The Stovebolt Site Forums The Shop Area Driveline 55.2 Master Cylinder replacement - looking for pointers

My master cylinder is leaking so I've decided it's time to replace it. I've read the manual and it appears pretty straight forward (disconnect everything, install new mc, connect everything, bleed brakes) but I'm looking for any tips and tricks that others have used. I've also worried about getting the bolts off that mount the mc to the frame, as they look in bad shape.

Leak - https://flic.kr/p/qYBCTj

Bolts - https://flic.kr/p/rg4uxB

Here's something to consider.

Dual master cylinder in a '56.

I would say to be aware that the brake line may break when you try to undo it. The bleeders may be a challenge too.

Good point. Tubing wrenches, available at a good flaps, are a must.

I hope you intend to replace the lines also. The bolts will come out probably. Everything looks to old, rusty and dangerous under there. It needs new lines, fittings, fluid. Check wheel cylinders, etc. also.

As mentioned, whenever you work on this old iron you can expect it to be a challenge. Sometimes you get lucky if you are able to get rusty components to break loose without breaking. Generally if the master cylinder is leaking the wheel cylinders could be leaking and/or frozen as well. As Bartamos stated it would be a good time to check out the entire brake system, there really aren't any shortcuts on brakes.
Fred

Brake lines rust from the inside out. Do it all, do it once, do it right.

Best advice right there!

Thanks guys. My truck is a little different, it's a 55.2 on a '78 blazer frame with the blazer rear end. The wheel cylinders were replaced last year along with new bleeder screws. I've inspected the lines and they show some rust, which worries me, but I'm not sure I can find replacements as the lines look custom. Assuming I don't break and lines when I install the master cylinder, I will probably take the truck to a brake shop and have them make news lines.

Do you mean the brake line bends look "custom"? With your set-up they had to bent by somebody for sure, but you can do it too.

Buy some brake line (stocked on a roll at some FLAPS), and the end fittings to go along with that tube bender from above. If you aren't comfortable flaring the line, some of the FLAPS I've been in had somebody that would show you how. This site probably has a video link somewhere on how to do it, but I don't know for sure.

Cletis & Longbox55 are right though- it's best to do all of it.

Brad

Custom is another word for DIY. Just get various lengths of tubing with ends from FLAPS and mix and match with unions to achieve hook up. Unless this is a show truck or similar.

@bartamos - I think I will try that first. Going to start measuring the lengths and taking photos of the different junction points and start from there.

They sell about 8 standard lengths, all have proper ends for either U.S. or metric. Get a bender and you're there. Inexpensive way to go. Fuel line also.

The web site I linked to lists the tubes I bought and where each was used.

'56 dual master

Link no good.

I used EZ Bend from NAPA but have seen it in other stores too. I used a small tubing bender but I did experiment with just my hands and it came out pretty good. I did read Cletis' short course and it really gave me the confidence in making a double flare. Double flare. I am getting ready to send the cab out for body work and I measured the original master cylinder position with the new dual master cylinders' position so I can make an access door since mine is on the frame not sure exactly where yours is since you have a newer frame than my 1956 3100.

I also bought this kit the DIY'er one and when I get ready to bleed the brakes and master cylinder it really made sense to me for working on my own stuff.
reverse brake bleeder. I can remember the days when my dad had me doing the pump 3 and hold over and over and over again. I bought the cheapest version since a do not bleed brakes to often.

I found this interesting about testing copper in brake fluid. test strips

Link repaired.

Ok, thanks again for the advice. Went ahead and ordered the same MC (I will give the dual MC a shot when I have more time). Ordered the rear brake lines as well from CI so I'm going to start with that and then get the other lines from napa. And the reverse brake bleeder has also been purchased. Thanks again to everyone and I will post once the project is complete.

Got the part in, and there are no instructions or tubes (thought maybe they would include some tubing to bench bleed it).

Do I need to bench bleed this or can I install it, fill it up and then bleed the brakes as normal (also putting in new lines)? I went to three different stores looking for a master cylinder bleeding kit and all said it had to be ordered.

http://www.classicindustries.com/product/1955/truck/parts/cx4843.html

Re MC: Place in vise. Plug holes, stroke with blunt tip rod till bubbles go away. Install MC and lines and all other brake system parts and then bleed the old fashioned way. Cardone and others stopped supplying tubes and switched to this method.

From the web: (Cardone)
Tighten bleeder plugs into ports
Support the master cylinder in a vise in a level position. Never clamp onto the body of the master cylinder.

NOTE: Units with remote reservoirs should be bled on the vehicle. It is VERY IMPORTANT that the body of the master cylinder be kept level during the bleeding process.
Fill reservoirs halfway or until reservoir ports are covered. Always use new brake fluid from a sealed container as specified by the vehicle manufacturer. Install reservoir lid so brake fluid does not spray from reservoir during bleeding process.
Using a blunt tool or dowel (brake pedal if mounted in vehicle), SLOWLY press in and release the master cylinder piston using short strokes of 3/4” to 1”. NEVER STROKE PISTON MORE THAN 1”. Repeat this step until resistance to piston movement is firm and less than 1/8”.

IMPORTANT NOTE: On step-bore master cylinders, WAIT 20 SECONDS BETWEEN STROKES. This will allow air trapped in the quick take-up valve to rise into reservoir. MASTER CYLINDER BODY MUST BE LEVEL.
Install master cylinder on vehicle. DO NOT remove bleeder plugs until brake lines are ready to be installed. This prevents air from entering the unit and brake fluid leaking out.
Remove one bleeder plug at a time from the master cylinder and connect the proper brake line to that port. Repeat this step for remaining brake line ports. Be sure fluid level is maintained during installation of brake lines and that all fittings are clean before installation. Bleed brake system according to vehicle manufacturer’s procedures and specifications.
Verify proper pedal action before moving vehicle. Do not road test vehicle until correct pedal feel and travel are obtained.

NOTE: If firm brake pedal action results using bleeder plugs, but becomes soft after installation in vehicle, the problem is not the replacement master cylinder

I am a little late to the party but they do sell rebuild kit for the master I rebuilt my master for $19. *It was in good condition to start only the rubber had fallen apart.

Well this has been a giant PITA. I'm still not done, going on 1.5 months. Installing the lines and running them was easy, but I have a leak coming out of the banjo bolt that won't stop. I've tried new copper crush washer, no luck; tried annealing the old washers (then sanding off the high spots), no luck and I'm at the point of giving up.

Where I really screwed up is I should have read Cletis' tutorial and just done that.