master cylinder fluid level

[paulbrgr9999]

I was just routinely checking things and opened up the brake master cylinder resivor and noticed a large discrepancy between the two levels. It appears that the rear brake resivor is lower than the front. I checked under the truck front and back and behind the wheels and the lines and cant find a leak.

I included a pic. I cant find a fill level mark on the master cylinder or in it so how do I know how much I should add? Should I fill it to the top?

paul

[Lee H]

I would fill it to about an inch from the top and monitor closely for a awhile. The fluid went somewhere. Maybe the brakes were not bled properly last time and they gravity bled them selves.

[PowerdbyChevy79]

Well there is more line to the rear so you fluid is just in the lines probably....if you didnt know what the fill level was before you could be chasing a ghost looking for a leak when there isnt one.. get under ur truck and check the lines..if you dont see any oil stains coming from the lines....then your not leaking...just fill it again and watch it more closely...this how you become one with your c10..you know all the ends and out...

[paulbrgr9999]

I filled it. Ill watch it closely. Check every few hundred mikes for a while. I cant find any leaks. Brakes work fine, at least for drum brakes.

going to do the swap soon I hope. Maybe we will discover a leak while doing that.

thanks for all the info. This forum is amazing.

paul

[seth7843]

The wheel cylinders could be leaking inside of your brake drums. It wouldn't hurt to pull the drums and insect them.

[cdowns]

while your at it pulling the brake drums and seeing if you have any brake shoes left to stop in case

[LSUMurse]

Originally Posted by seth7843

The wheel cylinders could be leaking inside of your brake drums. It wouldn't hurt to pull the drums and insect them.

X 2

I found a small leak from a wheel cylinder that I didn't see on the outside.

[BLT gmc]

The brake fluid may be burnt in the combustion chambers of the motor.

[LSUMurse]

Originally Posted by BLT gmc

The brake fluid may be burnt in the combustion chambers of the motor.

Huh?

[BLT gmc]

If there are no visible external leaks to explain the loss of fluid and there is a confirmed decrease in the master cylinder level above and beyond normal wear/adjustment of the brake shoes, the most likely cause is a leaking master cylinder. This fluid will leak into the cab/ firewall or it can be sucked up by engine vacuum if the power vac assist is bad. Once vacuumed up off to the cylinders to be burnt. This can be hard to see and find

[LSUMurse]

Wow, never heard of that. Seems like the truck would run like warmed up donkey crap.

[paulbrgr9999]

Originally Posted by LSUMurse

Wow, never heard of that. Seems like the truck would run like warmed up donkey crap.

Truck runs great! I doubt its burning brake fluid. It does however use massive amounts of gas even when not under a load. Steady 60 on the freeway, no head wind, maybe 10mpg! But I still love my chevy!

[67 chevelle]

lossen the 2 nuts that hold the master to the booster , pull the master forwaed slightly , if it is wet behind you need to replce the master , and probably the booster also , most times they will not leek into the cab or firewall as the booster catches and contains the fluid , if its not wet , put the 2 nuts back on , takes all of 10 minuets to check

the fluid should be an 1/8 inch for the lid of your master

[BLT gmc]

Wise advise 67 Chevelle. This phenomonia usually happens very slowly, un-noticeable at first. But like most things it will worsen at variable rates. At first you may not notice any engine difficulties. But if the leak is large it will definately affect performance, idle, exhaust will be white with tons of smoke in a massive leak or if the vacuum gets a big snort of brake fluid because the angle of the master cylinder booster changes with the truck.

[paulbrgr9999]

Thanks for the info. When I loosen those two bolts and pull forward will I effect the brake line? I dont want to have to bleed the brakes.

[BLT gmc]

The procedure 67 Chevelle described should not introduce air into the closed system. The lines have a little "wiggle" room. Good luck, Bruce

[Ironangel]

The scenario 67 Chevelle described actually happened to me...I didn't realize the fluid was leaking directly into the hydrovac unit until it failed while I was standing on the brake at a drive through window. The brake pedal suddenly went to the floor and no more power brakes! ...There is enough flex in the lines to move the MC forward enough to take a look behind the MC without loosening any brake line fittings