Master cylinder for a SWB car

[Seppo]

I have a 68SWB car with a 3.2 engine.
I have upgraded the entire front suspension to a late Carrera 24mm caliper and rotor.
In the back has the original vented "L" brake caliper.
Which master cylinder should I use? The late lwb 19mm m/c or the Mercedes ATE non boosted m/c. ATE 03-2123-3402.3?

Thank you in advance

[Bill Verburg]

Originally Posted by Seppo

I have a 68SWB car with a 3.2 engine.
I have upgraded the entire front suspension to a late Carrera 24mm caliper and rotor.
In the back has the original vented "L" brake caliper.
Which master cylinder should I use? The late lwb 19mm m/c or the Mercedes ATE non boosted m/c. ATE 03-2123-3402.3?

Thank you in advance

I seem to recall those rear calipers have the same 35mm pistons as the later m rears

If so
19mm M/C gives 41.311 pedal ratio
22.6 M/C gives 29.352 pedal ratio
23.8 gives 26.467 pedal ratio

You could use any of them I'd prefer the 22.6 myself, it's like the Goldilocks story, too soft, too hard just about right

the 22.6 I believe is the VW one that Elephant uses w/ their 930 BBKs

[Seppo]

Measured the rear caliper today and it is 38mm,
Somebody told me to use later M calipers in the rear, or a 930 turbo setup for the entire car.

[mepstein]

I don't think M calipers will fit on SWB trailing arms.

[jmz]

Originally Posted by mepstein

I don't think M calipers will fit on SWB trailing arms.

-I have them on the rear of mine. I am using an adapter from PMB.

[Bill Verburg]

Originally Posted by Seppo

Measured the rear caliper today and it is 38mm,
Somebody told me to use later M calipers in the rear, or a 930 turbo setup for the entire car.

If they are 38mm pistons then they are the later versions and should be paired w/ the later vented rotor, the 35mm version were used w/ the solid rotors

The above answer is still ok and I'd still prefer the 22.6, 19.05mm was stock on those

[Seppo]

Originally Posted by Bill Verburg

If they are 38mm pistons then they are the later versions and should be paired w/ the later vented rotor, the 35mm version were used w/ the solid rotors

The above answer is still ok and I'd still prefer the 22.6, 19.05mm was stock on those

Yes this is a late version with vented rotor. I will look for a 22.6 Thank you Bill.
And the 930 turbo braKe setup? Maybe it is overkill.... and hard to fit everything under 6" rims

[Bill Verburg]

Originally Posted by Seppo

Yes this is a late version with vented rotor. I will look for a 22.6 Thank you Bill.
And the 930 turbo braKe setup? Maybe it is overkill.... and hard to fit everything under 6" rims

930 while very nice is overkill and very expensive

The tires are going to be the weak link w/ 6" wheels and associated tires

even w/ 7s the older finned 930s need to have the fins shaved or use a small spacer

The only time 930s will make a difference is at a track event and even there the lighter the car the less stress on the brakes and the less need for 930s

You can see the relative brake torque and bias from the various setups here

[jmz]

I agree with Bill. 930 brakes would be silly on this car. The car is light and doesn't have much tire patch.

On my 68 SWB, I have the Alpha aluminum brembo brakes up front with modified M calipers with a spacer and adapter to fit on the back. Vented rotors...think SC and 944 if I am not mistaken front/back. 19mm master cylinder. It is a very appropriate setup for my car. ...car has a 2.8 twin plug in it so it scoots along pretty good.

You can find the alpha calipers on here, early911s or maybe 914 world occasionally.

You can also check with Eric at PMB.

EDIT: I just read you added late model suspension up front so no need for the Alpha caliper. You could likely run S, SC or something up front. Those should balance well with the M in the back I think but Bill can confirm with all his knowledge spiffy charts!

[Seppo]

Originally Posted by jmz

I agree with Bill. 930 brakes would be silly on this car. The car is light and doesn't have much tire patch.

On my 68 SWB, I have the Alpha aluminum brembo brakes up front with modified M calipers with a spacer and adapter to fit on the back. Vented rotors...think SC and 944 if I am not mistaken front/back. 19mm master cylinder. It is a very appropriate setup for my car. ...car has a 2.8 twin plug in it so it scoots along pretty good.

You can find the alpha calipers on here, early911s or maybe 914 world occasionally.

You can also check with Eric at PMB.

EDIT: I just read you added late model suspension up front so no need for the Alpha caliper. You could likely run S, SC or something up front. Those should balance well with the M in the back I think but Bill can confirm with all his knowledge spiffy charts!

I use wide A calipers on the front.
Other question: I have some issue driving over 100mph, the car doesnot straight running, the wheel alignment should be ok. If I put some extra weight in the trunk its getting better.

[Bill Verburg]

Originally Posted by Seppo

I use wide A calipers on the front.
Other question: I have some issue driving over 100mph, the car doesnot straight running, the wheel alignment should be ok. If I put some extra weight in the trunk its getting better.

The SWB cars are the twitchiest,the first factory attempt at a cure was placing weights in the front bumper ends to increase the cars polar moment
the second and final fix was to move the wheels back creating a longer wheelbase, this was further done on the 996 and again 991

A friend has an RSR built on a 65 tub he moved to the longer '69-89 wheel base

[Seppo]

Tested the 930 shaved caliper and it fits under my 6x15"with a 10mm spacer
What do you think to the following setup?

Front
930 caliper 4x38mm piston
304x32mm disc

Rear
Wide L caliper with 2x42mm pistons or Wide L caliper with 2x38mm pistons
290x20mm disc

M/C 23mm early type non boosted



The car is 2620 Lbs with 39/61 weight distribution

[jmz]

That’s a fat SWB.

[Seppo]

Originally Posted by jmz

That’s a fat SWB.

Well yes
100L tank + Aircon + Driver + front bumper weight....