Summarize the 6MT Situation For Me

[Chris D]

stock clutch is not the best, over engineered. The 2025 with 4.88 works great, in the 7500 miles on it so far no issues what so ever. The 2019 4:10, 35's worn out the stock clutch about 40K, the centerforce only lasted until we think someone used 4th gear to back down a hill or R as a brake to head down the hill and absolutely smoked it. The solid flywheel really improved clutch performance and virtually eliminated stalling.

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[hephaestus]

Aftermarket clutches all feel 1000% better but all seem to suffer from lubrication issues after 10k miles or so (factory clutches have also been reported to have some issues here but it is few).

Lubrication issues? The only lubrication anywhere in a clutch is the throw-out bearing. Curious to what you are referring.

Also curious what aftermarket clutches you're referring to and what your experiences with them are. I've read and heard that many of the aftermarket clutches do not play nice with the factory programming and render the vehicle basically inoperative.

I have no experience with aftermarket clutches in a JL. If I felt confident that one offered a better feel and performance without conflicting with the factory software, it would be high on my list of desires.

 

[hephaestus]

In brief summary what is the exact issue with the manual trans in the JL? Is it all of them? What about the JK?

2018 JLUR w/M6 trans here. I've also owned and DD'ed manual transmissions for most of my life. (Mostly diesel trucks, but one or two Hondas as well.) Coming from decades of ownership experience, my observations are:

Stock clutch hydraulic system is complete trash. 90% of the pedal does nothing, everything is in the last 10% of the pedal.

Flywheel makes stalling abnormally easy. (Although a competent driver can work through that.)

Gear spreads are screwed up. 5 & 6 are basically the same gear, effectively making it a 5-speed transmission.

The reprogram they send with the recall is all kinds of screwed up. My jeep spent an entire month at the dealership trying to figure out the programming after it effectively disabled the vehicle. Wish I would have just skipped that altogether.

As others have said, a tune and 4.88's went a long way to making it all bearable again, but the core issues are still there.

Had I appreciated how truly bad the M6 was going to be, I would have bought an auto. I only keep it now because my plan is, and was always, to someday alleviate these issues with an LS and an NV4500.

 

[Ol’ Timey Manual SWB Guy]

I agree with what was written above. If you wanna go even farther back, IMHO “the 6MT situation,” as you phrase it, is that engineering decisions were made to maximize fuel economy in the EPA test circuit.

In addition, first gear is extremely tall. So people who’ve driven manuals for decades still stall-out this vehicle in its stock config. Also, the 3.6 doesn’t throw a lot of torque with the stock tune, at low RPM, on 87 octane.

Those factors of “the situation” ask quite a lot of the clutch. You’ll have to rev higher and bleed-in the friction quite slowly within that 10% of pedal travel, as mentioned. Now that asks rather a lot of the driver too; the JL 6MT (stock) is not a good car to learn to drive stick. It’s unforgiving.

This particular (low mass) clutch, in turn, is not 100% up to the task. All the more so, when tire size and mass are increased…. as Jeepers tend to do.

The good news is that fully all those factors can now be controlled with simple owner mods. Merely regearing and running only 91 octane solves almost everything, from what I can tell.

And, yes, 5th gear should’ve been a tooth lower. Or 6th a tooth higher True.

 

[gek]

@Bryce919er
Aftermarket clutches all feel 1000% better but all seem to suffer from lubrication issues after 10k miles or so (factory clutches have also been reported to have some issues here but it is few).


Lubrication issues? The only lubrication anywhere in a clutch is the throw-out bearing. Curious to what you are referring.

Also curious what aftermarket clutches you're referring to and what your experiences with them are. I've read and heard that many of the aftermarket clutches do not play nice with the factory programming and render the vehicle basically inoperative.

I have no experience with aftermarket clutches in a JL. If I felt confident that one offered a better feel and performance without conflicting with the factory software, it would be high on my list of desires.

After about 10k miles or so, it appears that the throwout bearing builds friction and doesn't allow the clutch to fully release, causing you to not be able to shift into 1st and sometimes 2nd. This has been reported on all aftermarket clutches and a few factory ones, however there are a few people who have tried CF's hydraulic bearing, but don't have the amount of miles on it yet to really know if it helped.

I installed an ACT JP6 after 15k miles. Stock clutch looked fine. I had zero issues for another 15k miles then on my way home from a wheeling trip I noticed the pedal groaning and started to get lockout in 1st gear at stop lights.

@SadRobot's manual compilation thread has a lot of info, but this was the first sign of her clutch issues so I knew what was coming.

https://www.jlwranglerforums.com/fo...g-into-1st-reverse-compilation-thread.141518/

I did not need any programming for the clutch it just worked, and for a while it was glorious. It felt great and performed great, but I wasn't going to pull the trans every 15k miles to clean and re-lubricate. It is the 19A recall software that rendered the vehicles inoperable. I have heard nothing about an aftermarket clutch causing an issue like that.

As of now, to my knowledge, none of the aftermarket manufacturers have solved this issue. I personally think it is a combination of issues. The lubrication and the addition force wearing out the master and slave cylinders, but there is not confirmation of that.

 

[hephaestus]

After about 10k miles or so, it appears that the throwout bearing builds friction and doesn't allow the clutch to fully release, causing you to not be able to shift into 1st and sometimes 2nd. This has been reported on all aftermarket clutches and a few factory ones, however there are a few people who have tried CF's hydraulic bearing, but don't have the amount of miles on it yet to really know if it helped.

Thanks for the links. I'll peruse through them later when I have more time. But I'm confused about your TO bearing statements. Are you saying that the issues stem from using aftermarket TO bearings, or from stock bearings on aftermarket clutches? How would an aftermarket clutch change anything about TO bearing lubrication?

 

[bllprk]

Summary:

The JL design included a clutch that is a twin disc, dual mass flywheel. This is different than the JK which has a solid flywheel and single disc clutch.

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Early on, there were some cases where the JLU clutch would slip while engaged, generate enough heat to break apart an inner flywheel causing metal to shoot thru the bell housing and thru the gas line causing a fire.

Jeep eventually replaced all the clutches with a recall and there have been zero fires with the new design. (I think)

If you have a 6MT that has the recall, or is newer, you should have zero issues with the fire problem.

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Aftermarket companies have made replacement clutches. Some are dual disc, some are single. They are not perfect. If you want to swap to an aftermarket clutch, please do some research into the options. There are pros and cons to each design.

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If you decide to change tire size or gear ratios, please do some research because there are extra software steps you must take to ensure it works. This is true for both OEM and Aftermarket Clutches.

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I love my 6 speed. I am thankful to drive it each day.

 

[yokramer]

Design and gearing bad
Aftermarket clutches also bad
Dont bother with it and get the auto

 

[Reflektr]

All of the above basically sums it up pretty well. The clutch design is the main hurdle. The clutch disc cannot freely travel, thus making shifts notchy or sticky and very inconsistent. I thought it might have just been mine, so I test drove a couple new ones for comparison. The new ones that I drove were even worse-off than mine. I could barely get the one into reverse to back out of its parking spot. At first I chalked it up to sitting and not being driven. Then halfway through my test drive it about locked me out of 2nd and 3rd. What gets me the most is somebody actually let that fly.

 

[WXman]

In brief summary what is the exact issue with the manual trans in the JL? Is it all of them? What about the JK?

The issues:

- Shifter throw resembles a 1978 dump truck

- Pedal feedback is non-existant and unpredictable

- Stock clutch in JL units is particularly garbage and was the source of at least one recall

 

[Celtics18]

28k+ kms
2023 stock clutch, 4.88, 37s, have not done any recalls, silky smooth and no warnings / issues so far, touch wood

 

[LKG]

I agree with what was written above. If you wanna go even farther back, IMHO “the 6MT situation,” as you phrase it, is that engineering decisions were made to maximize fuel economy in the EPA test circuit.

In addition, first gear is extremely tall. So people who’ve driven manuals for decades still stall-out this vehicle in its stock config. Also, the 3.6 doesn’t throw a lot of torque with the stock tune, at low RPM, on 87 octane.

Those factors of “the situation” ask quite a lot of the clutch. You’ll have to rev higher and bleed-in the friction quite slowly within that 10% of pedal travel, as mentioned. Now that asks rather a lot of the driver too; the JL 6MT (stock) is not a good car to learn to drive stick. It’s unforgiving.

This particular (low mass) clutch, in turn, is not 100% up to the task. All the more so, when tire size and mass are increased…. as Jeepers tend to do.

The good news is that fully all those factors can now be controlled with simple owner mods. Merely regearing and running only 91 octane solves almost everything, from what I can tell.

And, yes, 5th gear should’ve been a tooth lower. Or 6th a tooth higher True.

I think you hit the nail on the head! The only thing I would add is the lousy throttle response. For an old head like me that has only ever driven manuals with mechanical linkage, waiting for the ECM to decide when to add/reduce fuel can be extremely frustrating. Personally I put about 70% of the stall blame on said electronic throttle.

 

[gek]

Thanks for the links. I'll peruse through them later when I have more time. But I'm confused about your TO bearing statements. Are you saying that the issues stem from using aftermarket TO bearings, or from stock bearings on aftermarket clutches? How would an aftermarket clutch change anything about TO bearing lubrication?

They come with lube. ACT comes, or at least it did, with some purple-ish ceramic lube. And in testing I think they've tried no lube and other types with no luck. Sadrobot was a guinea pig for some of their testing, and none of it seemed to fix the problem.

I think most aftermarket kits use a factory bearing other than CF hydraulic one.

 

[LSJKU]

Now that asks rather a lot of the driver too; the JL 6MT (stock) is not a good car to learn to drive stick. It’s unforgiving.

I do agree with OTMSWB Guy on this. I've driven manuals all my life and the Jeep 6MT is pretty unforgiving, but not impossible to fix.

Mine is a Jan/Feb 2025 build. I ordered the 6-spd with the 3.6L and factory 4.88s, and they now turn 38" Toyo RT Pros on Method 703s. My first impressions when I picked up the Jeep was absolutely no feel to the clutch plate engagement, mushy at best. I had to adjust my driving habits to compensate for the light flywheel and poorly designed gearing @GabeBoyTheGreat mentioned. The worst was not being able to easily "feather" the clutch in situations that demanded it.

But I'm happy with the clutch performance now. I changed out the clutch pedal return spring with a lighter ACT one and asked @bmpcamry09 to specifically address the tip-in power when he tuned my 3.6L. I think clutch engagement feel could be even better by totally removing the clutch pedal return spring, such as @AmericanPatriot100 has done, but no return spring could potentially lead to its own problems down the road.

I'm not aware of an aftermarket clutch maker that has truly solved the factory clutch shortcomings yet. They all seem to have problems creeping in around 10k to 15k miles. And i've had the long-term plan to do an SRT/Tremec swap since before I bought the JL. That's still an option. But right now, I'm more than satisfied with the lighter return spring and Brad's tuning that the clutch feel and performance are no longer an issue. And the mid-range torque and power increases from Brad's tune have the SRT/Tremec swap on hold as well. I'm not saying I will definitly not do a swap, I may eventually do it anyway bc I am an old-school V8-Jeep guy. But "as-is" now, my little JL is nothing short of a blast to drive.

 

[GabeBoyTheGreat]

I think you hit the nail on the head! The only thing I would add is the lousy throttle response. For an old head like me that has only ever driven manuals with mechanical linkage, waiting for the ECM to decide when to add/reduce fuel can be extremely frustrating. Personally I put about 70% of the stall blame on said electronic throttle.

A tune helps with the throttle response. It is still not as good as a mechanical throttle, but the tune makes a noticeable difference.

Even with the tune, the lightweight flywheel is still an obstacle. In general, you should be able to creep along with no throttle input using only clutch, but the JL really struggles with that, especially in R. Too much clutch engagement without throttle causes the lightweight flywheel to slow down too much, and the 3.6l can't keep itself alive.

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