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How To Bench Bleed a Step Bore Master Cylinder


Hey Everyone, Today I’m going to show you a couple different ways to bench bleed a Step Bore Master Cylinder. Let’s Go. When installing a master cylinder, it is important to get all the air out of the system. If you don’t, it could cause poor brake performance, a soft or non-responsive brake pedal, and you might need to do the job again. Step Bore Master Cylinders are more difficult to bench bleed than conventional master cylinders. They use an internal valve, called a Quick Take-Up Valve, that traps air, causing difficulty in bleeding. Step Bore Master Cylinders also have a larger primary bore, which takes longer to refill while bench bleeding. The preferred method of bleeding a Step Bore Master Cylinder is to use a brake syringe such as the Cardone Master Cylinder Bench Bleeder tool. To bench bleed using this tool, the first thing you want to do is mount the master cylinder in a vice by clamping on to the mounting flange. Make sure the mount is level, and avoid clamping onto the casting body, since that could damage the unit. Next, place a drain pan under the master cylinder to catch any fluid that’s expelled during the bleeding process. Then remove the protective caps in the primary brake line port, and fill the reservoir with fresh, clean brake fluid. At least halfway. Draw some fluid into the syringe, and then purge the air from the syringe. Starting with the primary inlet in the reservoir, inject brake fluid until clear, non-aerated fluid flows from the primary brake line port. Then, refill the syringe, purge the air again, and inject the fluid into the primary brake line port until no air bubbles are visible in the reservoir. Do the same for the secondary inlet and secondary brake line port, and complete the install following your OE Approved Service Manual. If you don’t have a syringe available, you can still do a traditional-style bench bleeding procedure, which requires stroking of the piston, and is much more time consuming. There’s a slight variation between bleeding a Step Bore Master Cylinder and a conventional master cylinder, so pay close attention to the process. Again, mount the master cylinder in a vice by the mounting flange, keeping it level. Then, install the supply plugs into the primary and secondary brake line ports of the master cylinder, and fill the reservoir half way with fresh, clean brake fluid. Using a blunt tool to press the piston using a short stroke of an inch or less, and hold for 20 seconds. Make sure the stroke doesn’t exceed 1 inch, or else you could damage the seal. Keeping the piston depressed is the key to getting all the trapped air out of the Quick Take-Up Valve. It’s important to wait at least 30 seconds between strokes to allow the larger primary bore to refill with fluid. Repeat as necessary until no air bubbles are visible and the piston travel is less than 1/8 of an inch when stroking. Finally, complete the install following your OE Approved Service Manual. As you can see, the Cardone Bench Bleeder Tool definitely helps speed up the bleeding process, saving you valuable time, and eliminating the chance of having to do the job twice. That’s all for now. Hope this instruction has been helpful. Thanks for your time, and I’ll see you on our next edition of ProTech.

10 thoughts on “How To Bench Bleed a Step Bore Master Cylinder

  1. I just bought a master cylinder for a 1970 Chevy.ย  The bleed kit was those 2 plugs.ย  Will this video adequately show me how to bench bleed my master cylinder?

  2. The quality of A1 Cardone rebuilt master cylinders suck. I personally have replaced three master cylinders all on Chevy trucks and 2 of them I got as the Booster/Master Cylinder assembly and ALL 3 master cylinders LEAK at the reservoir tank grommets. The most recent one I replaced I had to take back off the vehicle and return it to the auto parts cause it would NOT push fluid to the rear brakes and further inspection revealed that it wasn't even doing a full stroke when the brake pedal was depressed, exchanged it for yet another cardone master cylinder and installed it only to find out this one leaks at primary port for the front brakes. The flare nut is as tight as I can get it without stripping the threads and still leaks like a water fall during brake application. I think Cardone could spend a little more thoroughly inspecting the cores they receive and focus on providing LEAK FREE rebuilt units for the price of replacing them and being charged a core fee until you install this junk and take your original back to get your core deposit returned.

  3. Will this process work if the step bore master cylinder is already put in the vehicle ?
    Would my local auto parts store have that siringe you use in the video

  4. Killer video man, really valuable and cool stuff, keep up the good work. I have a channel that could be able to help you out if you are interested in mixing and mastering. Have a good one mate! ๐Ÿ™‚

  5. Why not place the syringe on one of the open ports first and extract the air and maybe some brake fluid out through the open port. Then fill the syringe with fluid from the reservoir and pump the fluid through the same port to finish getting the air out. Cap off the port and repeat the process for the second port. Seems like it would make a lot less of a mess that way. I might try this or the vacuum bench bleeding method. The method that uses the tubes to pump fluid back into the reservoir is for the birds.

  6. I used this syringe for the 1st time today on a Cardone reman booster/master cylinder combo. It works great! Fast and easy bleeding. I will never go back to the old way

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