'71 240Z Soft/Weak brakes after master cyl change.

[Connor280ZX]

Recently installed a new master cylinder in my Z due to the fact that the old one wanst sending fluid to the rear brakes. I installed this new SANYCO aftermarket cylinder. Had to bend the front line slightly to get it to fit right. I think i made a mistake because when bleeding, i forgot about the bleeders on the cylinder themselves, and went straight to the ones on each brake... Once i realized my mistake, went to bleeding the cylinder since i wasnt getting much pedal pressure at all. Worked air out of it for a few days. After close to two bottles of bleeding, the pedal feels a bit stiffer, but still doesn't feel right at all.

 

Here's whats happening: Basically i don't get any pedal pressure untill i push it down about half way, then i feel the brakes coming on, but weaker than i would think. Between half way down, and not at all there is this whoopie cushion sound coming from above the pedal. No idea what's going on here... I think either this master cyl is defective, or there's still a bunch of air in the cylinder thats not coming out.

 

Let me know what you guys think.

[Domzs]

Pump your brake pedal a few times . If pedal feels firm after pumping then you have air in the system . Compare old cylinder to the new to see if they are the same . Mainly , where the push rod goes in , make sure depths are the same . Good luck .

[johnc]

Check to make sure the MC you have has the front and rear brake ports in the same place as the one you replaced.

[nsanow]

I had this exact issue and chased it for months!!  Drove me crazy.  Basically no pressure until almost the very end and then brakes would grab.  It ended up being the brake booster that was leaking somewhere.  What was even stranger was that it held pressure!!!  But since I couldn't figure it out and that was the only thing I hadn't changed I gave it a shot and it worked!!

 

Even my certified mechanic who helped me on it couldn't figure it out.

[Connor280ZX]

The pressure feels the same to me each time, even if i pump on the pedal.

The depths look the same to me, however the port for the front brake reservoir is located maybe half of an inch further than the old MC. 

 

I had this exact issue and chased it for months!!  Drove me crazy.  Basically no pressure until almost the very end and then brakes would grab.  It ended up being the brake booster that was leaking somewhere.  What was even stranger was that it held pressure!!!  

Uh oh, the booster, huh? Now that's an expensive part... I have noticed that where the booster linkage comes out of the firewall there is leakage of brake fluid from the previous cylinder... I assume that has probably screwed up the diaphram in there.

[Malarkey]

I had a similar problem after redoing the whole brake system on a 240. My issue turned out to be the reaction disk had come off inside the brake booster.

[Connor280ZX]

I had a similar problem after redoing the whole brake system on a 240. My issue turned out to be the reaction disk had come off inside the brake booster.

Were you able to repair the booster? Or did you have to replace it entirely?

[Malarkey]

The disk is just a round piece of rubber that is used like a spacer. I took the booster off and shook it and could tell it was inside. Once I got it out I glued it in place before I put it all back together. There is a cutaway view in the FSM that references it, but it is easy to miss.

[Connor280ZX]

Update: New booster, new master cyl, new rear wheel cylinders, a gallon brake fluid of bleeding, and no change. Still getting no resistance with a whoopie cusion sound, untill the pedal reaches the bottom, then the brakes grab... So im out of ideas. You guys have any?

[Tony D]

"The depths look the same to me, however the port for the front brake reservoir is located maybe half of an inch further than the old MC."

 

As John C said, make sure you got the CORRECT MC...

There are two, one with "F" in the front of the MC, the other with "R" at the front of the MC. If you swap them, you get the EXACT feeling you describe.

 

The early cars had brake pipes from the MC that went straight down. Later cars had them "X" under the MC as  the body tubing didn't change, but the location of "F" and "R" on the MC did.

 

If you have a later car with an early MC, or an early car with the later MC, and hooked your lines up the way they were originally, you get absolutely NO pedal until the very bottom of travel and then it's almost like an on-off switch where there's nothing, nothing, nothing, brakes (but you have so little pedal travel left you bottom out and what brakes you get you get and pumping doesn't help it at all.

 

Here, a photo would hit it right off.

 

You can NOT go in and say "I want an MC for a 240Z" if you do, you will likely get the later assembly as it was 72-78.

[Connor280ZX]

You're exactly right, Tony. On the new MC, they are inverted completely. Front is "R" and rear is "F". Seller claims "Guarenteed to fit 70-71 Nissan 240Z" I wish my local autoparts stores carried these things so i could compare both in person. I'll just save up the $300 for an OEM one so i don't have this problem again.

[Tony D]

Yeah, but which one do you have?

[malibud]

Can he just get a 79' zx 15/16" ?

Edited September 19, 2014 by malibud

[Tony D]

Can he just get a 79' zx 15/16" ?

No, it will do the same thing as any other MC if the F goes to the R, or the R is going to the F.

It would also be a 'late' configuration, reverse of the earlier cars.

 

That has  yet to be determined.

Edited September 20, 2014 by Tony D

[Connor280ZX]

On this MC, The "R" is where "F" should be, and "F" is where "R" should be. A local Pick N Pull has a '70 with a grade "A" MC, so they say. They want $40 for it, i'm going to pick it up and hope it works alright.

[seattlejester]

If the other master cylinder doesn't help try bleeding both lines in pairs. Especially the rear. Random customer at the parts store suggested it for older cars, and it ended up helping.

 

Are you using a vacuum bleeder?

[Tony D]

On this MC, The "R" is where "F" should be, and "F" is where "R" should be. A local Pick N Pull has a '70 with a grade "A" MC, so they say. They want $40 for it, i'm going to pick it up and hope it works alright.

 

MY SUGGESTION WOULD BE TO GRAB THE CROSSED LINES FOR THE LATE MC AND INSTALL THEM ON THE NEW MC YOU HAVE! You can bend up the stock lines but it won't look as good.

 

Use the later (cheaper, easier to source) MC and get the proper lines to do this. They screw in to the MC and Shuttle Valve down below and the conversion to late MC is COMPLETED. Bleed and be DONE with it.

 

I have done that on two cars previously since the price of the early MC's went up... Take the MC and LINES from the junkyard car.... Keep the MC as a CORE ONLY.... keep the original lines with it, and get the proper "Crossed Lines" for the later MC and install them.

 

This will cure the problem.

 

I would not trust my life to a Junkyard MC.

 

The crossing of "F to R" IS THE PROBLEM, nothing else is wrong...this happens all the time, and happened to me personally when a PO did it....his exact words were "I didn't like how those brake lines crossed under the master cylinder so I straightened them out to clean up the engine bay".... So yeah, your stock lines CAN be crossed to fit the later MC and it will work but they will be a royal beyotch to get straight into the MC! Just buy a set of 72-78 lines and install them on your early system. That is IT to do the conversion to the later master cylinder. Bleed it and be amazed.

 

In fact, you can get the stock lines and stock cylinder from the junkyard as a core set....and just bend the lines you have. That will solve it as well.

[Connor280ZX]

Bent the lines up to cross into the correct port, and unfortunately there is very little change in the pedal travel. The brakes come on maybe 1/4 to 1/2 of an inch sooner on pedal travel, but all else is the same. Bled through about a pint of fluid. When i had the MC out, i looked at my old one and the input does look slightly different, so i think thats probably my problem.

[Tony D]

" i looked at my old one and the input does look slightly different, so i think thats probably my problem."

 

What does that mean?

 

"The brakes come on maybe 1/4 to 1/2 of an inch sooner on pedal travel"

That's actually quite huge, in terms of a master cylinder... leading me to the next question:

 

I gotta ask, have you adjusted your rear brakes properly? Grabbing at 12:00 and spinning the wheel it should only spin 90 degrees (1/4 turn) if it goes more than that, it's too loose and needs adjustment.

 

This is generally the cause for excessive pedal travel and everybody misses it as the assumption is you have them properly adjusted to begin with. You usually have to back the brake adjuster back off to even remove the brake drum.

Edited September 22, 2014 by Tony D