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grahamkissack's Avatar
 
Join Date: Apr 2004
Location: Vancouver Island
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Bench bleeding a MC was a waste of time

Just installed a new mc tonight for my SC as part of my effort to achieve braking nirvana. To do everything right, I also bench bled the mc before hand. I just filled the reservoir to the point there was fluid in the reservoir bottom and down the hoses to the mc. It took about 5 pumps on the end of the actuator on the aluminum housing before the pair of tubes back to the reservoir ran bubble free.

I took off the tubes and proceeded to install the assembly. I guess thats why they call it gravity bleeding!...I lost most of what I put into the mc through the open ports as I connected the brake lines. By the end of the process, the first few pumps of the mc were air again. Perhaps I'm an idiot, but I just don't see anypoint in wasting time and creating a mess with this step. Usually when I install brake components, I don't spill a drop. This time I put my paint in jeopardy and left a disaster in my trunk.

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Old 07-12-2010, 10:20 PM
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Your right, It's not like a 64' Chevy!! Fluid flows down hill pretty well.
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Old 07-13-2010, 11:12 AM
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I had the same experience the first time I replaced a MC. The second time I didn't bother bench bleeding and had no problems. It was a much cleaner repair with out the bench bleeding step. With a pressure bleeder and a round of traditional bleeding, all air was forced out of the MC.
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Old 07-13-2010, 02:33 PM
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I had the same experience - but bench bled the MC only to remove any particulates, etc. that might have somehow found their way in (even though they cap the openings).

Only want to add that getting OEM brake switch w/ the MC ensured that I wasn't replacing these items since I had gone cheap with the VW equiv. in years past. I really don't like replacing the switches and having to bleed those ports! Folks might weigh the cost of replacing the MC outright if they "lose" their braking lights via bad old switches and they know the MC is hitting its shelf life.
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Old 07-14-2010, 07:05 AM
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i never pre-bleed them. waste of time.
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Old 07-14-2010, 08:57 AM
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Agreed, waste of time and a big mess.
I hook up the reservoir lines and leave the hard lines a little loose. I fill the reservoir and let it sit until the fluid drips out at the hard line fittings and then tighten them. It gets the air out faster than trying to pump it out. I also loosen the fittings at the calipers and let it sit until they drip and then tighten each one. Then I loosen the bleeders at each caliper and let them drip, tighten them, and bleed normally. It keeps it from being a frustrating job, unable to pump the air out for too long.
Additionally, it cuts back on the whining sound escaping from you helper's lips, "my leg hurts!".
I had a pressure bleeder and I've had a vacuum bleeder but I like to do it like this because it's more effective IMO.
Old 07-14-2010, 09:08 AM
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Quote:
Originally Posted by sww914 View Post
Agreed, waste of time and a big mess.
I hook up the reservoir lines and leave the hard lines a little loose. I fill the reservoir and let it sit until the fluid drips out at the hard line fittings and then tighten them. It gets the air out faster than trying to pump it out. I also loosen the fittings at the calipers and let it sit until they drip and then tighten each one. Then I loosen the bleeders at each caliper and let them drip, tighten them, and bleed normally. It keeps it from being a frustrating job, unable to pump the air out for too long.
Additionally, it cuts back on the whining sound escaping from you helper's lips, "my leg hurts!".
I had a pressure bleeder and I've had a vacuum bleeder but I like to do it like this because it's more effective IMO.
Next time, perform this procedure with a PVC tube attached to the bleeder screw. Curved upward, you can observe the air bubbles exiting. No bubbles = no air in the system. You can also pump the pedal to help evacuate air on both ends of the system w/o drawing in any air. Minimum waste of BF too, especially the pricey stuff.

Sherwood
Old 07-14-2010, 12:51 PM
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Get a power-bleeder (or pressure bleeder) and save yourself the time of "bench bleeding" the MC.
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Old 07-14-2010, 01:03 PM
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Guys,

I replaced my complete brake system over the Winter... Big Red calipers,new 23mm master cylinder,stainless flex lines and had to hand fabricate all four solid lines !

I just added a minimal amount of fluid to the new master before installing it and used gravity to bleed the whole system,including the clutch slave cylinder since i was now going to use ATE blue to be sure all the old fluid was out !
After i got some pressure in the system,my son and i bled the old fluid out the old fashion way,push down,hold ,bleed ,release and keep going ...

Although shortly afterwards i purchased a motive bleeder from Pelican with my last order !
Wish i had the Motive earlier,wouldn't have had to bribe my son with pizza for the help ... lol

Cheers !
Phil
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Old 07-14-2010, 02:53 PM
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Jack
 
Join Date: Aug 2009
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Though I haven't done a break job on my P-car, having done it on a Land Cruiser and Early Bronco, I would say that this is the best power bleeder I have used. I borrowed it from a mechanic friend, it worked great.


VACULA Automotive Products

Don't know how much they cost, or where to get one....

-Jack

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Old 07-14-2010, 05:12 PM
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