Clutch Goes to Floor Now and Again

A

APSilva-87X-TampaFL

Daily Driver
I'll be ripping it apart this weekend but wondering what you guys might think is the issue.

Last couple of times that I've taken my X to work, the clutch will go to the floor at least once. Always when sitting at a light in neutral. I'll step on the pedal to shift into 1st, feel the slightest amount of resistance while saying, 'ohh crap'. The pedal doesn't return and then I'll do the familiar move of slipping my toes under the pedal to bring it back up. On the next stroke, everything is back to normal and working as best as a clutch pedal gets on an X.

I replaced both cylinders about a year and half ago. After the first event, I checked for leaks, slave hose bulging, and so forth. I found nothing. I bleed it just as a precaution and to flow some new fluid through the system. The fluid ran clean without any signs of air in the system.

I'm thinking that either I've got an issue with my OEM reservior hoses or one of the cylinder rubber seals is going south.
 
That sounds to me like the slave cylinder piston is being pushed all the way in. So when you step on the pedal, the pedal is only pushing the slave cylinder piston to take up the slack.

The 5 speed slave cylinder had a spring located at the end of the slave's push rod. This spring's purpose was to hold the rod in place along with the slave's piston and thus take up the slack. Without it the slave's piston can retract back into the bottom of the cylinder's bore. It then requires a full stroke of the pedal to push the slave piston back out and against the rod and push the rod and clutch arm out to the pressure plate.

This is really more of an inconvenience and a real problem.
 
I have the small spring at the end of the slave rod but not the bigger spring that on my 87 pulled the clutch release arm towards diaphragm spring. I'll try reattaching the BIG spring and see if that clears things up. I removed the spring since my next to last throw-out bearing wore through the diaphragm spring.

Steve Hoelscher said:
The 5 speed slave cylinder had a spring located at the end of the slave's push rod. This spring's purpose was to hold the rod in place along with the slave's piston and thus take up the slack.
Click to expand...
 
I had this prob once.

As a temporary bandaid on the problem you can put a couple inch slice into a tennis ball, then stick the ball on the back of the pedal arm directly beind the pedal. The ball will compress and spring back when you step on the pedal. It does take a bit more pressure to shift, but it works well enough as a temorary fix. You will need to put a wrap of duct tape around the ball and pedal to keep it there, but you won't have to dig your toes under the pedal to return it.

I used this method back in 1980 on my brand new X. The pedal would go down and stay there quite often. It's really a bad situation from a driver safety standpoint. Your attention is definitely not where it should be while you are working to free the pedal from the floor.

The dealer said that Fiat was issuing new pedal return springs to replace hte obviously weak original, but it would be a few weeks till they got the part. Well, my trusty tennis ball got me through those 3 weeks. The maintenance manager brought the ball out to me when they did the repair and said it was a great idea and he planned to use it as a top gap for other customers.
 
Steve, sounds like you may know what that spring is for..

The factory manuals were never very explicit about the purpose or use of the small spring at the tip of the clutch slave rod. It sounds as though you have an understanding of it.

Let me see if I understand what you said. First a clarification. The piston in my slave cylinder rests pretty much at the bottom of the bore all the time. And the only way I can find to get immediate contact with the slave rod is to use the rod adjusting nut to extending the rod towards the slave cyinder piston until it contacts it in its position near the bottom of the bore. In doing so the spring at the tip of the rod is pretty much compressed to a crunch. In other words, I would be better off without the spring since it is holding the rod away from the piston unless I screw it towards the piston. At which point there is no spring action.

But what you are saying is that the piston should normally reside somewhere inboard of the bottom of the bore. Correct? If so, how does one go about ensuring that condition is met? I have a completely new A-Z clutch hydraulic system.
 
It might be easier to simply explain the function of the two springs and why Fiat changed them.

To note the differences I will start with the 4 speed. The 4 speed has only a single spring. Its a simple return spring that holds the clutch arm push rod tight against the slave cylinder piston. This pushes the slave cylinder piston all the way to the bottom of the bore when the pedal is released. The adjustment nuts on the push rod is the mechanism used to set the clutch pedal height. For this reason, as the clutch wears, the adjustment nuts must be used to maintain proper pedal height and free play.

The 5 speed, slave is "self adjusting" like most modern hydraulic clutches. It requires no adjustment to maintain clutch pedal height. This is because the adjustment is inherent in the hydraulics. Note that the 5 speed doesn't use a return spring. Instead there is a spring that holds the clutch arm out so the release bearing is held against the pressure plate spring. The pressure plate's spring and the clutch pedal return spring are used as the only return mechanism.

With the release bearing held against the pressure plate spring, and no clutch arm return spring, there is no mechanism to push the slave cylinder piston to the bottom of the slave cylinder bore. Because the slave cylinder bore remains filled with fluid there is no additional free play.

As the clutch wears, releasing the pressure plate pushes the release bearing and therefore the clutch arm and ultimately the slave cylinder piston further into the bore. This simply pushes more fluid back into the reservior. Thus the pedal height and release point is maintained.

The little spring on the end of the slave cylinder push rod is there to keep the push rod in place. Without it, vibration can allow it to gradually push the slave cylinder piston back into the bore and cause the problem described in the orginal post.

If you remove the primary spring that holds the release bearing against the pressure plate, the same thing can happen. It then requires a complete cycle of the pedal to push the slave cylinder piston out into position.

You can convert your 5 speed slave cylinder and clutch arm back to the 4 speed style of return spring if you don't want your release bearing to run constantly. All you have to do is remove the standard 5 speed tension spring and replace it with a 4 speed spring. If you do this, it is now necessary that you periodically adjust the clutch via the slave cylinder push rod. Also, the little spring at the end of the push rod is no longer necessary.

Hope this solves the mystery of the two different mechanisms.
 
Steve, wow, it's all becoming much clearer now!

This should be in "Best Of" as it is a little discussed area of the differences between 4 and 5 speed Xs, and, more importantly, the design of the slave release set up. And it makes sense. Obviously the release bearing is happy with its extra duty on 5 speeds as I have not notice especially short lives for release bearings.

Paul, sorry for high jacking your thread, but I couldn't pass up hearing more from Steve's expertise on this topic. As noted a few threads ago, we all need a thorough discussion of the hydraulics to help resolve just the type of issue you have been having...among other things.
 
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