Good luck in searching for a new master cylinder for your truck. I have a 1966 GMC 5500. Yours might be heavier duty. I replaced a two chamber master cylinder (clutch and brake). The brake line led to a hydrovac unit that has also needed replacing. To get a replacement master cylinder, I needed to search to find a unit with brake and clutch bores and stroke that held the right amount of hydraulic fluid. This was done with much needed help from members of this forum. The replacement part also needs to have holes in the right places to bolt to the firewall, and you need to think about the availability of dust boots. You can find my thread for this under "Master Cylinder Frustration" by JRMunn.


JRMunn