240z Master Cylinder Help

[Tom Donnelly]

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.

You had me thinking about it for a moment. I originally wasn't sure whether switching them out would even work, then whether it was even legal!

[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