Opening Bleeder Screw To Retract Caliper Piston

[The Critic]

Earlier today, I had a local tire shop perform a front brake job (replace front brake pads and resurface front rotors) on my friend's 2009 Fit.

The tech who did the brake job believes in the theory of opening the bleeder screw while retracting the pistons. I watched him do this and wondered if air would be introduced into the system. He told me that he always opens the brake bleeder screw while retracting the pistons, and has never had to bleed the brakes afterwards. The reason why this works in his opinion is because you are essentially gravity bleeding the system and as long as you close the screw right as the piston fully retracts, there is no problem.

Sure enough, I got the car back and the pedal felt fine, maybe slightly soft. But after a pad bed-in, the pedal felt great-- no discernable difference from before the brake job.

Does anyone else open the bleeder screw to retract the caliper piston? I understand the theory behind it, though OEMs say there isn't enough fluid movement to cause any problems.

Thoughts?

 

[tonycarguy]

That's an odd thing to do. I never touch the bleeder nut when changing brake pads. It remains closed the entire time

 

[mechanicx]

I don't see any harm it doing that way but I don't really see any advantage. It would keep the master cyclinder at about the same level as it was instead of increasing the level. I think no air would enter through the bleeder because the bleeder is at a high spot on the caliper assuming the caliper was not turned at a odd angle while being retracted.

 

[JustinH]

I have never seen anyone do this either.

 

[The Critic]

Originally Posted By: JustinH
I have never seen anyone do this either.


Quote:
There are two schools of thought on preventing debris from being flushed into the anti-lock braking and master cylinder assemblies when the piston is seated in the caliper bore. The first “school” opens the bleeder screw to relieve pressure as the caliper piston is seated. The second “school” clamps the brake hose closed with a pair of hose-clamping pliers to prevent debris from back-flushing into the master cylinder. The first-school method is the most commonly accepted because there’s less chance of inadvertently damaging the hose.


http://www.import-car.com/Article/70130/tech_feature_disc_brake_caliper_service.aspx

 

[Dan55]

On some vehicles the pistons do not retract easily and the opening the bleeder makes things alot easier. To service the rear discs on my 2000 Passat I had to buy a special tool http://www.harborfreight.com/automotive-...-kit-97143.html

 

[CharBaby]

Since the piston needs to be pushed back into the caliper in order to fit over the new pads, I do open the bleeder screw when pushing the piston back in. This does help prevent debris from traveling back through the system and contaminating the ABS sensors. I then procede to bleed that caliper prior to closing things up. I only started doing this with vehicles equiped with ABS. Prior to ABS, I pushed back the piston without opening the bleeder screw and never had issues.

Now that I do have vehicles with ABS, I bleed the brake system more often(often when rotating tires) than I previously did on vehicles w/o ABS. Just don't want to replace any sensors if I don't have because of contamination. IMHO, it's just good preventative maintenance. While I'm in there, I may also relube the sliders if things seem to be hanging up.

 

[REDDOG]

My dad taught me to open the bleeder screw. Always have and have never had a problem or an ABS light. I would personally demand it be done this way too if I weren't doing it myself. It naturally flushes the "nastier" portion of the fluid out.

 

[fdcg27]

This is considered "best practice" for the system.
Unless the system is actually allowed to run dry, there is no chance of air being introduced.
While I usually don't open the bleeders, I have been told that it is highly recommended for vehicles with ABS.
It isn't the sensors you'll mess up, since they are entirely external to the brake hydraulics, rather it is the electro-mechanical valve unit itself which may suffer, which would be fairly costly to have to replace.

 

[spasm3]

i open the bleeder, because the fluid most likely to have debis is the fluid in the caliper, i don't want to push and crud back up in to the line or master cylinder. I open it, push the piston in,after loading the pads, i bleed the caliper thoroughly.

 

[hounddog]

Always open the bleeder valve.Most techs do.If not besides crud you can blow fliud out of the master cylinder and eat paint away or get it on fenders etc.

 

[Zaedock]

Having worked in a shop, unless changing the caliper, I never opened the bleeder screw. I simply used my home-made tool and retract the piston (didn't want to give my arm or leg to the Snap-On or Mac guys to buy one).

I don't turn a wrench anymore, but I still do it the same way on my own vehicles. The thought that "junk" may get pushed back into the rest of the system makes sense to people, but if you take the average GM DBC-7 brake system - there's like 10 solenoid valves that operate the ABS. That can generate "junk" too. Remember, it's a mass produced automotive system.

IMO, the solenoid block and master cylinder probably contain more contaminants than the caliper. Some brake guys do it the other way as described above with the opposite thinking, but either is fine.

 

[Zaedock]

Originally Posted By: hounddog
Always open the bleeder valve.Most techs do.If not besides crud you can blow fliud out of the master cylinder and eat paint away or get it on fenders etc.


Maybe in your neck of the woods. In my experience, most techs don't want to bother and just retract the piston. In 20+ years of automotive experience, I've never seen a retracting caliper "blow" fluid out of the master cylinder. I've seen plenty of techs spill it all over when pouring new fluid in though.

 

[Steve S]

On ABS brakes you open the bleeder.

 

[cjcride]

Nice read.

 

[Craig in Canada]

I do exactly this, for several reasons:

1/ the worst fluid will be down in the caliper - the most seal rubber, moisture, contamination and the most temperature cycles. If you're not flushing the system this pocket of fluid is one you certainly want OUT, not pushed back up the line into the rest of the system.

2/ Opening the bleeder makes the piston extremely easy to compress instead of having to force fluid back through the lines, ABS, master cylinder etc... No special tools, prying, less chance of damaging something by slipping, dropping, gouging.

3/ You run absolutely no risk of absent-mindedly overflowing your reservoir when pushing the pads back.


IMO, ANY brake service should be followed by at least a quick bleed so "possible introduction of air" is a non-issue. A couple of pedal pumps worth of bleeding is a no brainer - why would anyone NOT do this when replacing pads/rotors?

I usually completely bleed through (i.e. flush) the brake and clutch circuit fluid during any brake work and try to do it once per year even if no brake work is required.

 

[QuadDriver]

1) when using your handy dandy brake caliper retracting tool (spreader from cal-van, a large c clamp, or a set of strong hands) the OEMs are pretty specific you SHOULD not force fluid back up past the ABS unit.

2) disk brakes use like 4-5 times the fluid of a wheel cylinder and unlike a wheel cylinder do not retract after use, so by opening the screw and using a bleeder tool (some plastic hose and a little bottle) to collect the fluid, havent you essentially changed MOST of the hydroscopic fluid in the disc system?

Its a pretty good idea what you mechanic did....

 

[mechanicx]

I agree. I think the idea of debris getting pushed back into the ABS unit and causing problems is a little exaggerated. Besides the real solution is to just bleed the brakes ocassionally. A lot of posters say they open the bleeder. But for a pad job I don't think I've noticed anyone doing it. It's not in most service manuals that I've seen. In fact usually they tell you to siphon brake fluid from the master cylinder in case there is to full of fluid level in the MC for piston retraction.

But like I said it couldn't hurt even if it doesn't help much. And best practice would be to bleed/flush the brakes at pad change anyway. But that's another thing that usually doesn't get done.

 

[hounddog]

I ran shops 25 plus years and turned wrenches.When pushing a piston back in with a topped off master cylinder just where do you think the fliud goes? It comes out of the top of the master cylinder! Either it gets by the cap and drips all over or it pops the cap/cover off.Lots of techs just don't give a rat cause its not their vehicle.Granted if the master cylinder is low on fliud that won't happen or hasn't been topped off due to pad wear.

 

[The Critic]

Interesting experiences. I've personally never opened the bleeder screw, as I felt that the less that I touched them, the better, considering how many stories you hear about bleeder screws snapping off.

Since the pedal feels great after the pad bed-in (possibly better than before the brake job), is there any reason for me to be confirmed about air in the system? The car is a 2009 so it isn't due for a brake flush until the three year mark.