A 20.64mm or 22.22mm Master Cylinder Option, ...the "How-to" thread Options

[tomeric914]

My apologies in advance if this has been documented on here before.

Is 19mm too small and the Mercedes 23mm master cylinder too big? Well I've got a solution that is just right.

I was looking for a 20.64mm master cylinder option and stumbled across a thread on Pelican where someone had put a 1990's Corrado master cylinder in a 911 or 914. There was only but one picture and not much of a write-up so I figured I'd try and document what I did.

This master cylinder uses the same pushrod that you already have, though some adjustment will be necessary. You will also need to bend new brake lines if you want to do it right.

As with any brake work. If you don't know what the hell you're doing, don't do this.

Parts:
357 611 019 - this is for the 20.64mm master cylinder

357 611 019 B - this is for the 22.22mm master cylinder

911 355 322 00 - straight reservoir feed fitting

911 355 323 00 - angled reservoir feed fitting

7mm blue braided brake reservoir hose



You'll need to decide which master cylinder is right for your application. For example, my braking system is pretty much all mid-1980's Carrera sized calipers and referencing Bill Verberg's brake page, I found that the mid-1980's Carrera used a 20.64mm master cylinder. I also knew that my pedal travel was more than I liked while on track.

https://members.rennlist.com/1976c38/brakes.htm

I purchased all of the parts through Pelican, the 357 611 019 (20.64mm) is an ATE unit made of aluminum and was only about $100. The 357 611 019 B (22.22mm) is made by a few companies, is a cast iron unit and about $50.

Here's where you are today:



1. Drain your reservoir using a turkey baster so you don't wear the entire contents of the reservoir.

2. Disconnect all brake lines, the reservoir feed lines and unbolt the master cylinder.

3. Loosen the locknut and unthread the master cylinder pushrod from the pedal cluster, then run a tap through the threaded portion still on the pedal cluster to clean it up. Make sure the threads on the pushrod are clean and that the locknut threads all the way down on the pushrod. (I had to find a thinner locknut for my application. You may or may not need to do the same).

4. Unbox your new master cylinder and pop in the fittings as shown in the picture below. Use a dab of brake fluid to help lubricate the fitting where it inserts into the master cylinder. ALSO, you'll need to plug one of the extra ports on the master cylinder that you aren't using as seen below. I placed a piece of tape over all of the openings while fitting the master cylinder to keep dirt out.



5. Grease the tip of the pushrod before installing the master cylinder. Torque the two 8mm nuts to 18 ft-lbs. I left the washers off. VERY IMPORTANT - now adjust the pedal free play to approximately 1mm by turning the pushrod inside the car at the pedal cluster. Once adjusted, tighten down the locknut. Make sure that the brake light switch lever is in the correct position to actuate when the brake pedal is depressed.



6. Back under the vehicle, decide how you will connect the reservoir to the master cylinder. The metal ends of my plastic lines were rusty so I decided to cut them off and use a short length of 7mm blue braided reservoir hose to each line. You could also run the blue braided hose all the way from the reservoir to master cylinder. Use a dab of brake fluid to make it easier to install the hose on the fittings.



7. Next, bend new brake lines for the front brakes and a short piece for the rears.



8. Last, but not least, bleed the brakes reinstall the bottom pan and enjoy your new firmer, but not too firm, pedal feel!

[h16]

I made this mod recently - I underestimated a couple of the steps. I did start with a stock master cylinder in 1974 914-4. I do have BMW 320i calipers up front, so I think they use a little more volume than stock 914-4 calipers.

After this mod, my pedal travel is greatly reduced, very different feel but I am not disappointed.

As usual, I learned a lot in this first experience that I might do slightly differently the next time, I'll will pass on some observations in case they are of use to anyone.

If I could do it all over, I'd run new reservoir lines the whole way from reservoir to master cylinder - all cloth/rubber in one piece, and get ride of the feeder tube lines that are part plastic part metal. Easier said-than-done, though, because I suspect I would need to pull the gas tank to properly achieve that (I think the stock plastic lines may be clamped to body somewhere behind the tank).

My metal ends on reservoir lines were entirely solid and not really rusty. If you plan to cut them, it is really hard in the cramped space behind the steering rack. I tried using one of the small micro pipe cutters, and it was an ultra marathon because the steel in the tubes is incredibly thick. I finally gave up and used an air cutoff tool which was pretty dicey due to the limited clearance.

Acquiring the 7mm braided fuel hose at all took some time (amid Covid 19 craziness) - it's not a locally-available item that I could find (by default I don't call Porsche/V2 dealers, probably should have)

Determining the perfect length for the fuel hose is tricky when trying to section it in, in this cramped space- since hose is so stiff and it's a short run to the master cylinder.

I advise NOT installing the plastic fittings into cylinder until you have high confidence that length of hose is correct, then inserting fittings into hose first before final installation of the cylinder. Extraction of the fittings (without damage) from the cylinder does not seem easy - but I stopped short of doing so since I couldn't afford to ruin the only 2 fittings that I had.

I used NiCopp to make new brake lines - worked like a charm - so much easier to shape than old-school steel lines.

Flaring bar tools to make bubble flare really let me down. After much trial-and-error I discovered "Titan Tools 51535 3/16-Inch Double Flaring Tool" - this thing is a gem. I made 6 successful bubble flares without a failure and without any need for redo.

This mod does eliminate the internal fail sensor in the master cylinder - which the old master cylinder had. I don't think a light is needed to tell me when the master cylinder has failed and goes to the floor - so I just ziptied the connector nearby and carry on without it.

Good luck to all - I found the original article and steps to be very valuable and well documented.