Master Cylinder Replacement

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86 720
Posts: 199
Joined: Tue Sep 29, 2009 11:55 am
Car: 1986 720 4cyl Standard Cab

Master Cylinder Replacement

Postby 86 720 » Sun Feb 13, 2011 6:42 pm

Finally got to replacing my brake master cylinder in my 86. Never done it before, but with the help of a friend, was able to get done and back on the road in 2 hours.

Items needed:

DOT 3 brake fluid
10mm box wrench
1/2" open end wrench
vacuum hose
replacement brake lines. Note there is only ONE rear rubber brake hose. That is because the rubber brake hose is used to jump the gap between the rear hardline and the axle. That is it! Simply hardline on the axle between the two sides. You'll see in the pics.

According to the parts store, there are 4 hoses for the front: 2 for left and right "outer" and 2 for left and right "inner". However, from what I could see, there are only three for the front, 2 left and right "outer" and 1 right "inner". The "outer" brake line goes from the hard line on the frame to the caliper. The "inner" goes from the firewall hardline and jumps the gap to the frame hardline on the passenger side. You'll see what I mean when you take a look. I did not see an "inner" brake hose on the driver's side.

Removing the two hardlines from the existing MC. After that, remove the two nuts holding the MC to the booster. Note you do NOT need to disconnect the brake pedal to do this. Image

MC removed. The new one is slightly different in that the low level sensor is part of the cap in the new unit, and it is separate in the old one.
Image

New MC with the rear brake lines ready to be bench bled. You can do the bench bleeding with the MC installed on the booster. Simply connect the new brake hoses to the new MC and route the hoses below the fluid level in the MC. After done, wipe off any excess fluid off the rubber.
Image

Bench bled, cheating a little. Tip: when connecting the old hardlines to the new MC, do NOT bolt the MC to the booster yet. Connect the hardlines to the MC FIRST than bolt to the booster. If you connect to the booster first, the front brake hardline is difficult to line up with the MC, and there might be a small chance of cross threading.
Image

The is where mine was leaking. The rear of the old MC was allowing fluid to drip down the booster and onto the fender. You can see the affects of the fluid on paint!
Image

Rear brake line. This is what I'm talking about the rear only requiring one hose. Had to use some WD40 for the top connection.
Image

Bleeding is simple. Take the appropriate sized box wrench on the caliper valve, insert the vaccum hose onto the nipple with the other end in a container, and have your friend pump the brake pedal. Continue until all the old dirty fluid is out, and there is no more air bubbles. Continue to all 4 brakes.

The changes were amazing! can stop a LOT better and surprisingly simple!


User avatar
fastboatman29212
Posts: 497
Joined: Sun Jul 25, 2010 6:45 pm
Car: left this forum. Sold my truck.
Location: South Carolina

Re: Master Cylinder Replacement

Postby fastboatman29212 » Mon Feb 14, 2011 6:00 am

Good job! I will definately refer to this if I ever need to change my brake MC.

synack7350
Posts: 366
Joined: Sun Jan 09, 2011 3:08 pm
Car: nissan '83 720 king cab pickup 2wd 2.4L Z24
Location: Boaz, AL

Re: Master Cylinder Replacement

Postby synack7350 » Sat Sep 03, 2011 5:49 pm

wonder how hard it would be to install a smaller brake booster? that thing is so friggin huge.


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