The Stovebolt Site Forums The Shop Area Driveline Replacing my Brake Master cylinder - 55 C3100, first series

HI All,
As I get my 55 C3100 ready for winter, I am planning on either overhauling or replacing my Master cylinder as it is leaking brake fluid. I still have the OEM braking system ( drums on all 4, no power brakes) and the master appears to be original. the brake lines themselves are in great shape as they were replaced within the last 2 years before I bought the truck.

I have verified that my brake fluid is leaking only from the master, and not at any of the line junctions or at any of the wheels. I have noticed there are both rebuild kits and complete replacements available. I am leaning towards replacing the unit entirely ( about $200 for the unit) as I am unsure as to the overall shape of the existing master and have no idea of its age.

I am by no means a master mechanic and I have taken a look underneath and it looks like something that will take me all day with lots of swearing and such, but it looks like it is doable by me- although, I would say at the outer edge of my comfort level.

So my question to those of you who have undertaken this is what should a barley functional wrench like me look out for in terms of problems I may encounter, or things I need to verify while doing the R&R? - I see two main bolts holding the master to the frame, a pin held in place at the front plunger via a cotter pin and of course the two main brake lines attached. I will plan on bleeding the brakes (once I learn how ) after R&R the cylinder, but I always seek guidance of the crew on this forum

Any help would be appreciated

Thanks!

Joe

Be sure to "Bench Bleed" the master cylinder before you install it.

They are easy to rebuild yourself as long as it does not have major pits in the wearing surface of the cylinder. Get a brake cyl. hone from a Chinese tool store or you local parts store.
If you bench bleed it like JHR says & bleed it at the lines that connect to it after it is put on you should be good to go.

And pay no attention to the ones who are going to post that bench bleeding is not necessary.

I started bench bleeding all master cylinders once 50% of brand new ones suddenly started showing up bad.
Prior to that happening I never bench bled a 3100 master cylinder...
(Ignore if you wish.)

Never not bench bleed a master cylinder even when they always came out of the box good. There is no reason to pump air into the brake system making bleeding take longer and wasting more brake fluid. Besides it's the way my dad did it before the war.
Jeffrey

Hi All
Thanks for the good replies - I am sorry to ask, but having never done a "bench bleed" - is that simply filling the master cylinder up with brake fluid and hand pumping the plunger until all air is out (and adding more brake fluid as necessary) before installing?

Yes. Some MCs come with fittings and hose to make it easier. I made a set using brake tubing and fittings.

I have always installed and bled my 1954/55 replacement original-style single-chamber master cylinders and brake lines as described in the Chevrolet/GMC Shop/Maintenance Manuals. I do not recall seeing instructions on bench-bleeding the master cylinder.

If I used non-original-style dual chamber chamber master cylinders and/or disc brakes, I'd bench bleed.

I have no problem seeing that people recommend bench bleeding. But, I have had good brake pedal since 1968 (except once, when Jim Carter sent me a worthless/pitted replacement/new master cylinder).

I agree with Tim. You might want to make sure that you can move the bleeders on all four wheel cylinders before you start the job.

Specific to rebuild. I am in the same place you are in regards to the overall system. All is original. I recently rebuilt my master cylinder. As Wrenchbender stated, they are easy to rebuild. Only a few parts that pop out and pop in very easy. I had no problems at all after the rebuild. Much cheaper than a new one.

Hi All
It took me a while to get back here, but I wanted to thank all that responded. I especially appreciated the good suggestion to check the bleeders - I took one attempt and 3 of the 4 will be quite a challenge for me and my lack of experience/tools - I have made the conclusion that I will get this work done at a shop I trust - Thanks for the help!

Joe