I deciced to re-build my brake master cylinder over the holiday. I have the kit for a Non- power steering car, as my car has arm strong kind. When torn down and honed, cleaned up and ready for the kit, IT DON'T FIT.  I have a kit that is for non-power for a 1 inch bore. The master cylinder is  1 1/8 in bore. The books have it listed as the correct kit/number. Do I have a car with a power master cylinder on a non-power car?  OR was the number on the kit wrong?  To make things more complex, the power kit is a 1 1/8 bore and a power master cylinder is 1 in.  Can BOTH bags be numbered wrong or is there a possibility that the cylinders can be interchanged?  What to do?  THANKS

In theory, the non-power brake master should have the smaller bore, but that may not always be the case. There's a chance the master has been changed somewhere down the line, OR it had the wrong one to begin with. On the assy line, if they ran low on power brake masters, but had plenty of non-power masters(or versa-visa), they would get an engineer to verify IF the parts would interchange AND function properly. If it would, then they would use the part they had on hand. If they would NOT interchange, they would check other GM car lines to see if what they were using would work. If they couldn't find a substitute part, the assy line would shut down...not something that happened a lot for parts shortages. There are many stories from assy line workers of having to go to a local hardware store for nuts/bolts/screws if they were in danger of running out before they were re-supplied from the manufacturers.
Back to the theory part....the non-power has  a smaller bore, which would give you more fluid pressure per square inch than the larger bore power master, so you could use the non-power on the powered car and be fine. The opposite would not be true...using the larger bore master where a non-power goes would lower your effective braking pressure.

Now that my head hurts, I would get a kit that fits the master you have, if it has been working ok for you in the past.


|UPDATED|12/27/2011 12:09:04 PM (AZT)|/UPDATED|

THAT is interesting Joel. Since I have had the car it has ALWAYS stopped hard. I am VERY confident that it is an original part as there were to many reasons why it could not have been changed. Paint, undercoating, just to name a couple. It was VERY nasty inside. SOOO... Should I keep it for use or look for a small bore to make it stop better? It is stamped with small numbers on the boss where one of the lines fastens. I do not know how to check date codes or have a listing of them, but there is one on it. It is cast in the housing.  THANKS   

Joel, I'm sure Mark will jump back in when he can....but since hangin with Mark I remember him telling me how hard his car is to STOP. This may explain that part, maybe the correct MC will give him the stoping distance he needs. Sure make sense

Mark....which car is this? The '72? See if you can post the casting number, and the tiny numbers you see by the fittings for the brake lines....that's the date code.
I will say that non-power DISC brakes will have a harder pedal than a car with drum brakes, anyway, but if you have the "wrong" master, it could certainly add to the pedal effort.

I was going to write them down last nite but did not.  I am gathering that the date code is D1 for the 72'. The other longer number is the part number I'm guessing.  I THINK the little numbers are/possibly _022. kind da hard to decifer. I'll have to look closer.  THANKS    

|UPDATED|12/28/2011 8:47:18 AM (AZT)|/UPDATED|

O.K., here's the scoop.  The 72'  non-power numbers are:  Casting number- 5480348 raised up casting, A depressed  D1 in casting, and a TG2200, OR 162200 in small print stamped in boss near the entry of one of the lines.   My 75' w/power brakes, also has a casting number of 5480348. A depressed stamp of D5 and small stamped numbers near line entrance of MC3348. It also has a stamped number in casting under the D5, of 284. It is my belief that they are both original equiptment.  They are both LARGE bore of 1 1/8 inches. THANKS