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914World.com _ 914World Garage _ Bench bleeding new MC
Posted by: mankowski Nov 4 2017, 05:36 PM
New 19mm ATE master cylinder is not moving fluid through rear outlet when attempting to "bench bleed." The MC is mounted on the car with ~5ft of tube from each outlet port back up to reservoir, with one tube in each of the two reservoir chambers.
Some fluid did pass through the rear outlet into the tubing at first but not even enough to get up to the reservoir, and now the fluid is stopped entirely. The fluid is moving fine through the front brake outlet.
It's my understanding that I should not be bottoming the MC piston out, but how far should I be pushing -- maybe further piston travel is needed? If so, I wonder why this be the case when the fluid from the front outlet is moving fine?
Or, is there more likely something blocking in the rear outlet or plastic fitting? But I can't imagine how that would happen in a brand new MC and bleed kit. 
Posted by: 76-914 Nov 4 2017, 05:39 PM
New 19mm ATE master cylinder is not moving fluid through rear outlet when attempting to "bench bleed." The MC is mounted on the car with ~5ft of tube from each outlet port back up to reservoir, with one tube in each of the two reservoir chambers.
Some fluid did pass through the rear outlet into the tubing at first but not even enough to get up to the reservoir, and now the fluid is stopped entirely. The fluid is moving fine through the front brake outlet.
It's my understanding that I should not be bottoming the MC piston out, but how far should I be pushing -- maybe further piston travel is needed? If so, I wonder why this be the case when the fluid from the front outlet is moving fine?
Or, is there more likely something blocking in the rear outlet or plastic fitting? But I can't imagine how that would happen in a brand new MC and bleed kit.
It's OK to bottom out a new MC. just not an old one that may have a "ring" built up in the cylinder that will rip the seal on the plunger.
Posted by: mankowski Nov 4 2017, 07:56 PM
It's OK to bottom out a new MC. just not an old one that may have a "ring" built up in the cylinder that will rip the seal on the plunger.
Okay, that makes sense, thanks! With the additional travel of the plunger, the fluid moved from the rear outlet as well, and I was able to get all the air out. 
Posted by: lonewolfe Nov 6 2017, 07:20 AM
Where did you get the bleed kit with the blue plastic fittings for the M/C?
Posted by: McMark Nov 6 2017, 09:25 AM
You don't need to let fluid out to bleed the master cylinder. http://www.914world.com/bbs2/index.php?showtopic=304882.
Bubbles will propagate up to the reservoir as you pump. Don't stop until it's got nearly zero movement.
Posted by: mankowski Nov 6 2017, 09:29 PM
Where did you get the bleed kit with the blue plastic fittings for the M/C?
Local O'Reilly's had the kit for $10. Comes with a variety of fittings and clips to hold the tubing at the MC. Unfortunately, the including tubing is black, which makes no sense because you can't see the fluid. So, I picked up some clear tubing at the local hardware. https://www.oreillyauto.com/detail/dorman-help--4422/tools---equipment-16488/tools-17919/mechanics-tools-16816/brake-tools-16514/bleeder-tools-17957/master-cylinder-bleeder-kit/13911/4527169/1970/porsche/914?q=bench+bleed
Posted by: mankowski Nov 6 2017, 09:44 PM
You don't need to let fluid out to bleed the master cylinder. http://www.914world.com/bbs2/index.php?showtopic=304882.
Bubbles will propagate up to the reservoir as you pump. Don't stop until it's got nearly zero movement.
Very cool idea, I'll definitely try this next time! I looked for more information about this "plug" method and found description of syringe bleeding the MC, which is yet another efficient method. There are surprisingly many ways to get this job done, but some look to be less messy than others!
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