Master Cylinder Help

[Alexlind123]

The bently just says to put the new one in and bleed the entire brake system normally. Is there anything that would make this process easier? Are there any problems that may arise?

[Jr ///M5]

Yes, you must "bench bleed" the master cylinder before installation, THEN you go about the normal bleeding process after installation.

Do a simple search on bench bleeding a master cylinder...sorry, but there's probably a site out there with pictures and the proper way of doing the bleeding process. I'll buy a couple of 1/8" pipe to hose adapters, some hose that fits the adapters and stick the hoses into a small cup of brake fluid. With everything attached where it won't tip over, pump the master cylinder shaft until all the air is expelled through the hoses Keeping it filled at the reservoir as needed. After it has bled out the air, install it, being careful about protecting the painted finishes from fluid. Then pressure bleed the rest of the system starting with the right rear wheel, then the left rear, then the right front and finally the left front. That is the sequence for left hand drive cars.

You can order a pressure bleeder, or make one yourself, True Value or Ace Hardware will usually have everything you need except the master cylinder reservoir cap, some GM caps will fit from the "HELP" section of your local auto parts store, another search will identify the correct cap. It will cost about $28 depending on your choice of gauges and fittings. If you're not into building stuff, then you can always use the "two-man" bleeding technique, which by the way is the preferred way to finish the bleeding process.

Good luck with the install, hope this helps somewhat....

JR

[joshua43214]

Bench bleed the new master cylinder before you install it, this will save you tons of headache. its important to remove all the air from the cylinder and the lines at the cylinder before you start bleeding the system as a whole, unless you have a pressure bleeder, it is really easy to leave bubbles in the system, and even with a pressure bleeder, the master needs to be prebled since a pressure bleeder won't remove the air trapped in little nooks.

bolt the new master cylinder up and attach the resavoir, do not hook up the lines. fill the resavoir and then tap on the side of the master cylinder to jigle up loose air. hold your thumbs over the holes and have an assistant depress the and release the pedal slowly, use your thumbs as valves to keep air from entering the cylinder. repeat until all air is purged.

hook up the lines, snug them up then loosen 1/2 turn. depress pedal and hold, tighten lines. repeat until all air is removed. 90% of the time you can remove all the air doing this. you can now proceed with bleeding at the wheels.

[Alexlind123]

This is very helpful, but i have one question. Assuming that there is some air left in the system up near the MC, wont i need to flush the entire system to get the air out that at the "beginning" of the system?

[joshua43214]

There should be no air remaining in the master cylinder when you begin bleeding the brakes, its ok to have a few bubbles in the lines at the cylinder when you start, its just nice to have none. do not turn on the ignition if there is any possibility of air in the lines. If the ABS pump kicks on for any reason, it could pull the bubbles in, then you have to go to the dealer to get it flushed. Probably won't happen, but no good reason to take the chance.

[632 Regal]

the MC will leak a bit of fluid once you are done with the bench bleeding process, hook it up, and dont tighten the lines for 5-10 minutes, this will weed out the air thats sitting at the top of the lines. then tighten and should be good to go.