JGC WK2 2012 Nag1 Thumping and vibration upon acceleration at speeds above 80km/h

[Reinardt22]

Jeep Grand Cherokee 2012 3.6 4x4 Limited - 184000km

I have been chasing after an issue with my Jeep since I got it. It vibrates upon acceleration usually at highway speeds at 100km/h on a slight incline.

Since chasing this problem I had done the following to fix it:

• Changed out both motor mounts (they were bad)
• Changed out the front and rear propshafts (driveshafts if you are from USA)
• Changed the transfer case fluid
• Balanced all of the wheels and confirmed that the tire pressures are good

The vibration got better and I took it on a 1400 km trip. All went well.
But just as I reached home, the Jeep started vibrating and at speeds of 80km/h or above when accelerating. It is like a thumping vibration, quite intense I might add. When going above 100 km/h it continues while accelerating, but goes above when I let of the gas pedal. It does the same when switching to neutral at that speed.

I am unsure what to do next.


I read that the torque converter in the NAG1 transmission can cause slippage etc. if the oil in the trans in low/high or contaminated.

There is no warning light illuminated, it shifts through all the gears normally and I am able to change the transfer case to 4 low and all works fine.

I thought of replacing the trans fluid and filter, the front and rear diff fluid as well with the hopes that I might fix this issue. Any ideas from the experienced WK2 owners out there ? Anyone having the same issues ?

[Rainier Vermaak]

Jeep Grand Cherokee 2012 3.6 4x4 Limited - 184000km

I have been chasing after an issue with my Jeep since I got it. It vibrates upon acceleration usually at highway speeds at 100km/h on a slight incline.

Since chasing this problem I had done the following to fix it:

• Changed out both motor mounts (they were bad)
• Changed out the front and rear propshafts (driveshafts if you are from USA)
• Changed the transfer case fluid
• Balanced all of the wheels and confirmed that the tire pressures are good

The vibration got better and I took it on a 1400 km trip. All went well.
But just as I reached home, the Jeep started vibrating and at speeds of 80km/h or above when accelerating. It is like a thumping vibration, quite intense I might add. When going above 100 km/h it continues while accelerating, but goes above when I let of the gas pedal. It does the same when switching to neutral at that speed.

I am unsure what to do next.


I read that the torque converter in the NAG1 transmission can cause slippage etc. if the oil in the trans in low/high or contaminated.

There is no warning light illuminated, it shifts through all the gears normally and I am able to change the transfer case to 4 low and all works fine.

I thought of replacing the trans fluid and filter, the front and rear diff fluid as well with the hopes that I might fix this issue. Any ideas from the experienced WK2 owners out there ? Anyone having the same issues ?

Chat to Ryno at Vtec Motors. He rebuilt the NAG1 in my WK and it is as new.

[Commander]

Was the carrier bearing replaced with the rear prop shaft? Kinda sounds like a bad carrier bearing I exerienced in my Treg, when it vibrated it was really bad.

[Rainier Vermaak]

Jeep Grand Cherokee 2012 3.6 4x4 Limited - 184000km

I have been chasing after an issue with my Jeep since I got it. It vibrates upon acceleration usually at highway speeds at 100km/h on a slight incline.

Since chasing this problem I had done the following to fix it:

• Changed out both motor mounts (they were bad)
• Changed out the front and rear propshafts (driveshafts if you are from USA)
• Changed the transfer case fluid
• Balanced all of the wheels and confirmed that the tire pressures are good

The vibration got better and I took it on a 1400 km trip. All went well.
But just as I reached home, the Jeep started vibrating and at speeds of 80km/h or above when accelerating. It is like a thumping vibration, quite intense I might add. When going above 100 km/h it continues while accelerating, but goes above when I let of the gas pedal. It does the same when switching to neutral at that speed.

I am unsure what to do next.


I read that the torque converter in the NAG1 transmission can cause slippage etc. if the oil in the trans in low/high or contaminated.

There is no warning light illuminated, it shifts through all the gears normally and I am able to change the transfer case to 4 low and all works fine.

I thought of replacing the trans fluid and filter, the front and rear diff fluid as well with the hopes that I might fix this issue. Any ideas from the experienced WK2 owners out there ? Anyone having the same issues ?

Hello??

[iandvl]

Hello??

Just saw this now. It must be an aural pleasure owning a jeep.

[Reinardt22]

Hi Rainier

Sorry for only replying now, it has been a busy couple of weeks.

I took it to workshop for an overall inspection.
They advised that there is nothing noticeably wrong and suggested I rebalance the propshafts and that my transmission seems fine.

I will be doing that next and see if it doesn't resolve my problem.
I have been driving the Jeep and it is not that noticeable, thus it might be that the shafts might be unbalanced.

I looked around a bit and saw that The Propshaft Doctor in Pretoria is recommended.

Will post an update as soon as I was there.

[Alwyn777]

Hi Rainier

Sorry for only replying now, it has been a busy couple of weeks.

I took it to workshop for an overall inspection.
They advised that there is nothing noticeably wrong and suggested I rebalance the propshafts and that my transmission seems fine.

I will be doing that next and see if it doesn't resolve my problem.
I have been driving the Jeep and it is not that noticeable, thus it might be that the shafts might be unbalanced.

I looked around a bit and saw that The Propshaft Doctor in Pretoria is recommended.

Will post an update as soon as I was there.

You can also give SAJCO in Randburg a try. They have been in the business for years and with good reviews and personal experience

[Commander]

I speak under correction, but my old WJ was able to drive with the front propshaft removed, might be worth removing front and rear alternatly and seeing if anything changes. It could be that the Jeep doesn't drive like that, but I suspect it might... Might be worth a try if you are getting desperate...

[3bar]

if you have never changed / serviced the transmission its crying out for some attention now

if it was a prop shaft balance issue it would occur every time a certain rpm would be encountered - which this doesn't appear to be
if it was transfer case it would be gear ratio (and hence rpm) based - which this doesn't appear to be

if it occurs under acceleration / adding additional load to the vehicle (ie pressing the throttle down and requesting more torque) and then a vibration occurs - its transmission slippage - either in the torque converter "plates" (most likely) or in a "clutch band" in the gearbox

If you have a proper OBD scan tool that can monitor the gearbox this is easy to see - the gearbox has an input speed sensor, and an output speed sensor and you have engine rpm - so you can measure and see the input engine rpm, you can see the gearbox input speed - after the torque converter and you can see the output speed going to the transfer case / diff

you will always have a "slippage" between engine rpm and gearbox input speed as its an auto so it will never line up perfectly but what you need to watch on the scan tool is for a drop off / spike / abrupt change of input speed rpm when it drops low - as the torque converter slips then it grabs (makes the vibration) and then either normalizes or repeats

chances are if you scan the gearbox you will have "pending codes" where the gearbox tcu is not happy but it hasn't yet tripped a light - and these codes will confirm the existence of a problem

so rather do a filter / full fluid flush x 3 - probably equal to 3 x times the volume of fluid in the gearbox as its impossible to get all old fluid out in one go, budget about 15 to 20 litres - unless you very experienced to drain the torque converter at the same time, so you will always have old and new fluid together, hence why you do it 3 times

or you can squeeze a bottle of dr tranny in and see what that does - dr tranny "deglazes" the torque converter clutch faces / plates and removes the slippage that occurs - but you often end up with that material causing issues elsewhere - which likely means a fluid and filter change again

some people add the dr tranny and leave it at that if it fixes it
if it doesnt then chances are you need a new / refurb torque converter - the gearbox analysis with a proper scan tool will confirm if its the torque converter or deeper in the box

Me I would try dr tranny and if it works then do a full fluid flush and filter and if it comes back dr tranny it again and leave it

its the 180 odd km without maintenance thats the real root cause here - but if it doesnt happen / shudder all the time its probably savable - if you jump on it now



thinking back to my old Hemi Grand Cherokee the only time I had a driveline vibration was the front diff mount that was finished - absolute pita to change but the fixed my issue - but it was pretty easy to hear and feel and you could invoke the noise on pull off but it would vibrate once under way - check that - you may be lucky and its front diff mount (easy to check) and its not the gearbox but your symptoms really really point to gearbox issues / shudder