1-Ton Master Cylinder Reservoir Losing Fluid
 

1986 C-3500 single cab dually w/hydroboost. Front discs, rear drums.

The pedal was a little soft today, so I opened the master cylinder. The fluid started to run out over the top of the back reservoir. (I assume that's for the front discs.) The front reservoir was nearly empty. It appears that fluid is being transferred from the rear brake reservoir to the front. Is that possible, or is the rear brake system simply leaking?

Thanks for your help, Les

Re: 1-Ton Master Cylinder Reservoir Losing Fluid
 

Anyone???

Re: 1-Ton Master Cylinder Reservoir Losing Fluid
 

My 79 GMC 1 Ton loses fluid too. Also has the Hydroboost system. Mine appears to push fluid past the lid and seal for some reason... i replaced the gasket under the lid and it still leaks. Maybe mine is building up too much pressure. Really not sure.

Re: 1-Ton Master Cylinder Reservoir Losing Fluid
 

Mine does the exact same except Im losing it out of the large reservoir in the MC. I think it leaking from the bottom of the hydro boost. Between where the MC and the hydro meet.
Like there's too much pressure
Never been able to figure it out other than just replacing the hydro.