Bench bleeding the Master cylinder

Tiny
R.D.
  • MEMBER
  • 2009 DODGE CALIBER
  • 2.0L
  • AUTOMATIC
  • 110,000 MILES
They send to plastic fittings to screw into the holes and say to push the rod down no more than an inch then wait a few seconds for the air to bleed, the problem is these plastic fittings they send leak the fluid out a little and also let air back into the cylinder. I feel like I have gotten all the air out of the cylinder but when I install in on the car the pedal still goes to the floor. The system does not appear to have any leaks anywhere.
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Sunday, February 18th, 2018 AT 1:31 PM

4 Replies

Tiny
CJ MEDEVAC
  • EXPERT
Let's bleed it on the car!

Screw in the plastic fittings pretty snug.

Put the hoses on and wrap some masonry cord a few times around the tubing where it shoves onto the plastic fitting and tie it off. (now they will not blow off!)

Two people.

One on the pedal (instructed to only push the inch worth- you can even put a piece of wood behind the pedal as a stop).

The other person will hold the ends of the hoses submerged inside the master cylinder fill hole. This will keep air from sucking back in. Stay submerged until you are done. (there may be a strainer grid inside the master cylinder fill hole that you may have to remove (replace later) to get the tubes into the brake fluid.

On some I have bled, I will pinch the hoses with my fingers, thus creating a "check valve effect", allowing fluid through the hoses but not backing up. Careful, too much of a pinch will blow the hoses off of the plastic fitting.

Once you get it moving and the air mostly disappears you can stop pinching.

Continue "pedaling" until no air travels through the tubes, just plain ole brake fluid.

Take out the plastic fittings and connect the brake lines.

Continue by bleeding the wheels, never let the master cylinder get low on fluid or you will be bleeding the master cylinder all over again.

Different master cylinders may have their own little differences, look at the video at the end of this link, it may show you how to access the fluid through the fill hole.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

This link came from "repair guides" at the top of our pages, check it out, there are other brake related guides in there along with a bunch of other vehicle repair information.

Let us know how it works out!

The Medic
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Sunday, February 18th, 2018 AT 2:12 PM
Tiny
R.D.
  • MEMBER
I made a mistake in my wording (to fittings) was supposed to be (yep plastic caps) not sure how your supposed to bleed the air out that way but you cannot tighten them down enough because they still leak fluid and suck air right back in. Says not to over tighten because of course you would strip the threads.
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Sunday, February 18th, 2018 AT 4:14 PM
Tiny
JOHNNY G.JR
  • MEMBER
Try some Teflon tape on fittings.
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Sunday, February 18th, 2018 AT 5:07 PM
Tiny
CARADIODOC
  • EXPERT
High guys. If I may butt in here, I can save some aggravation. First of all, you did not say why you replaced the master cylinder. What was the original problem?

This car more than likely has anti-lock brakes. If you try to bleed at the wheels, you are going to push air down the lines where there is not any now, and that will get stuck in two of the chambers in the hydraulic controller. If you let that happen, you will need a scanner to command the ABS computer to open two valves so the air can be bled out, then you will have to run that air all the way to two wheels.

A much easier trick is when starting from scratch, loosen the two soft metal line nuts at the master cylinder, unbolt the master and remove it from the booster, then use it as a handle to bend the steel lines upward a little. That will keep the brake fluid from running out of those lines. Remove the lines and that master cylinder. Do your bench-bleeding as well as possible, then install the lines onto it. Bend the lines down, then bolt the master to the power booster. Have a helper push the brake pedal very slowly while you watch the air bubbles blibbit out by the ports. It should take about fifteen seconds to get half way to the floor, then have him holler when he gets there. Tighten the nuts, then have him release the pedal quickly. Loosen the nuts again about 1/4 turn, then have him run the pedal again half way down. If you still saw some air bubbles, do that a third time.

In the dealership there was always a new kid who made a perfect assistant, and this was a good time to teach him why we never push a brake pedal over half way to the floor. This is not an issue with a master cylinder that is less than about a year old, but it is a good habit to get into. If your new master cylinder came with instructions stating to not push it more than an inch when bleeding it, there may be a valve in it that trips to block one port when unequal pressures build up due to a leak. I have not seen that on other car brands yet, but this causes a real lot of problems on GM front-wheel-drive cars. A lot of people replace the master cylinder to solve that, but there is a real simple way to reset that valve.

When the brake pedal is pushed slowly, it gives the air in the lines a chance to float back up as the fluid is going down. When the pedal is released quickly, any air bubbles will wash into the reservoir along with the brake fluid that is rushing back. I prefer to open one line at a time when doing this with a helper, but it takes longer that way. There is no need to bleed at the wheels because there is no way air went down those lines. I even do this myself at home when replacing master cylinders on my old vehicles. The brake pedal is mushy at first, but it is fine after a few brake pedal applications during my drive. Every spring when I hopped into my 1972 Challenger, I found non-existent brakes due to a leaky rear wheel cylinder that had been sitting for months. That allowed the residual pressure to bleed off, then the leak ran the reservoir empty. After that, gravity was not strong enough to empty the steel lines. I just refilled the reservoir about half way, pumped the brake pedal a few times, then drove off to terrorize the neighborhood. The pedal was fine after a few pumps, and road and engine vibration helped work the air bubbles back up where they could wash into the reservoir easier.
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Monday, February 19th, 2018 AT 4:04 PM

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