19 MM Master Cylinder Question

[Ryce Stallings]

Can you use the 1977 19 MM Turbo master cylinder in a 1977 911?

I have larger brakes on my car and need a new master cylinder.

[Bill Verburg]

Originally Posted by Ryce Stallings

Can you use the 1977 19 MM Turbo master cylinder in a 1977 911?

I have larger brakes on my car and need a new master cylinder.

Depends, some '77 have power brakes and some don't

power brake 911 for MY77 have 20.6mm m/c non power have 19.05mm
there was a one year only 20.6mm non power brake m/c for early MY69 but I haven't seen one for several decades

There are 2 possible larger m/c
VW Corrado(I've never actually used on butt it's said to work by reputable people) I forget how big and whether power or no

or 23.8mm
power brake cars use a '78-89 930

non power brake cars use ATE # 03-2123-3402.3 ports face left for US cars, there is another one w/ ports right for English versions

[Ryce Stallings]

My car doesn’t have power breaks. Is the ATE MC mentioned similar to the 19MM I asked about?

[Bill Verburg]

Originally Posted by Ryce Stallings

My car doesn’t have power breaks. Is the ATE MC mentioned similar to the 19MM I asked about?

similar yes, bigger yes
top 23 bottom 19, the extra length can present difficulties w/ the cross member but it can be done


installed 23mm



you want a kit that includes the pushrod which is different from a 19mm version and the lines and the plastic 45s


VW one



box

[SorenDK]

Originally Posted by Bill Verburg

Depends, some '77 have power brakes and some don't

power brake 911 for MY77 have 20.6mm m/c non power have 19.05mm
there was a one year only 20.6mm non power brake m/c for early MY69 but I haven't seen one for several decades

There are 2 possible larger m/c
VW Corrado(I've never actually used on butt it's said to work by reputable people) I forget how big and whether power or no

or 23.8mm
power brake cars use a '78-89 930

non power brake cars use ATE # 03-2123-3402.3 ports face left for US cars, there is another one w/ ports right for English versions

Hi Bill

Im curious about the VW m/c ... can you (or maybe) someone else cast some more lights on this? This m/c seems to be 22,2mm.

A more general question - under which conditions to people use the 23mm versus the 19mm? - non-boosted. I have a '74 with standard calipers rear - but will be putting the bigger 3,2 calipers front. This might require the bigger bore... but then again the 19mm might be sufficient - or maybe even better ??... anyone have thought on this?

[tdw28210]

Originally Posted by SorenDK

Hi Bill

Im curious about the VW m/c ... can you (or maybe) someone else cast some more lights on this? This m/c seems to be 22,2mm.

A more general question - under which conditions to people use the 23mm versus the 19mm? - non-boosted. I have a '74 with standard calipers rear - but will be putting the bigger 3,2 calipers front. This might require the bigger bore... but then again the 19mm might be sufficient - or maybe even better ??... anyone have thought on this?

I run a 23mm MC (non-boosted) with front Boxster front calipers on my 3.2 lightweight hot rod build. Requires a little more pedal effort, but I am OK with it.

[Bill Verburg]

Originally Posted by tdw28210

I run a 23mm MC (non-boosted) with front Boxster front calipers on my 3.2 lightweight hot rod build. Requires a little more pedal effort, but I am OK with it.

Hopefully you have Carrera 3.2 wide M rears , if so the pedal ratio is 32.91 exactly where you want it to be

Some racers even use the 23.8 non boosted w/ stock A & M , but the pedal ratio there gores to 26.467, you get exquisite control but it takes a lot of leg

[Bill Verburg]

Originally Posted by SorenDK

Hi Bill

Im curious about the VW m/c ... can you (or maybe) someone else cast some more lights on this? This m/c seems to be 22,2mm.

A more general question - under which conditions to people use the 23mm versus the 19mm? - non-boosted. I have a '74 with standard calipers rear - but will be putting the bigger 3,2 calipers front. This might require the bigger bore... but then again the 19mm might be sufficient - or maybe even better ??... anyone have thought on this?

You size the m/c to get the pedal ratio where you want it

useful range is ~45 to ~30, w/ boost you can go lower

the lower the better control but the more effort is needed, really low can be quite fatiguing if you are in the car for long track sessions

higher gives you worse control for less effort, only useful for casual street driving or little ole ladies

[tdw28210]

Originally Posted by Bill Verburg

Hopefully you have Carrera 3.2 wide M rears , if so the pedal ratio is 32.91 exactly where you want it to be

Some racers even use the 23.8 non boosted w/ stock A & M , but the pedal ratio there gores to 26.467, you get exquisite control but it takes a lot of leg

Yep Carrera rears.

[Walt Fricke]

Short answer - using wider calipers (so you can use wider brake disks) doesn't require - or really benefit from - a larger master cylinder, unless the caliper pistons are themselves wider. In your case, the front pistons are the same, but the rear pistons are wider. Left alone, this would give you more rear brake bias than is good. Porsche left the MC diameter alone, but added a brake pressure limiter for the rear to deal with this, and in particular to prevent the rears from locking up before the fronts under hard braking (and especially, panic/near emergency braking).

That is what you should consider doing.

Locking the rears before the fronts usually causes the car to spin, even with the steering pointed straight.

[Bill Verburg]

Originally Posted by SorenDK

Hi Bill

Im curious about the VW m/c ... can you (or maybe) someone else cast some more lights on this? This m/c seems to be 22,2mm.

A more general question - under which conditions to people use the 23mm versus the 19mm? - non-boosted. I have a '74 with standard calipers rear - but will be putting the bigger 3,2 calipers front. This might require the bigger bore... but then again the 19mm might be sufficient - or maybe even better ??... anyone have thought on this?

As Walt says only bigger caliper pistons require a bigger m/c

A?M or wide A/ M the pedal ratio w/ stock non boosted m/c is 41.311, w/ a VW 22.2 it goes to 30.42, w/ 23.8 it goes to 26.467

Again the lower this # the better control at the cost of extra leg

Of the the 3 choices stock for street use, the VW for performance, I'd avoid the 23.8 for all but the most extreme and robust track guys