Thursday, March 8, 2012

Hydraulic Clutch Master Cylinder Work

I have to begin by apologizing for the poor photographic account of this latest work as I had a minor camera glitch (actually operator error) that prevented me from capturing some early “set-up” and template making shots, but hopefully you’ll get the idea.

A long time ago, I decided that a mechanical clutch linkage was not going to fulfill the design intent I had in mind for my car.  The factory 70 Mustang clutch “Z-Bar” linkage intrudes heavily on the under hood space where you’d rather put headers and generally clutters up that corner of the engine bay.  After a lot of research, I decided I liked the look of the latest generation of hydraulic clutch kits from Modern Driveline.

Since my plan is to run a “Z-spec” T5 transmission and late model Fox body Mustang bell housing, clutch, 157-tooth flywheel and mini-starter, I wanted something that was simple and easy to install.  Generally speaking, I seem to have gotten that in this kit.
Knowing ahead of time that Mustang firewalls are all over the map as far as hole stamping locations are concerned, I was prepared to have to do some tweaking to the parts to make them fit as I had intended.  As such, when I began to trial fit the clutch master cylinder mounting flange to the inboard side of the firewall, I knew right away what measures would be required to make it fit properly.  So out came the template paper and off I went.

The flange, as it is shipped, is a symmetrical shape, but I quickly learned that to fit my specific car, I would need to trim and contour the right side edge of the mounting flange to work with the stamping contours of the firewall.  My mission was to do nothing more than drill the required mounting holes and as luck would have it, I was able to meet that goal with very careful positioning of the flange.
With the mounting flange modified and fitting the firewall well, I moved to the outboard side of the firewall and with the help of my Dad, was able to secure the mount into place to verify the fit of the master cylinder and the original booster.  Fortunately, the Wilwood master cylinder bolted right up to the base adapter and the factory booster popped right into place with absolutely no interference whatsoever.  The fit is snug, but extremely clean and tidy.  Coupled with the rack and pinion steering and a restored booster, this area of the engine bay should be very clean and functional with a look that defies the observer to recognize it as anything but stock.  So far……I love it!

Here is the modified Modern Driveline hydraulic clutch master cylinder mount in place.  The mount comes as a symmetrically profiled part, but I was pretty sure that wasn't going to work out of the box on my car.  I was right, but the correction was easy with an accurate template and a few minutes with the grinder.

Here is the firewall mount for the master cylinder.  The original clutch rod hole is intact and unmodified although the new master cylinder hole location is to the far right of the original (larger) clutch rod hole in this shot.

Here is the Wilwood master cylinder mocked up on the new mount.  Cleeeeeeeeean!

Here is the view of the new master cylinder and pushrod from the "business end".

The clearance to the original vacuum booster is quite adequate even though this shot makes it look rather close.

This view give a much better idea of how much clearance there actually is.  I think I'm going to like this!


  1. Hey Alex! Thanks for the comment. I am really excited by the clean look and reduced complexity of this setup. Hope it works just as well!


  2. Thank you for this. I've been searching all over the internet. I am largely concerned with clearance of my booster with this application. Could you tell me the number stamped at the top of your Bendix booster? You see I have a 1970 Mach one with an FMX automatic transmission and I going to a manual T5. I'm worried that my booster may be larger than the one you have in these great photos. If not a number maybe the circumference of the widest part of the booster?

    Thank you in advance!

    Doug Palmer

    1. Hello Doug! The number on my original Bendix booster is 6945 and it is 7.5" O.D. at the joint seam flange (e.g., largest diameter). I am pretty sure there were only two different boosters in 70 and the Bendix is the smallest O.D. I think the other is a Midland unit, but I don't have any dimensions on it for reference. Hope this helps a bit either way.


      Sven Pruett

    2. Sven you just saved me a great deal of Grief! That is the same booster that I have. when you look at that spot where I have to drill through the firewall it looks too tight to clear the booster. but your image clearly shows it's tight but it works. Thank you for going the extra mile!!!!

      Doug P

    3. Doug,

      Glad I could help! I was in the exact same boat a several months ago and it is definitely a little daunting to see how snug things look without all the pieces at hand. Keep in mind I had to modify the flange of the inner support quite a bit to fit the firewall features correctly, so be prepared for that possibility. Of course, please feel free to shoot me a note if you hae any questions.