master leaking fluid

[okie77]

hi there everybody, I have a 73 4x4
I noticed while under the hood that my master cylinder was leaking from the bottom and running down the brake booster and fluid being pushed out from the cap and running down the side. So I changed the master cylinder, but the problem still persist. Not sure if I got a bad cylinder or what.
I know there's no gasket between the booster and cylinder so and the only seal is on the piston of the cylinder, so I'm coming up blank on why it's happening. Any help would be great

 

[PrairieDrifter]

There doesn't have to be a gasket between the booster and the master, there shouldn't be any fluid in between them. Check on the firewall under the dash of you have brake fluid leaking from the back of the booster in the cab, and check the brake lines and the rest of the system for kinks, leaks, ect. It seems like the booster, check the check valve that goes from the booster to the intake also.

 

[okie77]

have checked all lines and we did a bleed job it after and everything worked good. I'll check the firewall area and check valve.
thank you

 

[PrairieDrifter]

If you end up taking the master off put a punch or something that fits in th back of the master unless it has a rod coming out of The master but either way loop the brake line outlets into the reservoir just with a little hose and fill with fluid them push in and out with a tool or that rod that you may have be careful not to bottom it out just 3/4 of the way in and see if you are getting fluid from the back of the master. The rear seal on the brake cylinder in the master may be leaking.

It's also not impossie for it to be a bad part, I saw plenty of defective parts within five years at my old job

 

[okie77]

damn good idea didn't think of doing that.
thanks for the idea

 

[PrairieDrifter]

No problem that was what I did every time I did a master cylinder job on an old grain truck or whatever else, we called it bench bleeding. It reduces the amount you have to sit in the truck and pump the pedal so long haha its too much of a workout.

Let us know if you find the problem

 

[79K10]

i did mine just like that, i didnt know you couldnt push it all the way, i did, seems ok lol ...

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those clear hoses, pointed plugs and clamp came with the MC

 

[PrairieDrifter]

Usually you'll be alright but you aren't supposed to fully push it in. It over extends the piston in the master, farther than it can go in normal operation on the vehicle.

 

[79K10]

Usually you'll be alright but you aren't supposed to fully push it in. It over extends the piston in the master, farther than it can go in normal operation on the vehicle.

good to know, thanks ... guess its a good one then!... haha
i wont be doing that again ... It didnt seem to take too many pumps the clear the air out. Is the bench bleed really that necessary? I feel like it would have been the same as if i had just installed it and done the bleed with the peddle... or does it really get that last bit of air out that you cant do with it installed? lol

heres a good before shot of mine...

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might as well toss in the after

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def worth the $15 or whatever it was lol ... yes thats blood on the booster and the brake line, the old one didnt like the idea of going in the trash and sliced my knuckle lol

 

[PrairieDrifter]

What you're doing basically is making sure there's no air in the master so when you install it and put the brake lines on and start pumping the pedal you're not pushing air into the lines so you don't have to bleed the whole system more than you need to. if you bench bleed the master correctly as don't move the brake lines too much when removing and installing then that means you have less work to do and less air to push out so you could bleed the whole sytem in one go around or two.

**** the first thing I did was put a master on my c10, bench bleeded it stuck it on and I had a firm pedal right away. Still bleed the system to make sure but I wouldn't have been worried even if I didn't bleed the whole system

 

[79K10]

I see what youre saying, makes sense. Thats the ideal outcome.
I was just thinking, next time ill mount it to the booster and run the clear lines to the top and bleed the air that way, I didn't mean hook everything up dry

 

[PrairieDrifter]

We just bench bleed it Cuz when you order it you don't have to take it off or install it yet it's right there to bleed it. Bleeding brakes is a two person job unless you have a pressurized bleeder. And yeah you definitely could install it and the bleed just the master but maybe it's a bad part then you have to take it off again and it can get pretty messy.

I knew you didn't mean install it dry it's just easier to get it and bench bleed it right in front of you instead of sitting in the cab and makes less of a mess in your engine compartment