Clutch and pressure plate issues

[CapeArt]

there have a been a significant number of them exploding.

"significant number" = ??

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[58Willys]

We have tested the JL clutch quite extensively (not sure which letter revision). Being a twin disc, it requires very little clamp load to hold torque.

You say "being a twin disc" - are you saying the JL clutch has two friction discs? I keep hearing about JL dual clutches, twin clutches etc...; but looking at parts diagrams all I see is a single dual mass flywheel, a single friction disc, and one pressure plate. Dual friction discs are common these days, but to me this is a single disc with dual friction materials; or different friction materials on the flywheel and pressure plates sides. Like one grabby and one softer.

I have not taken a JL clutch out so I don't know; maybe someone who has could post a pic of this twin disc.

Thanks

 

[BuyHold]

We have tested the JL clutch quite extensively (not sure which letter revision). Being a twin disc, it requires very little clamp load to hold torque. From our calculations the stock clutch will hold 340-360ftlbs which should be sufficient for the stock motor. The pedal load is very light because of the pressure plate's weak diaphragm spring compounded by a new hydraulic ratio, different from the earlier JK. In a pedal load test on a JL that had only 21k miles, we found it took just 12 pounds to push the pedal down at peak and provided less than 2 pounds pushing back on the clutch pedal return stroke! That is ridiculously light and it felt terrible!

Unfortunately we also discovered some of the OEM cast materials are gray iron rather than ductile (or nodular) iron. When gray iron is repeatedly overheated, it is prone to catastrophic failure since it is weaker and develops cracks easier than ductile iron.

It has been reported that Jeeps with clutch explosions (not all) are happening while driving on the highway which tells me it is not because of disengagement. As pointed out already, if the clutch was overheating because it wasn't fully disengaging, then the Jeep wouldn't shift or not very well.

Not to say this is the only problem, but we think the biggest problem is preload on the weak pressure plate, since the stock clutch should be capable of holding the power if allowed to fully clamp. IMO this preload is either the friction in the pedal/hydraulics preventing the clutch from obtaining full clamp load, or the driver resting his/her foot on the super light pedal unknowingly causing the clutch to slip and overheat.

Please check out our new clutch offerings for the JL/JT just released at advancedclutch.com. I can share more information, including testing graphs when I am back to work next week.

This appears to be the most founded opinion I have heard since it appears to be based on more than speculation (as I admittedly have been doing).

Thank you.

 

[mwilk012]

Wikipedia? Really? And in the article you linked, the vessel is kept full of water - that's the whole point.

Umm, no? It has a steam bubble maintained at the top of the pressurizer. If allowed to go solid, plant pressure transients due to temperature change can be up to 100x that of a system with a bubble.

 

[JeepinPete]

You say "being a twin disc" - are you saying the JL clutch has two friction discs?

It is a twin disc. The second disc is built into the pressure plate assembly. Hence the large external spline on the free disc to connect the two.

 

[JEEP4U]

Heat and hydraulic fluid seepage/leakage is what you have to keep an eye on. If buying a new manual verify the the hydraulic lines are enclosed or covered with heat protection. This is a must, for the exhaust cat is located in close proximity to the hydraulic lines. Not a good combo. There is not much airflow when rock crawling around the countryside. As everyone who wheels the JL body....the engine compartment gets very hot.

Note: The brake and clutch hydraulic system share the same reservoir. Changed mine out for Pentosin DOT 4, when I upgraded to D60 axles and brakes.

 

[zrickety]

The issue WAS they aren't FULLY disengaging, with so few cases, and basically no new ones in many months in so hard/late to track now. No matter what people say Jeep and Stellantis at that is smart, they fixed the issue that was going on, Techs not doing their job right is a whole differnt thing. The first step to the initial recall was if ther is any customer concern, perform the the clutch hold test. Basically this was clutch drop the Jeep at 2K RPMs with the parking brake engaged. If it stalled immediatly, clutch passed and then you continue with just the line repair as needed. If the Jeep stayed running for any time at all, or outright never shut off, replace clutch assembly and related parts. This was also a test to be performed in the second recall as well after the update was performed, again, I'm sure many techs ignored it.

There's still videos online of people having the clutch pedal stuck to the floor, many videos. I also know of one where someone replaced the clutch assembly with a centerforce prior to the first recall as they where also having the clutch pedal issue and where smelling clutch. A couple days later all the same issues arose, they said the Centerforce was terrible and blah blah blah. Then the recall came out, they got that done, said they would update with a new video and another replacment clutch. Both the update video and the orginal video where they showed the pedal issue where deleted. I beleive they made like an update, but no video stating the recall fixed there issue, and stated an apology. Good luck finding that but you get the idea.

If the pedal is on the floor, was that just a fluid leak or a damaged pressure plate?
A leak I understand. A slipping clutch I understand. Just haven't seen 'significant' posts about those issues. When I tuned my GTI, the stock clutch would slip at full throttle. I learned to limit the power and drove it for years until the slave cylinder leaked. The JL clutch is light, that's true, but I have never felt it slip in gear. Is that common? I haven't seen people post about it.

 

[Swisskidd]

Heat and hydraulic fluid seepage/leakage is what you have to keep an eye on. If buying a new manual verify the the hydraulic lines are enclosed or covered with heat protection. This is a must, for the exhaust cat is located in close proximity to the hydraulic lines. Not a good combo. There is not much airflow when rock crawling around the countryside. As everyone who wheels the JL body....the engine compartment gets very hot.

Note: The brake and clutch hydraulic system share the same reservoir. Changed mine out for Pentosin DOT 4, when I upgraded to D60 axles and brakes.

Good points! I change the brake fluid annually on our JK, including the clutch side of the system. Will do the same on the new JL.

 

[58Willys]

It is a twin disc. The second disc is built into the pressure plate assembly. Hence the large external spline on the free disc to connect the two.

Interesting. So the forward facing piece of the pressure plate has friction material on it, not a smooth metal surface similar to the flywheel?

 

[mwilk012]

If the pedal is on the floor, was that just a fluid leak or a damaged pressure plate?
A leak I understand. A slipping clutch I understand. Just haven't seen 'significant' posts about those issues. When I tuned my GTI, the stock clutch would slip at full throttle. I learned to limit the power and drove it for years until the slave cylinder leaked. The JL clutch is light, that's true, but I have never felt it slip in gear. Is that common? I haven't seen people post about it.

It's common enough that a recall was issued, revised, a class action lawsuit was started, and dozens of people have posted about clutch fires or explosions between here and the facebook group. It's not good.

 

[IanNubbit]

If the pedal is on the floor, was that just a fluid leak or a damaged pressure plate?
A leak I understand. A slipping clutch I understand. Just haven't seen 'significant' posts about those issues. When I tuned my GTI, the stock clutch would slip at full throttle. I learned to limit the power and drove it for years until the slave cylinder leaked. The JL clutch is light, that's true, but I have never felt it slip in gear. Is that common? I haven't seen people post about it.

No slipping not a problem unless the clutch is already smoked. But prolonged slipping engagement over and over eventually does smoke the clutch, then the one time you do go to go on it, boom goes the bell housing

 

[58Willys]

No slipping not a problem unless the clutch is already smoked. But prolonged slipping engagement over and over eventually does smoke the clutch, then the one time you do go to go on it, boom goes the bell housing

That should not result in a fractured clutch bell housing boom. Should result only in a worn out friction disc.

 

[IanNubbit]

That should not result in a fractured clutch bell housing boom. Should result only in a worn out friction disc.

Worn out disc, then heat, then failure through cracking and separating, then goes threw bell housing.

 

[Actman]

Mwilk012: "That isn't what happens to a mixed fluid such as the imaginary brake fluid with air bubble acting as a piston in a system that is vented to a reservoir..."

It just seems like you're just introducing words to confuse things. For gases, PV=nRT. That is absolutely accurate. The pressure of a gas does increase linearly with temperature.

The arguments over pressure/volume/liquid/gas are irrelevant. It is not confusing. Mwilk012's statement above is spot-on. When your foot is off the clutch pedal, a port opens in the master cylinder to the reservoir and it the hydraulics self-adjust. In other words, there is no pressure allowed to build.

 

[Actman]

Attached is a graph of the pedal test we performed at ACT. Earlier I said peak was 12lbs, but it was actually 17lb as shown (bad memory on my part). The difference between the down stroke and up stroke is friction in the system.
Black is from a JL with 21K when we got it in. The peak on the down stroke felt ridiculously soft and fell off sharply. As you can imagine, the return stroke felt like it was sticking to the floor.
Red is the same OEM clutch but we reset the adjustment mechanism on the pressure plate, and lubricated the guide tube, clutch arm, etc. Basically, red is as good as it gets with the same clutch.
In the near future I am hoping to "pull back the curtain" (so to speak) and start a new thread breaking down the attributes of the stock clutch systems to reduce the speculation. Hopefully it won't bore people too much with tech geek stuff.

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