Hey guys, just a quick tech question:

I was going to replace a friends rear pads but could not for the life of me get the calipers to swing out. The pads had worn 90%-100% and pistons are fully out so it's all the parts are acting on each other. If i disassemble the whole caliper the rotor comes with it. Tried to force the pistons back but to no avail. Am I doing something wrong? The car is a 97 Nissan Bluebird if that helps.. On a side note, belt replacement on the KA24DE is a bitch!

Get the manual and read that before you break anything!

did you crack the bleed nipple to relieve pressure?

The manual is useless I've read it already! And i was under the impression if you crack the nipple air gets in? I'm not bleeding just changing pads. I could and probably am wrong though :D

Oh and to add from what we did at TAFE i don't recall any nipple cracking for pad changes.

air wont get in unless you pump the brake peddle and it is on the return stroke

He means loosen the nipple to allow fluid to escape as the pistons move in. TAFE people don't know everything!

If its the type where the pads also act as the handbrake, then the pistons need to turn while they move in. The old first gens had rear calipers like that. Like I said, read the manual properly, don't just swear at it. lol

If its the ordinary caliper design, most likely problem is that the pistons have moved out too far, and have tipped over slightly to jam them in the caliper bore, seen that happen. If the pads are worn more on one end than the other, this might be the problem. The only solution is to take the piston right out, see if the bore is damaged, clean it out and reassemble. If the bore is stuffed, replacement is needed.

It would help if you could post the relevant picture of the caliper from the manual, or a pic of the caliper itself.

Ah yeah, that makes sense and I remember learning about that now. Thanks altera! I'm having a crack at it with the proper tools tomorrow so hopefully that works.

Ok well i found the proper section in regards to the brakes. These are the type which act as the handbrake. I'll follow the instructions properly and see how I go. I'll play around with the nipple too :D
Oh and trust me, i definitely don't claim to know everything! I just never opened up the nipple when we changed pads over at school so didn't think it was required.

Thanks for the help!

Just goes to show . . . . school isn't real life! lol I'm glad you found the right page in the manual. lol

Ummm from memory are these not the screw in pistons as the handbrake is part of the claliper

Also, YES air can get in if you release the nipple, if this is required then there is something wrong and the issue needs to be resolved

i aint going to argue with a 40yo mechanic but care to explain how air is able to get in?

It will. But he will need to bleed the brakes (and change the brake fluid) as pushing the pistons back will stir up the grot in the cylinder and move any air there is in there now back up the brake lines and cause spongy or uneven brakes. On such an old car (which by the sound of it doesn't get much attention), just replacing the pads is a half assed job anyway. Pull the pistons out, clean them up, fresh fluid, lubricate moving parts, bleed. Good as new.

It will. But he will need to bleed the brakes (and change the brake fluid) as pushing the pistons back will stir up the grot in the cylinder and move any air there is in there now back up the brake lines and cause spongy or uneven brakes. On such an old car (which by the sound of it doesn't get much attention), just replacing the pads is a half assed job anyway. Pull the pistons out, clean them up, fresh fluid, lubricate moving parts, bleed. Good as new.

so basically it wont let air in and will just stir up existing air in the caliper?

If you are putting pressure on the piston to reseat it into the bottom of the bore and then open the bleed nipple as the piston moves, no air can get in. It just makes it easier to move the piston and makes sure no rubber debris gets pushed back up to the master cylinder. I always replace the fluid in the master cylinder and clean that first (using a syringe), refill with fresh, then take the caliper off the car (still connected to the hydraulic line) and use the brake pedal to pop the piston out. Clean it out, reassemble with new pads, bleed, and repeat for the other side. Usually there is a lot of black rubber bits in the bore, and some light surface rust on the piston.

ok then ,but what if you don't touch the piston and undo the bleed nipple how does air enter?
of course over time air will get into the brake lines, but lets just say the brakes have just been bleed then you undo the nipple how does atmospheric pressure compress a liquid? or am i missing something?

Hes had his brakes done one year ago, thus why it's only going to be a pad replacement. I also don't have the tools to do a bleed and everything else and I am still learning and don't want to do a bleed until i am shown at work and I am comfortable doing it. I realised now that the problem nothing was coming apart is because the handbrake was on, yes I'm an idiot I know! These are the screw type Mal and i won't be touching the nipple as i Am 99% sure that it was just the handbrake that was stopping me from undoing anything, again... Still learning! Although that was just a oversight on my part :S

You should for starters never pop a piston out unless you intend to replace seals, check the bore of the caliper for roundness etc etc

When you undo the bleed nipple, as you push the piston back, the time where you hold it stationary to do up the nipple the piston can pop back out a fraction and draw air back into the caliper. Regardless if you have air back in a line or a caliper you will get a spongy brake pedal.

Again, if a piston is tight it is time to properly overhaul the caliper, not just clean muck out of it. Is a bit like doing an oil change without doing the filter.

Also, cleaning the master out first is how I do the brake fluid change, then pump the new fluid through the system, anything lose will come out when you bleed the brakes, no need to pop pistons out

Agreed. Not needed. I like to pop the piston out to check the bore. I had a car - long time ago - where a front piston somehow caught on the inside of the caliper and cracked it, instant loss of any brakes at all. Fortunately it let go with a crack as I was pulling up to a traffic light and almost stationary only 2 corners from home. I'm also prone to pull master cylinders apart to check for grot, check bores and estimate how much life the seals have left in them. Crazy, I know . . . . lol

Little known fact: The old Sigmas had proportioning valves in the master cylinder which clogged up to the point that the rear brakes wouldn't work at all. Also, the fronts were prone to become unbalanced due to accumulated grot in then. On a dry road, and with normal braking, you wouldn't notice. Howsoever, in an emergency stop, like a dog runs out in front of you, or normal braking in the wet, one front wheel would lock up, with the other three doing not much at all and the car would sail on regardless. Both happened to me, in different Sigmas. An easy fix was to dismantle the master cylinder, rear brake drum cylinders and front calipers and keep them clean. I don't make assumptions about brakes, I like to check everything. Yes, even testing them (and ABS) regularly on a quiet road. Call me paranoid, my brakes are my friend but I need to feel that I can trust them after the Sigmas. lol

Max, Very different days to Sigmas, they had the valve in the master because of the rear drum brakes, no other reason.

Add to this that you are doing far more harm in pulling things apart and add to this yet again that with dual circuit braking systems of our cars also being diaginal oppersite system as well, the chances of no brakes in 1 in a million

If you get an old rubber back into a bore in a different postion or you snag an old rubber and not know it, is far more dangerous

Lets face it, most cars out there with well over 200k and over 10 years old are running original master cyl and calipers, even those which have not had proper brake fluid changes which is often overlooked

End of the day is your choice but I would leave well enough alone

And thank goodness brakes have improved! You are right though, beyond the occasional "test" braking session, I should leave things alone. I will try really hard to fight the temptation! lol (Unless my little tests show up any problems - haven't yet on any Magna)

Interesting read there fellas, again, thanks for the advice on brakes. As noted, it was the handbrake *facepalm*, everything popped out and a quick run to bunnings to get needle nose pliers and job was done in 30 mins!