Master Cylinder Wear

[jrcotner]

I dismantled the master cylinder for my stuck rear diff lock, and found the piston end (with the cross in it) had become disconnected and jammed in the bore. There was obvious bore damage. However, since I had the other masters out, I inspected them as well and found some visual marring, but nothing I could feel. The manual says 4 microns is the maximum amount of acceptable wear, but I have no way to measure that. So, what is the rule of thumb for master cylinder bore wear? Is any visual marring cause to replace the master? Considering that the difference between the cost of a new master cylinder and a rebuild kit is pretty substantial, I want to make sure I need to replace them before I lay out the money.

[jrcotner]

Also, is there a good way to replace the seal in the middle of the piston? It looks like it could be easily damaged stretching it over the cup on the end.

[audiocontr]

Im sorry I do not have an answer on how much wear is acceptable. I was skeptical of the seal when i rebuilt mine, but simply replacing the o-rings did the job.

[jrcotner]

I may as well replace everything since I have it in pieces anyhow. Hate to damage the seal.

[Jim LaGuardia]

Scoring on the piston is no big deal, slight scoring in the cylinder is acceptable, but clean the bore with scotchbrite pad and brake cleaner.
The piston seal is easy to install, just make sure the rubber is lubed and above 70deg F, it is fairly easy.
Use common sense and all will work out in the end

[jrcotner]

Should I be concerned about the marring in the cylinder bore?

[jrcotner]

I ended up replacing the stuck master (bore looked bad) and rebuilt the other two. Once I got them out, it only took about ten minutes per cylinder to rebuild them. All work great now.