leaking master cylinder, what's the deal?

[MartyG]

I've been dealing with this for about 6 months and trying to figure out what this might bethis is my daily driver around town and I generally have to fill up the front reservoir every 5 days
I'm seeing fluid around the outside and underneath the master cylinder and I'm wondering if it's just the cap or too much pressure from the brake booster
the cap is in perfect shape and seems to be making a good seal but I don't know

anyone ever had this?

 

[Yeller]

And I thought I was all alone. the cap is probably tweeked a little in the front. After messing with mine for about a month trying to get it to seal I bought a reman master cylinder and just changed the cap and retainer. Been fine ever since.

 

[Apogee]

...I'm wondering if it's just the cap or too much pressure from the brake booster
the cap is in perfect shape and seems to be making a good seal but I don't know

anyone ever had this?

There shouldn't be any pressure in the reservoirs, only a squirt of fluid from the compensator ports when the brakes are applied. Pressure is on the output port side only. My guess is your cap isn't sealing properly. You can bend your bale to be tighter, however some MC's just seem to leak.

 

[Rustytruck]

Pull the cap off and look at the print of the casting on the gaskit. there should be a visual sign if the top is sealing properly. Are you filling the master cylinder properly? there should be about a 1/4" from the brake fluid to the lowest point of the casting. When you apply the brakes the fluid swells a little. If you remove the cap and press the brake the fluid should rise a little if it spurts like a fountain you have either air in the lines or a mastercylinder bypassing.

 

[MartyG]

Will do, thanks Rusty

 

[gtnorga]

I've read the cap is a common problem. Try a big hose clamp arount the peaks. That cured mine.

 

[BRONCONY]

I had one like that too and always leaking. Bought a new one and didn't help. Just cut one gasket and doubled them up. Stopped leaking for now.

 

[TwoDalesDad]

I used a couple Zip Ties around the MC and Cap....seemed to work....a hassle to add to though..

 

[surfer-b]

Like stated above the cap is tweaked, or bad casting in the reservoir. Look at the top of the master cylinder, where it seals, and make sure there are no ridges or burrs in the casting, I have seen this before causing it to leak.

 

[pcf_mark]

I used the hose clamp method too. I used several new and used caps no luck. Try the hose clamps - worth a try.

I have hydroboost that I think aggravated the problem.

 

[chuck]

The bad cap should not cause the res. to go empty. Low maybe, check the rear wheel cylinders for leaking. Some info you might already know. Brake fluid attracts water, water makes rust that makes more leak which attracts more water that causes more rust etc, etc. So everythime you remove the cap you need to wipe the cap and M/C. If you have rust remove it and see if that fixed the leak. Putting more pressure on the cap might fix the problem for now but the rust is still building and if the water gets in it will also get into the lines and cylinders. That (rust) is the main reason for M/C and wheel cyliners to fail. IMO

 

[bronconut73]

I've struggled with the leaking cap issue as well. One day I was fed up. I profiled the top edge of the mc with a file while it was up side down in a vice. I then removed the bail and bent it very evenly into a tighter fitting position. Finally I cleaned up the seal to be sure there were no irregularities in it's surface.
It has been leak free for years after that effort.

But having said all that if you don't notice it obviously leaking down the side of the mc and taking paint off of your fenderwell and frame then maybe you better follow Chucks advice. Having to re-fill that front reservoir every five days would have alot of brake fluid all over your fender and frame.
Check those rear wheel cylinders thoroughly.

 

[BCH BRCO]

On both of my Broncos with the power brake conversion I had problems with fluid leaking out from under the cap. As mentioned earlier in this thread I also removed the wire bails and replaced them with Stainless steel hose clamps. No more leaks!
I also had another problem where brake fluid leaked out of the master cylinder on the back side where it mates to the vacuum booster because the seal had failed. I'm happy to report the Duff's replaced the master cylinder even though it was beyond the warranty period by a few months!

Beach Bronco

 

[Yeller]

Mine would go empty, it leaked bad