clutch issues

well in november my stock clutch gave the ghost at 132K so I had a local shop do the replacement. All was good till recently when I started doing the leap frog move on the road every so often when starting from full stop in 1st gear. It seems to be more likely to happen when I'm carrying passengers (as in extra weight) and on steep onramps on the freeway that crawl (traffic control light and many cars).... in any case I still have abotu 2K miles on the warranty (I drive a lot... I'm at 140K now) so I took the day off yesterday and stopped by the shop that did it. The mechanic took it for a test drive and well... it didn't happen. So I got in the jeep, he sat in the passenger seat and off we went. I had it happen once, although it wasn't as bad as it gets sometimes (it's not only intermittent but it's intensity varies). He claimed that I let go of the clutch to early (rapidly?). This is kind of an odd explanation, as I have not changed my drivng style and I have always been driving stick shifts. Also I haven't had it happen before swapping out the clutch..... now since the owner of the shop wasn't in that day I will be coming back either Fri eve or Monday eve to take him for a test drive, but if I can't reproduce the symptoms he won't do any work on it ....

Anyways, I guess my question is if the rapid letting go of the clutch (I really don't think I'm doing it faster then I used to, but now that I"m second guessing myself I really don't know anymore) could cause the leap frog effect? Now for kicks I let go of the clutch in what I'd consider rapid manner and I effectively stalled, but had one big jerk/jump instead of 5 or 6 leaps (without stall). Also the incline/onramp on the freeway, I don't really let go the clutch all the way as I'm moving only about 5 feet and I don't get to complete teh transfer from released clutch to depressed gas pedal only so the letting of the clutch too early doesn't make sense there either.

Does anyone have any suggestions? comments? thoughts on this matter?? Cause to me it feels like the clutch is kind of slipping: it grabs then lets go... and grabs again and lets go and results in a violent leap/jerk motion.

btw, I did check the fluid in the clutch and it looks good. TO cover some other points: this is the self bleeindg master/slave so there is no way to bleed it plus it does feel right on the pedal (firm and at the right height).

Did they resurface the flywheel or replace it?

I have also driven standard transmissions all my life -- a lot longer than you've been driving. I'm well into my second million miles. The clutch in my '88 MJ is almost impossible to engage smoothly. It's hard to know if the shaky starts I experience are the same as yours, though.

When I was first learning to drive, I still remember that if I revved the engine too much and dumped the clutch too fast, the clutch would bounce against the flywheel and the start would be VERY "lurchy." The problem I have with the MJ is not that, it's more like intermittent slippage.

I know that the truck has a transplanted YJ tranny and transfer case, so the kid who had it before me drove it hard enough to blow up one transmission. There's no way to know if they replaced the clutch when they swapped the tranny, but whether they did or not I'm guessing the kid slipped the clutch a lot (the fenders were badly hacked, so he was running big tires through stock 3.07 gears) and probably hot-spotted the flywheel.

I believe it is now universally recommended to resurface the flywheel when replacing a clutch. But there's also a rumor that the newer XJs have a flywheel that's somewhat convex (concave?) rather than flat, and that it has to be replaced rather than resurfaced. I cannot find reference to that in the FSM and it doesn't make sense, but I have seen it reported "more than twice" (as a friend used to say).

Just some thoughts to discuss with the shop owner.

From the 94 FSM, Page 6-3:

Flywheel machining is not recommended. The flywheel clutch surface is machined to a unique contour and machining will negate this feature. However, minor flywheel scoring can be cleaned up by hand with 180 grit emery, or with surface grinding equipment. Remove only enough material to reduce scoring (approximately 0.001 - 0.003 in.). Heavy stock removal is [bold]not recommended.[/bold] Replace the flywheel if scoring is severe and deeper tha 0.76 mm (0.003 in.)

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Whose brand clutch did he use as a replacement.... I remember ALOT of bitching here from a few owners who used aftermarket clutchs and were not at all happy with the differences. Matter of fact I can not remember anyone ever saying 'I replaced my factory clutch with xxxxx brand and it's just the cats meow now'... The other thing too, I have never seen it written anywhere but on those rare occasions when I have needed to do a clutch I generally drive it for a few hundred miles and gently engage and disengage as I'm driving. Kind of a breakin like you do for disc brakes.

I'm not one to argue with an FSM, but I know machining the flywheel made a difference on my MJ. I replaced the clutch (hastily) last November but didn't resurface the 'wheel. All was well for the first few hundred miles, but then it started to "shudder" like yours just enough for me to feel it. A few months later when I had the driveline torn apart again, I pulled the 'wheel and sent it to a trusted local machine shop and had them turn it and press in a new pilot bearing. It's now as smooth as a baby's butt.
Of course, maybe it's apples-to-oranges, 'cause mine's an 87, 2.5, AX5. YMMV (?)
Jeff

For starters, I don't recall the name of the manufacturer of the clutch, but IIRC when I talked to somebody after I had the clutch replaced, it sounded they used the same manufacturer as OEM. In regards to the flywheel, it was supposed to be replaced(I talked to them about it), but maybe they just resurfaced it. I will have to ask him when I stop by.

Btw, it kind of seems to me that if I over rev it a bit (but not too much) I can avoid it when I feel it start happening (it's hardt o explain but I have a "starting symptom" that I can feel)....

So far all great suggestions... anyone else??

OK, I just remembered that my receipt was still in the car and it says that I got the fly wheel resurfaced. The question is though how much was it resurfaced? There is probably no way to determine that after it was done, is there But I think it might have been done quite a bit as it is hidden on the bottom of the receipt in the outside sublet repairs (that's how I missed it originally... damn)

Anyways, the clutch brand is Borg Warner.

OK, now that I think about it if the clutch was resurfaced will it cause the intermittent problems that I am having? Saying that the FSM says not to do it, might not be enough and I don't want him telling me that this would not be the problem and send me on my way if I can't reproduce the problem...

I will be bringing my FSM with me when I go to talk to him, but is there anything else I should know or be aware of??

Don't know what to tell you........ Historically, I've always been told either resurface or replace the flywheel when you're in there. And this is the first vehicle that says "no machining."

I replaced mine 3 years ago, it was pretty badly scored up. Last May when I was back in it, the flywheel (60,000 miles) still had all of the original tool marks, except for the outer inch where the clutch disk rode and that was smooth, no scores at all. I left it in, just scoured it a little.

I've gone back and re-read your original post. I suspect there may be a bit of a terminology problem, the clutch is disengaged with the pedal all the way down, and engaged when the pedal is up. Your symptoms sound a little like clutch chatter. There may be some crud on the clutch disk. It may be possible that it's not fully engaging either. Do you have any free play at the top of the pedal stroke?

ChiXJeff said:

I've gone back and re-read your original post. I suspect there may be a bit of a terminology problem, the clutch is disengaged with the pedal all the way down, and engaged when the pedal is up. Your symptoms sound a little like clutch chatter. There may be some crud on the clutch disk. It may be possible that it's not fully engaging either. Do you have any free play at the top of the pedal stroke?

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Yeah... I switched them(terminology).. or the clutch folks switched them on me

What do you mean by free play?

There should be a short bit of play at the top of the pedal stroke, before you feel the resistance of the throwout bearing pressing on the pressure plate fingers. It should be under an inch of play at the pedal, probably more than a half inch.

ChiXJeff said:

There should be a short bit of play at the top of the pedal stroke, before you feel the resistance of the throwout bearing pressing on the pressure plate fingers. It should be under an inch of play at the pedal, probably more than a half inch.

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OK, I never really paid attention to it... I will make sure to test that out while driving back home from work today

Kejtar said:

OK, I never really paid attention to it... I will make sure to test that out while driving back home from work today

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Yeah, I get about 1/2" to 1" of freedon on the pedal.

Kejtar said:

Yeah, I get about 1/2" to 1" of freedon on the pedal.

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That's a decent sign that you're fully engaging the clutch, that the clutch disk is about the right thickness, and the flywheel hasn't been machined down too far.

I assume that the transmission does shift reasonably well, i.e. you're not having to force it into gear through the synchronizers. That would be pointer that the clutch is not fully disengaging.

ok, so what else can it be?? in general it does shift well...

I'm thinking it has to be related to that "unique contour" on the flywheel. I don't know if that is related to a "unique contour" on the pressure plate and/or clutch disk, but let's assume for the moment that the pressure plate probably has a matching contour -- which it pretty much would have to in order to provide uniform clamping of the disk to the flywheel.

Now let's further suppose that the shop bought the correct clutch for your year XJ, so the new pressure plate has this unique contour. But they resurfaced the flywheel, so it now has a standard, flat NON-contour. This would mean that your new clutch cannot be fully and evenly engaged, because the surface of the pressure plate is not parallel to the surface of the flywheel. The clutch disk would wear prematurely on either the inner or outer edge (depending on what this unique contour is). In addition, when engaging the clutch from a stop, rather than the entire surface being brought into contact between the pressure plate and flywheel uniformly, that inner or outer edge would come into contact first and wear quickly. That could lead to slippage when engaging the clutch gently, which is the way a clutch normally should be engaged.

Unfortunately, the only way I can think of to test this hypothesis is to remove the clutch and inspect the disk for uneven wear.

Eagle said:

I'm thinking it has to be related to that "unique contour" on the flywheel. I don't know if that is related to a "unique contour" on the pressure plate and/or clutch disk, but let's assume for the moment that the pressure plate probably has a matching contour -- which it pretty much would have to in order to provide uniform clamping of the disk to the flywheel.

Now let's further suppose that the shop bought the correct clutch for your year XJ, so the new pressure plate has this unique contour. But they resurfaced the flywheel, so it now has a standard, flat NON-contour. This would mean that your new clutch cannot be fully and evenly engaged, because the surface of the pressure plate is not parallel to the surface of the flywheel. The clutch disk would wear prematurely on either the inner or outer edge (depending on what this unique contour is). In addition, when engaging the clutch from a stop, rather than the entire surface being brought into contact between the pressure plate and flywheel uniformly, that inner or outer edge would come into contact first and wear quickly. That could lead to slippage when engaging the clutch gently, which is the way a clutch normally should be engaged.

Unfortunately, the only way I can think of to test this hypothesis is to remove the clutch and inspect the disk for uneven wear.

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That's what I"m thinking and I think that that's the line I will take with the shop and if need be threaten with credit card stopping the payment

ok... quick update. I went there Fri and the guy wanted to tell me that the problem is in my tcase.... I heavily disagreed and he asked me to come in Sat morning as he will ask his friend (owner of another shop) to come in and take a look at it. And of course he discounted the convex flywheel theory immediately.

In any case today the "specialist" took a look at it, test drove it and of course... no symptoms today (but at least I had plenty symptoms yesterday so they knew that I wasn't pulling this stuff from thin air). Anyways the "specialist" did say he heard of the special clutches and fly wheels and also the owner of the shop called yesterday after I left a dealership which did confirm an existance of a special fly wheel.... so on Monday it's going to get a new clutch and flywheel and I will have to pay for the cost of flywheel - cost of machining on the old flywheel that I already paid... I will be watching them like a hawk as they are doing replacement LOL

I hope you get a chance to inspect the disk that comes out. It will be interesting to see if it's worn unevenly.