Topic: brake booster to MC push rod

[ford mach]

I'm installing an original rebuilt Bendix 6945 brake booster on a 69 428 car, the booster to MC rod end surface is nearly flat. I bought a Rabestos 36251 and MB 7161 Master Cylinders, both have a concave radius on the piston surface where the booster rod seats which doesn't seem right.
After looking at pics of other original boosters I've seen both flat rod ends and more rounded ends, is the flat correct if so our there any MC's that are better suited?
I attached a picture of the rod end and a spacer with a similar radius for reference.

[JohnSlack]

I'm installing an original rebuilt Bendix 6945 brake booster on a 69 428 car, the booster to MC rod end surface is nearly flat. I bought a Rabestos 36251 and MB 7161 Master Cylinders, both have a concave radius on the piston surface where the booster rod seats which doesn't seem right.
After looking at pics of other original boosters I've seen both flat rod ends and more rounded ends, is the flat correct if so our there any MC's that are better suited?
I attached a picture of the rod end and a spacer with a similar radius for reference.

This issue came up recently on the BOSS 302 website, my recently rebuilt booster (1969 1/2 BOSS 302 July build) and it was returned with the square end. My DNO master cylinder is set up for a round rod end, my original master cylinder used a square end. I'm looking into using my original piston to rebuild my "new" master cylinder from DNO. There are warnings against using flat ends with rounded pistons and vise versa.


John

[ford mach]

Thanks for the reply, for now I'll be swapping out my flat end for a rounded type. Let me know what you find out about using an original piston to rebuild the new MC.

Bob

[JohnSlack]

Thanks for the reply, for now I'll be swapping out my flat end for a rounded type. Let me know what you find out about using an original piston to rebuild the new MC.

Bob

Will do.


John

[JohnSlack]

I'm taking my DNO master cylinder apart to dimensionally compare the pistons in the next few days. If I can not do the piston swap I have done enough comparison of the radiused bore that I personally for my own use and going to spot face the bottom of the bore to the flat dimension and shape.


John

[Bob Gaines]

I'm taking my DNO master cylinder apart to dimensionally compare the pistons in the next few days. If I can not do the piston swap I have done enough comparison of the radiused bore that I personally for my own use and going to spot face the bottom of the bore to the flat dimension and shape.


John

I'm sure that many interested myself included would like to know how that works out so please do. Best of luck.

[JohnSlack]

I'm sure that many interested myself included would like to know how that works out so please do. Best of luck.

Bob,
I'm going to be holding off for a few days, I ordered a 7/16 end mill with a 0.020" radius edge to eliminate the "sharp" corner at the bottom of the bore. It should still clean up. So I am going to get to the real world work I've got to get finished, before playing with my stuff. But I will definitely be keeping you all in the loop.


John