63 Thumbscrew master cyl

[Rex T.]

I have a "thumbscrew" type master cylinder, casting number 5462225, with a 1 inch bore. Can anyone tell me if this is an original 63 master cyl for std or power brakes? Thanks, Rex #8089

[Mike M.]

Re: 63 Thumbscrew master cyl

63 vet master cyl( excepting the ZO6) all used a thumb screw mast. cyl with a 7/8" bore while the 63 chevy pass. cars used the 1" bore.mike

[Bob R.]

Re: 63 Thumbscrew master cyl

I thought the 1" bore was used on a power brake system while the 7/8" was used on manual brakes. I am quite sure the master cylinders for poware and manual are not the same. Maybe some else could comfirm this.

[Verne Frantz]

Re: 63 Thumbscrew master cyl

Rex,
The 225 1" master was used on passenger cars with power brakes. Passenger cars with the metallic brake option received the same 7/8" master as the '63 Vette used.
Verne

[Philip Whitaker Member# 2024]

Re: 63 Thumbscrew master cyl

Rex,

According to the judging manual the M/C should be cast 5462389. The same casting is used for both P/B and non P/B. The P/B master cylinder will have a bleeder valve on it while the non P/B will not. There is a P/B master cylinder up for auction on ebay right now. You might want to check it out.

Phil

[Loren L.]

It's for a Pontiac *NM*

[Joe L.]

Re: 63 Thumbscrew master cyl

Bob-----

For 1963, the Corvette master cylinder for either manual or J-50 power brakes was a 7/8" bore master cylinder. It was GM part number 5462385. This number is not found on the master cylinder, though.