70-72 master cylinder attachment hardware question

[Mike E.]

The master cylinder attaches either to the firewall or to the power brake booster. Each has a pair of studs the master cylinder slides over. What holds the master to those studs--a pair of washers and nuts or a pair of flanged nuts?
My 1970 AIM indicates a call out for the change from nuts and washers to flanged nuts in April of 1969. In reality, i have found 70 and early 71 to have nuts and washers, with later 71 and 72 having the flanged nuts.
The new JG indicates the two types, but nothing beyond that.
My best semi-educated guess is the change happened between 71 7500 and 12000.
I would be happy to have you support or disprove my theory. What have you on your car?

[Daniel K.]

Re: 70-72 master cylinder attachment hardware question

Mike: My '71 with 49,000 miles falls in the lower half of the range of '71's you're looking at. It has the remnants of the "YA" broadcast code tag on one of the bails holding the master cylinder cover, which I hope indicates that the master cylinder is unmolested, but I haven't ever actually checked the casting number or looked for the "DC" stamp described in the TIM&JG. I will be tinkering with the car in about a week and will let you know what holds the master to the firewall on my car then.

[Terry M.]

Re: 70-72 master cylinder attachment hardware question

Mike
FWIW: My 1970 (A29) PB has nut & lock washer