Sometime in the middle of a 2 hour drive, my clutch pedal suddenly developed a big slack spot in the travel- at rest, the pedal flops down about an inch and a half from where it should normally be, which makes shifting challenging (to say the least). In order to start off from a stop, I have to stop the engine, put the car in first, then restart and go with the clutch pedal depressed, as it only seems to disengage partly. I tried bleeding the sytem, with no effect, so I am guessing it's either the clutch slave or the master cyclinder- is there a way to tell, or should I just bite the bullet and buy a new clutch master cylinder or both?
Has anyone experienced this?

Sounds like you have a leek in the line or the components. check your master and slave.

I suspect it's not that simple, as the fluid level has not gone down in the month since this happened suddenly, and there's no evidence of a leak anywhere (except the engine- that's for another post)

Did you check to see if your clutch banjo did not slip/break off?

If not, I would still suspect the master, especially if it is original. I am in the middle of a complete rebuild using Rodney's Master and Slave and TFS's steel pedal. Everything is wonderful.. I havent even gotten the master yet, but the adjustable banjo is just too much.. I have to get it so I can adjust to my comfort.

Good luck!

Check the clutch fork arm at the slave cylinder. If it's the stamped steel arm, I had mine crack and bend. This may be your problem if it was sudden and you have no fluid loss.

Also check your pedal bushings, if it has one.

I doubt your master or slave is bad.

There is a spring in the Master Cylinder. The spring in the MC is to return the pedal to the rest postion. If the pedal isn't returning all the way to the rest position it would have to be caused by most likely the Master Cyliner or perhaps the pedal/linkage. The pedal/linkage can be visually inspected. What happens when you pull the pedal up to the normal rest position?



(to the doubters - If hydraulic pressure was needed to return the pedal to the rest position you would not be able to bleed your clutch)

[This message has been edited by phonedawgz (edited 09-19-2010).]

And check that your pedal isn't bent. If it's bent downward, it could cause it to sit lower than the brake pedal, and the master cylinder piston could not be getting pushed in all the way, if you're hitting floor early, causing the slave to not fully extend.

Thanks for the advice, everyone!
The fork arm appears to be a casting (this is an '88 4 cylinder- dunno if that makes a difference)
The pedal has a weird twist to it which appears to be stock, but does not appear to be bent otherwise.
When I pull the pedal up to the normal rest position, it just falls back down with no resistance to its new and improved position.
The banjo bolt is still in position, although I found a little bit of fluid on the shaft, so it might have failed up there. If not that, a failed return spring in the master cylinder makes more sense to me, so I'm going to order a new one from Rodney.
Besides, I've always wanted an adjustable banjo bolt....

I finally replaced the clutch master cylinder this weekend and wanted to let you know what I learned. replacing the master cylinder was actually easier than I feared; the biggest problem was that I had a very hard time removing the cotter key from the clutch pedal connection point and could not see it well enough to be effective, so I worked for some time to flatten the ends with pliers and push it out of the hole with no success. Only after many attempts was I successful in pushing it through, at which point I discovered it was actually a spring clip all along.

I used to be able to see what I was working on when I was younger.

The next problem was bleeding the system, and since I had no helper available I decided to try the "gravity system" of bleeding first. I parked the car on a steel hill, filled the reservoir, and opened the bleed valve. After 10 minutes about a teaspoon of fluid had run through, and as the rate of fluid drip appeared to be getting even slower I then jacked the front of the car up about a foot to no effect. I think the gravity method may work if all you want to do is replace your fluid, but if you have caused a major disruption to the sytem and introduced a big air bubble (likely in the tubing loop at the top connection to the master cylinder) you can't start a siphon at that point. So the gravity sytem did not work for me.
So I found a stick the right length, and was able to place one end on the clutch pedal and the other on the high back portion of the driver's seat. When I relocated the top end of the stick to the lower back of the driver seat, it would completely depress the pedal, and I was able to start bleeding the clutch properly- open the bleed valve, depress the clutch, close the valve, release the clutch, repeat, repeat, replenish the fluid at the master cylinder, open the bleed valve, depress the clutch, close the valve, release the clutch, et cetera. It was a slow process involving a lot of walking, and I could not really see what was going on at the bleed valve (although I could occasionally hear squirting noises back there).
I could see that it was going to work eventually, but luckily my dad showed up to help. Although he cannot get int the car to depress the pedal (he has severe physical limitations) he was able to reach through the window and manipulate the magic stick.

So we we were able to bleed the system until the rusty fluid was gone and the fluid was running clear.

Elated, I jumped into the car and fired it up, only to discover that the clutch pedal was mushy throughout its range of motion and would not fully disengage the clutch, same as before I went through this exercise, although the slack part of the pedal motion was fixed. (I guess the spring was broken, but have not actually checked that yet.) At that point I had to drive about 150 miles, something I have been doing all along while my clutch has been scewed up, so I figured I would go ahead and do it again and load up the car and go, and I would bring along what I needed to bleed the system again when I got to my destination. So I went in the house and got my stuff, loaded the car, hopped in and fired it up, and discovered that in the 10 minutes the car was sitting there resting the clutch had completely recovered itself and it was back to normal.

Lessons learned-
1. replacing the master cylinder is easy
2. it's not a cotter pin
3. get help to bleed the fluid
4. don't despair
5. you probably don't need your banjo bolt to be adjustable, but it does not hurt.

So you had a bubble of air near/in the master cylinder. The MC at rest opens a 'bypass' port that allows fluid to flow back into the resivour. Sometimes when people run low on fluid and just add, they get the same as you, that is at first it's sloppy but let it sit a bit and the bubble works it's way out. Since the first part of the line goes down, and then flat, I suspect that is why the gravety method didn't clear the bubble.

Cool cool that you got it figured out.