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I'm changing out my brake master cylinder, and I'm wondering if anyone knows the gap specs between the power booster rod and the plunger in the master cylinder. It seems like it's .020 to .060, but I'm not sure. I'm at .029 right now and want to be sure that's a good gap before I assemble.
BTW, this adjustment rod is frozen solid... no turning it.
Too much gap creates extra pedal travel doing nothing.
Too little gap will not allow the pistons to retract into the calipers.
Then you have a constant drag of pads on rotors, and the smell that goes with it.
The threads on the rod look like crap. Couple drops of PB Blaster, wait. Repeat.
It should move soon.
Last edited by HeadsU.P.; Sep 27, 2024 at 08:03 PM.
You want a gap to be certain. So you are certain that the piston in the master can retract all the way.
so, your at .029" Gap. Your rod is frozen. But you indeed have a gap. I'd say your good to go.
I am using that tool. I checked the gap using a feeler gauge between the tool and the rod sticking out of the power booster and it's at .029. So it sounds like that is a good setting to have.
You want a gap to be certain. So you are certain that the piston in the master can retract all the way.
so, your at .029" Gap. Your rod is frozen. But you indeed have a gap. I'd say your good to go.
There's really no exact number for this in spite of whatever you Google on the internet. The FSM only specifies a J22647 tool that just checks the push rod adjustment on the booster only and doesn't take into account of any machining variations of a master cylinder. I think CSSBinc spec is a a good one. With that said, I set my gap to zero. I don't see the any reason to have a gap. But 1/16 of a inch gap, no way Jose.
You need to keep in mind that there's about 1/16 of an inch of piston travel before the compensating port is blocked and the master cylinder can start to build pressure.
And why do we set our clutch pedal free play to one inch? Seems alot doesn't it?
And when setting up valve clearances on solid valve trains, why not right on zero for maximum lift?
Why do we need end play in our wheel bearing assembly's ?
Because when dealing with metal one must consider that with heat parts expand and with cold parts contract. Thus we need a margin of safety.
Would I ever set a master cylinder pushrod to zero clearance on ANY Car, Truck or Motorcycle?
ABSOLUTELY NOT!
So, that's my 2 cents, from a professional mechanic who has worked 6 days a week with hardly ever a vacation for only 50 years.
Perhaps someone with more experience will correct me with a extremely good explanation.
Until then. Clearances are necessary.
Regardless, you have to allow the pads to retract and some of the DOT3 to retract back to the master.
Would you ever consider pulling the Parking Brake Handle up just a smidge and drive around?
Of course not. Why not? You don't want your rear brakes in constant contact?
Same deal with the hydraulic portion of the system.
C3 Power Brake Booster
