Question about changing brake pads. 

"marshknute" (marshknute) 10/09/2015 at 07:36 • Filed to: None

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Some of you may remember that I !!!error: Indecipherable SUB-paragraph formatting!!! to bleed my brakes a few weeks ago. Well I’m about to swap the stock brake pads for racing pads in anticipation of an upcoming track day weekend. Basically, I don’t want to fuck up again, even if I’m not bleeding the brakes this time. Your input would be much appreciated.

Anyway, I’ve changed pads before, and it’s always annoying trying to compress the pucks enough for the new pads to fit.

So my question is this: if I open the hood and unscrew the cap to the brake fluid reservoir, will it make it easier to compress the pucks? Or will doing that allow air to get into the system via the open reservoir?

Countach for your time:

SidewaysOnDirt still misses Bowie > marshknute 10/09/2015 at 07:47

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Opening the brake fluid reservoir will not get air into your lines. Sometimes, the pads do not come with supporting hardware, and I’ve made the mistake of not noticing that my old pads have shims and the new ones didn’t, so that’s something to keep in mind. What ended up happening in that case was the caliper pistons got overextended, and the braking point was very close to the floor. It felt like air in the system, but wasn’t.

That Bastard Kurtis - An Attempt to Standardize My Username Across Platforms > marshknute 10/09/2015 at 07:52

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Yeah, I always pull the cap before compressing the piston. Just be aware that if you’re reservoir is very full, you might get some fluid overflow when you compress them. I have a syringe I use to suck a little fluid out, then top it off after I'm finished.

BigBlock440 > marshknute 10/09/2015 at 07:53

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Opening the reservoir cap won’t do anything, and forcing the calipers back without cracking the bleeder valve could force fluid through the valves the wrong way and fuck shit up. At least that’s what I’ve heard, but I’ve never taken a proportioner valve or master cylinder apart to confirm. Still though, just crack the bleeder valve.

McMike > marshknute 10/09/2015 at 08:07

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The only reason to take the cap off is if you need to remove/add some fluid.

At one point, your pads were new, and the reservoir was full. As your pads wear down, the pistons gradually come to rest more and extended (they don’t retract when you release the brake) With with more fluid behind them now,the level of your fluid in the reservoir will be lower.

If someone topped off the reservoir during the life of the pads, you will have too much fluid in the reservoir when you try to put the pistons back in. It will overflow and make a big mess.

I usually remove 3/4 of the fluid in the reservoir whenever I do brakes. you can always top it off when you’re done.

Nisman > BigBlock440 10/09/2015 at 08:30

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Don’t do this. I’ve never heard of anyone cracking open the bleeder valve to compress the piston. I don't think it would hurt anything necessarily but it's totally unnecessary.

SnapUndersteer, Italian Spiderman > marshknute 10/09/2015 at 08:42

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Yes, you should remove the cap to help make it easier to compress the piston back in.

I always do so.... shit I did it last night while doing this on my BMW

Hiroku > marshknute 10/09/2015 at 08:56

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Yes, opening the cap could help. Just make sure the fluid level isn’t too high or it could overflow out of the reservoir when you compress those pistons (brake fluid is terrible for your paint). If it is near the “max” line on the reservoir, just take some off the top with a syringe or turkey baster and toss it away (don’t reuse it).

Also, more importantly, crack open the bleeder valve on that caliper before you attempt to compress the pistons. Not only will it make it MUCH easier for the piston to go back into its bore, it’s also not a good idea to send old, dirty fluid back up into the lines and into the ABS actuator (or so they say, I’ve never had problems with it personally, but it doesn’t hurt to be extra careful with these things IMO). You must bleed the system if you do that, though. It is good practice to bleed the lines after a brake pad swap anyway.

Also, try using a C-clamp and an old pad to compress the pistons, makes the job a piece of cake. Make sure to compress it slowly, so as to avoid damage to the master cylinder.

Happy wrenching! :)

Hiroku > Nisman 10/09/2015 at 08:57

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It does make compressing the piston much easier though, and it doesn’t do any harm, so why not do it? You just need to make sure to bleed the system when you’re done.

jariten1781 > marshknute 10/09/2015 at 09:00

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I’ve always removed the cap because that’s how I was taught forever ago. I believe it doesn’t really do anything, but it also doesn’t hurt so whatever...inertia.

If you don’t have caliper retractors pick some up or borrow them from the store. It's a lot less painful than using a C-clamp or pliers or whatever other ghetto method I tried before.

crowmolly > Nisman 10/09/2015 at 09:10

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I know plenty of people who do this.

qbeezy > marshknute 10/09/2015 at 09:37

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Well there is a consistent opinion on how to do it here /s

Nisman > Hiroku 10/10/2015 at 09:17

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I don't always need to bleed my brakes when I do pads or something so it just makes more work in the end. If your planning on bleeding anyway then go for it.

Hiroku > Nisman 10/10/2015 at 15:49

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Well I like taking the opportunity when doing pads to get some fresh fluid in the lines so I always bleed afterwards.