Help! I did not bench bleed the master cylinder before installing it. I converted my 70 Skylark to disc. I ran new lines up front and back to the rear axel. I bled all four corners of the car and then realized I had to bench bleed. I would like to avoid the spill and mess of removing the master. The back reservoir seems to be air free. Can it be bled without removing?
Sorry, you need to bench bleed it. You'll be able to push both pistons to max stroke that way to remove all air. You can't guarantee full stroke with the factory pedal linkage, and you could be chasing a soft pedal. Devon
is that why i have to pump my pedal a few times before i get good pedal? i didnt bench bleed mine either but ive bled the brakes 5 times and all the lines and hoses are new. not trying to steal, just a simple question
It's a good bet, Lonnie. With it mounted in a bench vise you can coax all the air out because you have the advantage of the extra travel. You can get into trouble doing it with a master cylinder that hasn't been honed/rebuilt, though. When you push the pistons deep into territory they haven't seen since a long life of service, the crud in there can end up damaging the seals. Standard practice for me if the master cylinder is coming off is to pull it apart and clean & inspect it to see how the bore looks, and give it a cleanup hone if it's ugly. Devon
I am not convinced of the necessity of bench bleeding. I worked as a mechanic in this era of cars, and have replaced many masters without bench bleeding. It can be as simple as having a little patience and just letting them gravity bleed, or as expensive as towing to the shop for a power bleed. If you have replaced the calipers and all, it is likely that you have bubbles in them. Try tapping on them with a leather or hard rubber mallet to break them free, and keep bleeding. Be really careful about how far you stroke the master cylinder. If one side has air, and you can deep stroke it (like all the way to the floor) you can damage it. That depth of stroke is not meant to happen. Also, you can "bench bleed" it on the car, but it's mighty messy, and I don't recommend it if your under- hood is in nice condition. Just take the lines off and have someone pump the pedal slowly in half-strokes while you hold your fingers over the outlet ports. Light pressure, with the fluid allowed to flow out going down, to save that nice lacquer paint job.
