Brake fluid leak
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Junior User
Joined: Oct 2014
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Brake fluid leak
A couple of days ago I noticed a small puddle of liquid in the cab of my 72 f100. I checked to see what it was and it turns out it is brake fluid. I traced the leak back to a rod the pushes in when I push on the brake. The rod seems to go through the firewall into the master cylinder. Any tips on how to fix or should I just replace the whole cylinder. I do not have power brakes. For right now I have a rag under the rod catching the leak. It doesn't leak much but is noticeable. Thanks for the help
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It's like pulling a thread off on a sweater Jake, here to tell ya! LOL, seriously be safe and inspect everything. It just stands to reason, that if the M/C is worn out, the wheel cylinders and hoses are also about done, right? Then, the hard lines...
Decide what you want to do, there are some decent front disc kits that include everything with new power booster reservoirs and the like.
Renewing a stock system is a PITA and isn't any cheaper if hired out, but I think drum brakes are somewhat unfairly maligned. It sure is easier to change brake pads though.
Welcome to FTE btw
Decide what you want to do, there are some decent front disc kits that include everything with new power booster reservoirs and the like.
Renewing a stock system is a PITA and isn't any cheaper if hired out, but I think drum brakes are somewhat unfairly maligned. It sure is easier to change brake pads though.
Welcome to FTE btw
Cargo Master
Joined: Mar 2014
Posts: 2,031
Likes: 72
Been there done that with my 69 - on vehicles with the power booster, you don't have the "benefit" of the fluid leaking in your cab.
I ended up pulling the mat out when I replaced my MC to make sure the brake fluid did not cause issues with my floor board (it was pretty wet under there). It leaks, not only down onto the floor, but behind the firewall pad and under your carpet/mat.
On your MC replacement, pay attention to the fittings from the MC to the brake lines. There are differences in sizes of fittings.
I did the power booster/front disc swap on my 71. I won't be doing it on my 69.
I ended up pulling the mat out when I replaced my MC to make sure the brake fluid did not cause issues with my floor board (it was pretty wet under there). It leaks, not only down onto the floor, but behind the firewall pad and under your carpet/mat.
On your MC replacement, pay attention to the fittings from the MC to the brake lines. There are differences in sizes of fittings.
I did the power booster/front disc swap on my 71. I won't be doing it on my 69.
Senior User
Joined: Sep 2009
Posts: 474
Likes: 3
From: Central Wisconsin
Make sure that it's not just your MC cover leaking. I had fluid on the inside of my floorboard coming from the same spot as yours. The fluid would seep out of the cover, and back into the cab when I parked the truck on the slight uphill grade of my driveway. When I parked the other way, the bottom of the MC would be wet. I flat filed the top of the MC reservoir and put small shims under the contact points of the cover. No more leaks.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Make sure that it's not just your MC cover leaking. I had fluid on the inside of my floorboard coming from the same spot as yours. The fluid would seep out of the cover, and back into the cab when I parked the truck on the slight uphill grade of my driveway. When I parked the other way, the bottom of the MC would be wet. I flat filed the top of the MC reservoir and put small shims under the contact points of the cover. No more leaks.
The Chinese seem to think it was better to vent the lid over the gasket lip seal.
Where as the oem specs vented the upper part of the lid..
Did what you did, plus rebent the clamp a little worked for a while then leaked again..
Pick up a new chrome M/C lid at the good guys car show for $3 bucks with vented upper lid works great no more leaking.
I new, I should have not bought any brake cylinder stuff online.
As the turn around time is to slow. Plus having the vehicle down for 8-14 days waiting for a replacement. But if all the lids were the same Chinese style.
Orich
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Cargo Master
Joined: Mar 2014
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glad to hear it is supposed to vent. Mine seeps some around the gasket, but the vent is in the top of the lid near where the hold-down clamp rests.
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Lead Driver
Joined: Apr 2011
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From: El Dorado, Arkansas
The vent should be for the atmospheric side of the MC seal. There will be a vacuum on the fluid side when you apply the brakes.
The bellows in the lid seal will expand and contract with the vacuum on one side of it and atmospheric pressure on the other.
You don't want a direct path for air to get into the brake fluid. The moisture in the air will rapidly degrade the brake fluid. This will lower the fluids boiling point and the moisture will begin to rust internal brake components, causing them to prematurely fail.
The bellows in the lid seal will expand and contract with the vacuum on one side of it and atmospheric pressure on the other.
You don't want a direct path for air to get into the brake fluid. The moisture in the air will rapidly degrade the brake fluid. This will lower the fluids boiling point and the moisture will begin to rust internal brake components, causing them to prematurely fail.
Lead Driver
Joined: Aug 2003
Posts: 7,592
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From: **** hole San Jose ca.
Orich
Laughing Gas
Joined: Nov 2013
Posts: 1,207
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From: S.E. Louisiana;so far USA
It would be good to check all the possibilities which have been suggested, however if it's an old master cylinder, it's likely that the fluid is leaking past the cylinder's piston and running down the rod to the cabin. The cylinders are rebuildable in theory, but usually, if it is old the cylinder's bore is usually pitted and/or worn which means that a rebuild won't work. On hard-to-find cylinders, re-sleeving is a possibility. Rock Auto has a great selection from $16 up plus shipping. Be careful with the brake fluid; it can double as paint remover. 
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
It would be good to check all the possibilities which have been suggested, however if it's an old master cylinder, it's likely that the fluid is leaking past the cylinder's piston and running down the rod to the cabin. The cylinders are rebuildable in theory, but usually, if it is old the cylinder's bore is usually pitted and/or worn which means that a rebuild won't work. On hard-to-find cylinders, re-sleeving is a possibility. Rock Auto has a great selection from $16 up plus shipping. Be careful with the brake fluid; it can double as paint remover.
I should have taken my own advise. It still ended up being $54 bucks. with shipping. Same as loco parts stores
Which, I could have gotten a few miles away at Auto Zone or ORilley's with ez returning it.
Orich
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Junior User
Joined: Oct 2014
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Thanks for all the help! Looks like I'll be replacing the MC in the near future. Other problem that's started to occur as I noticed the leak was that the truck pulls to the right when I step on the brake. What could cause that? Thanks
Logistics Pro
Joined: Nov 2012
Posts: 4,308
Likes: 19
From: Las Vegas, NV
improperly adjusted brakes, blocks hose/line, leaky wheel cylinder...
does it pull from the rear or in the steering? that will tell you front or back but it sounds like you need to take a look at all of them.
does it pull from the rear or in the steering? that will tell you front or back but it sounds like you need to take a look at all of them.