"S" brake upgrade

[Joe Ricard]

Just completed the "S" brake upgrade on my 78 928. I got the whole deal except the master cylinder. The results are REALLY long pedal travel with Easy effort. Sort of what I expected but didn't realize it would be so pronounced or exagerated. So with my early booster how big of a Master cylinder can I put on?
VIN ends with 0347. Small booster. Yes I believe the system is properly bled. ZERO air!

[rich]

If it were me, I'd match the master cylinder with the caliper volume. Just use the proper "S" part and your done.

[Joe Ricard]

The reason I say this is when I bought my last master cylinder it was required for me to give the Model year and VIN to get the part to fit the booster. I would think I can get a bigger booster and then matching Master cylinder. Apparently there was a change in mid year production in 78. Guess which end I am on.
As far as I know the fire wall for the cars is the same so, as with other newer parts they should all bolt on. Just takes money
Just as long as I don't find another use for my new Milwaukee sawzall.

[Wayne 962]

I believe that the chassis is the same there, and that you can just bolt in the larger MC...

Should work ok...

-Wayne

[Joe Ricard]

Just talked to the P.O. of the "S" brakes he said from his references that the Master Cylinder size was the same until 83. What actually changed was the size of the bosster. 9 inch to 10 inch. The next most modern Master cylinder was for ABS equiped cars. Problem with this is it was no longer diagonal circuits.
Did do another complete system bleed seems to be better but it mat just be me trying to console myself for the additional wrenching. When I do get a firm pedal and figure out what the problem is I will post it.

[Wayne 962]

What is the method you are using to bleed?

-Wayne

[rich]

I'm no sure but, The 10" booster change may require changing the brake pedal assm. I think I read some where this changed the leverage, and maybe the travel?
That makes sense to me, If you increase the volume of fuid needed to fill the "S" calipers and Porsche didn't change the MC, they must have just changed the pivot point on the pedal. That would have shortened the travel but made it harder to push. Hence the increase in the booster.
so get the correct "S" pedal assm. AND the booster.

[Joe Ricard]

Well I had my 16 yr old son do the pedal work. PUMP PUMP PUMP then I opened the bleed screw. I had a clear tube conected draining into the bottle. My son would push the pedal to the floor and hold it till I closed the screw. Then repeat till all bubbles were gone. I did this on the fronts first, then right rear left rear and back to the right font, left front. Plus while I was there I did the clutch. couldn't hurt. I have about 25 miles on the car since sunday. the pads look as if they are all bedding in correctly. and they all release Slightly and evenly from the rotor. BTW I do have stainless flex lines. Had stainless on car before never gave me any trouble. Well got to drive it to make it better.