1-Ton Master Cylinder Reservoir Losing Fluid - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ghostflyer · 01-15-2017, 09:52 PM

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

ghostflyer · 01-17-2017, 12:11 PM

Anyone???

erichevy · 01-17-2017, 01:12 PM

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.

walkerb · 01-18-2017, 08:37 AM

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.

01-15-2017, 09:52 PM	#1
ghostflyer Registered User Join Date: Oct 2011 Location: Olympia, WA Posts: 23	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 Last edited by ghostflyer; 01-15-2017 at 09:55 PM. Reason: Clarification in title

01-17-2017, 12:11 PM	#2
ghostflyer Registered User Join Date: Oct 2011 Location: Olympia, WA Posts: 23	Re: 1-Ton Master Cylinder Reservoir Losing Fluid Anyone???

01-17-2017, 01:12 PM	#3
erichevy Registered User Join Date: Aug 2014 Location: Marshall Michigan Posts: 72	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. __________________ 1979 GMC C35 - Farm Work Truck 1986 GMC C25 Crew Cab 1987 SWB R10

01-18-2017, 08:37 AM	#4
walkerb Registered User Join Date: May 2010 Location: Rochester NY Posts: 831	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. __________________ 1973 k20 Suburban 350 1974 Custom stepside c-10 250 1975 Chevy stepside 454 1986 K30 Crewcab SRW 350 R.I.P- glimmertwin01- board member and good friend, you will be missed

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