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Old 09-01-2017, 08:16 AM
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Auto transmission bucking 1-2 and 2-3 shifts

So I'll try to keep it brief while giving as much of the full picture as I can.

We picked up the wife's 2013 JKU with just shy of 60k on the odometer. 3.5" AEV lifted, all proper with drag link flip and whatnot on 35's. Speedometer properly calibrated, so hopefully that means shift points also in proper place. Now at 68k miles and still exhibiting the same symptoms it always has...

So, since we bought it, it's had this issue of bucking on 1-2 and 2-3 shifts in D, and we've done some light troubleshooting....
1) There's no grinding, scraping, or "cachunk" noises that go along with the bucking itself, only a bit of a "thud" when the next gear engages.
2) We've changed Trans fluid and filter, and tcase fluid. Doing these at the same time was probably not the best troubleshooting, but such is life. These seemed to bring the bucking down a little, but probably just placebo affect.
3) Engine RPM associates indirectly with bucking. On shift point for 1-2, engine will spin up a bit as it bucks and then a slight "thud" as 2nd gear engages. Same is true for 2-3 shifts, with a 50/50 chance of engine RPM increasing momentarily (maybe 1/4 second duration, RPMs up 50-100) after the bucking, then a slightly harder "thud" into 3rd gear.
4) This happens most often when being fairly gentle on the accelerator, and when I drive the JKU, I try to give it a mix of gentle and "spirited" acceleration. On spirited acceleration the bucking is either non-present or just barely noticeable 80% of the time, and 20% of the time just as bad as when being gentle on the accelerator. When being gentle, it's more like 95% certainty it'll buck.

Questions, comments, thoughts? Have I missed something so monumentally stupid in troubleshooting that I deserve to have my man card confiscated? Should I give it a go in manual-shift mode to see if the problem persists?

Thanks
O_E

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Prior/Prior/Sold - 1995 Hunter Green YJ - SOA, 35's, etc... More rust than vehicle
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Old 09-01-2017, 08:18 AM
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Forgot to mention, I did search before posting this, and found nothing that mirrors the symptoms we're seeing. Looking for bucking found plenty of manual transmission questions, and folks having problems with Reverse to Drive shifts in 4hi. All the above I posted happens in 2WD. Haven't had much chance to drive it around in 4WD...

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Prior/Prior/Sold - 1995 Hunter Green YJ - SOA, 35's, etc... More rust than vehicle
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Old 09-01-2017, 02:13 PM   #3
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Have you checked for codes? Not all trans. problems will trigger a code, but that should be checked right after the fluid level is checked (operating temp. in park) and any and all trans. related computer updates. If the fluid is fine, there are no codes and all updates have been completed then the usual suspects with that type of problem are solenoid packs, valve body and torque converter. Since it seems to shift more normally at increased rpm's you might be looking at a solenoid pack issue, given that there aren't any updates that haven't been completed. Plus, are you sure that the gearing wasn't changed from stock by the previous owner.
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Old 09-02-2017, 08:27 AM   #4
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I had a similar issue. I'll try to keep this as short and sweet as possible.

2013 JK -- When I was approaching 60K miles my transmission would not automatically downshift from 4 to 3. The issue continued to get worse. It expanded to other shift patterns. I had the thump just like your are describing. However, it would shift fine if I manually shifted gears. No problem at all.

There was no MIL.

The transmission shop that I frequent just wanted to dump a whole new transmission in. I wasn't satisfied with that answer and set out to actually break something. I drove it hard, really hard, ignoring all the warning signs that something wasn't working properly. I got a MIL.

Several codes were in there indicating that the input speed sensor performance was erratic and the transmission couldn't utilize torque management because of that.

The speed sensors are on top of the valve body, soldered to a conductor plate. I ended up replacing the whole plate, it was only about $150 on amazon.

On the next test drive, weird things were still happening. I followed my same troubleshooting procedure. It needed a crank sensor too.

Let me know if you'd like further assistance. Finding information on our transmission is easier if you use Mercedes Benz NAG1 as keywords.

I can e-mail images too if that helps.
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Old 09-02-2017, 08:34 AM   #5
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I've had problems like this as well. I also struggled to diagnose.

1. Try manual shift mode.
2. The speed sensors in these sit on top of the valve body and get dirty. Once they are dirty the computer struggles with torque management.
3. Believe it or not crank shaft sensors can cause weirdness like this.
4. Not all codes will light the MIL, some may show as pending.
5. Sometimes, throw caution to the wind and just drive it hard, you'll be surprised how the codes start flying and give you a baseline to work off.
6. The conductor plate in these transmissions are known to slowly fail. The MB guys pretty much consider it a wear item.
7. Using Mercedes Benz NAG1 as keywords will yield a lot more information when searching for information on our transmission.
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Old 09-25-2017, 12:24 PM
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Quote:
Originally Posted by Bertman View Post
I've had problems like this as well. I also struggled to diagnose.

1. Try manual shift mode.
2. The speed sensors in these sit on top of the valve body and get dirty. Once they are dirty the computer struggles with torque management.
3. Believe it or not crank shaft sensors can cause weirdness like this.
4. Not all codes will light the MIL, some may show as pending.
5. Sometimes, throw caution to the wind and just drive it hard, you'll be surprised how the codes start flying and give you a baseline to work off.
6. The conductor plate in these transmissions are known to slowly fail. The MB guys pretty much consider it a wear item.
7. Using Mercedes Benz NAG1 as keywords will yield a lot more information when searching for information on our transmission.
Sheepishly coming back to this 3 weeks later, having only done one of the above... I tried manual shift mode, and it was smooth as butter. Does that point one direction or another? It's one of those things I don't want to just throw parts at, and knowing my luck driving it hard will break something...

Thanks, everyone, for the advice, hoping one step at a time will get this resolved before things get too broken to salvage.

Thanks
O_E
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Wife's - 2013 True Blue JKU 4-dr Sport Unlimited - AEV lift, 35's, regeared, JWS headlights
Prior/Sold - 2003 Audi RS6 - RNS-E, KWV3's, K40HW, Execu-rocket
Prior/Prior/Sold - 1995 Hunter Green YJ - SOA, 35's, etc... More rust than vehicle
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Old 09-26-2017, 09:02 AM   #7
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Originally Posted by Other_Erik View Post
Sheepishly coming back to this 3 weeks later, having only done one of the above... I tried manual shift mode, and it was smooth as butter. Does that point one direction or another? It's one of those things I don't want to just throw parts at, and knowing my luck driving it hard will break something...

Thanks, everyone, for the advice, hoping one step at a time will get this resolved before things get too broken to salvage.

Thanks
O_E
I'd say that a faulty sensor is causing your truck to not be able to utilize torque management. In my experience I've had the speed sensor and the crank sensor cause these problems. The speed sensor is a bigger job than the crank sensor. Speed sensor will take a couple hours, crank sensor is about 5 minutes. So I wouldn't just want to throw parts at it. I'd get a good code reader on it. Something that can detect Pending codes. I've had good luck with Innova. I'd go all in and get yourself something with ABS and SRS access. It really will eliminate a lot of guess work.
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Old 09-26-2017, 11:04 AM
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I'd say that a faulty sensor is causing your truck to not be able to utilize torque management. In my experience I've had the speed sensor and the crank sensor cause these problems. The speed sensor is a bigger job than the crank sensor. Speed sensor will take a couple hours, crank sensor is about 5 minutes. So I wouldn't just want to throw parts at it. I'd get a good code reader on it. Something that can detect Pending codes. I've had good luck with Innova. I'd go all in and get yourself something with ABS and SRS access. It really will eliminate a lot of guess work.
Thank you sir. I had the Jeep at a local shop this morning to help with parking brake adjustment. They hooked up their scanner and found no codes set or pending. Ugh. They seem to think that the issue has to do with the tune that was done via AEV Flashcal by the previous owner. May be time for me to get a real tuner?

O_E
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Prior/Prior/Sold - 1995 Hunter Green YJ - SOA, 35's, etc... More rust than vehicle
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Old 09-26-2017, 11:18 AM   #9
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Flashcal or Flashpaq ? Flashcal doesn't touch your TCM.
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Old 09-26-2017, 11:29 AM   #10
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tranny is warrantied for 100,000 miles/5 years on your year jeep so I would take it in and see what they say.
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Old 09-26-2017, 01:08 PM   #11
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Thank you sir. I had the Jeep at a local shop this morning to help with parking brake adjustment. They hooked up their scanner and found no codes set or pending. Ugh. They seem to think that the issue has to do with the tune that was done via AEV Flashcal by the previous owner. May be time for me to get a real tuner?

O_E
I'd highly doubt it. I've done more than a few tunes on vehicles since a 2001 vintage. The only time I ever ran into a problem was over battery voltage while writing a tune. I'm talking full blown custom LS type stuff. An off the shelf tuner isn't going to cause these kinds of problems. It worked fine with that tune in it for many miles? Correct?

I've found the MOPAR dealer network around me to be rather useless. I've handed them already diagnosed warranty work and they still failed.

If you don't want to invest in a code reader or push the truck to the limit, I'd suggest pulling the crank sensor and looking for gunk built up/cleaning it. Next, I'd drop the valve body and do the same with the speed sensors.

If those two options don't work, the cam sensor is next in line.
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Old 09-26-2017, 01:16 PM   #12
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I just re-read this whole post. In addition to my previous post, you want to be sure that you have a strong battery. Under voltage and Over voltage can have a huge impact as well.
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Old 09-26-2017, 01:18 PM   #13
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.....and by local shop, with all do respect, do you mean a dealer, a performance shop or an old dude with a $14.99 OBDII?
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Old 09-27-2017, 01:52 PM
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Quote:
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I'd highly doubt it. I've done more than a few tunes on vehicles since a 2001 vintage. The only time I ever ran into a problem was over battery voltage while writing a tune. I'm talking full blown custom LS type stuff. An off the shelf tuner isn't going to cause these kinds of problems. It worked fine with that tune in it for many miles? Correct?

I've found the MOPAR dealer network around me to be rather useless. I've handed them already diagnosed warranty work and they still failed.

If you don't want to invest in a code reader or push the truck to the limit, I'd suggest pulling the crank sensor and looking for gunk built up/cleaning it. Next, I'd drop the valve body and do the same with the speed sensors.

If those two options don't work, the cam sensor is next in line.
Previous owner tuned it, assuming AEV flashcal or procal since it was with an AEV 3.5" lift. Agree the dealer network is useless thus far, but I have yet to take it into the one dealer who might be able to help due to the traffic getting there and back (6 miles, an hour plus each way in bumper-to-bumper). I don't have the cash to throw parts or getting a multi-hundred-dollar tuner.

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I just re-read this whole post. In addition to my previous post, you want to be sure that you have a strong battery. Under voltage and Over voltage can have a huge impact as well.
Brand new battery under previous battery's warranty (thanks, Triple A!), symptoms remain.

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.....and by local shop, with all do respect, do you mean a dealer, a performance shop or an old dude with a $14.99 OBDII?
A well-respected performance / repair shop used their thousand-dollar OBDII box to try pulling codes, all was clean.

When I search for crank sensor, all I can find is camshaft position sensors and they don't seem like the type I could easily pull and de-gunk. Any chance you could be a bit more specific?

Thanks
O_E

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Prior/Sold - 2003 Audi RS6 - RNS-E, KWV3's, K40HW, Execu-rocket
Prior/Prior/Sold - 1995 Hunter Green YJ - SOA, 35's, etc... More rust than vehicle
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