Brake Piston Question


#1

I’d like to change the front brake pads on my '93 infiniti g20 soon, and it’s my first time doing it on that car. I know that, as part of the process, the brake piston needs to be pushed back to its original, flush position, which will allow the new brake pads to fit.

I read on some forums that you need to bleed the brake line while you push the piston back, which will relieve the pressure and prevent sediment from screwing up the ABS system. I’ve also read that bleeding the brake line is unnecessary: that you can just open the reservoir cap and push the piston back in.

Have you guys heard one way or the other? Any recommendations?


#2

You always want to open the bleeder valve as you are pushing the piston back on cars with ABS so you don’t push the fluid up into the ABS unit. If you coordinate opening the bleeder while you are pushing the piston back, you won’t get any air in the system and won’t need to bleed the system when you’re done. I believe on the rear brakes, the piston is screwed back in and not pushed in. That’s what I’ve done on all of mine with ABS. Don’t take a chance on it. ABS units are expensive.


#3

You read correctly. Open the bleeder valve, then push the piston back and close the valve immediately. Yes, it prevents ABS problems.


#4

Before opening the bleeder, hang a clear plastic bottle half full of fresh fluid as close to the bleeder as practicable, then put a clear plastic tube from the bleeder into the fluid in the bottle. That way, when you push the piston in, the fluid in the caliper will flow into the bottle. The air in the tube will burp out. When the drawback occurs (and there is always drawback) it’ll draw fresh fluid into the caliper from the bottle.

This process prevents air from entering the caliper, making bleeding unnecessary, clears some of the used fluid from the caliper, and also allows the purged fluid to be replaced by fresh fluid.


#5

I have NEVER opened up the bleed screw when pushing in the caliper piston. I have also owned and worked on a G20 as well. Hell…sometimes you can actually use a small prybar or large flathead and insert it into the top of the caliper and pry back the main piston by prying slowly and steadily on one of the brake pads…before you begin the brake pad replacement.

If you want to do this the easy way with NO PROBLEMS…Don’t touch the bleed screw unless you open the system. I must have done 2000 or more brake pad replacements…and NEVER ONCE have I opened up a bleed screw to push in the main piston.

If I am wrong in doing so then I have never had a single problem…in over 27yrs doing so… So…If I am incorrect then I am incorrect… But…again…never, not one single issue…EVER…by doing it this way. Save yourself the work and possibility of introducing Air into the system by NOT touching the bleed screw. If you DO touch it…make sure you put a piece of rubber hose on the end of the nipple…this will hold a column of fluid…and will prevent air from getting into your system.

Personally…I wouldn’t touch that bleed screw

Blackbird


#6

Opening the bleed screw is taught in school. It is done to eliminate the chance of damaging the ABS due to contaminated fluid pushed backwards through it. I guess you prefer to take that chance.


#7
I have NEVER opened up the bleed screw when pushing in the caliper piston

I never did either until I started owning vehicles with ABS.


#8

@MikeInNH‌

Surely in 27 years, Honda Blackbird has done countless brake jobs on ABS cars

If he says he’s never had a problem with his method, I believe him

There’s also something that wasn’t mentioned . . . if you flush your brake fluid every 2 years, like you’re supposed to, you’re not pushing nasty old crud back up into the ABS hydraulic unit


#9

I believe Honda, and in all honesty I think the danger of backdriving contaminants into the modulator is exaggerated, but I still refer the pee-bottle method.

The valves in the modulator are open in their inactive state, so there’s no danger of harming them through back pressure, but I still like the pee-bottle. Call me overly cautious.


#10

For a 2010 Honda Insight, the Factory Service Manual makes no mention of opening the bleeder screw before pushing a piston into the caliper.


#11

I’ve never seen it in any of the Hayes or Chilton Manuals either.

But at some point when a brake line ruptures and you need to bleed that caliper or cylinder you’ll never get that bleeder screw broke loose without breaking it off. Then you may as well buy a new csaliper or cylinder. After a few years of that screw never being broke loose it’s rusted tight.

And as db4690 stated you should flush the system every few years.

I’m sure @Honda Blackbird has never found a need to flush a system either.

Yosemite


#12

i ve never had too much trouble with bleeder valves, the brake lines themselves are another matter


#13

I don’t open the brake bleeder screw when I change pads on my early 90’s Corolla, neither did I on my 70’s VW Rabbit, but neither of them had ABS. If I had ABS I’d follow the directions in the vehicles factory service manual exactly, as not doing so could prove expensive. I think that’s the best advice, just do it exactly the way the factory service manual says to.

The factory service data on my Corolla doesn’t require to open the bleeder when replacing front pads. I just do what it says, step by step, move the piston as much as is needed so I can get the new pads back in. I haven’t done this job in a while, but if I recall correctly I remove the caliper, leaving the hose connected, hang the caliper from something nearby using some bailing wire so it doesn’t stress the hose, then I use a C-clamp and some pieces of wood (as a buffer to avoid breaking something) to move the caliper open. I first check to make sure the fluid level isn’t near the top of the plastic bottle, b/c I don’t want it to spill out and make a mess when I compress the piston.

A couple of hints. When doing pads for the first time, remember to only do one side at a time. Don’t start on the second side until the first side is all put back together. First, you want to have one for reference in case you forget which part goes where. Second, if you remove both calipers, and force the piston on one side, it can cause the piston on the other side to fall out, which is no good.

No harm done to take some photos of course before starting. It’s critical all of the anti-rattle springs, shims, pad support plates, wear indicator plates etc are all installed where they are supposed to go, and oriented correctly, otherwise you will be dealing with problems later.

The other problem a first-timer can experience is the piston getting slightly cock-eyed in the bore. That could cause it to stick and the brakes won’t work. So it’s important to visually check and make any adjustments necessary so the piston is seated properly in the bore before considering that side done.

While this method usually doesn’t introduce air into the system, I still always replace the brake fluid in the bottle with new, and bleed the two caliper’s I’ve just worked on so there’s fresh fluid throughout.

Edit: One more hint. On some cars the rotor can fall off if you don’t secure it properly when removing the caliper. A rotor falling on your foot is best avoided.


#14

So much for Chiltons. In my 09 Pontiac Chiltons, in two different places, it says to add/fill the coolant with ethylene glycol. Nothing about Dexcool. My understanding is that mixing green with Dex causes big gobs of goo. Personally I’d take anything in Chiltons with a grain of salt and verify. Like I said with my diesel, even the factory manual was not correct in setting the injector timing. Manuals are great but they aren’t always gospel.

There are best practices and then what people get by with. I prefer best practices which would be opening the bleeder. I believe the modules are somewhere around $1000. Kind of high risk for a simple matter of opening the bleeder. Perhaps it took a while for any ABS problems to develop and the customer never put two and two together. Then again maybe its only a problem in 10% of the cases but who wants to be the one that loses?

Just my two cents and the advice is free.


#15

When it comes to repairing things that I do not completely know about I consider the cost I would have if I messed it up to the cost of having a professional do it.


#16

@Yosemite‌

I don’t think it’s fair to assume Honda Blackbird doesn’t believe in brake fluid flushes

Just because he doesn’t crack the bleeder during a brake job doesn’t necessarily mean he also doesn’t believe in brake fluid flushes

I think you may be getting a little ahead of yourself

No offense or disrespect intended


#17

I don’t recall seeing any of my coworkers open a bleed screw when retracting a caliper piston in the last 25 years. Half of the ABS pump, accumulator and actuator failures that I see occur before the first brake pads replacement, I don’t think the method of retracting the caliper piston has anything to do with these failures. If this is the cause the procedure in the service manual would change and the manufactures wouldn’t be on the hook for so many ABS recalls.

I have seen a few vehicles towed in after amateurs opened the bleed screws when replacing the pads. When the ignition is switched on the ABS module recognized a change in the system volume, (not reservoir) set a fault and disabled the brake system. The fix is a one hour bleed procedure with the scan tool.


#18

@db4690; you are right and I was just thinking about that while I was eating dinner.

I appologize to @Honda Blackbird, it was wrong of me to assume something that I know nothing about. It was a rude move on my part.

My wife cooked again so you can be assured that I will suffer tonight.

Yosemite


#19

@Yosemite‌

Burnt pork chops?

Or is she just busting your chops?


#20

Rare Pork chops!!! Good guess though.

She’s the only woman I know that can burn water!!!

Yosemite