This is a long debate that I've seen all over the web. I replaced my rear pads and rotors yesterday following instructions done by Eric the car guy (www.ericthecarguy.com). He insists that the brake lines must be pinched off (vice grip with rubber hoses) with bleeder screw cracked open when turning (rear) or pushing (front) the caliper piston back in. This prevents back flow into the master cylinder passed the seal. Now, I personally had a fuss over this because brake fluid started leaking from the bleeder screw even after I tightened it. I had to make it real tight then it stopped leaking. So on the left rear side, I didn't perform this procedure. I read some comments on the web and some guys insist that a high pressure hydraulic line should never be pinched.
I'm asking if you guys ever do this. I did a few brake pad changes on my old 98 V6 Accord and I never had to do this. If someone here works for Honda, please chime in on this.
I've done brakes on my own cars for many years, and never pinched a line, or opened the bleeder bolt, when pushing the piston back in. The level in the resevior just rises, so you don't want it to be full, when you push the piston back in.
Don't pinch the lines, you could damage them and if they fail, they'll do it while you're under braking. Some reason never to hang a caliper from the line.
But DO open the bleed valve when pushing the piston back in. The crappiest fluid in your line is in the caliper and you want to avoid pushing that fluid into the ABS system.
So I have one guy here says to do it. But without pinching the brake line, you will still have some fluid that back flows. I think it's better off just doing a complete brake system flush.
No fluid will back flow unless you push the piston really quickly or keep the bleed valves closed. Gravity and a couple of check valves will help the fluid stay down.
We have to push the pistons in anyway. Otherwise there is no way to be sure an air pocket or old fluid is still in the cavity.
Been doing my own brakes since '96 and I've never opened the bleed screw OR pinched the line.
I did have one car I had to open the MC cap to allow the air to back out because the pressure wouldn't allow me to push the piston back in. I believe this is where the whole open the bleed screw thing came from...some mc caps seal so well that opening the bleed screw makes it much easier to push the piston back in. Especially with old rusted iron calipers you used to find on cars built in the 80's
The worst would be to contaminate the ABS/Stability pump and related systems.
Less bad would be overflowing the MC reservoir and spilling paint removing brake fluid in the engine bay.
Openning the bleed valves isn't mandatory. Above all, it speeds up the subsequent bleed process. For a "like new" bleed, the pistons need to be all the way in.
As for pinching the lines, no way i'm ever doing that. I've seen a brake line failure and i'm glad I wasn't in that car when it turned sideway under heavy braking...
Ok, so I'm not calling Eric the guy wrong, but from I've read with most people out there, they refuse to clamp the brake lines. I would agree in this case. Actually, I don't even want to open the bleeder screw anymore because I don't have the means to bleed the brakes with a one man bleeder kit. I will just open the master cylinder cap. I've never had problems in the past anyway.
You could at least get rid of most of the old fluid from the caliper.
Just pump the brake pedal slowly afterward and top off the MC reservoir. You'll have done a partial bleed. Don3 let the reservoir empty itself and suc in air !
I specifically stopped by Honda today to ask. I spoke to a mechanic and was told that they NEVER open the bleeder screw when pushing the piston back in. So there you go. Honda trained mechanics don't even do this.
1.) It used to be that you can get away with clamping brake hoses with vice grips and rags (to protect the brake hose). (You'd be an idiot to clamp brakes hoses with only a vice grip and without anything soft in between.)
However, some of the newer brake lines started using metal wire in the brake line, so what would happen when you clamp down on them is that they would crimp and stay that way, and you'd have to end up replacing that brake line.
The decision to clamp or not to clamp is based soley on what type of brake line you have.
2.) It's true that the worst junk is stored in the caliper. You don't want to push that junk back into the ABS module or the master cylinder. There are cases where the ABS light comes on because that junk gets clogged in the ABS solenoids. You don't want to do a brake job and then have the ABS light come on. Also, another reason you don't want to push fluid back into the master cylinder is because the master cylinder piston is used to traveling on a certain portion of the master cylinder bore. That portion of the master cylinder bore is worn away. If you force the master cylinder piston to travel to the portion of the bore that it usually doesn't go, the seals inside the master cylinder will go bad and start leaking. Then you will have a sinking pedal. You don't want to do a brake job and then have a sinking pedal afterwards. Hey, it happens from time to time, if you have been in the business long enough. Bottom line is you have to crack open the bleeder valve, before you slowly push the piston back in. If you don't, you will suffer negative consequences from time to time. That is the cost of being lazy and not cracking open the bleeder valve.