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Brake fluid shelf life ?


Guest abh3usn

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Guest abh3usn

Is there a general rule of thumb on how long a bottle of brake fluid is good for once opened? I know you should flush the system every two years so I would assume what's left in the bottle also absorbes moisture and is no good at a certain point.

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Brake fluid is hygroscopic and immediately picks up moisture from the air left in the container. Since moisture is compressible and brake fluid is not, why risk it?

In my experience, brake cylinders are often ruined by water settling in the lowest part of the system, typically the wheel cylinders and calipers. Since oil floats on water, this makes sense. I had always thought that brakes were a sealed system which made me wonder where the moisture came from. I've been told that brake systems are actually open systems with fresh air being sucked into the mc every time you apply the brakes.

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Guest abh3usn

I thought this was an interesting topic as I am restroing the brakes on my '77 MGB. I'll keep the open system in mind when the project is complete and flush the system when required.

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I just did the brakes on my boat trailer. I drained the brake fluid out of the lines and blew compressed air through them. I then injected acetone into the lines and let it sit overnight, removing the rubber hose first. I blew the lines out again and a slew of gunk came out. The second treatment with acetone did the trick as very little corrosion came out.

I understand that this is the preferred method if you're changing to a synthetic brake fluid.

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Guest simplyconnected

Sealed metal cans can store DOT-3 better than plastic containers.

http://www.rotorsandpads.com/Performance-Friction-Z-Rated-Dot-3-Brake-Fluid-16-oz-025-0001.aspx

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barry Wolk</div><div class="ubbcode-body">Brake fluid is hygroscopic and immediately picks up moisture from the air left in the container....</div></div> Hydroscopic means DOT-3 picks up water anywhere it can find it, in the air that goes in the bottle, in the top of the M/C, in the small openings around the wheel pistons, etc. I won't open my M/C on a rainy day. It saturates at 6-7%.

DOT-3 is glycol/ether based, NOT petroleum. Any kind of oil in your fluid will swell seals, making pistons stick (usually when you depress the pedal, the brakes stick in the locked-up position).

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barry Wolk</div><div class="ubbcode-body"> ...brake cylinders are often ruined by water settling in the lowest part of the system, typically the wheel cylinders and calipers. Since oil floats on water, this makes sense.</div></div>

Fresh DOT-3 has rust inhibitors which go away upon water saturation. Water dilutes throughout the system until saturation, then it pools. Pooled water FREEZES (and boils). Anyone with ABS should take special warning: Change your fluid every 24K miles, which keeps your fluid "dry".

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Guest simplyconnected

Brake fluid always was, and continues to be hygroscopic (sorry for the mis-spelling earlier) - meaning that it absorbs moisture like a sponge. Leave a container of brake fluid open for a few hot, humid summer days, and it will likely absorb enough moisture to render it un-useable according to DOT specifications. Hydraulic clutches use DOT-3 and they too, need to be changed at 24K.

There are differences in DOT-3 fluids. Check out this site as they rate according to price vs value of various brands:http://www.timskelton.com/lightning/race_prep/brakes/brake_fluid.htm

(Mind you, these are racers who always demand maximum performance.)

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Guest simplyconnected

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barry Wolk</div><div class="ubbcode-body">...being married to a walking dictionary. She belongs to the Grammar Police.</div></div> To keep on subject, ask Glynette, at what point is DOT-3 spent after it's opened.

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