Diagnosing Clutch Issues: Help/Advice Wanted

[NickyV]

Hey there! So, I've had my clutch worked on twice in the years I've owned my 1987 MJ.

 

The first time, after about a year, the clutch's master cylinder was leaking. I do not recall if this was the issue the first time around, but it definitely was the second time. I know that is a common issue with these vehicles. I am eventually going to need to redo my fuse box...

 

The second time, I took it to a mechanic I liked a lot better than the first. He and his team were very thorough. Explained everything to me. Pictures and videos provided. The whole nine... It was great! Except, I can feel my clutch going soft again.

 

First time this happened, I took a peek in the master cylinder reservoir and it was dry. That's what used to happen... However, this time around I'm not seeing evidence of the DOT-3 fluid on my shoes or fuse box or anywhere.

 

Just a few nights ago, I was noticing the clutch was feeling soft again, so I took a peek in the master reservoir and it was full.

 

TL;DR:

 

- Clutch is going soft.

- Replacing DOT-3 fluid will bring it back to functionality (with plenty of pumping of clutch pedal)

- But the fluid does not appear to be leaking from master cylinder - at least not into the cab.

 

Thoughts:

 

- Maybe it's leaking on the other side of the firewall?

- Maybe we are dealing with something in the slave cylinder or somewhere along the line?

 

Advice (?):

 

- What should I do?

- Where to start?

- Diagnostic procedures?

 

Background/Capabilities:

 

- First time I had the clutch done, I also had the plates replaced, so hopefully that is still good. I don't think it's an issue with the plates. It seems like an issue with the pressure in the system.

- I did bleed the clutch myself once. I'm not confident I did a perfect job, but I do know I can do it.

 

[eaglescout526]

Have you crawled underneath to see if you have fluid leaking out of the bell house? The modern makes of the internal slave are garbage and barely last long. 
But this is why I sought out the 84-86 external slave setup for my 88

[89 MJ]

I’ll second checking out the slave cylinder. I bet that is starting to leak. If it looks dry, you should be able to bleed it again and that should cure it. But that fluid is definitely going somewhere. 
 

To make sure it isn’t the master leaking, just take a look at the paint underneath the master cylinder. Brake fluid will eat the paint, so it’ll be wrinkly if it’s leaking. 

Edited Monday at 08:12 PM by 89 MJ
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[Eagle_SX4]

Sometimes the master or slave cylinders will suck in air but not leak. It is very hard to diagnose but could be your issue. I had a new brake master that did this and could not get my brakes bleed. I figured it out by making a short brake line that returned directly to the reservoir and was able to see bubbles flowing into the master cylinder.

[pizzaman09]

When I bought my truck, the slave cylinder would suck in air, the pedal would get softer and softer until it just couldn't disengage.  For a while it was manageable, once very few months I would bleed it.  However it got to the point of every week and then ever quicker.  Being that I have an AX-15, I did the external slave swap.

 

You have a Peugeot transmission so that isn't a direct option.

 

If you want to learn to bleed the clutch easily, just fill the master cylinder, crack open the slave bleeder, and let it gravity bleed.  Let it bleed until the stream is constant.  Close the bleeder, top off the fluid in the master and it will be nice and firm.

 

I wish you luck, finding a quality internal slave cylinder now a days.

[89 MJ]

1 hour ago, pizzaman09 said:

When I bought my truck, the slave cylinder would suck in air, the pedal would get softer and softer until it just couldn't disengage.  For a while it was manageable, once very few months I would bleed it.  However it got to the point of every week and then ever quicker.  Being that I have an AX-15, I did the external slave swap.

 

You have a Peugeot transmission so that isn't a direct option.

 

If you want to learn to bleed the clutch easily, just fill the master cylinder, crack open the slave bleeder, and let it gravity bleed.  Let it bleed until the stream is constant.  Close the bleeder, top off the fluid in the master and it will be nice and firm.

 

I wish you luck, finding a quality internal slave cylinder now a days.

He’s got an AX4, but otherwise yes. Finding a good slave will probably prove difficult, so the external slave for the AX4 and AX5 might be the best way to go. 

[pizzaman09]

9 hours ago, 89 MJ said:

He’s got an AX4, but otherwise yes. Finding a good slave will probably prove difficult, so the external slave for the AX4 and AX5 might be the best way to go. 

Aw, I didn't notice that detail. 

External slaves are just nice as they are more accessible for when they need servicing.  Plus it seems that the external slave cylinders are better quality.  It helps that they have less internal seals.

[NickyV]

Thank you all so much! This business about internal vs external slave cylinders is refreshing my memory. I did a bunch of research on this years ago. Hopefully I took good notes. I’ll have to check ye-olde Google Doc.

 

@Eagle_SX4 and @pizzaman09: The possibility that it is sucking in air is intriguing to me. I feel like that might explain some of the weirder symptoms I’ve experienced over the time I’ve owned the truck.

 

For example, sometimes the clutch will lose pressure completely and then get pressure back, all on its own. Does that sound like an “air in the lines” symptom?

 

If this is part of the issue, what do you suggest besides resetting with a gravity bleed? Finding a gasket of the right size/shape to place on the master bath underside and of the master cylinder cap? Or is air more likely getting sucked in at the slave cylinder? Or is it a bit of a crapshoot as to where the air is getting in?

[pizzaman09]

Mine was sucking in air at the slave cylinder, hence all it took was cracking the slave bleeder for 5 seconds until the stream of fluid didn't have bubbles.

 

However mine never came back after going soft like you are describing.  It is possible that you are getting air at the master and then it is bubbling back up into the reservoir.  That said usually it is the slave that goes bad.