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Discussion Starter · #1 ·
OK, I've checked out all of the stuff in the search engines and can't find the answer. When bleeding your brakes after a simple pad change up front, should you leave the resevoir cap on or off, or does it make a difference. Just curious. I know it's a stupid ?, but one that I thought would create a little thinking.
 

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Discussion Starter · #5 ·
why would you bleed them after just changing the pads?

:beer Ding, Ding, Ding, we have ourselves a winner folks. Doesn't matter if the cap is on or off, because there's really no need to bleed the brakes after just changing the pads. However, when you do bleed the system, cap on or off really doesn't matter, as long as you don't run the resevoir too low, like to let air into the system again. I was really bored this morning, can't you tell.
 

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As a general rule, the cap should ALWAYS be on. Brake fluid is very hygroscopic, and it attacks paint, and keeping the cap on (even just resting in place) will limit its exposure to air AND keep it from splashing when you release the pedal.

But like they said: you shouldn't bleed brakes just for a pad swap. Use a squeeze bulb to empty the reservoir, then rinse it with brake cleaner to remove any solids & remove that, then compress the calipers to drive more fluid up & remove that (with any cleaner left in the reservoir), and refill with fresh fluid.
 

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another vote for cap on, period.

good read here:
http://www.babcox.com/editorial/bf/bf40142.htm

to sum it up though, in Steve's post he mentions "hygroscopic" which means the fluid will attract moisture...from the air....every time you open the cap. This moisture helps create rust in the system and helps break the fluid down, so there is no sense in leaving it open so that it can attract all the more moisture.
 

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make sure you replace the fluid with dot 3 or 4 at least 1time every 2 years !! this will make the hydraulic components last longer.. if it is black or dark brown it needs replacing:popc1:
yea, that's pretty much the schedule I try to work on, ever 30-36 months. fluid always will look nice.
 

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Your method sounds like it could double the time of a pad swap.
Not really - it takes less than a minute to pull all the fluid out, shoot some brake cleaner in, & pull that out. Then, after the calipers are compressed & the autoadjusters are extended, a few more seconds to pull out that fluid. :shrug
..."hygroscopic" which means the fluid will attract moisture...from the air....every time you open the cap. This moisture helps create rust in the system and helps break the fluid down...
It doesn't really "break down" the brake fluid; it just contaminates it, like getting coolant in the engine oil. The oil doesn't break down either, but the contamination keeps the oil from working.

Since water boils at a MUCH lower temperature than brake fluid, you lose braking as you add water to the hydraulics because steam compresses, like air in the lines. Emptying the reservoir with each (or at least every OTHER) pad swap removes the majority of water (with the majority of the brake fluid) from the system, resulting in better braking, consistently. And it costs less than $5. ;) A small price for a LOT more safety for your life, your property, and everyone else's lives & property. :thumbup
 

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Since water boils at a MUCH lower temperature than brake fluid, you lose braking as you add water to the hydraulics because steam compresses, like air in the lines. Emptying the reservoir with each (or at least every OTHER) pad swap removes the majority of water (with the majority of the brake fluid) from the system, resulting in better braking, consistently. And it costs less than $5. ;) A small price for a LOT more safety for your life, your property, and everyone else's lives & property. :thumbup
:stupid

Any time I put new brake pads on I usually try and empty the master cylinder and then bleed the front/rear brakes so I flush the old fluid out of the lines. I just keep bleeding until clear/clean fluid comes out. I do a LOT of work on brakes that most people don't but I consider it a safety issue. Any used car or truck I buy usually gets new wheel cylinders, drum brake springs, pads, calipers, all hoses, and a master cylinder. The hoses on my Bronco were shot, got the calipers on special for something like $15 for the pair, wheel cylinders are cheap, etc. Brakes aren't something I take chances with and wait for problems to happen.
 

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IMO, bleeding brakes unnecessarily is just asking for air in the lines. I don't usually even bleed when I change a MC or HCU; I just reverse-bleed.
Usually depends how you bleed. I always have a helper sitting inside while I open the bleeders. I open the bleeder, they depress the pedal, I tighten the bleeder, they raise the pedal, and then repeat. Takes a while (and hard to describe without sounding dirty) but I've never had air in the lines after I've done that...and I've got a lot of dirty fluid out of the lines too. Wheel cylinders are usually one of the first parts of a brake system to corrode so I try and get as much of the old fluid away from them as I can. Plus the extra bleeding gives you a chance to remove the bleeders, wire wheel them, and apply antisieze and replace the dust caps. Pumping the brakes up and then cracking the bleeder open is just asking for extra air in the fluid.

Derek
 
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