Brake bleed disaster - Page 4 - PeachParts Mercedes-Benz Forum

Brian Carlton · #46 03-19-2006, 04:57 PM

Quote:

Originally Posted by t walgamuth

i dont touch the piston.

i pry between the brake pad and the rotor.

prying between the pad and the piston, i agree, be a bad idea.

tom w

Yes, I'm aware of that.

When you first pry with a screwdriver......at the very edge of the pad, the piston will move in a reasonable manner because you can't easily skew the pad due to the very low clearance between the pad and the rotor.

But, as this gap is increased, the pad will apply all the force from the screwdriver on one edge of the piston. Now, if you can get the screwdriver near the center of the pad and lever the pad away from the rotor, the chance of binding the piston is minimized. Or, if you pry from both sides, simultaneously, the chance of binding the piston is minimized.

If you simply pry from one side in the valiant effort to move the piston back by nearly 1/2", the chances are high that it will bind up somewhere along this trip.

TwitchKitty · #47 03-19-2006, 04:57 PM

RTFB. Read the book and believe it.

Most brake fluid is an alcohol based product and is hydrophilic so it will become contaminated with water from exposure to the atmosphere. If your brake fluid has been changed in the last couple years and is free of contamination then the c-clamp method is fine on a car with single-piston calipers.

If your brake fluid is contaminated it is going to ruin your calipers anyway so you may as well change them now if you can't bleed them.

If your bleeders don't look new, replace them when you loosen them, they are cheap.

Brian Carlton · #48 03-19-2006, 04:59 PM

Quote:

Originally Posted by TwitchKitty

RTFB. Read the book and believe it.

RTFB........

.......you invent that one yourself??

t walgamuth · #49 03-19-2006, 05:03 PM

have you actually tried the screwdriver method?

the moment of most vulnerability is the first part of the push, when the piston is most extended. the more it goes back in the cylinder the less chance there is of it binding up. the cylinder acts as a guide and the further back the better the piston is guided. hence the example i stated of a very worn rotor and a very worn pad being the most vulnerable to jamming.

tom w

Brian Carlton · #50 03-19-2006, 05:09 PM

Quote:

Originally Posted by t walgamuth

have you actually tried the screwdriver method?

the moment of most vulnerability is the first part of the push, when the piston is most extended. the more it goes back in the cylinder the less chance there is of it binding up. the cylinder acts as a guide and the further back the better the piston is guided. hence the example i stated of a very worn rotor and a very worn pad being the most vulnerable to jamming.

tom w

Sure, I've used it plenty of times. I don't bother with a C-clamp unless the caliper is off the vehicle.

Yep, the further the piston is extended, the more risk you have. But, the risk is lessened when the pad is very close to the rotor and increases when some space opens up. The reason is the inability of the pad to rotate at the far side due to the proximity of the rotor.

When I do it, I use two screwdrivers.

The fact that you now agree that jamming is a possibility confirms my original statements.

t walgamuth · #51 03-19-2006, 05:23 PM

just how do you get the second screwdriver in there without opening up a gap with the first?

tom w

Brian Carlton · #52 03-19-2006, 05:24 PM

Quote:

Originally Posted by t walgamuth

just how do you get the second screwdriver in there without opening up a gap with the first?

tom w

You can't.

You have to start the prying with one and then........after you have a bit of space......you insert the second one from the opposite side.

t walgamuth · #53 03-19-2006, 05:27 PM

of prying with the first screwdriver is the moment most likely to induce a jam.

tom w

Brian Carlton · #54 03-19-2006, 05:30 PM

Quote:

Originally Posted by t walgamuth

of prying with the first screwdriver is the moment most likely to induce a jam.

tom w

In actuality, that's not the case.

As mentioned above, you get leverage off the opposite end of the pad so that the force on the piston is "somewhat" concentrated in the center of the piston.

As the gap widens, the force is now much closer to the edge of the piston and the potential for a jam increases.

t walgamuth · #55 03-19-2006, 05:31 PM

disagree.

as you drive the first part of the screwdriver into the space between the pad and rotor all the force is applied at the edge where the wedge is driving in. only after you have created enough space for the full shaft of the screwdriver in can you apply force in the center or on the opposite edge.

tom w

Hernando5w126 · #56 03-19-2006, 05:36 PM

a c clamp is a must tool to do the brake pistons. level and smooth.

Brian Carlton · #57 03-19-2006, 05:38 PM

Quote:

Originally Posted by t walgamuth

disagree.

as you drive the first part of the screwdriver into the space between the pad and rotor all the force is applied at the edge where the wedge is driving in. only after you have created enough space for the full shaft of the screwdriver in can you apply force in the center or on the opposite edge.

tom w

The force from the screwdriver is applied at the edge of the pad. But, that's not your primary concern. The question is where the force is applied to the piston.

When you first jam the screwdriver between the rotor and the pad, you get some leverage because the far side of the pad tries to move in the opposite direction. It can't easily do this because the rotor is in the way. Therefore the point where the force contacts the piston is closer to the middle of the piston.

This only works for the very first 1/8" or so.

aklim · #58 03-19-2006, 05:56 PM

A trick I was taught was to heat the nipple (ooooh baby) and touch the threads with a candle. Let the wax melt into the threads. Seems to have worked. As to the nipple breaking off, well, If you moved it once every other year, I doubt it will break since it won't gather rust and you won't twist that hard. Also make sure you use a 6 point socket instead of a wrench as I have rounded off too many of those nipples and then you have to use a set of vice grips. All this nipple talk makes me think of vices.

As to using a C-clamp without the nipple being loosened, you are pushing all that old crap back into the brake system. I tweak the nipples off and then bleed the brakes. Following what Midas does isn't the best idea here.

Tiredofagasser · #59 03-19-2006, 11:39 PM

ZZZZZZZZZZZZZZ- Put this to bed

t walgamuth · #60 03-20-2006, 09:12 AM

in reality brian and i do it the same way.

tom w