Installing new master cylinder on 70 duster and there is a little rubber grommet or piece of tubing in the package???? Does this go on the rod first and then bolt the master on??? What does this do---Of coarse no instructions in box with master---When i took off the old master there was nothing on the end of the rod Thanks-Steve

It sounds like the keeper for the rod. It goes on the end and keeps the rod from falling out of the master cylinder and loosing your brakes. There is usually a indentation in the end of the rod for the keeper. Once it's in they don't come back out which is a good thing...

Sound like the grommet the goes on the end of the pushrod to keep it in place in the master. You'r old one may have disentigrated. Does you push rod have a grove roulghly about the size of the grommet about a 1/4" back from the tip?

How in the world can the rod fall out once the master is bolted on??

because there is nothing holding it in

slide the rubber grommet onto the pushrod 1st & check that your MC has the machined recess inside for the grommett to expand into & lock against. all manual MC's are "supposed" to have the recess as opposed to the smooth taper(w no recessed area) inside the power brake MC piston & it must have the recess. the brake pedal can come back far enough to let the pushrod fall out if it wasn't locked there. Install the MC,line up the pushrod & push er in & capping the MC with a pair of brass plugs helps greatly with this & even a bit of rtv to help is slide in & lock easier & then the rtv locks it tighter when it sets up.

The lock ring is used only on manual brake cars. If you have power brake, do not use it.
If you are a manual brake car put the ring on the shaft and lube it with some silicone, or brake fluid and slip it in the master, give it a tug or two to make sure it is properly seated and your cylinder has the groove for it.