why is my master cyl. doing this
 

My master cylinder is weeping slowly from the fr. resorvoir to the back one. Is manual brake setup with drum/disc setup on a 80,s truck. The old one did this so I thought there was something wrong so I replaced it with a new one and this one is doing it too. Where is my problem ?

Re: why is my master cyl. doing this
 

I'm not sure I follow what your seeing....how can you tell?..,both sides should be full

Re: why is my master cyl. doing this
 

the fr. fills up the rear one and then it leaks. This takes about about 3 weeks then I notice a spongy pedal and I then take a turkey baster and take some fluid out from the rear and put back in the fr. reservoir . The rear reservoir is full to the top and of course it leaks when I pull the lid off at this point. The pedal is now fine at this point

Re: why is my master cyl. doing this
 

Ok I understand what your saying now
There is a seal between the reservoirs..but 2 masters doing the same thing makes me wonder if the issue lies elsewhere.. I'm wondering if your proportioning valve could be transferring fluid to the wrong side..
Might be worth swapping it out

Re: why is my master cyl. doing this
 

Ok I will have alook. At least it,s a starting point. Thanks

Re: why is my master cyl. doing this
 

Is this truck converted from power to manual with the booster removed?

Re: why is my master cyl. doing this
 

no

Re: why is my master cyl. doing this
 

So it’s stock then.
I was thinking pedal ratio might be the difference.
Does your brake pedal have two holes in it where the brake rod attaches to it.