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Where's the brake fluid going?

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RenoHuskerDu

Where's the brake fluid going?

After a couple months of being driven not-quite-daily, I found the brake fluid low. Because we'd never done the rear brakes, I figured it was time and expected to see a leaky wheel cylinder.

No, they were dry. We did the rear brakes anyway. But now I'm scratching my head. This is a new master cylinder, just this year.

How does this dual reservoir system work? It's not front and rear, is it. It's primary and secondary, I seem to recall.

If there's no brake fluid traces on the wheel cylinders or calipers, no smell of brake fluid down on the driver floor area, and no traces of fluid leaking out of the dual reservoirs or master cylinder, then where could it have gone? I saw another thread out here where it was leaking out right at the cap, but as you see in the photo, that lip area looks solid on my brake MC.

Reno in Central Texas, 86 F250 XLT Lariat eclb 2wd 6.9, plus 2 Bricknoses, 1 Aeronose that's getting a Bullnose front clip, and parts trucks. Busy lads, father and sons wrenchers.

reamer

Re: Where's the brake fluid going?

out the exhaust?
MC leak in to the booster, booster vac. in intake?

1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks

Gary Lewis

Re: Where's the brake fluid going?

Administrator

Yes, it can go out the exhaust. Or down the firewall, either inside or out.

Or, out under the cap, maybe on the engine side where you can't see it. I had this on Big Blue.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

grumpin

Re: Where's the brake fluid going?

Did you check your front brake pads? As they wear the fluid will go down.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

reamer

Re: Where's the brake fluid going?

That's an awful lot of fluid loss from pad wear, …..

1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks

RenoHuskerDu

Re: Where's the brake fluid going?

In reply to this post by grumpin

I will check them. But there are reasons why we don't wear its brakes much.

1) We live in the country
2) We don't have big hills
3) It's a manual tranny
4) It's a 420 with only 160hp lol

Reno in Central Texas, 86 F250 XLT Lariat eclb 2wd 6.9, plus 2 Bricknoses, 1 Aeronose that's getting a Bullnose front clip, and parts trucks. Busy lads, father and sons wrenchers.

RenoHuskerDu

Re: Where's the brake fluid going?

In reply to this post by Gary Lewis

OK, I'll bite.

Out the exhaust?

Reno in Central Texas, 86 F250 XLT Lariat eclb 2wd 6.9, plus 2 Bricknoses, 1 Aeronose that's getting a Bullnose front clip, and parts trucks. Busy lads, father and sons wrenchers.

Ray Cecil

Re: Where's the brake fluid going?

RenoHuskerDu wrote

OK, I'll bite.

Out the exhaust?

If the master is leaking fluid into the booster, the vacuum inside the booster can pull fluid into the intake of the truck, where it gets burned and goes out the exhaust.

1988 F250 Supercab Longbed 7.3 IDI, C6, 1356, GEARVENDORS, 4.10 Sterling with autolocker

1986 F150 302, C6, 9" 2.75, Wood Flatbed

85lebaront2

Re: Where's the brake fluid going?

Administrator

Diesel engines have a external vacuum pump, belt driven on Ford's that provides the vacuum for brakes, HVAC and transmission sinal on the C6.

The two reservoirs are, small for rear brakes and large for the front brakes, the reason is the caliper pistons keep moving out until the pads are exhausted. I would look at the steel lines under the truck, in particular where the line turns from down the frame to go inward for the rear brakes, there is a low area that collects dirt and water and will cause the line to rust through (ask me how I know).

Here is the best picture of the area I could find, red line is the brake line to the load compensating valve.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

RenoHuskerDu

Re: Where's the brake fluid going?

That is good to know, and I thank you for it.

But the larger of the two was the low one, which is for the front brakes. So I don't see how a leaky line to the rear could pull down the front brake fluid level.

This truck was from central Cali before it moved to Central Texas, so it's about as rust-free as one could hope for.

Reno in Central Texas, 86 F250 XLT Lariat eclb 2wd 6.9, plus 2 Bricknoses, 1 Aeronose that's getting a Bullnose front clip, and parts trucks. Busy lads, father and sons wrenchers.

Ray Cecil

Re: Where's the brake fluid going?

If there isnt any leaks in the cap, steel lines, proportioning block, rubber lines, or calipers.....then it must be leaking past the master cylinder into the bottom of the booster. Seriously, where else could it go? The fluid could be sitting in the bottom slowly eating its way through the diaphram in the booster.

Is the booster old?

Anyone wanna suggest a method to see uf there is fluid in the booster?

1988 F250 Supercab Longbed 7.3 IDI, C6, 1356, GEARVENDORS, 4.10 Sterling with autolocker

1986 F150 302, C6, 9" 2.75, Wood Flatbed

85lebaront2

Re: Where's the brake fluid going?

Administrator

Pull the check valve out, stick a small piece of vacuum line in and use a baster to see if fluid comes out. Other is remove the master cylinder and see if there is fluid behind it against the seal on the booster, if there is remove the seal, and have someone push the pedal down, if you strike fluid, there is your problem.

Bill AKA "LOBO" Profile