240z Master Cylinder Help

[Tom Donnelly]

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

[JeffYoung]

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?

[Tom Donnelly]

Yep. Stock proportioning valve.

[pballance]

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.

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.

[Tom Donnelly]

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

[JeffYoung]

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.

[quadzjr]

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.

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]

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...

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

[billf]

Tom Donnelly,

Sorry, I didn't see this topic last month, or I'd have replied to it then.

If you are still working on this project, I may have a few words of advice for you. I have been doing this same project during the last few years with VERY BAD RESULTS, due to the following. I'll cut to the chase:

1970 240 Z, master cylinder replacement (I actually replaced all components of the hydraulic system). Datsun Parts House listings have a different cylinder than the original. It turns out to be the 260Z/280Z cylinder that is sold for replacement (there was no listing for the original cylinder). It has the output lines reversed (no problem), and one other difference. It uses the matching pushrod (adjustable rod that exits the front of the cylinder and enters the Power Brake Booster) which is the same style as the early one, but longer. Let me be clear, here. The 260/280 used a different cylinder and pushrod. This is the reason my project lasted so long...I never knew of the longer pushrod, and was not able to achieve a solid pedal after bleeding. As soon as the difference was noted, the brakes were functional (last summer to be precise).

Relative to IT rules, (I am also a racer in IT), this is actually a listed replacement part from Nisson/Datsun, so there is no problem using it in class,and brake lines are free. Besides, as you noted, the cars are on the same line.

I hope this is some help to you. I also hope you didn't find the problem that I lived withl

Good racing,

Bill

[Tom Donnelly]

Bill,

Which one has the longer pushrod? The master cylinder I got from Nissan has the reservoirs in the right (old style) place. But the pedal pressure isn't to my liking, compared to what I remember.

Thanks,
Tom

[billf]

The pushrod from the 260Z/280Z was longer than the original 240Z pushrod. Tha lack of length (when the 240Z pushrod was used) means that the pedal motion was wasted (not transferred) to the master cylinder. As the pedal was depressed the pushrod had to travel thru dead space until it finally met up with the master cylinder piston. By then, the pedal was way down toward, or onto, the floor, depending on how short the rod was.

The 260Z rod, being longer, filled the empty space so that the pedal motion directly translated into piston motion. The 240Z rod was not able to adjusted out to the proper length.

Remember that you have to have a final adjustment of the pushrod length per the Datsun shop manual, measuring the protruberance of the rod from the inside of the Power Booster. If you are going to use the 260 cylinder, the 260 measurement must be used (they didn't mention that). For that you have to have access to the 260Z manual.

Incidentally, only one other problem that I know of can cause a low pedal. There is a "thing" in the system that, if it falls out, will leave a low pedal. It is black rubber, cylindrical, and about 1/4 inch thick with a pecular name. It is in all the diagrams (drawings) of the inside of the power booster. The name escapes me at the moment. When manipulating the front of the power booster it can, literally, fqll out of position into the inside of the power booster. You will not know this unless you look with a mirror, inside the power booster, at the center of the shaft of the booster...it will be black. By inserting a small metal probe, and tapping it, you can feel whether it is rubber or metal. Soft feeling means it is rubber. Hard, metalic sounding, and it is the steel cylinder the "thing" resides in...and the thing has fallen to the bottom of the power brake booster. The shop manual directs you to look for it, and if returning it to its position, to use some type of stuff to hold it in place, even though it sits in its own little hole, while the booster is being rebuilt.

I have not had THAT problem, so I don't know how low that would leave the pedal when the "thing" is missing, and the length is 1/4 inch shorter. The pushrod difference in length is greater than 1/4 inch.



Bill

[pballance]

The "thing" is the reaction disc.

[billf]

Thanks...I couldn't remember, and I don't have access to the book. Now I can sleep soundly tonight!!!!

Good racing.

Bill