Concern with new replacement master cylinders

Since i assisted a member with help in diagnosing a condition with brake lockup, I realized that most who have replaced their master cylinders have to adjust their power boosters apply rod.

Seems that new replacement master cylinders have a closer position to the apply piston on the plunger rod.

Digging further on past threads, and my own obseravtions in disassembly of an oem master cylinder, that there may be concern with how the new replacements are assembled.

Not that there is a change up of internals, but the lack of a minor part that can effect the apply rod engagement. From what i see stock master cylinder has a washer before the clip to retain the assembly. Without the washer the cup of the apply piston is closer in its seating position than oem. Thus if that is the case, it would be the root cause to why many are required to readjust the apply rods when going from stock or early rebuilt to newly rebuilt unit.

Just on what i gather, and I am bringing it up as there may be some willing to dive further with comparing an oem core components to a new rebuild, at the backend assembly, for apply rod cup distance.

I would have but, I am not using AMC oem components on my build to compare with.

Any observations are welcome...

990V8 wrote: Good point, could cause lock-up, or the opposite - pushing air due to the master not being able to return and replenish.   I bought a new master from Rock and just fitted it with no adjustment, but I have single-circuit with a remote servo so perhaps different.   I suppose the end float on the servo push rod should be about 15 thou.   V8

I gathered all the items on my oem master, which is not power assist, but assume there is or should be some preload to the cylinder from seating further out in the bore.

There is 2 washers along with the retaining clip, and are about .150 in thickness. Though i do not have a micrometer to verify actual total thickness.

Including the retaining clip to the brake piston apply rod makes it even more set into the bore.

I will post a picture of all the components that effect piston preload for its release depth. As thin as they are, they add up. I imagine that if cutting cost on rebuilding or producing new units, limiting the amount of washers during assembly, will be the issue in the need to readjust the booster apply rod.

304-dude wrote: Here is the parts from an oem master cylinder... they are in order of placement, going left to right for 1st to last. Note: the first item is a retainer/keeper that grabs on the apply rod end via a grove to clinch by the teeth. The second is a normal washer for spacing and retension of the keeper to the apply rod, to keep the rod end attached to the master cylinder. The third is a beveled spring washer (teeth facing washer) to force any components away from the locking spring clip which is the last component to the assembly.

990V8 wrote: On another forum, there's a chap with a Spitfire (car, not plane) having trouble with a new master, and I reckon that's a pushrod clearance issue. Shame we can't just bolt new parts on our cars without checking them, but I guess we have to be glad that we can get new parts at all.