Chattering Noise when Accelerating Manual Transmission

[ruggburnout]

You basically summarized the biggest reason I haven’t been back to my local dealer despite the persistent engine noise and the occasional squeak from my Mojave shocks. People love having a warranty but when the techs doing the work are inept and indifferent it’s a lot harder to bite that bullet. Even worse when most dealerships don’t support warranty repairs with a loaner, which is damn near unheard of.

I'm probably one of the biggest anti-franchised dealer people out there. The franchise dealership system is set up for the dealers to make money. They will screw the customer and the OEMs every chance they get. Look at the political lobby that the dealership network has... that tells you all you need to know. They spend loads of money in government to protect their lucrative racket.

I don't totally blame the mechanics because they have to rush jobs to make money. If they don't work ridiculously quickly, then they will struggle to earn. That money goes into the pockets of the owners of the dealerships. That being said... everyone was telling me unsolicited the mechanic doing the work was a excellent engine guy. The Service Advisor, the shuttle driver... But end of the day... he messed up big time. Forgetting to torque bolts on the cam caps is as bad as it gets. There is a specific torque sequence and it is a very fine process to ensure the correct pre-load on the cam bearing surfaces. To somehow skip that process is worrisome at a minimum. You should be double checking the torques and turning the camshaft to ensure it is spinning with low drag. Did he do these steps? Makes me wonder.

When I am out of warranty, I am done with dealerships. I will do the work that I cam myself. For work I can't do, I am already asking around for independent shops that people trust. I'd rather build a relationship with a small shop that I can trust, then hoping that some guy doing a rush job is qualified and actually gives a shit.

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[onewhippedpuppy]

Trust me, you are preaching to the choir. I am an engineer and used to be a heavy diesel mechanic before college. I used to own a used car dealership and have always done my own maintenance and repairs. I am consistently disappointed every time I have paid someone else to work on my vehicle. I read your post and immediately think to myself, “how much to replace cams myself”? Because I have no faith in them doing it correctly.

 

[ShadowsPapa]

My thoughts on why vehicles with manuals seem to hear this noise more... Automatic shift points are probably not getting into the 3000+ rpm for very long or at least long enough to notice the noise. With the manual, you are controlling the shift points and will definitely sit in the 3000-4000 rpm range where the noise is most clearly heard. I found the only time I really heard it while driving was 2nd gear starting around maybe 2500 rpm up to maybe 4500 rpm. First gear is revved out so fast that I could never really fully discern the noise. Second gear doesn't have the road and wind noise, so the noise stands out. Third gear and beyond, the road and wind noise pretty much drown it out.

You are hearing a different sound than what many with the stick are hearing, however. yours was a "different rattle". A tech here even confirmed it was more of a rattle than an engine valve train issue.
The valve train has apparently been "reprogrammed" to run the high lift differently so if it's a rattle associated with valve train, can't say automatics won't hear it. Even then, originally these were set to kick into high lift at 2800 rpm.
Now it's been changed.
There's people here with the manual transmission rattle that have had it for over a year - without change.

When towing with mine, it's in the 3,000+ rpm range a lot - not just when shifting but it actually stays about 3,300 RPM for miles. On flatter ground, 2500 rpm and I've seen it over 4,000 rpm quite a bit on severe hills here.

BTW - we've had our share of Grand Cherokees, so far, zero engine issues. My wife has had at least 2 with this generation 3.6 and a couple prior to 2016.

So how do we explain the tech, and others, who have said it's not engine related, or who have driven for a year or more with the rattle?

 

[ShadowsPapa]

Again, mine is an AUTOMATIC (and of either of my Gladiators, I never heard a rattle, ping or unusual engine sound at all, ever) but the comment about RPM and such got me to trying harder to keep track and listen.
My truck - maxed out on payload. 300 pound blade up front, 210 pounds of sand in the back, receiver platform so I could go pick up a snow blower and not lift it high or over the sand bags, my steel bumper, winch and me - I'm sure I hit the 1,000 pound mark.
Snow plow on the front was like raising the jib sail that thing way out front catching our constant wind here.
Plus - once I get off our backroads and hit the bypass where the limit is 65, it's literally over a mile of a decent grade. That means I drove with that truck trying to accelerate, loaded, up a hill, getting up to 65 and into traffic. The engine stayed right at 3,000 rpm when it finally did upshift until I hit the flats then it hit about 2700-2800 for another mile. Then I hit the point where it goes up slightly again toward Altoona. Again, 3,000 RPM. Other than hearing the engine trying to kick out some torque and climb the hills and keep up speed, it was quiet. (it was at that time I wish the exhaust wasn't SO quiet, I'd like a bit of a growl)
Anyway, my JT spent a lot of time in the 3,000+ range today, miles worth. Then when I picked up the snow blower, there was even more drag on the poor thing.
Weight, wind resistance, cold, denser air, blade acting like a big wind catcher up there, I know I was in "high lift" for a good share of that trip - not a single rattle of anything, shield, bracket, or valve train.
Other than the temperature on the dash saying it was 88 outside when it was really about 14, and the HVAC being funky lately, lovin' this truck like I did the prior one.
Only when my wife is in the truck does it get "more moderate' driving, so it's not like I drive like "grandpa".

 

[onewhippedpuppy]

ShadowsPapa does highlight a concern that I have - if this is a cam issue, why does it only affect those with a 6MT? There have been incidents of JT owners with automatics that have suffered from advanced camshaft and follower wear, but they haven’t reported this noise. I agree that the automatic would have different shift points, but to say that it never accelerated through 3,000 RPM in 2nd or 3rd gear doesn’t seem realistic. I can’t help but feel like this is an issue specific to the manual transmission, but I’ll be damned if I know exactly what. I also think about my friend who has a high mileage JKUR 6MT that has had the exact same noise since new - if this was advanced cam wear, how is his Pentastar still going strong at over 100k?

 

[NachoRuby]

ShadowsPapa does highlight a concern that I have - if this is a cam issue, why does it only affect those with a 6MT? There have been incidents of JT owners with automatics that have suffered from advanced camshaft and follower wear, but they haven’t reported this noise. I agree that the automatic would have different shift points, but to say that it never accelerated through 3,000 RPM in 2nd or 3rd gear doesn’t seem realistic. I can’t help but feel like this is an issue specific to the manual transmission, but I’ll be damned if I know exactly what. I also think about my friend who has a high mileage JKUR 6MT that has had the exact same noise since new - if this was advanced cam wear, how is his Pentastar still going strong at over 100k?

At this point, I still think it's a resonance. What exactly is resonating, I don't know. I don't think it's a cam issue because it stops at WOT, even in the range where it normally would do it. Give it the beans, and it stops immediately. My guess is that it's related to the hydraulic cables once they insulated them post recall. At a certain rpm range (2800-3200) and part throttle, I think they are vibrating on the firewall or under the hood somewhere. Mine has done it off and on since 2300 miles, so essentially since new. I'm now at 29000 miles. It's not worse, it's not better. Exactly the same.

We have a JKU with an MT. But I haven't noticed it on there. It has about 100k miles now. It makes all kinds of other sounds (normal old jeep noises), but not that one.

 

[NachoRuby]

I just got back from a long road trip with my MT gladiator. I can now say unequivocally, the noise is coming from the pedal itself. It's the plastic vibrating.

Whenever it'd make the noise, if I'd just barely touch the pedal withy foot. It'd stop instantly. I didn't do this for very long of course, but I tried it 3 times. And it didn't even take enough pressure to slip the clutch or anything. I just barely touched the pedal with my foot, and the noise stopped. It's the pedal itself. Now, I don't know if it's due to something on the other side of the firewall touching the assembly, but it's definitely the pedal. That actually has me a lot less worried.

 

[OHJeeper]

I just got back from a long road trip with my MT gladiator. I can now say unequivocally, the noise is coming from the pedal itself. It's the plastic vibrating.

Whenever it'd make the noise, if I'd just barely touch the pedal withy foot. It'd stop instantly. I didn't do this for very long of course, but I tried it 3 times. And it didn't even take enough pressure to slip the clutch or anything. I just barely touched the pedal with my foot, and the noise stopped. It's the pedal itself. Now, I don't know if it's due to something on the other side of the firewall touching the assembly, but it's definitely the pedal. That actually has me a lot less worried.

I'll try this trick as well and report back.

I've narrowed it down to 2500-3000 RPM only when under load (like uphill) and in 2nd gear for me.

 

[be77solo]

I just got back from a long road trip with my MT gladiator. I can now say unequivocally, the noise is coming from the pedal itself. It's the plastic vibrating.

Whenever it'd make the noise, if I'd just barely touch the pedal withy foot. It'd stop instantly. I didn't do this for very long of course, but I tried it 3 times. And it didn't even take enough pressure to slip the clutch or anything. I just barely touched the pedal with my foot, and the noise stopped. It's the pedal itself. Now, I don't know if it's due to something on the other side of the firewall touching the assembly, but it's definitely the pedal. That actually has me a lot less worried.

I have confirmed the same on mine. It's always in the 3-3.5K range, and simply putting my foot on the clutch pedal stops it, and lifting off the pedal it comes right back.

I initially posted otherwise, thinking it wasn't the pedal, but further experimenting has confirmed it. Now what that actually means to fix it I have no idea.

But I have zero thoughts that's it the CAM or anything, it's just something vibrating/resonating in that particular RPM range.

 

[ruggburnout]

You are hearing a different sound than what many with the stick are hearing, however. yours was a "different rattle". A tech here even confirmed it was more of a rattle than an engine valve train issue.
The valve train has apparently been "reprogrammed" to run the high lift differently so if it's a rattle associated with valve train, can't say automatics won't hear it. Even then, originally these were set to kick into high lift at 2800 rpm.
Now it's been changed.
There's people here with the manual transmission rattle that have had it for over a year - without change.

When towing with mine, it's in the 3,000+ rpm range a lot - not just when shifting but it actually stays about 3,300 RPM for miles. On flatter ground, 2500 rpm and I've seen it over 4,000 rpm quite a bit on severe hills here.

BTW - we've had our share of Grand Cherokees, so far, zero engine issues. My wife has had at least 2 with this generation 3.6 and a couple prior to 2016.

So how do we explain the tech, and others, who have said it's not engine related, or who have driven for a year or more with the rattle?

I should clarify that my rattle ended up being valvetrain tick and not the rattle that others with the manual are hearing. I initially thought my noise was possibly related to the manual because of the similarity of the description of the noise. Once I determined that my noise was in the engine from revving at a standstile in neutral, I was able to further determine it was valvetrain. Especially since it got worse from initially hearing it in late September to late October, when it became very apparent above ~2500 rpm.

The Pentastar Upgrade base engine calibration was changed to essentially be in high lift all the time as I mentioned before. This part of the calibration is on all vehicle models with this engine whether AT or MT. So this wear condition can happen on any model. I was only mentioning that the dealership mechanic said he has seen this mostly on Grand Cherokees and typically with way more miles than my vehicle. That is just one mechanic and it doesn't mean that is the only model.

As this is most likely a wear issue due to increased duty cycle, it doesn't mean all camshafts and followers will wear... It's just a statistical luck of the draw thing... with the losers being a higher percentage than should be acceptable. Not to mention you have 12 followers per vehicle so you have 12 parts that could potential wear that hurts you statistically.

 

[ruggburnout]

ShadowsPapa does highlight a concern that I have - if this is a cam issue, why does it only affect those with a 6MT? There have been incidents of JT owners with automatics that have suffered from advanced camshaft and follower wear, but they haven’t reported this noise. I agree that the automatic would have different shift points, but to say that it never accelerated through 3,000 RPM in 2nd or 3rd gear doesn’t seem realistic. I can’t help but feel like this is an issue specific to the manual transmission, but I’ll be damned if I know exactly what. I also think about my friend who has a high mileage JKUR 6MT that has had the exact same noise since new - if this was advanced cam wear, how is his Pentastar still going strong at over 100k?

To clarify, my thought on not hearing it as much in automatics isn't because it never accelerates through 3000 rpm. Just that with an automatic, you are not controlling the rpm sweeps as much as a manual so you may pass through the rpm range that you would hear it quicker... So you may not perceive the noise as easily. I only heard it in 2nd gear around 2500-4000 rpm or so with my manual and that was more to do with wind and road noise as you speed up for higher gears. And first gear rpm sweep is so quick, that was very hard to hear any noise before shifting to 2nd.

As this is a wear issue, not all engines will have the problem. I just got the bad luck of having one go bad at 24000 miles. Some will happen later... most will probably never have an issue. Regardless, it is a problem that needs fixed because more are failing then should.

 

[ruggburnout]

I just got back from a long road trip with my MT gladiator. I can now say unequivocally, the noise is coming from the pedal itself. It's the plastic vibrating.

Whenever it'd make the noise, if I'd just barely touch the pedal withy foot. It'd stop instantly. I didn't do this for very long of course, but I tried it 3 times. And it didn't even take enough pressure to slip the clutch or anything. I just barely touched the pedal with my foot, and the noise stopped. It's the pedal itself. Now, I don't know if it's due to something on the other side of the firewall touching the assembly, but it's definitely the pedal. That actually has me a lot less worried.

So only thing with slightly depressing the clutch pedal... The master cylinder has a bleed hole that is open when the clutch pedal is not depressed. It only takes maybe 5mm of pedal travel to close the bleed hole and to start slightly compressing the hydraulic fluid. It is possibly in the pedal as you stated, but by depressing the pedal slightly it may also be compressing the fluid and causing the hydraulic pipe or hose to move enough to not rattle... just a thought.

 

[onewhippedpuppy]

I played with this on my drive to work, pushing the pedal slightly definitely seems to make the noise go away. I’ll try a few more times to see if it’s consistent.

 

[Rtrono]

I tried mine too. It went away when touching the clutch pedal.

 

[onewhippedpuppy]

I’ve tried this over the last week and it’s 100% consistent, light pressure on the clutch makes the noise stop. Now the question is why?

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