Brakes leak but no fluid on driveway?! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bucannon · 04-22-2020, 04:34 AM

So it's been a while since I've driven my 86 C10. Last time I drove it the right front caliper siezed, so now I have to address the issue it's had for a while. It has been leaking brake fluid from the front half of the resivour when sitting but I can't tell where it's leaking! There is no fluid that I can find on the ground.

Anyone ever have a similar issue?

I'm probably going to replace both calipers up front and the flexible lines when I get home from offshore (work). Would a bad master cylinder or booster be a culprit?

Thanks in advance guys

rpmerf · 04-22-2020, 06:24 AM

Top off the fluid. Press the pedal (slowly) a couple times. Follow the lines from start to finish, look for wetness. Might have someone else press the pedal while you look.

Dead Parrot · 04-22-2020, 07:41 AM

Is the the large or small side of the MC? Small side is for the rears, large for the front. Just had something similar on my 86 K30-CUCV. Somehow one of the link pins from the wheel cylinder broke and got loose inside a rear drum. It was leaking fluid inside the drum. First clue was the brake light coming on. One side looked darker on the outside then the other so I started there. It was the bad side but there was no fluid on the ground even with the rear brake side of the MC being empty. On my CUCV, the rear brakes are ran from the small but front side part of the MC.

It might be possible for fluid to leak from the MC into the vacuum booster and get sucked into the motor if the booster is also EOL. Or just leak there slowly.

bucannon · 04-22-2020, 11:14 AM

Ahh good to know it is the front (smaller) side of the master cylinder that is draining. So in that case it's the rear drums, or the lines leading to them...

My fear has been that it is seeping into the booster and getting sucked into the engine. Since I've let this truck sit up alot the past 2 years I haven't changed the oil so I don't know if any has gotten in there, or would it burn off in combustion?

STOCKISH · 04-22-2020, 01:56 PM

Also, if you dont see anything external, pull the master cylinder and see if its leaking into the booster.

04-22-2020, 04:34 AM	#1
bucannon Salty Sailor Join Date: May 2009 Location: Savannah, Ga Posts: 603	Brakes leak but no fluid on driveway?! So it's been a while since I've driven my 86 C10. Last time I drove it the right front caliper siezed, so now I have to address the issue it's had for a while. It has been leaking brake fluid from the front half of the resivour when sitting but I can't tell where it's leaking! There is no fluid that I can find on the ground. Anyone ever have a similar issue? I'm probably going to replace both calipers up front and the flexible lines when I get home from offshore (work). Would a bad master cylinder or booster be a culprit? Thanks in advance guys __________________ 86 c-10 Custom Deluxe Savannah, Georgia

04-22-2020, 06:24 AM	#2
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Brakes leak but no fluid on driveway?! Top off the fluid. Press the pedal (slowly) a couple times. Follow the lines from start to finish, look for wetness. Might have someone else press the pedal while you look. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

04-22-2020, 07:41 AM	#3
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,519	Re: Brakes leak but no fluid on driveway?! Is the the large or small side of the MC? Small side is for the rears, large for the front. Just had something similar on my 86 K30-CUCV. Somehow one of the link pins from the wheel cylinder broke and got loose inside a rear drum. It was leaking fluid inside the drum. First clue was the brake light coming on. One side looked darker on the outside then the other so I started there. It was the bad side but there was no fluid on the ground even with the rear brake side of the MC being empty. On my CUCV, the rear brakes are ran from the small but front side part of the MC. It might be possible for fluid to leak from the MC into the vacuum booster and get sucked into the motor if the booster is also EOL. Or just leak there slowly.

04-22-2020, 11:14 AM	#4
bucannon Salty Sailor Join Date: May 2009 Location: Savannah, Ga Posts: 603	Re: Brakes leak but no fluid on driveway?! Ahh good to know it is the front (smaller) side of the master cylinder that is draining. So in that case it's the rear drums, or the lines leading to them... My fear has been that it is seeping into the booster and getting sucked into the engine. Since I've let this truck sit up alot the past 2 years I haven't changed the oil so I don't know if any has gotten in there, or would it burn off in combustion? __________________ 86 c-10 Custom Deluxe Savannah, Georgia

04-22-2020, 01:56 PM	#5
STOCKISH Formerly- 1972SuperCheyenne Join Date: Oct 2008 Location: Wake Forest NC Posts: 5,782	Re: Brakes leak but no fluid on driveway?! Also, if you dont see anything external, pull the master cylinder and see if its leaking into the booster. __________________ --Josh My Build Thread:http://67-72chevytrucks.com/vboard/s...d.php?t=799218 A good crossthread is better than Loctite any day. Life is not about what you have, but who you have to share it with.



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