Ft master cylinder bore repair

Post by **Suzsmokeyallan** » Sat Aug 01, 2009 2:45 pm

I was testing out a theory about repairing master cylinder bores and surprise surprise you can actually add plastic steel to the corroded areas and restore the bores smoothness.
So why would you do this?? well you would if the cylinder is NLA or because youre always trying to go against all 'normal' thinking.
Clean the bore out properly and use an etching solution on the bad areas inside with a q tip to clean the recessed sections.
Then wash and dry it properly for proper adhesion of the glue, if not ,,well it wont stick obviously..
Then apply the plastic steel and make the sections where you put the glue only slightly higher than the bore itself, then use a smooth small stick to drag it across in an arc of the sections so it forms evenly to the bore.
This is so when it dries and sinks it will be nearly the correct height and not a blobby mess inside in those areas.
Then you'll need to use an adjustable reamer to CAREFULLY cut away the high sections of glue, adjusting it as needed so you slowly open the bore back to its correct size all the way through.
Once the bore has been returned to its correct size, use an internal caliper to check this, then polish the surface back with some 600 then 1000 sandpaper rolled into a tube and WD40 as a lube, or a hone tool if you have one that size.

H2RICK · Post by **H2RICK** » Tue Aug 04, 2009 9:51 am

Now that's a slick trick, Allan.....labour intensive....but slick. It'll be interesting to see if the plastic steel holds up to immersion in brake fluid over the long haul. Did you use a Devcon product of some kind ?? Or what ??

Post by **Suzsmokeyallan** » Tue Aug 04, 2009 2:24 pm

Rick i had to do this to the KZ440 cylinder as it was really bad in a few spots and especially by the main seals sliding surface.
I could probably just get another used one which would probably have more of the same problem or even worse so for now this will have to do.
If i didnt repair it, the fluid would 'backfire' out that section on each return stroke of the pistons main seal travel and seep out.
These cylinders have a steel liner which i thought would be better than the plain bored aluminum type, apparently thats not the case seeing how this one ate away in some areas compared to say a GT one.
So we will see about the longevity of the Devcon plastic steel which i am very sure will work.
If it can withstand being made into a part of a piston and work in that environment I'm sure it will work as a filler in the bore.
Mind you, I'm using DOT5 silicone fluid so that is more forgiving than the mineral based ones.

TLRam1 · Post by **TLRam1** » Tue Aug 04, 2009 2:33 pm

What did you use for etching?

tz375 · Post by **tz375** » Tue Aug 04, 2009 2:43 pm

You have to be extremely careful with this sort of "repair". Any of the epoxy that brakes loose could easily cause your brakes to jam and fail.I
personally would not do this on any vehicle of mine.

If you do go ahead and try it, it is really important to be 110% sure that the metal is clean and etched.

A better solution is a thin wall steel sleeve, but that takes a little more work.

rngdng · Post by **rngdng** » Tue Aug 04, 2009 6:41 pm

I have used a brake cylinder hone to "repair" MC's. I haven't been forced to use JBWeld, but I would...... in a heartbeat!

Lane

Post by **Suzsmokeyallan** » Tue Aug 04, 2009 8:32 pm

Richard i had thought of reaming out the existing bore and fitting a thin walled piece of stainless steel or similar but i didn't have it, nor the time to hand for this job at this moment.
I don't see this as a major problem simply because on this part of the cylinder the problem area is right where the main seal and piston flange sits at rest, so as you barely move the lever towards the free play, its instantly off of the repaired section.
My main concern was that it was so badly pitted at the lower arc of this cylinder i knew it would leak even with new rubbers.
Thats why i believe it was caked up in old fluid, so it had to be leaking from this problem and the old rubbers as well.
For etching the steel or aluminum you can use a mild acid and brass bristle brush to clean the section of any residue and then perform a visual check after drying it out properly.
Besides if the repaired material does move ill know instantly as the fluid will be shooting out the back portion of the lever in a flash.

tz375 · Post by **tz375** » Wed Aug 05, 2009 7:49 am

Allan,
As long as other people reading the post understand the risks involved and have the experience to determine when it's appropriate to use JB weld, that's fine.

Post by **Suzsmokeyallan** » Wed Aug 05, 2009 10:52 am

I could not agree more, common sense should always prevail, and in such instances i would not be advocating all manner of issues can be instantly fixed by just slapping a bunch of JB weld or plastic steel into a cylinder bore and all is well.
As a person effecting a repair you the owner need to use sound judgement and think of the consequences.