trouble retracting brake caliper pistons

[mvmcali]

finally did my first brake job , replaced pads only in my 2001 QX4

i had a very hard time pushing the caliper pistons back into their housing. I did buy the generic tool for it and used the old brake pad to push against the tool . the tool has a hand knob but I needed to put a plumbers wrench on it to get the pistons to retract.
why so hard , did i do something wrong?

- i did not bleed the brakes, ie. open the little valve on the caliper.
-I did take the top off the reservior (but i dont think think this did anything
-I did pump the brakes when I first had problems, because i read it on the internet but i dont think it made a difference

[mdmellott]

why so hard , did i do something wrong?

You probably should have bled the brake system. Old brake fluid oxidizes and contaminates the system. Since the fluid does not circulate within the system, the worst of it is stuck in the brake cylinders, where it sees the most heat and stress. You may have pushed contaminants into the brake lines and clogged them. A clogged brake line is the only reason I can think of for why it was so hard to push those pistons in. The only issue I have ever had is topping off the reservoir, after bleeding the system, before pushing in the caliper pistons to install the new pads. The overflow mess out of the reservoir is a mistake I won't forget or repeat again.

Keep bleeding the brake lines until fresh clear fluid is coming out. You should always flush the entire system this way when bleeding the brakes to ensure long life of all brake system components.

[mvmcali]

hmm. i think I understand what you are saying but , having watched a few 'pros' explain on youtube (for whatever thats worth , none said to bleed the brakes. just push the pistons in and that they should retract easy.

So , to be clear. i think you are saying I should have loosened the little bleeder valve on the caliper body and THEN pushed the pistons back in? and the fluid that I am then pushing will exit via the valve rather than going back up towards the reservoir?

one other thing that didnt make sense, is that when i pushed the pistons back in (an enormous effort like i mentioned), i was surprised to see that reservoir level did not change, any idea why that would be?
thx!

[mdmellott]

Yes. Pushing the old brake fluid out of the opened bleeder valve will ensure badly contaminated fluid in the calipers does not get pushed upstream through your brake lines. On a well maintained brake system, that has had fresh fluid flushed through the entire system every time new pads are installed, this would not typically be necessary because there would not likely be excessive contamination build up anywhere in the system. So, I typically just push in the pistons, install new pads, and then flush the entire system until fresh fluid starts coming out of the bleeder valve.

The "one more thing that didn't make sense", is kind of a problem. The only ways it would be possible for you to push in the caliper pistons without the reservoir level rising are: (a) The expelled brake fluid from the calipers is leaking out of the system somewhere, or (b) The highly pressurized brake fluid being wrenched out of the calipers is turning one or more or your flexible brake lines into a balloon. The brake fluid will not compress like air does. It has to go somewhere and it should have been pushed easily into your reservoir. A massive amount of air in the lines would compress but it should still get pushed into the reservoir unless you have a a seriously clogged system.

There is a lot of damage that can happen to the brake system's anti-lock braking system, load sensing valve, master cylinder, brake cylinders, brake hoses and lines, if the entire system is not periodically flushed from the reservoir on through and out of the brake cylinder bleed valves.

[mvmcali]

thanks. yes, im very familiar with the incompressibility of a liquid vs a gas so I understand your point about it being a serious issue if the fluid being pushed out of the pistons is not showing up in the reservior... its possible that i didnt really notice the level increasing... if I compressed the pistons lets say 7mm, should htat have made a very noticible increase in the reservoir level? im trying to imagine the surface area of the 2 pistons vs the surface area fo the reservoir...

also. do you think all the years i have been getting my brake jobs at a local shop (probably 4 or 5 with 160k miles ) , do you think they have been bleeding the brakes? I never really thought about if that is part of the garden variety brake job.

[mdmellott]

Any volume of fluid pressed out of the caliper brake cylinder would have been noticeable in the reservoir level if you had noted the level to begin with. A quarter inch or so pressed in isn't much but it would have been enough to notice.

Flushing the brake system sometimes sets off a debate with some mechanics. I have never had a shop service my brakes, rotors, or drums. Always did it myself, on every car I have owned for the past 48yrs. Drums and rotors I would replace myself or drop the old ones off somewhere to have them resurfaced. Some say flush every 30K miles or 2yrs, which ever comes first, but I just do it whenever I change my brakes or 5yrs or so have gone by since the last time I did it. I don't know if there is actually a Nissan/Infiniti factory recommended timeframe for this.

It's not a typical brake job service to flush the entire brake system when you get a basic brake job, so it's possible your ride has never had it done before. You would have to ask your mechanic(s) that worked on it in the past to know if that service was ever provided.

[VStar650CL]

thanks. yes, im very familiar with the incompressibility of a liquid vs a gas so I understand your point about it being a serious issue if the fluid being pushed out of the pistons is not showing up in the reservior... its possible that i didnt really notice the level increasing... if I compressed the pistons lets say 7mm, should htat have made a very noticible increase in the reservoir level? im trying to imagine the surface area of the 2 pistons vs the surface area fo the reservoir...

also. do you think all the years i have been getting my brake jobs at a local shop (probably 4 or 5 with 160k miles ) , do you think they have been bleeding the brakes? I never really thought about if that is part of the garden variety brake job.

Shops do not typically bleed brakes when replacing pads, it isn't necessary in a healthy system. Bleeding is part of a brake flush or replacement of hydraulic parts. When the pads are badly worn on all four wheels, typically the fluid level in the reservoir will rise from just above Min to near or at Max. In most systems, compressing individual wheels will only move the reservoir a few millimeters, especially if the pads are moderately worn and not on their last legs. So if you weren't paying close attention, it's entirely possible you simply didn't notice the increase.