240z Master Cylinder Help

Tom Donnelly

Tom Donnelly

New member
OK, here's the dilemma. My old z was a 73. For which I had a buncha spares. The new car is a 1970. The brake master cylinder is different and worn out. And $250 - $311. The 70 thru 71 has the lines flip-flopped, actuating the rears first. And I have several new spare masters for the later models.

Can I ..

1) Swap the brake lines and use the newer master cylinder? Even new its $178 at Nissan. $59.00 at NAPA.
2) Find the correct one cheap anywhere?
3) Rebuild if the bore isn't shot?
4) Sell the newer ones here to somebody and use the cash to buy the $250 one?

Tom
 
I think a brake master is an "assembly" for purposes of the update/backdate rule. I'd use the 73 master and flip the lines.

Is there a stock proportioning valve?
 
I would use the later master and move lines. IIRC, there is a difference in bore of the cylinder in the 73 or 74 and later from 7/8" to 15/16" but I have been wrong before and probably are this time. :shrug:

I would have to look it up to be certain. A common change is to swap reservoirs from front to back and vice versa.

If the 70 model bore is good, sell it over at classic Z's to recover the cost of the changes you make.

From the GCR:

"c. Brake lines may be replaced with steel lines or Teflon-lined
metal braided hose. Lines/hoses may be relocated and may
be given additional protection. Brake fittings, adaptors, and
connectors are unrestricted. Brake system circuitry may be
revised, but no modification or substitution of the original
master cylinder, its location, or mounting is permitted. Cars
with antilock braking systems must disabled ​
​
​
​
​
​
​
​
​
a minimum of
three wheel speed sensors. Components that perform no other
function than to assist in the activation of the ABS portion of​

the brake system may be removed."


I say go for it, you are not substituting the OEM master cylinder but revising it. :) under the update rules.

 
Paul and Jeff,
Thanks for the quick replies. Here's what I'm wondering. Is the early master actually better because it works the rear lines first? Or does that matter in a hydraulic system?
And, if the bores are different, will I need to go to a newer proportioning valve?
And if the bores are the same, still the same question. And why did Datsun swap in the first place? Was it a problem that needed correcting?

Why didn't I buy a British racecar?

Tom
 
I don't think it matters which circuit gets actuated first, but if you switch them buy a cheap line pressure gauge and make sure you get 500-600 lbs or so at the rear drums and 1100+ at the fronts. Easy to do.

I would either remove the stock proportioning valve and plumb in an adjustable or use the one that coorelates to the master cylinder you are using.
 
I actually already have a '73 stock proportioning valve and an adjustable one. And one brand new oem master for a 72+. And 2 good spares. So its beginning to look like its swap time. I wonder if there's an advantage to the early model master though?

And are the calipers and wheel cylinders the same?

Too many dang questions, I just wanna drive.

Tom
 
JeffYoung said:
I don't think it matters which circuit gets actuated first, but if you switch them buy a cheap line pressure gauge and make sure you get 500-600 lbs or so at the rear drums and 1100+ at the fronts. Easy to do.

I would either remove the stock proportioning valve and plumb in an adjustable or use the one that coorelates to the master cylinder you are using.
Click to expand...

+1, I am by no means a hydraulic expert but it shouldn't matter.

The replacement cylinder should be marked, as the oem, with F for front and R for rear circuitry. There should also be a bore size marked on the cylinder. 7/8" covers up to the ZX's I think and they went to a larger bore.

Remove the OEM distribution/proportioning valve and plumb straight to the brakes. Install a in car bias valve for the rear brakes, driver accessible, and make sure the parking brake and cable assembly is installed. Use the parking brake to adjust the rears when the pedal starts getting soft during a race. :)

good luck, and make sure you have cooling ducts to the fronts, at least 2 :)

just saw your update:
Wheel cylinders are not the same depending on the year. Later ones are easier to come by. Calipers are the same.
 
I'll look this week and see If I have a spare brake mechanism and relay set up. Cables are tough. OEM are ~ $250 IIRC. I found a new manufactured reproduction on ebay for about $100 shipped to the house. I recall seeing some on ebay recently along with the brake assembly as well.
 
Tom,
If Paul doesn't have an e-brake mechanism/cable I would bet we have one in our pile of parts (full warehouse of datsun stuff), and if not we have a parts car that definitly has one. Let me know if you're interested. [email protected].

chris
 
Tom:
Glad you have new OEM because I've seen and heard of a boutload of cheapy rebuilt masters being bad right out of the box.
 
pballance said:
From the GCR:

"c. Brake lines may be replaced with steel lines or Teflon-lined
metal braided hose. Lines/hoses may be relocated and may
be given additional protection. Brake fittings, adaptors, and
connectors are unrestricted. Brake system circuitry may be
revised, but no modification or substitution of the original
master cylinder, its location, or mounting is permitted. Cars
with antilock braking systems must disabled ​
​
​
​
​
​
​
​
​
a minimum of
three wheel speed sensors. Components that perform no other
function than to assist in the activation of the ABS portion of​

the brake system may be removed."


I say go for it, you are not substituting the OEM master cylinder but revising it. :) under the update rules.
Click to expand...

Doesn't the bolded line taken from the GCR explicitly state that he has to run the master cylinder that came in the car? Wouldn't it be considered a subsitution? you are subing out one part for another.. even though they are within the spec line. I love/hate grey areas...
 
Tom Donnelly said:
A racer's dream. A warehouse full of spares. That's cool. I have a basement 1/4 full of spares. It goes fast though.
Click to expand...


We most likely couldn't do this without all the parts. I wish all of them were primo items, but some of the stuff is from z's that were dissembled 20 years ago, and not all of it is racer stuff. I think my uncle had 8 dashes lined up the other day!!
 
quadzjr said:
Doesn't the bolded line taken from the GCR explicitly state that he has to run the master cylinder that came in the car? Wouldn't it be considered a subsitution? you are subing out one part for another.. even though they are within the spec line. I love/hate grey areas...
Click to expand...


It's on the same spec line and its the same car as well. 1969 - 1973 240z. Same as having a choice of E88 or E31 heads. Or manifolds. Or using the aluminum hood on ITS RX-7's. Not grey at all. Some came with power steering, some not, so you can run either.

So I'd say its ok. Still haven't decided which way I want to go though.

Tom
 
My bad.. As soon as I posted that and left work.. I thought about it opn the drive home and felt like a dumb a**. The ITB mustang is a shining example of this of the ability to update and backdate within a spec line. Please omit my previously un-thoughtout comment. :rolleyes:
 
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