In an effort to fix what feels like a soft pedal and maybe a stuck check valve, I thought I would start by bleeding the master cylinder. (A cheap bit of maintenance to start with before trying to replace the master cylinder or wheel cylinders) I have bled the brakes countless times but never the MC.

After doing a bit of research here is what I think I need to do. Can someone please correct any steps or make additions? Thanks!

1. Pump the brakes.
2. Loosen a brake line connection to the master cylinder.
3. Let any air out.
4. Tighten and check to see if any fluid needs to be added.
5. Repeat process for other brake lines.
6. Bleed the rest of the brakes as I always have starting furthest away from MC and moving my way to the closest.

 

Yep that looks about word for word out of the Haynes manual

Rob

 

Thanks Rob. I thought I read it like that in the Haynes manual but it just doesn't seem right to me Will air not get back into the MC if I just crack the lines and let the air out? I assume air may get into the brake lines too and that is why you have to bleed the brakes afterwards.

 

you shouldnt have air in the master cylinder and also it will bleed out if you bleed the brakes throughly correct??

 

Wait, yeah, I think you must be right... Seems to me that you would get the air out of the MC if you bled a ton of brake fluid through the system at the wheels. Can someone clear this up for us?

 

when you bleed the brakes tyou are bleeding air out from the ENTIRE system, just start with the brake furthest away from the MC, and dont forget to do the LSPV also...

 

Cool. We don't have LSPVs though. At least I know I don't because I have a 4runner w/ ABS. I think I will skip straight to replacing the wheel cylinders since I have bled the system so many times. I think they have rusted and gotten pitted from getting stuck in the mud too many times. It feels like I have to pump the brakes twice to get them to really push hard on the drums and then once they are, it feels like they are slowly moving back to there normal position causing some drag on the brakes.

 

No, the master cyinder will push the air bubbles through the system to be bled out at the wheels. Do not crack the lines at the MC or you may make your problem even worse.

If you can't get the bleeders open, then try a heavy penetrant like PB Blaster and soak them everyday (soak them after work so the truck sits all night) for a week and see if they budge. If you get one free, then make sure to replace the bleeder with a new one.

If you can't get them free, then I'm afraid the only way you're going to solve your mushy pedal problem is to replace the offending cylinder(s) or caliper(s). I suggest using a homemade power bleeder to bleed the entire system when you finally get them all open.

Finally also make sure your drum brakes are adjusted properly because that can add alot of pedal travel if the adjuster isn't working correctly.

 

So do not crack the brake line at the MC.. ??

Just properly bleed brakes (starting at the furthest).

What if you just did a brake job on the front, should you still bleed from the back? or can you just start on the passengerside front, then drivers front?

 

Correct.....the only time a master should be bled is if you are installing a new one. It needs to be "bench bled" before it is installed.

If you do a brake job you shouldnt have to bleed. No air enters the system unless you remove a line.

 

you only need to bleed MC if you replace it or if you let fluid go down to low when bleeding wheels

bleeding wheels will bleed MC, it could take longer than for wheels to get a bubble all the way down and out.

Like said, check you rear brake adjustment!!! It will make it feel like it takes 2 pumps if it is out of adjustment.

if your pedal is sinking after applying full pressure, check cylinders (including MC) for leaking/replacement