Bob Zetnick

'29 DA Master Cylinder

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I was checking my brake light why it was so dim and then not working when I found that my master cylinder quickly drained my brake fluid from the canister. I bought a kit 11 years ago, installed the rebuilt master cylinder and had it checked 8 years ago and finally filled it 18 months ago. I have less than 100 miles on the car since driving it again last year. I got under the car and it had all leaked out where the piston rod enters the boot. I have looked at this post from 2011, but it deals mostly with the piston / spring chamber at the front of the master cylinder, not where my leak is. I have not taken the master cylinder off yet to look at the leak more closely. I have looked at drawings and photos, but can't see if there is some kind of seal / flange that seals the piston rod w/ the boot....or maybe I installed improperly....so I have a few questions:

 

1) Anyone have photos / ideas about the connection between brake piston rod and rubber boot?

2) If my boot looks okay can I reuse the kit I have installed though 11 years old?

3) Anyone know where I can get a kit if I have to buy new? I haven't tried NAPA yet (I don't think they go back to '29), but the sources I had several years ago have dried up.

4) Lastly, I think White Post rebuilds these, but not cheap...I may try Romar ....anyone have other sources? I rebuilt this and had it checked and it still failed, so maybe time for a professional! I'm just glad I wasn't driving when it failed!

 

Thanks in advance for any thoughts / ideas on this.

 

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There should be a rubber cup that fits next to the piston. I suspect you will find that the fluid leaked from around it. Zeke

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When you filled the cylinder 18 months ago, are you sure it was still pristine clean and smooth in the cylinder bore and not corroded? Any roughness in the surface would cause a leak past the cup. If this is the case, it will need a hone, clean and fit a new cup.

 

If it were mine, it would be out and forensically disassembled on the bench fairly soon. Make sure the lip on the cup is perfectly sharp all around, coz it will leak if it is not.

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So, got the master cylinder out today.....rubber all seems in good shape. Got a photo of the piston, the parts as they came out of the cylinder and tried to get a shot of the cylinder walls. The cylinder walls seem clean, not polished like a babbitt bearing, but clean...so not sure what to do here. Again the massive leak occured between rubber boot and piston rod behind frame member. Do you think I need resleeved / cored? Ideas as to what went wrong? I think I like the mechanical brakes on my '24 better! :)

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Fluid coming out at the piston rod indicates it has got past both cups into the boot.

 

If the chamber between primary and secondary cups was full of fluid as well as the space under the filler, fluid must come out somewhere when you push the pedal down. Look really carefully at port #6 and at port #9 and make sure you can get the cup past them without damaging the edge. Make sure there is no roughness on those port openings.

 

Also, don't fill it to the brim: there must be a bit of space to push fluid into the filler from between the cups.

 

The cylinder must be smooth with no pits or dents. It might have nice cross-hatched hone marks.

 

What is the edge of the primary cup like? It must be sharp with no dents or other damage. If in doubt, replace that cup - just the cup - they are inexpensive.

 

What should the secondary cup expander #4 look like? I can't see it in the photo. If that cup doesn't seal, it will leak as you describe.

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1 hour ago, Bob Zetnick said:

I think I like the mechanical brakes on my '24 better

Amen to that thought.  Once adjusted only wear changes things.  I am so happy that my Pontiac has mechanically operated brakes.

 

I do wish you well on repairs to your hydraulic system.

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23 minutes ago, Spinneyhill said:

Fluid coming out at the piston rod indicates it has got past both cups into the boot.

 

If the chamber between primary and secondary cups was full of fluid as well as the space under the filler, fluid must come out somewhere when you push the pedal down. Look really carefully at port #6 and at port #9 and make sure you can get the cup past them without damaging the edge. Make sure there is no roughness on those port openings.

 

Also, don't fill it to the brim: there must be a bit of space to push fluid into the filler from between the cups.

 

The cylinder must be smooth with no pits or dents. It might have nice cross-hatched hone marks.

 

What is the edge of the primary cup like? It must be sharp with no dents or other damage. If in doubt, replace that cup - just the cup - they are inexpensive.

 

What should the secondary cup expander #4 look like? I can't see it in the photo. If that cup doesn't seal, it will leak as you describe.

Thank you for the info. Spinneyhill! I'm afraid I'm not much of a mechanic!  I basically clean / restore parts and put them back together (probably part of this problem) ...anyway, I have no idea what ports #6 and #9 are nor what secondary cup expander #4 is. I do appreciate your responses though.

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1 minute ago, Tinindian said:

Amen to that thought.  Once adjusted only wear changes things.  I am so happy that my Pontiac has mechanically operated brakes.

 

I do wish you well on repairs to your hydraulic system.

Thanks....I had someone pull out in front of me a little over a year ago and the '24's brakes worked well.....made a lot of skidding noice, but stopped quickly!

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I am a big fan of having both master and slave cylinders sleeved in stainless steel. If working OK, leave alone, but if I have to dismantle anything, I always re sleeve. It just removes any doubt and should be good for life. Brakes ARE pretty important!

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