22mm Brake Master Cylinder?

[Myami]

Hi Pelicans,

I am looking at improving the brakes on my 71T. I will be purchasing the PMB 3" upgraded "AM" calipers, but would like to increase the brake master as well to improve pedal feel.

The general consensus is: skip the 23mm+ brake master. Noted. I have seen a number of passing references to a VW brake master (22mm) that is said to bolt in without issue. Based on my research, the VW part number is: ATE 357611019. For those in the know, is this number correct? I have also read that a 22mm from Mercedes will work--I'm open to this option as well.

Any feedback on the intended upgrade would be appreciated, though I am aware of the increased pedal effort and am not concerned . . . unless those in the know say I should be.

TIA.

[Bill Verburg]

Originally Posted by Myami

Hi Pelicans,

I am looking at improving the brakes on my 71T. I will be purchasing the PMB 3" upgraded "AM" calipers, but would like to increase the brake master as well to improve pedal feel.

The general consensus is: skip the 23mm+ brake master. Noted. I have seen a number of passing references to a VW brake master (22mm) that is said to bolt in without issue. Based on my research, the VW part number is: ATE 357611019. For those in the know, is this number correct? I have also read that a 22mm from Mercedes will work--I'm open to this option as well.

Any feedback on the intended upgrade would be appreciated, though I am aware of the increased pedal effort and am not concerned . . . unless those in the know say I should be.

TIA.

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

also
ATE (ports face left)23.8mm m/c # 03-2123-3402.3
or
early 69 911used a 20.5 mm mc Porsche # 901.355.012.04 ATE # 3.2120 - 3901.3
updated version 911.355.012.02

W 911 A/M calipers the pedal ratios are
stock 19.05mm 41.311
20.5mm 35.674
20.64 mm 35.192
22.2 mm 30.42
23.8mm 26.467 Recommended for experienced hardcore track use only

lower pedal ratio is better toa point w/ better feel and control

[grantmax]

Originally Posted by Bill Verburg

lower pedal ratio is better toa point w/ better feel and control

Incredibly helpful--thanks, Bill!

In your experience, is the 20.64mm an appreciable improvement? I don't want to overdo it, but I am certainly after a lower pedal ratio.

Also, it appears as though the 20.64mm master will be tough to find. The ATE 22mm units are readily available though. Do you have any experience with the 22.22mm unit?

[Bill Verburg]

Originally Posted by grantmax

Incredibly helpful--thanks, Bill!

In your experience, is the 20.64mm an appreciable improvement? I don't want to overdo it, but I am certainly after a lower pedal ratio.

Also, it appears as though the 20.64mm master is made by TRW. Any issue there? ATE is preferred, of course.

20.64 is incrementally better.
t
Personally, I like 30+/- but an argument can be made for any of them depending on the driver and usage.

The lower the pedal ratio the more effort that driver needs to use, over time that can be fatiguing, the return for a lower # is better control at the edge. For street use you are rarely at the edge.

The upper limit is ~50 here the m/c can't move enough fluid fast enough to work at the edge, for safety you want to be no higher than ~45 which to me is too mushy.

Never heard of a TRW m/c part # for these.

[grantmax]

Originally Posted by Bill Verburg

20.64 is incrementally better.
t
Personally, I like 30+/- but an argument can be made for any of them depending on the driver and usage.

The lower the pedal ratio the more effort that driver needs to use, over time that can be fatiguing, the return for a lower # is better control at the edge. For street use you are rarely at the edge.

The upper limit is ~50 here the m/c can't move enough fluid fast enough to work at the edge, for safety you want to be no higher than ~45 which to me is too mushy.

Never heard of a TRW m/c part # for these.

Ah, ok. So moving to the 22.2 unit isn't outside the realm of reason then. And, based on your preference, the 22.2 is close to ideal. Good news: the ATE 22.2 MC was easy to find.

I have seen a number of posts suggesting the 23.8 unit requires too much effort and should be avoided. I wonder if that was the MC in the 84 targa I had years ago. The brake pedal was quite firm on that car.

[Bill Verburg]

Originally Posted by grantmax

Ah, ok. So moving to the 22.2 unit isn't outside the realm of reason then. And, based on your preference, the 22.2 is close to ideal. Good news: the ATE 22.2 MC was easy to find.

I have seen a number of posts suggesting the 23.8 unit requires too much effort and should be avoided. I wonder if that was the MC in the 84 targa I had years ago. The brake pedal was quite firm on that car.

The discussion here is only relevant to non boosted brake 911, ie '76 and earlier( and a few rare '77 versions)

The vacuum boosted cars from '77 on use either 20.64(stock 911) or 23.8(930)

w/ boost you can go below 30 comfortably,

the issue w/ non boosted 23.8mm m/c is it's physical length, It just barely fits w/ a bit of effort, into the allotted space. These all need a longer pushrod so it's best to buy a kit which includes the m/c the matching rod, the plastic port adaptors and hose.

the 22.2 and smaller all use the same push rod and it's smaller and it has 2 sets of ports for, the stock 19 and 23.3 are left facing ports.

for boosted brake cars the 23,8 mm 930 m/c is a straight swap w/ no issues.

[grantmax]

Excellent. Thanks for the clarification, Bill.

Looks like ATE only makes a 20.6 unit at present (https://www.pelicanparts.com/More_Info/357611019.htm?pn=357-611-019-INT&bc=c&SVSVSI=4236).
The 22.2 on offer is made by TRW (https://www.pelicanparts.com/More_Info/357611019B.htm?pn=357-611-019-B-M80&bc=c&SVSVSI=4236).

In your opinion, would a larger m/c on stock non-S calipers be worthwhile?

[PeteKz]

Bill, great info. Let me verify what's in my 1973T. I understand that they used 19mm MC's, and that's what you show. Correct?

Something I've been thinking about for awhile, and might make a winter project: Switching to later SC or Carrera struts (mine are the Boge of that era), to get the larger M calipers on the front. I would keep my 19mm MC at first, and see how I like the pedal effort and feel. Anything I should watch out for?

[rsscotty]

It has been a few years, but when I was involved in a 73 RS type race car build, I sourced a 944 aluminum stepped master cylinder instead of using the normal go to 23mm. Pedal effort was less than the 930 as I remember. Worked great with the caliper combination ..had 930 fronts, rears were a smaller Porsche aluminum caliper, I don't recall which one. It took some work for mounting it and clearing the 15" wheels.

[Bill Verburg]

Originally Posted by PeteKz

Bill, great info. Let me verify what's in my 1973T. I understand that they used 19mm MC's, and that's what you show. Correct?

Something I've been thinking about for awhile, and might make a winter project: Switching to later SC or Carrera struts (mine are the Boge of that era), to get the larger M calipers on the front. I would keep my 19mm MC at first, and see how I like the pedal effort and feel. Anything I should watch out for?

yes, 19.05 was used for most of the pre '77 911s

there was a 1 year early 69 911 that used a 20.5 mm mc Porsche # 901.355.012.04, 911.355.012.02 updated version,
ATE # 3.2120 - 3901.3
but these are very difficult or impossible to come by

changing from the M/M to A or S/M doesn't change the hydraulics at all, so for performance use going bigger than 19 is a good and 23.8 is a bit much for most users

[Bill Verburg]

Originally Posted by rsscotty

It has been a few years, but when I was involved in a 73 RS type race car build, I sourced a 944 aluminum stepped master cylinder instead of using the normal go to 23mm. Pedal effort was less than the 930 as I remember. Worked great with the caliper combination ..had 930 fronts, rears were a smaller Porsche aluminum caliper, I don't recall which one. It took some work for mounting it and clearing the 15" wheels.

The stepped m/c 's are a poor mans alternative to a twin master setup w/ less flexibility and much lower cost

[H-viken]

I believe PMB has a 23,8 mm master cylinder with the same outer dimensions as the 19mm, i.e no fitment issues on the non boosted cars

[thetorch]

Originally Posted by Bill Verburg

yes, 19.05 was used for most of the pre '77 911s

there was a 1 year early 69 911 that used a 20.5 mm mc Porsche # 901.355.012.04, 911.355.012.02 updated version,
ATE # 3.2120 - 3901.3
but these are very difficult or impossible to come by

changing from the M/M to A or S/M doesn't change the hydraulics at all, so for performance use going bigger than 19 is a good and 23.8 is a bit much for most users

Interesting. I have a Sept '68T built '69 that appears to have it's original MC, but it has no part number on it, and the only markings are ATE and "19".

[spuggy]

Originally Posted by rsscotty

sourced a 944 aluminum stepped master cylinder instead of using the normal go to 23mm.

Oh, interesting, had no idea that the 944 M/C used differential bores. Although I found this drawing some time ago that clued me in that the 993 did:




Does anyone know the specs/sizes of the 944, 951 and/or the 993 M/C bores? I'd presume 964 probably also used them? And perhaps the RS variants used interesting ratios?

Yes, my brakes are too front-biased for optimal balance, but I'd like to keep the servo/avoid fitting the twin M/C setup

[Bill Verburg]

Originally Posted by thetorch

Interesting. I have a Sept '68T built '69 that appears to have it's original MC, but it has no part number on it, and the only markings are ATE and "19".

It's a 19.05mm version then

the 20.5 would have been used on the S and maybe E

[Bill Verburg]

Originally Posted by spuggy

Oh, interesting, had no idea that the 944 M/C used differential bores. Although I found this drawing some time ago that clued me in that the 993 did:




Does anyone know the specs/sizes of the 944, 951 and/or the 993 M/C bores? I'd presume 964 probably also used them? And perhaps the RS variants used interesting ratios?

Yes, my brakes are too front-biased for optimal balance, but I'd like to keep the servo/avoid fitting the twin M/C setup

The 993 uses a Lucas 23.8mm on vacuum boosted or 25.4mm or different 23.8mm on electro hyd boosted systems, none are compatible w/ the 911 boosters, and none are stepped
964 used 20.64 on vacuum boosted systems and 25.4 like the 993 on electro-hid boosted systems, again none are stepped.

[Myami]

Originally Posted by Bill Verburg

It's a 19.05mm version then

the 20.5 would have been used on the S and maybe E

Bill: In your opinion, would maintaining the stock M calipers (recently rebuilt and shod with RS4s) and installing the 20.6mm ATE m/c referenced above yield a noticeable difference? Not night and day, but a moderately firmed pedal that engages slightly higher, perhaps?

Thanks in advance.

[rsscotty]

The specifics on the 944 brake master up to the end of 86 model year are 23.81/19.05
87 model year was 23.81/20.64 Both are stepped aluminum

[Bill Verburg]

Originally Posted by Myami

Bill: In your opinion, would maintaining the stock M calipers (recently rebuilt and shod with RS4s) and installing the 20.6mm ATE m/c referenced above yield a noticeable difference? Not night and day, but a moderately firmed pedal that engages slightly higher, perhaps?

Thanks in advance.

M/M and A/M and S/M all have the same hydraulics
so yes
W? 911 A/M calipers the pedal ratios are
stock 19.05mm 41.311
20.5mm 35.674
20.64 mm 35.192
22.2 mm 30.42
23.8mm 26.467 Recommended for experienced hardcore track use only
each increase in m/c size is incrementally better,

the def. of better here is higher and firmer requiring more leg