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press brakes once - no brakes. pump to stop on a dime.

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if i press the brakes like normal....i get nothing.

 

if i pump them three times they lock up awesome.

 

is that a bad mastery cylinder or air in the lines? they wouldn't stop that well with air in the lines would they? or could it still be air in the lines?

 

background is i swapped in new dual piston calipers, pads, and rotors onto my 1997 Impreza OBS. bleeding was a PITA. a friend pumped the brakes ten thousand times first go around. now i believe all the air is now out with the assistance of a Motive Power Bleeder.

 

i did not do the ABS sequence.

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When you bleed your new master cylinder place a piece of 2x4 under the brake pedal so it can't go all the way to the floor. That may be what messed up your old mc.

 

PS Bleed the mc at the lines first as I described in your other brake thread.

 

Edit: Nevermind, I see you have a pressure bleeder now.

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if i press the brakes like normal....i get nothing.

 

if i pump them three times they lock up awesome.[...]

background is i swapped in new dual piston calipers, pads, and rotors onto my 1997 Impreza OBS. [...]

I'll give you some general info that might lead to a solution of the problem.

 

Obviously, a single stroke of the master cylinder should move the caliper pistons (or wheel cylinders, if drum brakes) so that the friction material makes contact with the rotor (or drum). The master cylinder has to match the requirements at the wheels, in terms of fluid volume delivery (and pressure, but let's forget that for this discussion). If you change the calipers, you have to make sure that the area of the two pistons doesn't materially exceed that of the single one in the calipers being replaced. Otherwise, it's possible that not enough fluid will be delivered by a single depression of the brake pedal to sufficiently move pistons at the wheels, requiring pumping to compensate.

 

If you find that the pedal is hard enough after pumping, the master cylinder is probably not defective, especially if you can hold pressure on the pedal for a while and it doesn't sink. However, if the "new" brakes have greater fluid volume requirement, the master you're using might not be adequate. Since I don't know the specifics of your swap, Gary, I don't know whether that applies to your circumstances or not.

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Grossgary,

Just a thought, based on a situation I recently came across on a friend's jeep. When you changed the calipers ... did you put the correct caliper on the correct side of the car both front and rear? What I'm driving at .... are the bleeder screws at the top of all of the calipers? My friend's jeep did pretty much like you describe, certainly because of the air in two of the calipers. My apologies if everything checks out correctly.

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If you went full stroke on the MC when bleeding the brakes most likely you will need a new MC. The bore wears over time and all the junk is pushed to the end of the stroke.

 

When you go full stroke, which does not happen normally, the seals get into this stuff.

 

I have 3 or 4 spares, let me know if you need one.

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My humble comments :-)

 

 

It's not a volume problem. The MC can deliver the goods if it's in good condition.

 

Off hand, yes, I would think MC too, IF there really is no air in the lines. So, check as stated above that the bleeder screws face the right way - up!

 

You might also want to check the drums in the rear - assuming that's what you've got - and adjust the shoes all the way out so they reach the drum. If the clearance is too high (frozen auto adjuster?) your pedal will drop quite far.

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that master cylinder got worked over like a 50 year old Farm All tractor, so that's a good suggestion.

 

so the brakes will lock up really tight even with air bubbles?

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Sure, once you compress the air bubbles, they will transmit the pressure.

 

Of course, if you drive and brake a lot, the brakes get warmer, the air bubbles bigger, and you'll never get a firm pedal.

 

Any conclusion on the caliper orientation?

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Any conclusion on the caliper orientation?
i'm out of town at the moment so i'll have to check when i get back. i only did the fronts, is it possible to install them on the "wrong side"? guess so?

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Yep, it is. The bleeder screw should be in the "top" of the two possible positions. You'll notice an L and an R near the bleeder.

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When you changed the calipers ... did you put the correct caliper on the correct side of the car both front and rear? What I'm driving at .... are the bleeder screws at the top of all of the calipers?
nice hit - that's exactly what it was. i had them on the wrong side, duh! swapped sides, bled them and they stop awesome! thanks guys.

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