Bleeding Master cylinder on car
 

Am about to replace the 2 lines that feed down from the master cylinder as they got damaged by a falling block and tackle from an overhead hoist :ack: Luckily, this seems to be the only damage.

I have read posts before about bench bleeding new master cylinders before putting them on the car. I wondered if before the new lines are fitted, I could simply refill cylinder ( fluid was lost ) and bleed it using two small pipes that feed back into it by slowly pressing the brake pedal and then refit new lines.
Thanks.

It's best to bench bleed it, and then bleed again after it's in the car.

Yes. You can... cut the lines short, like a couple inches and put some hose on them and run back into the cyl. Pump it until theres no bubbles.. same difference..
I would have the new lines in before removing the old ones and hook the new ones up immediatly making sure theres plenty of fluid in the resivoir. Be sure to keep plenty of fluid in there while the new lines are filling up. You can gravity bleed them and they will use fluid quick. Watch it. If it emptys you have to start over..

One of the reasons for bench bleeding is that you can get the master cylinder sitting level. On the car the front is usually elevated. You could jack up the rear of the car enough to get the master cylinder sitting level before the bleeding, but if you're going to that much trouble, the mc is not that hard to remove.

You can do it with the lines on the car if the rest of the lines are mostly filled with fluid. Slide some vacuum line over the new lines and fill them up with fluid. Then hook up to the master cylinder and get most of the air out of the four corners.

Crack the lines loose at the master cylinder and run them like they are bleeders. Gotta wrap rags around the lines in the car and put a pan under the master cylinder... some drip will find paint. Hold pressure, crack the lines loose fluid and air will bubble out of the threads. When it is just fluid, go bleed at each corner again.

Its easy enough to do, but if you can bleed it on the bench do it as its a lot easier. The above works if you don't have some spare lines. (I figured out how to do it on a master that had a remote resevoir and I had nothing that fit the ports! :crazy: )

Yes, the M/C must be level while bleeding. That is why they tell you to "bench" bleed it. I wouldn't try it any other way as you are asking for trouble. If you frequent this forum often, I'm sure you have seen many posts where members are having mucho trouble bleeding their brakes. :flag: