Hi guys.  I just recently found your website so this is my first posting.  I have a perplexing problem I'm hoping one of you may have some answers for or some first hand knowledge about.  About two years ago the original clutch master cylinder on my '87 coupe ran dry, probably from its limited use and age.  I had both the master and the slave cylinder replaced by a corvette repair shop.  The master immediately had a problem where it would lose all hydraulic pressure but then return the next time I pressed the clutch in.  The shop replaced that master and the next one lasted a year and then the reservoir went dry.  The shop replaced that one and it lasted only a few months or so and then it lost hydraulic pressure to the point where I had no clutch at all.  This last scenario has happened about 4 times or so now.  The shop keeps replacing the master and it only lasts a few weeks or a few months then goes out.  I'm on about the 6th master now and it just went out last week.

It seems hard to believe that all these master cylinders are complete junk, so I had him replace the hose the last time, but the new hose didn't solve the problem. It's always the master, but they don't last.  Can there be some other part or problem that's causing the masters to go bad?  From the limited research I've been able to do, it looks like there were a couple different versions of the 4+3 for that year and I wonder if the currently produced master cylinders meet the specs for one version of the trans but not the other.  I've also seen a service bulletin that there may be inadequate retention of the push rod bushings, but that was back in the late 1980's.  I would think that these new parts built today corrected that problem.  I know GM doesn't make the masters anymore, but I can't seem to get hold of a decent part.  I'd like to keep the car as it's a great commute car consistently averaging 25 mpg and has less than 78,000 miles, but it rarely runs and when it does I don't trust it.  I apologize for the long post. Any help would be greatly appreciated.  Thanks. 

calling dr joel (adam's apple). he is da man to ask about this as he is a trans specialists besides being a walking service manual.
my question is do you keep going back to the same shop? if so maybe you should try somewhere else.
hopefully joel will see this thread and can give you a heads up on this. let us know how you made out.

Welcome to C4VR, first off!
My experience has been that if one of the hydraulic components, fails, the other will fail, or has already failed. When doing hydraulics on clutch systems, it is always best to replace both at the same time.
My best guess on why you've replaced so many is that either the shop is getting bad masters, or the system is not being bled properly. Bleeding the clutches on the earlier C4 Corvettes has ALWAYS been a major pita.
Are you getting NEW masters, or remans? I've got a box full of remans that never worked right out of the box....
IF the master is going "dry", there has to be a leak in the system, or it is not being bled properly...
hth

I know of no different variations of the 4+3 units, in regards to the clutch hydraulics.. I think there was an upgraded slave cylinder at one point, but I don't remember when it was, or what models it covered. I believe any slave you get now will be the newer style. The change was to simplify the bleeding procedure.
Adams' Apple2011-06-16 20:22:16

Thanks guys.  Yes, I've been going back to the same shop each time in part because he's been replacing the masters under warranty, so I only paid for the first master in addition to the slave and now the hose.  The reservoir doesn't always go dry (it did once), indicating that there is not a leak in the system.  The last one he replaced he said that there was metal floating in the system which doesn't sound good.  It's like the masters keep self destructing, like maybe they can't handle the pressure.

Well, my repair shop called and said they've located an A/C Delco master cylinder that they should have in about a week, so L guess I'll soon enough find out if the Delco part is a better product.