Baffling Bendix Master Cylinder

[Coelacanth]

My master cylinder started leaking a few months ago where it bolts to the booster, below the lower 2 bolt holes. Upon removal, I found it's the desireable Bendix unit, so I want to have it rebuilt. The P/N on the bottom shows '22268' but not sure what the last 2 digits are; possibly '24' or '84'...would anyone know? It's from my 1970 Charger 500, 383 Magnum, rear drum/front disk power brakes. The piston diameter is 1-1/8". To my knowledge it's original.

What's baffling me is I can find no way to remove the piston. There is no bolt anywhere on the cylinder body, nor inside the pots. I can see no circlip or anything else retaining the piston inside the bore. What's the magic holding it inside?

The bore looks better than I expected, except for the outermost 1/4" or so. I was quoted $800 CAD to re-sleeve and rebuild it, which seems very excessive...especially when you can buy a complete booster, firewall mount plate and master cylinder assembly for under $300 USD, though the ports are on the fender side instead of the engine side. Looking forward to your advice and thoughts.

 

[davek]

you could call these guys,post 2 master cylinder rebuild services

 

[Coelacanth]

Interesting. In that topic's first post, the P/N was 2226821. Mine might actually be the same P/N. However, his unit has a bolt on the side, mine has no such bolt. I'm the kind of person that likes to know or learn everything he can about his cars rather than trust someone else, and if I'm in over my head or lacking the correct tools, that's when I'll bring it to someone. I'd really like to be able to disassemble this MC myself and see the piston and seals myself, but nobody and nowhere I've checked seems to know how the piston can be removed.

It went IN somehow, so it must also come OUT.

 

[HEMIB]

Clean up the bore with a rotary brush then lube & put a shot of air in the front should push out

 

[Dave6T4]

Usually, that boss on the bottom of the M/C is drilled and tapped for a retaining screw.

 

[XS22J8R]

Casting number should be 2226821 and the boss on the bottom of the casting should be tapped for a retaining bolt.
Forcing the piston out with compressed air usually works, but if not, the commercial rebuilders force them out with grease.
Brake and Equipment warehouse in Minneapolis is the go-to source for rebuilding Mopar brake parts.

 

[440 4 speed]

Check with Nigel, National Moparts, Mobile Parts might have kits or your local parts supplier. If I wanted to rebuild mine I would go to our local WSSL store, and see if they could order a kit. Quite a few of the parts stores send their stuff to Accu Llne in Winnipeg. As individuals we cannot go directly to them.
If you have a Bendix booster would you please send me the measurements of the spacer that goes on the studs, mine went AWOL along with the washers that are on the pin connecting the levers.
Our factory Bendix booster have ports on the fender side. Both cars are the same and factory original.

 

[Coelacanth]

Clean up the bore with a rotary brush then lube & put a shot of air in the front should push out

Thanks HEMIB, that was the ticket. I put the cap on, blocked the rear port and shot some air from my compressor into the front port, and the piston popped out about 1/8" It was just enough for me to gently press my thinnest flat screwdriver into the tiny groove between the outermost piston ring and the rubber seal and carefully eke it out. I was careful not to touch the outer ring of the piston or the bore, just levering it out from the inner edge of the ring. What popped out looked like this, not surprisingly. I'll clean up inside the bore with my rotary tool and brush. I assume you can still buy parts to rebuild these pistons? The piston will get a soak in EvapoRust before I have a closer look.

My MC never had any retaining bolt tapped into it, this is how it was manufactured. It looks like the booster pushrod and a bit of pressure from the ring seals are pretty much the only thing keeping the MC piston inside the bore.

EDIT: Looking at this assembly, after it's all cleaned up and assuming the piston bore isn't scored or otherwise damaged--as the car hasn't been started in 12 years or driven in over 20--it's the rubber ring seals that are probably the reason why the MC leaks. Is that a good guess?

 

[HEMIB]

Good Stuff, If the piston bore is damaged in any way it is toast
It may work on initial brake but will leak down under pressure

 

[RJRENTON]

Good Stuff, If the piston bore is damaged in any way it is toast
It may work on initial brake but will leak down under pressure

If you are concerned about numbers matching/build date, the bore could be re-sleeved to use the origional type of rebuilt piston to be able to maintain original uniform braking pressure.....just a thought.....
BOB RENTON

 

[Dave6T4]

The rear brake circuit piston is still in the back of the M/C bore. Give it another shot of air to pop it out.

 

[Coelacanth]

Thanks Dave, I got the rest of the piston popped out. After a 24-hour soak in Evapo-Rust and some wiping with a toothbrush, it looks much better. I also gently polished the piston bore, which had no scoring. There was some brown crusted-on guck around the outermost 1/4" or so of the bore, and similar guck on the outer ring of the piston, I carefully removed that with gentle polishing with a flapper wheel. I honestly wasn't expecting it to help much but after reassembling everything and letting it sit for 2 days, and also throughout the bench bleeding process, it isn't leaking at all, not even so much as seeping from beneath the piston. I had to use the zip-tie and some big washers to retain the piston as my original master cylinder lacks the retaining screw on the bottom. I made sure the piston was sticking out by about 1/8" just like the new master cylinder I bought to do what I could to make it leak, but it wouldn't leak a drop. I'm thinking--and hoping--that the crusted-on guck was enough to make the seal fail and cleaning that up to a nice round bore and seal surface was the trick.

The spare MC I bought from RockAuto is just in case, but that one has the ports on the fender side. I'm hoping my original won't leak when reinstalled on the booster so I don't have to buy new brake lines.

 

[Fran Blacker]

You could have your master sleeved and reuse it? The rebuilt master might have the same guts as your original all that's different is port location. If you dare pop rebuild apart for a look see. Those MC's like yours are $100's of dollars on ebay needing rebuild. I'd like one because the brake lines hit the the electric panel on inner fender with starter and horn relays. Had to flip one of the relays, forget which.

 

[Coelacanth]

You could have your master sleeved and reuse it? The rebuilt master might have the same guts as your original all that's different is port location. If you dare pop rebuild apart for a look see.

Yes, that's an option and I was quoted an astronomical $800 CAD to do this. Heck, you can buy an entire remanufactured booster, MC and frame bracket assembly for $300 USD, as an option...but that unit also has the brake lines on the wrong fender side.

The MC from RockAuto has the exact same piston assembly. I was considering using that in my original one but for shits & giggles, I reinstalled the original assembly after it was cleaned up and crusty guck polished out...fully expecting it to leak, and was surprised it didn't leak even the slightest amount after 3 days.

The only minor challenge to reinstalling it is keeping the piston inside, and snipping off the zip-tie and washers while quickly re-bolting it onto the booster, to minimize brake fluid spillage.

 

[Fran Blacker]

I'd shop around for that sleeve price.
hite post 540 837 1140 [email protected] www.ol[email protected] The guy is James Ament 717-807-4111
These were taken from Hemmings I haven't dealt with them except maybe white post 30 years ago. Both 4 new wheel cylinders a sent them to be sleeved. They called and ask why sleeve them? Don't what to worry about rusty WC's. Who ever did mine used brass and said use only DOT3 fluid.