As George says it was a great improvement. In fact I was glad we did it because enroute to ZCON on the I-95, George was behind me doing 65mph when some fools not far in front came to a complete stop. We both had to hammer the brakes very hard and both cars stopped safely. I don't think the other booster would have stopped as quickly.

For the drilling, just make a cardboard template to ensure it fits onto the new booster's stud holes and ensure it's outer edge is the same diameter.

btw we were able to do the work without removing the master cylinder from the brake lines. The only problem was losing the small clip on the clevis ..... a magnet on the side of a service light stole it from the drivers foot area/parts holder.

I don't think the smaller boosters are available and I was talking to a rebuild shop about getting diaphragms to rebuild some of the boosters I have laying around. I don't think they have a source for the smaller diaphragms any more so hence no rebuilt little boosters...

Charles

I have a small booster, worked when pulled about 8 years ago. $40 + shipping if you're interested.

The difference between 7" and 8.5" diameter doesn't sound like much, but this is pizza math! A 7" circle has an area of 38.5 square inches, and the 8.5" circle has an area of 57 square inches, nearly 50% more area for air pressure to act upon!

Further lack of progress with parts suppliers and the above helpful input are causing me to rethink a retrofit to the bigger booster. Interesting that Black Dragon lists a booster for '70-'71 and another one for '73-78. My guess is that the '72 model year spanned both boosters. The build date on my car is 12/71, so maybe it has the earlier (smaller diameter) booster.

Throw a tape measure on it.

The early booster is 7" diameter and the late booster is 8.5" diameter.

The new, larger booster is installed. I had to relocate all four holes out 1 cm and everything bolted up fine. It is a very tight fit between the clutch master cylinder and the bracket for the accelerator linkage with only about a couple of mm clearance on each side. You have to be very precise in drilling the holds, but they all landed on the pedal box interior to the firewall. I used some fender washers to hide the old holes on the inside. On the outside, the old holes are covered up by the larger booster.