I see a lot of master cylinder rebuild kits for 1966 f100's that are 1" bore but not 1 1/8". Even for a new MC, all I can find for 1966 is a 1 " bore. I found the 61-65 mc is a 1 1/8". My MC is a 1 1/8" bore and its a 66. I don't believe it was ever changed. Did 66's have the larger bore on 4wd's ? Are there rebuild kits for the 1 1/8" ??

 

The Orielly parts website lists a 1 1/8 bore M/C for a 1966 F250 4x4. That should do it.

 

Uh huh, the OP has an F100 4WD and O'Reilly is FOS!

1966 F100/250 2WD & 4WD: C5TZ-2140-A .. Master Cylinder - 1.00" bore.

1 1/8" bore: 1964/65 F250 2WD/4WD without Power Brakes: C1TZ-2140-B .. Master Cylinder / 1965 F250 2WD with Power Brakes: C5TZ-2140-B .. Master Cylinder.

 

ND - Thank you for the information. Is it possible that my 66 was fitted with a 1 1/8" bore mc because the truck was assembled in late 1965? As I mentioned in my last post, I believe this is the original mc. Only problem is mines a F100 not a 250
776039 = 1966, assembled in November 1965.

 

You believe it's the original M/C? Why? Who the hell knows what could have occurred over the past 47+ years.

C5TZ-2140-A .. Master Cylinder 1.00" bore.

1965 F100/250 2WD with/without P/B / 1966 F100/250 2WD/4WD without P/B.

 

I agree with you. I say I believe because (it leaves me an out ! LOL) it's been in the family since new, but......I only started driving it in 84. I know I never changed it and I do not recall my Dad changing it either. But you are correct, who the hell knows, I was young back then. Anyway, I appreciate all your input and help ! You are a great resource.