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-   -   Master Cylinder Conversion - Upgrade (http://www.m715zone.com/vb/showthread.php?t=9578)

Warthog June 3rd, 2008 01:14 PM

Master Cylinder Conversion - Upgrade
Hey Jon, do you want to add this to the manuals section?

Upgrade of Master Cylinder to Dual Cylinder

I know that many of us have done this conversion and fumbled our way thru it. This has been discussed many time but I have never seen any step by step with pictures. (Who needs instructions, just show me a picture)

I have the privilege of being mechanically inclined by learning from my dad many years ago. Wow… it’s been 34 years now, I sure miss him

I read most of the postings about this conversion and understood them but thought others might be confused.

This is not the only way of doing this….your mileage may vary…..

Some of the links on conversions:

and many more. Just do a search on master cylinder

I chose to use the late 60’s early 70’s master cylinder. Mainly because it was in stock.

Here is my parts list:

Master Cylinder #10-1331 - $16 plus $10 core

Napa 3/16 Union Inverted Flair – Female 3/8”-24 Inverted - BK 641-3290 $1.29 - far left
Weather Head 3/8” Inverted Flair - Plug - #131x3 - $1.79

I used these fittings because I was cutting my line to length and wanted to cut down on connections
Napa Brake Line Fitting 1/2”-20, BK 641-3321 $3.95
Napa Brake Line Fitting 9/16”-18, BK 641-3323 $3.95

If you buy ready made lines you will need these adapters. They are pictured on the right
Napa 9/16” Adapter – BK 641-3309 $3.49
Napa 1/2” Adapter – BK 641-3305 $1.99

3/16” steel brake line ~$5
1/4” steel break line. ~$5
(I purchased a 51” line because I was bending my own and I knew I would mess up, which I did. lol)


Remove you old Master Cylinder and mount the new one


Remove the line going to the rear cylinders and the line going to the master cylinder.


Install the plug going to the rear ( I removed the block to clean it and for pictures)


I used a coat hanger to get the general shape of my brake lines. There are many website that talk about making the brake lines. Just Google it.

Here is the end result. I chose to not install a booster at this time.




Notice the single fittings at the master cylinder?

All that is left is to bench bleed the M/C and bleed the system

Until next time
Wart Hog

white433 June 3rd, 2008 02:04 PM

There you go.
Your an allright guy! Keep your day job, nobody will ever hire you to write instruction manuals, you are too understandable. Thanks for this post, I have been meaning to do that but kept putting it off, not much longer now.

brute4c June 3rd, 2008 02:54 PM

Thank you!! That is the BEST post I have seen on converting the master cylinder...it wont get lost!
Great pics too!!!

Chumley June 3rd, 2008 03:08 PM

Awesome post!

compexp June 3rd, 2008 07:46 PM

Great write-up. I would recommend painting the master, as it will quickly cover with surface rust. Mine did. :mad:

fisherman June 4th, 2008 07:08 AM

You ever get brake fluid on paint. If you paint it and your top gasket of your masker cylinder weeps, like most do. You will end up with a gummy mess all over your master. Wipe it down with some pb or wd and it will keep the rust at bay for awhile.

Warthog June 5th, 2008 08:08 AM

One thing I forgot to mention.

After installing the M/C, doen't forget to adjust the pedal stop bolt on the top of the Brake Pedal Support Bracket (item #6 from figure 2-86, page 179 of the Oranizational Maintenance Manual -20).

This is a 1/2" bold that will adjust the excess play from the pedal. I had about 3/4" to 1" of play and I adjusted it to about 1/4"-1/2" of travel before the push rod engages the M/C piston.

No telling how yours has been adjusted over the years.

Wart Hog

vacca rabite June 5th, 2008 02:29 PM

Bookmarked so I can stop at Napa tomorrow with a new shopping list. :-) May as well renue the entire brake system this weekend. new brakes for the Porsche AND the 715.


Binford June 5th, 2008 05:28 PM

This is so funny as I had just ordered that very master cylinder and several of those adapter parts for my own upgrade! Got a remanufactured m/c though, so I am bringing it back since I ordered a new one from NAPA. Picking it up, and the rest of the adapters, at NAPA in a couple hours.

Binford June 8th, 2008 09:33 AM



One of the easiest upgrades I've ever had to do.

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