The amount that the nose of the push rod sticks out past the face of the booster is measured. Ford has a little height-gauge that is placed over the pushrod nose and rests against the booster mounting face - but a caliper or dial indicator will work.

If no one provides you the specs before tonight, I will post them when I get home and have access to the shop manual.

 

That would be great, thanks!

 

Here is the pushrod adjustment. Note that the measurement is taken from the flat surface near the mc mounting studs. When I did this check, I just used a piece of stiff cardboard to make a "gauge-tool" like shown in the picture.

 

Great, thanks so much! I'm curious to see what mine measures now.

 

Don't know what it is all about, but each time I get a rebuilt Ford booster from the store, they have this big warning on them "Don't pull the rod out of the booster, a reaction disc can get dislodged and will void the warranty". I know you did it, but I would try to avoid doing it again.

 

hmm...i wonder what that is about. I guess I don't know what exactly is going on inside the booster so i can't really say for sure. I was hesitant to pull it out but the rod has a disc on the booster end, maybe 3/4" or 1" diameter and 1/2" deep, which fits kind of snug into a pocket in the booster. It take a small amount of wiggling to get it in there but i thought it was very easy to feel if it was seated properly or not. I suppose if someone didn't get it seated and threw the master cylinder on and tightened it there would be issues for sure! or maybe there is more to it than that.

 

The Ford Service manual provides no warning about removing the rod (a.k.a. "piston") - but I have also seen the warning tag on those rebuilt boosters as Dave mentions. Although sometimes the warning is missing.

I wonder if some boosters do not have the concern/issue of the reaction disk falling out of place (maybe it's up to the internal design). Else the booster supplier was just sloppy and the tag was lost.

Either way its advisable to not pull the rod out to adjust it.

 

It looks to me like the reaction disc is the one i was describing on the end of the piston. I seems fairly solidly attached to the piston, but if it happened to come off and fall inside the booster a person would be in a pickle. I will adjust the piston without removing it.

thanks for the diagram!

edit: after a quick google search I think the above is wrong, the reaction disc is a rubber piece behind the disc on the piston i describe...

 

So does each different brand master cylinder need a different size gauge to set the length of the rod?

 

They are "supposed" to built to factory specifications (and usually they are a "factory part" that was just rebuilt with a slight honing and new seals), so you should not need to check - but since many of these rebuilt parts are coming from who-knows-where, it would be a good idea to check. You can use a caliper with the depth gauge (or a piece of rod) to measure how deep the master cylinder bore is then check the booster rod stick-out to be sure the booster rod will not be pushing on (depressing) the master cylinder any.

So if the booster rod is sticking out .995" your master cylinder bore depth should be 1.00"