[Grand73Am]

On my 79 TA, I'm going to install a new rebuilt factory original power booster and a new master cylinder that's like the original. Since these are stock replacement parts, I've never considered measuring the booster push pin to master piston clearance, since they aren't adjustable and should just fit as they are. I know that checking clearance on aftermarket power brake conversions is necessary, as those boosters have adjustable pins, so you can make sure you have the right depth to avoid preloading the master or leaving too much play.

But I recently got a booster pushrod measurement tool and decided to use it to see what clearance these stock replacement parts have. I expected there to be a tiny amount of clearance between the booster pin and the master piston, as you would normally want on the aftermarket setups. Instead, I found that the master piston and the booster push pin contact each other while the master cylinder body is still about 3/16" from seating flush to the surface of the booster. So, when the master is fully seated and bolted to the booster, the pin will have pushed the master piston inward by about 3/16". So that's 3/16" pre-load on the master!

So, I'm thinking this can't be right Surely that would cause a pre-load on the master and dragging of the brakes. Maybe it's a fluke with these particular parts. I have 4 TA's, all with stock disc/drum brakes, so I checked the measurements on them all to compare. They all measure the same way, with about 3/16" interference fit. They can't all be wrong. I figure that just must be the way they are.

I've driven 2 of the cars enough to know I've never had any brakes dragging or overheating. So, they do work that way.

The 79 TA I'm driving now has a low pedal. It stops but should have a better pedal. So I'm going to replace the old booster and master, and check out the rest of the system.

I posted this here because it was very curious to me, and wondered if anyone else had ever noticed this, or had ever bothered to measure the stock setup? Any thoughts as to why these brakes work despite the ~3/16" pre-load on the master. I posted this topic on the general forum, but decided to post the topic here too for those who have 77-81's. Thanks for reading! Steve