I just took off my aftermarket brake servo and thought I would share some
of my experiences. As many of you know, I have a Series V Alpine with
dual Webers. The stock brake master cylinder was too long and would
interfere with one of the Webers, so I found a shorter one from Pegasus
Racing. It has a smaller diameter cylinder - so it takes more travel to
push the same amount of fluid, making the pedal a little softer than
stock. The stock Series III-V master cylinder is 7/8" (or .875") in
diameter and I am running .70" (which I believe is the same as Series I
and II). Also, the Series I and II did not come with the booster, while
the Series III - V did.
I bought my booster from Victoria British. I bought the VB one over the
Sunbeam Specialties one because the VB one came with a "kit" and was
slightly cheaper, and SS may have been out at the time anyway. I later
found that the kit was 100% useless. I also later found that the boost
ratios were different between SS and VB:
1.9:1 VB
2.3:1 SS
2.7:1 Girling Recommended.
I say "Girling Recommended" because I wrote them and asked which one was
correct for the Alpine and they wrote back listing a third one. The one
Girling recommended is also listed for Jaguars (XK150, etc) and is priced
accordingly! Anyone know what the original stock ratio was? Is it
different for the 5" or 7"?
Since I was running a softer master, I figured a softer/lower boost ratio
servo would be fine, if not correct. Once it was up and running, I
actually thought that the servo was doing very little anyway because I
only pulled vacuum off of one intake runner - since the Weber manifold has
four separate runners rather than one joined intake chamber, like stock.
Now that I have removed the servo, I see that it was doing more than I
thought it was. The pedal pressure has gone up significantly. I am
sure I will get used to it though. Even though it now takes more
pressure, the brakes had too much travel with the .70 master and the
servo.
I don't know how it would run with the stock 7/8 master. Before I even
bought the servo in the first place, someone recommended removing the
servo and running a .70 servo. It has been so long since I have driven
the car with the stock set up (even when I first got it 17 years ago, the
servo sucked up brake fluid and didn't work right). So, I don't know what
is better. I think the Alpine is heavier than other sports cars of the
same era that ran the .70 without a servo - but I also can't comment on
all the other aspects that go to the "brake feel", such as size of slave
cylinders, drums vs disks vs disks and drums, rotor size, etc.
So there you have it.
Jay Laifman
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