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I have a 76 s30 280z with the toyota 4 piston calipers installed up front and stock drums in the rear.

 

I just installed a used 81 s130 280zx brake master cylinder and booster. Both bmc and booster were taken off a junkyard 280zx.

 

The install was pretty easy and straight forward. Just had to take off the spacer and flip the booster and everything bolted up fine.

 

I have bled the brakes in the proper order but there is a problem. The brakes don't work.

 

Basically with the car off the brake pedal builds no pressure. The pedal is spongey about 3/4 of the way down and then super loose at the last 1/4

 

When the car is on there is absolutely no pressure or resistance or anything. The pedal just goes straight down to the floor with no effort. The brakes don't even work a little.

 

From what I can tell there are no leaks. I read it might me be a push rod issue or brake pedal linkage? Any other suggestion on what the problem might be?

 

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Ok new problem...

After driving around I noticed the brake pedal would only need to be pressed a little for the brakes to work. There was very little brake pedal travelicon1.png before it got stiff. Then the brakes started to lock up. At first it felt like the ebrake was up then eventually the car would not budge. I had to bleed the bmc to get home.

Based off these brake symptoms I'm assuming the push rod needed to be adjusted. So I tried adjusting it but couldnt get a good grip with pliers... Any suggestions on how to adjust the pushrod?

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Use vise grips to hold the push rod. Make small changes and test drive the car. Carry a wrench that fits the MC bleeders to relieve pressure if the brakes start to drag/lock up. In that case just open the bleeder amd readjust the push rod.  If pressure has built up fluid will flow out  of the bleed screw.   You can do the adjustment without removing the MC. Remove the MC nuts and move the MC out and away from the booster.  You will know if the push rod is out too far if when pushing the MC onto the booster it springs back. Make small adjustments until the push rod just clears the piston cup inside the MC.

 

 

Be careful not to drop the reaction disk inside the booster. Do a search for "reaction disk" to see why.

Edited by Miles

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Ok I'll try using the vise grips. Just to be clear I should adjust the push rod inwards? Since my brakes are locking that means the push rod is too far out.

 

Also is it ok to bring the push rod out a little to get a better grip with the vise grips? I don't think my vise grips will fit into the small hole where the push rod is...

Edited by HaxMcJax

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Yes, you need to make the push rod shorter (inwards). You can pull the push rod out a bit but this is how you get into trouble with the reaction disk. If the reaction disk falls out the pedal will be low and the brakes will feel really odd. It is probably better to remove both the master cylinder and MasterVac and set the push rod length while holding the MasterVac with the push rod pointing up.

 

There are 2 push rods. One between the brake pedal and MasterVac and another between the MasterVac and master cylinder. Both push rods require free play. Push the brake pedal carefully with your hand and you should be able to feel 2 distinct changes in the feel. One when the brake pedal and its push rod begin moving the MasterVac and another when the MasterVac begins moving the master cylinder.

 

The service manual specifies the measurement for how much the MasterVac push rod should protrude past the flange where the master cylinder attaches. Up to 74 the length is 3.5 to 4.0 mm. For 75 and on the length is 9.5 to 10 mm. If you have parts from mixed years you might need to use something between these values. My car ended up at about 7 mm if I recall correctly.

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