Here is the final info that I have found.
Original Part=GM #3773856 1 1/4" Brake Bore 1 1/8" Clutch Bore
I could not cross this to anything but that is the casting number.
Raybestos MC19089 1 1/4" Brake Bore 1 1/4" Clutch Bore
Raybestos MC34404 1 1/8" Brake Bore 1 1/8" Clutch Bore
Centric 130.80018 1 1/4" Brake Bore 1 1/8" Clutch Bore
This would have been off an early 60's C80 or 2 tonish truck.
The Centric part is the correct one but... Centric option is 150$ as well as any other option with 1 1/4" dual bores if you wanted to make the case to step up the clutch bore. These are also not a readily available.
I think the wise experienced Sno-Drifter has already learned a few things for us and is passing it along subtle. The Raybestos MC34404 which has dual 1 1/8" bores is a readily available part and costs under 50$ or 1/3 of the Centric option. Quite possibly the reduction of brake bore size is an improvement due to allowing for a longer pedal throw and could reduce the sticking issue?
That sounds like the way to go. How about the fluid? Brake fluid or other option like ATF?
Hi
I found some different information. It is all based on replacing a bad master cylinder on a 1984 Tucker 1342. It was very difficult to find the cross-over part and bore dimensions.
The master cylinder was listed as a Delco 2621179 on the Tucker build sheet. Glad I had that.
Previous owner had replaced it with a master that had 1-1/8 bore cylinders for both brake and clutch. I don't know the brand but it looked like a POS. Rough casting, bad finish etc. It was only a couple of years old, according to the previous owner. There was internal rust in the bores. Clutch almost frozen and master brake cylinder was leaking.
The Delco 2621179 crossed over to a Raybestos MC19089 on RockAuto for $160 shipping extra.
The Raybestos Catalog shows the master to be 1-1/4 brake bore and 1-1/8 clutch bore.
Bought one from Amazon for $112 shipped. Very good deal all considered. If you know the part number, Amazon is generally pretty cheap. Shipping is fast and free with prime.
Ordered one, measured that bores and the Raybestos catalog and the Rockauto crossover are correct.
It fits the existing mounting.
I am going to install it in the next couple days. Flush everything and have a good look at the brake calipers. I hope it is compatible with slave cylinders currently on the machine. Who knows, someone may have known something and changed the brake caliper to be compatible with the master.
John