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Master Cylinder - U.S. vs ROW?

While browsing I found this:

Quote:
78-later brakes are excellent but on U.S. spec cars you will need to fit the Euro Rest-of-World master cylinder to correct bias orientation rearward. Verify your non-US car has not had the US master cylinder retrofitted over the years.
Is this common knowledge? Is it true? How does one identify the two different versions? The Euro M/C has more rear bias?

Old 09-27-2008, 09:26 AM
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Bump. Still searching for the answer
Old 01-25-2009, 02:11 PM
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I don't see how the master cylinder can bias to the rear.
The bias is engineered into the calipers themselves via the difference in piston sizes between front and rear calipers.
Note on the 930 the caliper housings and brake pads are the same....smart design.
But the pistons for the rear brakes are smaller in diameter and therefor apply less force to the rotors and less bias while operating under the same line pressures as the fronts.
Simple hydraulic theory.
Hope someone will enlighten me if I am wrong and the quote is real.
Fred
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Old 01-25-2009, 02:57 PM
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Although it is poorly worded, this could be a reference to the different sized M/C bores. For the 911 and 912, from 1965-67 the bore was 17mm - 901-355-011-01.
In 1968, it was changed to 19mm - 911-355-012-02. Then in 1977 vacuum power assist was introduced with the 20mm bore - 911-355-011-12 (the turbo was the same in 1976-77 but changed to a 23mm dual circuit version - 930-355-011-03 from 1978-89).
In 1989-94, the Carrera 4, and the new 965 turbo introduced in 1991, used a new 23mm hydraulic power assist unit - 964-355-903-00. In 1990, the Carrera 2 used a 20mm unit - 964-355-015-03 until 1994.
In 1992 the RS came with a 25mm master cylinder and the 993 followed with the same size in 1994.

Mark
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Old 01-26-2009, 10:00 AM
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Quote:
Originally Posted by fredmeister View Post
The bias is engineered into the calipers themselves via the difference in piston sizes between front and rear calipers.
Yes, except on the 3.2 cars, where the relatively large rear calipers would be too rear-biased without an external bias valve to compensate. But that bias valve is external to the M/C, so the quote still makes no sense.

Where did the original quote come from? The internet?

Never hurts to be on your guard - some books out there are less than 100% accurate...
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Old 01-26-2009, 11:06 PM
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Old 01-27-2009, 10:04 AM
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My understanding is that they basically sell one type now, and even the pre-78 cars get the same one. It may be the Euro version but I think it is the only one made.
Old 01-27-2009, 10:31 AM
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Quote:
Originally Posted by spuggy View Post
Yes, except on the 3.2 cars, where the relatively large rear calipers would be too rear-biased without an external bias valve to compensate. But that bias valve is external to the M/C, so the quote still makes no sense.

Where did the original quote come from? The internet?

Never hurts to be on your guard - some books out there are less than 100% accurate...
I have seen the quote at the Pat Williams Racing website. I am not sure if there is still a choice or if they (hopefully) sell the best version now...

Old 01-27-2009, 10:34 AM
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