Clutch not disengaging, ideas?

[JeepNoob]

Hey guys, haven't been around for a while as I've been able to solve most of my issues on this "raggedy ol' Jeep," but a new one has come up...

I have a '96 XJ with the 4.0, AX-15, NP-231, and an external slave cylinder set up. Last week when I was driving, I pressed the clutch pedal to brake for a red light and the clutch pedal just kinda went to the floor and wouldn't come back up. After some pumping on the clutch pedal, I was able to get it halfway up, but it still really didn't want to move. Wouldn't shift into gear and would grind if I tried to put it into reverse. After some inspection, I found the master cylinder rod was pretty much jammed in place, so I replaced the whole system with a new one that was pre-filled and supposedly bench-bled. When I tried it with the new system, there was a grinding noise with the clutch pedal pushed in. Pulled the transmission and confirmed my throwout bearing was grenaded.

At this point, I just decided to replace the whole clutch. Replaced the pilot bearing, seal facing the transmission and a light coating of grease on the inside and outside, cleaned the transmission bellhousing, had the flywheel resurfaced, torqued the bolts to 105 ft/lbs in a staggered pattern, clutch disc facing the flywheel the right way, pressure plate bolts torqued to 37 ft/lbs in a staggered pattern, greased the transmission splines, was careful not to get anything on the flywheel surface or clutch disc, yada, yada, yada. Only thing I did a bit differently was to loosen the pressure plate bolts up a little after I had torqued them to pull the alignment tool out, then I re-torqued them. After I got everything put together, I was still having the same problem. I heard some grinding, rattling noise without the clutch pushed in and I still couldn't get it into gear, grinding noise when I tried reverse. Found out I was able to start and drive the thing a bit with the transmission in 1st, but I gave up on that quick when I smelled clutch burning. It shifts fine through all the gears without the engine running. I should also note that even with all this stuff, the clutch pedal is still pretty low in terms of height.

Any ideas on what could be causing this? It seems to me like the throwout bearing isn't pressing on the pressure plate fingers like it should. I talked to my buddy who works at O'reilly's and sold me all this stuff, and he said even though the description on the hydraulic stuff says it's pre-filled and bench bled, it still needs to be manually bled a bit. I also noticed that the new master cylinder rod was straight, whereas the old one had a slight bend in it. Could this possibly be the issue? I was able to get this new one attached to the clutch pedal pin and held in place (not fun, had to pull the clutch pedal and monkey it back into place) but the eye on the rod seems to flex a bit when I push in on the clutch pedal. I've also read elsewhere of cracks and bent clutch pedals causing problems with clutch engagement. Anybody have any experience with this? Opinions? Other ideas? Thanks guys.

 

[old_man]

Sounds like you had a bad clutch master cylinder and now you need to bleed the new clutch master cylinder.

 

[Rick Anderson]

The proper way to bleed the clutch is to have the slave cylinder rod fully compressed inward, then open the bleed valve, closing it before letting up the clutch pedal.

But, the system is designed to gravity bleed (I think, NOT positive) so if everything is mounted correctly and you have enough fluid in it, it should bleed itself overnight.

The Master cylinder should be tilted upward, so air bubbles in the master cylinder flows up toward the reservoir, the Slave cylinder should be tilted ever so slightly upward so air bubble flow upward to the peak where the hose is at to the master cylinder. If they are tilted the wrong direction, air bubbles get trapped and the air doesn't get out of the system.

 

[old_man]

I vacuum bleed instead of gravity or pressure.

 

[Matthew Currie]

On a 96, check the pedal linkage itself. In this model, the MC rod is actuated by an arm that is welded to the pedal arm, in parallel with it. It's not uncommon for that arm to get bent, or even to come unwelded at the top. Somewhere deep in the archives here you might find a picture I took of my 95 showing how it should look, but I can't find it now. In any case, the extension arm should be parallel to the pedal itself. If it gets bent not only will it fail to disengage the clutch properly, but it will eat master cylinders.

 

[JeepNoob]

Okay, thanks for the ideas guys. As an update, I checked the slave cylinder today and it doesn't even HAVE a bleeder screw on it. It has the threads for one, but the bottom's just plugged off. At this point, I'm debating just getting a new slave/master cylinder set up from the junkyard, possibly the dealership, since the old master cylinder rod had a slight bend in it. Not sure why, but it seems to have been there to facilitate getting the eyelet on and off of the clutch pedal pin. I've also noticed all the parts store "replacement" master cylinders have a straight rod. The idea of vacuum or pressure bleeding occurred to me, but I don't see any way to make it work. The bleeder screw on the old slave cylinder wasn't set up like a brake bleeder screw, it was basically just like a small drain plug with an Allen head. I'll check the clutch pedal as well since I'll probably have to pull that to replace the bushings. I know what you're saying about the clutch pedal, I shamelessly stole this picture from.... well, from elsewhere.

 

[JeepNoob]

Update- Just pulled the clutch pedal, sure enough, it's bent. Almost exactly like the one in that picture. Looks like I'll be hitting the junkyard... Wonder if it would be possible to weld in some extra material to keep this from happening again...?

 

[Matthew Currie]

A: Yes, I'd weld it. If you look at the pedal as it's supposed to be, you'll see that there is no obstacle to a brace between the two pieces. My son's 96 had this problem, although it also came unwelded at the top, and he welded it up.

B: The slave cylinder actually does not need a bleed screw, because it displaces as much fluid as the plumbing between it and the master. If you fill the master cylinder reservoir nice and full, and then carefully unhook the slave, pull it out as far as you can without actually pulling it out of the bore, and then carefully push it back in as far as you possibly can, it should force the air all the way up out of the tube, so it fills properly when it recycles. If it's still a little soft, it will finish bleeding during the first few actual cycles of the clutch, as only a little air remains at the top. It actually works pretty well despite having no screw.