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Why do brakes go out on stored vehicles?

R

rossow (mn)

Member
No hydraulics on my old Fords, so may be off-topic here, but I'm sure some of you know: Why do brakes go out on vehicles in long-term storage? I have a lot of old cars and trucks, all in dry inside storage. (Old as in 1930s well into 1980s.) Sooner or later, the brakes disappear in anything stored for a few years or longer. Why? Is it a master cylinder that loses its seal, or wheel cylinders? I've never pursued the cause by inspecting the system. Evidence of cause? Ideas? Replacement of a system would be easy, cheap and wise if I wanted to make drivable. Today I'm just curious.

(It's often a race to see which goes first -- the brakes or the carburetor!)
 
Only guessing Rust.
Me electric brake drums rust and they don't work as well until rust cleans off with use.
 
Im guessing the soft goods take a set when there is no hydraulic pressure applied to them for a long time. Regular application of the brake or clutch peddle flexes these seals.
 


Geo. is somewhat right, except that it is the rust inside the wheel cylinders as opposed to just on the rotors or inside the shoes. The problem is that most brake fluid sucks moisture right out of the air. So unless your storage is aggressively climate controlled, every time you have a high humidity front come through you will have moisture condensing here and there all over your treasures and including inside housings which are vented. The moisture makes its way slowly down to the low points: the wheel cylinders. You can prevent this by replacing the fluid with silicone based fluid which doesn't absorb moisture.
 
Old brake fluid (DOT 3 and 4) are hygroscopic, meaning they absorb water which causes corrosion and part degradation. DOT 5 is silicon based and is supposed to be better but causes a softer pedal feel. They cannot be mixed. To change system must be drained and flushed.
 
A collector friend of mine has started using a silicone based brake fluid to try to avoid the moisture and rust problem. I have not asked him if it actually helps. He exercises his vehicles fairly often so he might not be giving it a fair test.
 
Im restoring a 1970 Mustang Fastback. Its been sitting for about a year and a half. I do believe it was driven consistently before I got it.
Im working on the front suspension so I decided pull the factory front calipers. Last time I drove it the brakes seemed fine. But I was amazed to find the caliper pistons stuck. Finally got the pistons loose. They were pitted all around. Luckily as that caliper was the Ford standard, new lifetime warranty are only $30 each. Im not sure of the cause I was definitely surprised at their condition. Im betting the back drums wont look much better when I get to them.
 
The older Corvettes were famous for leaking calipers and master cylinders. If they weren't pitted too bad a ball hone would knock the sharp edges off and then I'd put new kits in and silicone brake fluid, otherwise all new cylinders and silicone.
 
I am with a couple of the other posters. It comes down to the rubber seals. When in constant use, rubber stays pliable and flexible. When left sitting there not in use, the rubber does not get any movement, and because of that, it begins to stiffen up (set up solid) loosing its pliability and flexibility. The hydraulic pressure applied when put back in use, will just distort the seals that are no longer pliable or flexible. This will cause leaks and a non-functional system.
It's really not good on a lot of things to sit around and see zero use. Tires, batteries, belts, hoses, and so on. Not just brake systems. It would be way better for a vehicle to operate even once every 2 or 3 months, rather than not at all in long term storage.
 
Using silicone DOT 5 fluid is a common solution.

But the system must be completely flushed and best started from scratch with DOT 5 and all new components to be sure none of the old fluid is left behind.

Silicone fluid will not fix an already aging or leaking system, everything has to be clean and new, including the flex hoses. About the only thing that can be saved is the steel lines, and only if they are flushed and rust free.

Also the system should be tagged so only DOT 5 is used as a top up.
 
Your comment should be at the top. Everything you said is true. I have two ancient imported cars (Renault Caravelles) for which brake parts are rarely seen. The wheel cylinders do rust, right at the point where the seals are. Same with the master cylinder. I replaced the rubber wheel cylinder hoses (Standard SAE) and flushed the system with Alcohol. Replaced with silicone brake fluid. After over a decade, the brakes are still fine. BUT, they ARE spongy, giving a feel as if there's air in the line. But the braking is straight forward, so I know there's no air. Only issue is the master cylinder has the brake light switch as a pressure switch. Both no longer work--silicone making it insulated? Doesn't leak, so....
 
Brake fluid should be flushed out clear every two years or so. A few manufacturers recommend this service but many don't and I'm surprised it's not mandated as it's a safety issue of the highest priority. Also, the use of steel brake lines when, for a couple dollars more, they could have used stainless steel lines and avoided a lot of lawsuits.
 

DOT 5 any moisture that gets in it and it will, will puddle up and rust... Some manufactures I have ran across will void the warranty if dot 5 is used.


As posted its best to flush the fluid every couple years.
 
I have had experience with antique vehicles also and done a bit of research and repairs.
 
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