To be honest I have no idea. I think I found the specs before I bought it but I can't remember what they are now. There are not any real significant markings on the M/C to denote bore size but the number (20) does appear over the front half of the M/C. Maybe somebody here has access to a porsche 911 service manual and can answer this question.

Glad you agree. It all makes more sense now! Need to get a 23/19 m/c for the 03 :)

Yeah, I did several emerency stops with my car then, both dry and in the wet and the fronts always (just) locked up first!
A friend of mine with exactly the same set-up (stock VW front disks, 944 n/a rear and stock m/c) but in a 1300 ('68) model and a 2,7 ltr type 4 engine took it to the circuit and reported that on braking hard and steering into a corner, the rear did lock up first.
Now that is a very extreme situation, but shows it really is depending what you do with the car that dictates how you want to set it up!

Thanks Jeremy,
Walter

As I had mentioned earlier, I am leaning on using the Wilwood product line, instead of the 944 MC.

They have a 1-1/16" Tandem Master Cylinder Part # 260-4893

Dimensions and specifications for this master cylinder are as follows:
Piston Diameter 1-1/16 inch, which is equal to 26.98 or 27mm

Fluid Displacement 1.20 Cubic Inches
Stroke Movement 1.35 inch

Bias Split 69% Front, 31% Rear

Given these dimensions, can anyone “guesstimate” if it would be in the ballpark. I would imagine using a proportioning valve for the front. But I am still learning..
Based on earlier readings I would think that the stroke and amount of fluid would be enough to move the 944 N/A single calipers in the front and back.

Thoughts, or comments appreciated?
But based on the front to rear ratio, it would seem like to high 2.2:1.
Alex

Just got out and measured the cup sizes of my 944 turbo Cup brakes:
Front: 44,0 mm and 36,0 mm (radial mounted 928S alike)
Back: 30,0 and 28,0 mm

With a 944 n/a 23,81/19,05 (which is even more accurate if the bores are indeed 15/16" and 12/16"), that would give a ratio of 1,23 which is low, but similar to my old 03 which had 1,26 and braked like a boat achor :D
Already saw one on ebay ;)

Greetings,
Walter

Good idea.
It should be plenty.
Sorry I can follow Shads calculations and use them on my car but thats where my knowledge stops. As you say the ration front to rear comes out as very front biased, but I don't know how the % bias affects that ratio. I suspect you may be better choosing an option with an adjustable bias bar. This would be a better option than fitting a proportioning valve.

Walter did you do the calculations of your current cup set up (with the 19mm Bug MC) as a comparison?

Cheers
Jeremy

Jeremy..

What is an adjustable Bias Bar..

I assume that this is something built into the MC..

Why is this better than a proportioning valve.. Please explain..

I think I may know why, might have an idea, but in the interest of not sounding to silly please explain..

Thanks
ALex

Yes, I did: that is now a whopping 1.92 F/R ratio !!
As said before, this does explain my current enormous front bias. I hardly wear off the light rust on the rear disk!

Greets,
Walter

Alex

I believe that a bias bar allows you to adjust the ratio between the front and rear brakes at the MC. It keeps it even no matter what pressure you put on the pedal. So the percentage split you mentioned before would be adjustable on a bias bar type.

I had a quick look at proportioning valves once. My understanding was that they limit the maximum pressure to those brakes. ie the max pressure plateus at a value so even if you push harder their will be no more pressure applied. They are commonly used in the rear lines to prevent the rears from locking up first- so this makes sense, limit the max pressure available to the rears because at max braking (ie panic stop) there will be a lot of wieght on the front - even in a rear engined car (don't tell me you don't have wieght transfer- how hard are your springs!!! :D ).

But put the proportioning valve in the front line (which is commonly not allowed by authorities) and you limit the max power to the front brakes. I'm sure with an adjustable one it could be set up very well, but I think for the best set up you would be much better off with an adjustable bias bar.

Feel free to comment on anything that I may have explained incorrectly, its a big learning game for me too.

Walter- yes thats quite a difference between the Bug MC and the 944 MC. Ideally you'd get something in the middle that allows a bit of fine tuning to get it just right :cool:

Cheers
Jeremy

I found this regarding the 911 sc master cylinder bore...

http://www.germanlook.com/Forums/showthread.php?t=2908

Hello all

I have been meaning to reply for quite some time to let people watching this thread know how I got on with the 944 MC.

Well it took a bit of fiddling to make it fit which is why its taken so long. I ran 2 new front hardlines, and a short section to a T piece for the rear line. On the T piece I fitted the brake light pressure switch. I'll see how well this works, but have heard that its a bit slow to react. If need be I fit a micro switch to the pedal cluster.

The way I fitted the MC is nothing new, but being a RHD car I did discover that my rear line exits very close to the brace under the spare wheel well. This required a really tight curve to the brake line and also a bit of clearancing to the brace (punch and big hammer). I've also bolted the T piece to a bracket to support it, which I had noticed many people hadn't.

So its mostly bleed up and the pedal feel and travel is 100 times better. I have much less pedal travel than with the Bug master cylinder. The travel is about the same as a Bug MC and stock discs & drums. I have not driven the car yet, but that is hopefully getting closer and I can report back to any that are interested on how it stops and feels then.

Cheers
Jeremy

cool, feedback once you drive it would be great!

Later,
Jonathan

Figured I'd chime in again..

Looking for another option to get bias right. As it has been mentioned there may be some advantage to running mulit pot pistons. That being said... I have been researching the Wilwood Line of Calipers. There Forged Dynalite's with 1.75 inch pistons are made for different size rotors. Can't remember size of the N/A 944 but from a quick glance this morning they looked like 1".

I say this because I have been looking for Mulitpiston options that were inexpensive for my WRX, which sees the track. For my particular application, only a bracket needs to be made. Which is where the trial and error as well as some engineering come into play. The mounting method via bracket could be used with the 944 spindles to possible create a nice set up. For the WRX this enables me to use 16in wheels and clear my stock rims.

Thought that this could be another option.. I can machine a bracket but need to find out where to do it.. Getting the dimmensions will be trial and error but for about 125 a caliper, could not hurt.

Any thoughts.. haven't looked at the rear yet, but its probably a bracket away..

Not sure what type of metal to use..
i.e what grade steal or aluminum (sp) any thoughts.. I have heard of alumin. brackets braking..

From the info I have (Disc Brakes Australia, DBA) the original thickness is 20mm front and rear.

Check out Steve Cs brakes - he made a bracket to mount 996 rears to the original VW steering knuckle of his 1302.
http://www.clubvw.org.au/porsche_brake_photos.htm

Cheers
Jeremy

Were the later VW reservoir fittings you mentioned earlier correct for the 944 m/c ?

hot66

I can't say for sure about the VW fittings for the remote reservoir lines as mine didn't fit. My master cylinder is a stock one from a '71 1302. Ricola used the fittings from his Beetle master cylinder in the Porsche master cylinder but did mention that his Beetle mc was an after market one.

I found some fittings that did work successfully on an old BMW (7 series from '70s).

I don't know if VW changed the Beetle mc on later models than mine.

Hope this helps :)

Cheers
Jeremy