What are the odds of a clutch master and slave cylinder going bad at the same time? I ask because I just got done changing the slave cylinder and I still have spongy pedal. I am assuming they both were OEM. It's for my 85. Also it looks like it will be a real pain in the ass to change the master cylinder.

Just over 100k on the clock.

Is it possible the slave cylinder is not fully bled?

I don't think so. I spent over an hour bleeding it. used alomost a whole bottle of fluid. The parts are 30yrs old after all. It won't build any pressure.

yes... very likely... remember, they aged at the same rate... now you throw in the new slave, which requires greater pressure to activate.

That's what I figured Andy. Looks Like time to order a part.
How much of a pain is it to change?

reaching the bolts under the dash will suck.

Skinny arms help. I think I removed my seat to make it more comfortable to get to.

There's a cotter type pin way up in there that holds the pedal arm onto an eyelet on the end of the pushrod. The rest is easy.

How can you tell it has air in it? It's never going to be stiff, the pressure plate moves. Or is that with the slave dangling? Obviously don't push too hard on the pedal with it dangling though.

I would never feel comfortable with it so I'd always check the engagement with the rear on jackstands. You can even put the parking brake on just a hair to simulate a slight load on the drivetrain.

I'd stick one of those Earl's solo bleeders on there.

It is on jack stands. It doesn't totally disengage. It still grinds going in and out of gear.

They are a pain in the ass to bleed, almost drove me to buy a Phoenix tool. Andy probably remembers me getting towed to his house because I stopped at a brake shop in his neck of the woods to get my clutch bled because it was starting to grind on my way back from a trip. (I had a small leak that I put off and accidently pulled some air in.) I should have just nursed it home 2 more hours. They left me with 10X more air in there and undrivable.

Let the slave dangle from the car and pump the pedal up gently to fully extend the slave, then use a little force (not too much or you'll push the retainer clip out.) If it feels solid, the bleed is ok. It's impossible to feel if the bleed is good while installed on the clutch fork.

We bench bleed the clutch master cylinder and then used the Motive power bleeder. That was on the 3/4 Wilewood master cylinder to the hydraulic throw-out bearing.

This was the best up grade I did for my 87. The Motive power bleeder was easy and did a great job.

I had the slave go out in my 86 right after I bought it in 2013. While it was down I had my mechanic replace both the master and slave. Thing was he had the info from the fsm on how to bleed the system (I copied it for him) and he still didn't get it fully bled.

There's a Youtube video on bleeding the master cylinder using a piece of hose and a tip from a brake bleeding tip. After my mechanic gave up on bleeding the system I followed that Youtube info and did get some more air out, but not 100%

The finale was a suggestion I got from a former co-worker. Seems back in the 80's he was a GM mechanic and worked on some C4's among others. Here's the suggestion he gave me and I did and that finally solved my bleeding issue.
Take the cap off the master reservoir and insure it's not to the top but has plenty of fluid in it. with the motor off, pump the clutch a bunch of time (I think I did mine like 10 times in rapid succession) and the last time hold it down. Keep the clutch pedal down for about 5 minutes (to let the air work back up the hose to the curved section above the master) then slide your foot off the clutch and let it pop up on it's own. The idea is that the fluid rushing back from the slave will push the air out of the line back into the master reservoir and into the atmosphere (which it did in my case). I ended up doing it twice and have had a solid clutch ever since.

If you think you still have air is the line, it's worth a try - after all, other than a little time it won't cost you anything.

Just got the new master installed. Followed the manual for bleeding and the pedal seems to be nice and firm this time. Thanks for all the help guys. Next project is to put it all back together so I can drive it to work tomorrow.

Central coaster, what is a "Phoenix tool?"

Isster1, when you used your motive bleeder, which adapter did you use? Do you have the part numbers ?
Thanks guys.

it's a pump... it forces fluid up from the bleeder into the slave and then the master.

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Thanks Andy. I'll see what I can find online.