The master cylinder on my 1971 1.7 is leaking. I searched and haven't been able to find a DIY fix. From what I have read, the master cylinder can't be rebuilt any longer, I also read somewhere that a 911 master is an improvement over the 914. So, I am looking for the how to DIY and where should I purchase a new one? TIA

No, the 911 19mm MC is sized for the 911/914-6 brake system, while the 17mm is sized for the 914's brakes - so it's not an improvement, just cheaper since they're more made for all the 911s out there.

Try to stick with an OEM ATE brand from one of our member vendors (PMB, GPR, etc.) or a Porsche dealer or reputable Porsche parts retailer, There are knock-off FTE out there too, but IMHO not worth the lower cost for lower quality & lesser parts life.

There is a great explanatory thread on 914world about the 19mm MCs not being better, & 17mm being best for 914/4s - but I've lost that link to the topic, so maybe someone else can add it below.

...or PM or email to Eric Shea at PMB for the info on this subject.....
http://www.pmbperformance.com/teener.html

& Good Luck!
Tom
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The 19mm 911 master cylinder will give you a better break pedal feel, but it will not improve break performance with stock 914 brakes. In fact, it will reduce performance. I don't understand fluid dynamics well enough to explain why, but I've read explanations on this site from people who do.
Only use the 19mm MC if you're upgrading to larger calipers.

As mentioned, get your brake parts from PMB. Stay away from cheap chinese knockoffs. It's not worth risking the safety of yourself and everyone else on the road just to save a few bucks.

Yup, call PMB, Eric will set you on the right path.

Make sure you bench bleed the master cylinder before putting it in.

I'm about to replace my leaking 17mm master cylinder with an ATE 19mm. I did a lot of research on the site trying to determine whether to go with the 19mm or keep the stock 17mm.

A couple of authoritative members recommend 17mm, referring to Eric Shea/PMB's website for explanation. But, here is what PMB's site says about 17mm vs. 19mm:

Unless this is a "concours d'elegance" thing, do your self a favor and page down to the 19mm master cylinder. This is a slight upgrade in our opinion. With brakes we tend to shy away from the word "upgrade" as it gets bandied about a bit too much by the sheisters out there but, a 19mm will give you a slightly firmer pedal which we think is a plus. It will (laws of physics) take slightly more effort but, trust us, you'll get use to that in a few minutes. Better pedal feel and, the best is yet to come... LOWER PRICE.

Am I misunderstanding something here?

I have Porterfield pads installed, and the 17mm was already more pedal effort than most cars I'm used to driving, in case that makes a difference in the response.

Eric Shea is the guru of brakes. I have been using a 19mm master cylinder for the past 14 years.

Think of master cylinder size as a lever. Pretend you are removing lug nuts from your car. A short lever (large mc) requires more effort but less total travel. A long lever (small mc) requires less effort but needs more travel to move the same amount of fluid. Put a 23mm mc on stock brake calipers and the pedal will be rock hard but like removing lug nuts with a 6" handle (require tons of force). A 23mm mc might be a perfect size on a modern 911 with huge calipers so it's important to match the mc to the calipers on the car.

I've owned and driven stock 914's with both 17 & 19mm mc's. I prefer the smaller 17 for the lighter feel but I also like a light feel with more travel on all my road and mountain bikes. Many others like the firmer pedal feel of the 19mm mc but either will work fine and the 19mm is often less expensive.

with Mark.

You can use either 17 or 19. It'll only change the feel and not the performance. Bad knees? Weak legs? Enjoy power brakes on new cars? Get a 17.