed separately but first. This is a safety issue (having brakes working properly) so standard installation procedures must be followed. Luckily the brakes didn't go out while driving and cause harm to you or someone else.

[68shortfleet]

Your wasting your time bleeding that master cylinder. It has failed internally and is bypassing from one reservoir to the other. The obvious sign of this is one empty reservoir and the other is overflowing. No amount of bleeding will ever cause the reservoir to overflow.

Replacing that master cylinder with a quality and properly bench bleed unit is going to save you a lot of time and brake fluid.

[litew8]

Overflowing? Where'd you read that

[oldcane]

Where did you NOT read that? That's what this thread is about.

[litew8]

crap, my bad wrong thread

[oldcane]

I had to laugh. That sounds so much like something I would do.

[litew8]

Any update on this?

[oily]

68shortfleet has it right I think.
"The obvious sign of this is one empty reservoir and the other is overflowing.
It has failed internally and is bypassing from one reservoir to the other. "

[BLT gmc]

If these are vacuum assisted power brakes, the reservoir went dry with no obviuos leak, and now it is puking fluid. I would strongly look at the vac container. I suspect it has a hole internally, hence the loss of fluid with no leak. And now that you have put more fluid in it when you press on the brakes it pukes out the master cylinder. Bruce