Dual Master Cylinder (DMC) conversion questions

[Hugo Karasawa]

This happened because he did not have a dual circuit master cylinder.
The front right tubing was rubbing and lost the brake fluid.

356 Brake failure 01.jpg (141.85 KiB) Viewed 1048 times

356 brake failure 02.jpg (321.11 KiB) Viewed 1048 times

[Eric McKinley]

A very good reason to consider using one.

[David Jones]

Maybe my MC conversion was not done right, I did it myself but I was never happy with the brake pedal feel and never felt that the car stopped properly and I also never got a hard pedal or even any pedal resistance at all when one circuit was open. I just switched back to a single circuit with a 911 MC and the brakes now feel the way I expect and the car stops very well under hard braking situations. I had dual MC's on the race car so I know what it should feel like when one fails as I had it happen.
I also very carefully inspect my brake lines every time the car is on my lift and I feel that these cars were driven many hundreds of thousands of miles without brake issues with single circuit MC's, and they are also no longer daily drivers and not driven by folks in the main who will put themselves in situations where brake failure is a frequent contributor to accidents. I will put my faith in good maintenance and the original set up.
If someone can tell me how to get the pedal feel I want with the dual circuit system I may be persuaded to switch back but for now the "C" with disc brakes stays single circuit though my two drum brake cars have good brakes with the dual circuit system.
If you do have a dual circuit system please tell me how the pedal feels if you open a bleed nipple on either the rear or front circuit. How far down does the pedal go before it hits significant resistance, I felt no resistance at all and the pedal bottomed out if I opened either circuit.

[Wes Bender]

"This happened because he did not have a dual circuit master cylinder.
The front right tubing was rubbing and lost the brake fluid."

I beg to differ. It happened for the reason given in the second sentence. Owner or his mechanic should have been climbing under the car once in a while to check things. I'm not arguing against the dual circuit master cylinder, but there are a lot of single circuit cars out there that don't have front end damage.

[Hugo Karasawa]

Wes and David,
You are right it is not the fault of a single circuit master cylinder.
The owner and the mechanic are at fault of this accident, nothing to do with a dual circuit or single circuit master cylinder.

[Jim Goetz]

Good afternoon. Got a question about the conversion to a DMC. I bought the DMC from Zims quite a few years ago and am just getting around to installation, since I am replacing everything anyway. For the Zim conversion it appears I will have to shorten the push rod by 1/4" or more. Is this normal and correct for the conversion? Thank you all. The car is a 356B T6, I've owned it since 1968.

[Wes Bender]

Give Zim's a call and ask them.

[David Jones]

Jim, tried to send you a pm but you don't subscribe. PM me I have a short push rod from when I gave up on the DMC.

[Dave Erickson]

I recently installed the ZIM’s MC into my 356A, replacing a stock MC. The existing push rod worked with no issue. It did not even need to be adjusted, the clearance was correct. I think ZIM’s sells multiple MC’s though. I got the German one. For the reservoir I bought an original ATE reservoir from Wolfsburg West. It was a part for a 68 VW Bus and fit perfectly.

[Stephen Dempsey]

I also have the Zim’s kit but haven’t begun installation because I’m confused about the push rod issue. The instructions say the distance between the push rod and the DMC piston needs to be 1 mm and that it must be checked. How is this measurement taken and if adjustment is needed how is this done? If I sound ignorant it’s because I am. This is one thing on the car I’ve never messed with. Thanks.

Steve

[Kevin Wills]

It's not critical that it is exactly 1mm. Make sure when the pedal is all the way up it doesn't touch the M/C applying pressure. I just wiggle it to make sure it feels like 1mm-ish freeplay.

[Jim Goetz]

David. Thanks for the pic and sorry I haven't activated the PM option, didn't know there was such a thing. I will contact Al Zim first just to make sure I am doing things the right way, take a few detailed measurements, then get back to you as soon as I can. I did not expect to modify the push rod, expecting a straight forward installation. I have read all of Al's documentation about the replacement, and am still confused about this one issue. And maybe I'll hear from Al too.

[David Jones]

Jim, to enable private emails go to "user control panel" which you can access via a left click on your name towards the top right of this page, then go to board preferences and then answer YES to the email questions.

[Jim Goetz]

Dave, I made the change, done. But I think I am going back to a regular MC, I'm getting just too old to fiddle around down by the peddles (too fat too, had to remove the steering wheel and drivers seat to get in there....it used to be so easy!). When I'm done with all this I'm going to sell it anyway, 54 years is enough. I appreciate your help.

[Brendan Cormack]

Hi folks, I recently purchased a dual mastercyclinder from Zims. I have some questions about where is the best place to install the new reservoir. It seems to big to fit in the location of the original. Does anyone have any experience with this?