Strange master cylinder issue

[garberz]

I’m running a GM style master, disc/drum with hydro-boost. I’ve had this in place for the last 10 years and it has worked flawlessly. We’ll this week I’ve noticed brake fluid leaking from the cap. The reservoir for the rear brake was near empt, while the front reservoir is overflowing. I transferred some fluid back to the rear, but it continues to keep moving fluid to the front. This Is happening internally obviously. I’m going to replace the master, but just curious as to what’s going on. Any thoughts?

Mark

 

[B RON CO]

Hi, I have never heard of that before. and I have experience with the GM hydro-boost systems from the 80s and 90s. I would make sure the brake pedal is not hanging down. Good luck

 

[garberz]

Hi, I have never heard of that before. and I have experience with the GM hydro-boost systems from the 80s and 90s. I would make sure the brake pedal is not hanging down. Good luck

The brake pedal has always been the same. Very firm, short travel, and returns. The brake lights have never been stuck on.

Mark

 

[Wild horse 75]

I think the master is bypassing internally and forcing fluid from the rear to the front reservoir.

 

[Broncobowsher]

Internal seal in the master failing. Leaking between the two in a check valve fashion.
New master needed.

 

[DirtDonk]

Do they even sell rebuild kits anymore?
That used to be the normal thing to do when you had one that was otherwise in good condition, and the bore wasn’t rusted or pitted.
When master cylinders were $25, a rebuild kit was 4, or 5.
Same for wheel cylinders. Rebuilding was more common in my circles than replacing.

 

[ksbronco75]

did you ever get this issue resolved? Im having the exact same issue with a Master cylinder I got from Toms last summer. Part https://tomsoffroad.com/parts/67-75-ford-bronco-drum-brake-master-cylinder . I recently replaced all wheel cylinders, found 2 that were bad and leaking. replaced them all, took it out tonight and same issue. Rear is nearly empty, Front is full. already ruined the paint on my inner fender, so I was hoping you figured it out?

 

[EPB72]

did you ever get this issue resolved? Im having the exact same issue with a Master cylinder I got from Toms last summer. Part https://tomsoffroad.com/parts/67-75-ford-bronco-drum-brake-master-cylinder . I recently replaced all wheel cylinders, found 2 that were bad and leaking. replaced them all, took it out tonight and same issue. Rear is nearly empty, Front is full. already ruined the paint on my inner fender, so I was hoping you figured it out?

Call Toms and see if they will warranty the master cylinder , it needs to be replaced ....

 

[ksbronco75]

Spoke with Toms. This one is on me. I ordered the MC for drum brakes for my 75. But since it has a power brake set up on it, it needed the disc brake MC. Did not realize that when i ordered the part. So thats cool

 

[m_m70]

Rebuilding was more common in my circles than replacing.

Same here. Times have changed. I trust myself to rebuild OEM parts, if kits are available, more than the crap they're selling us now a days as new.

 

[garberz]

did you ever get this issue resolved? Im having the exact same issue with a Master cylinder I got from Toms last summer. Part https://tomsoffroad.com/parts/67-75-ford-bronco-drum-brake-master-cylinder . I recently replaced all wheel cylinders, found 2 that were bad and leaking. replaced them all, took it out tonight and same issue. Rear is nearly empty, Front is full. already ruined the paint on my inner fender, so I was hoping you figured it out?

I did. The master had an internal leak. I replaced it and everything is fine now. Except the cap leaks. I had to assist the bail with large hose clamp.

Mark