non boosted master cylinder question?

i just upgraded my 56 chevy single master to a 67 chevy dual master non boosted its all hooked up brakes work better than before i was just wondering why the hell the cap and seal leak is this comon on this master or maybe i have a bad seal. i had my girl friend pump the hell out of the brakes while i watched to see where the leak was and it didnt leak so i took the car for a ride and after driving for about 5 minutes i pulled over to check and there was a crap load of fluid burining off my fenderwell headers and the master was soaked i took a rag and tied it around the master to get home when i got there i poped the hood and it was soaked in fluid its deffinitley the cap but only in the front maybe to much brake pressure or maybe and over fill of fluid ? im stumped help

 

Long time no see. Could be the cap like you say. Who's unit is it ? (name brand or cheapo)

 

its a reman cardone usuall reman stuff cap looked factory glass beaded was a rbay score it works good and looks good but the capa nd seal leak alot

 

I have been wanting to do the same to my 53 ford.

I would just say check the cap and the seal. it cant be much else.

 

Not trying to tell you to go new, but I have given up on reman. brake stuff. I last faith when one went to the floor on me in less than a day. Tore into it to see what was up . Just complete junk......scored bore, lip on piston seal was rolled over and had a flat spot.

 

If you're going to buy reman, it's worth spending the $20 or so to buy them local at a parts house, so that at least if it takes eight of them to find a good one, you can exchange them no charge each time. Which, the '67-'72 Chevelle/'68-'74 Nova manual all-drum master is like $17, I can't picture doing better on one on eBay after the shipping unless you got it for like a dollar.

Just a thought, but if it's just too full, does it ever stop throwing fluid out? Sooner or later it has to either reach the point where it's happy, or run out - if it still stops good and has enough in it, maybe that's the solution. If it will keep doing it until you have none left, then there has to be some other problem, maybe how you plumbed it in or something.

 

Does the cap have a breather hole in it? i.e above the cap seal that vents to atmosphere. Maybe pressure is building up from applying and releasing brakes and forcing it out the cap. Just a thought...

 

You may be boiling your fluid. A couple of ways to do this, brakes dragging, engine heat on lines. I had a motorcycle with the small mastercylinder on the handlebars. It was a screw on cap, don't know what you have, got word from the factory to not over tighten. Tightening after snug caused the rubber wrinkle between the cap and cylinder.

 

x 2

 

I had a 70 Corvette 1" bore (manual brake) master do this once. It was from NAPA. They replaced it and it's been working fine...

I only buy newly manufactured parts for brakes...

 

The gasket in those is supposed to work like a diaphragm or bellows in that it is set up to move with the fluid That seals the system and the vent in the cap lets that diaphragm move. If yours has a flat gasket that would be the problem.

But overfilling and boiling the brake fluid due to the lines being too close to a heat source or the brakes being too tight could be a cause too.

And I am another one who wants the know why the hell you would buy a master cylinder off Ebay rather than just walk into a local parts house and buy one over the counter.
You can look up the part you want online on Napa's O'Reilly's or Autozone's web sites and walk in with the part number. You can even pay for it online on the O'Reilly's site and just walk in and pick it up. No fuss no muss and no having to answer why you are putting a 69 Master cylinder on a for example 56 model car. And you have a warranty from those without putting it in a box and mailing it back.

 

Look for nicks on the top lip of the cylinder where the lid seals.
They get pretty rough with the castings in the clean and rebuild process sometimes.
I have used a large flat file before to smooth the top surface and get them to seal.
Just be sure to empty the fluid and put a rag in to catch the filings.

 

well to answer the question of why i bought it from ebay..i red the stores reveiws it had all good no negitive feedback at all so for 40 bucks free shipping it seemd like a good price i have little to no time to get to the parts store these days with my job.

there is no vent hole in the cap
there is no bur around the edge of the master
as far as boiling the fluid the lines are clear of the headers i have fender wells and the lines are pretty far away there not as close as the headers would be in the stock position.

i left a message with the company saying how i was wondering if they had ever had this trouble with the master and without a reply i get an email that they had refunded my cash back to my card and how to if im not happy with the master just throw it away...so im mind boggled should i buy a brand new one or just buy a cap i mean i tested the brakes they work i drove around the block a couple times and stopped short and than stopped normal they grab just as good as 4 wheel drum will

what should i do other than the leak its fine ?

 

tighten the wire bail.
add another thickness to the gasket.
buy another cap/gasket.

 

Just went through this on a friends 31. Kept pushing fluid out like that. Jack up car after you come in from driving and have everything good and hot and been using brakes alot. See if any of them are dragging. Heats up fluid and pushes it back up in reservoir. His was doing it because M/C pushrod was too long. Adjusted it and problem was fixed.

 

jdj9410<SCRIPT type=text/javascript> vbmenu_register("postmenu_6839075", true); </SCRIPT>
Alliance Member

hey i do have drag on the brake drums but a small amount so the brakes will stop better .and as far as the push rod im using the stock 565 one on the 67 master another site said there was no diffrance and i could use the stock one with no trouble

 

chrisntx<SCRIPT type=text/javascript> vbmenu_register("postmenu_6839023", true); </SCRIPT>
Senior Member
tighten the wire bail.
whats that supposed to mean ?

 

He means flatten the U shape wire that holds down the cap abit so it puts more press on the gasket.

 

air in the lines will compress and releasing the pedal causes the fluid to rush back to the M/C and slosh out thru the vent hole in the rubber gasket. Just a thought.

 

got residual check valves to keep fluid from draining back??

 

oldcarfart<SCRIPT type=text/javascript> vbmenu_register("postmenu_6839774", true); </SCRIPT>
Member
got residual check valves to keep fluid from draining back??
i thought you didnt need these with this set up?

 

MAIN RULE #1......NO AIR to COMPRESS in brake lines. He said it stops very well. DD

 

ok i went outside before and was looking at the cap and gasket
this time really closely and yes the cap is vented on both sides very tiny holes but they are clean and clear and thats not were the leak is coming from,
so i realize that the hold down wire wasnt touching the front part of the master cap and thats were it is leaking from so i took the cap off and used a rachet extension and a small hammer and lightly taped the iside of the cap so it would raise the outside notch up so the hold down wire would now touch the cap and it seems its on there pretty good as of now havent driven it yet to see if it still leaks will do tomorrow.

 

He said the brakes worked "better". still could have air in the lines