FAD Failure

[Andy29847]

i'd say the other thing that it could "hurt" is wear on driveline -- could wear out my driveline u-joints quicker with the harmonic vibration at highway speed so I'm going to try to just keep it real slow lol

I get it. You have a vibration. You think it is the FAD. My perception is that the FAD is either on or off or broke. The truck should operate without vibration if it is on or off. If it is broke, you need to know that too.

What is causing the vibration? That would be my concern. An easy first thing to do would be to disconnect the front drive shaft and see if the vibration changes. Rotating the tires would be another thing to try.

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[jnack]

I get it. You have a vibration. You think it is the FAD. My perception is that the FAD is either on or off or broke. The truck should operate without vibration if it is on or off. If it is broke, you need to know that too.

What is causing the vibration? That would be my concern. An easy first thing to do would be to disconnect the front drive shaft and see if the vibration changes. Rotating the tires would be another thing to try.

agreed it's either stuck (electrical) or stuck (mechanical failure).

the vibration is caused by the drive shaft angle being too great for higher speed use. If i had minimal lift it might not be an issue but I have 4" of lift with 6.5 degrees of caster. my adams 1350 front driveshaft is fine for what it's designed for: 4wd at reasonable speeds but it was never intended to be spinning when the vehicle is @ highway speeds.

I was considering getting a solid front axle shaft but when I spoke with RCV they recommended against it unless it's a trailered strictly wheeling rig bc on highway with higher lifts the front drive shaft causes vibrations (what I'm experiencing). with the FAD stuck it's acting like a solid axle shaft thus rotating the driveshaft due to tires moving

 

[Jteakus]

Pull the FAD and see what is happening.

 

[Andy29847]

agreed it's either stuck (electrical) or stuck (mechanical failure).

the vibration is caused by the drive shaft angle being too great for higher speed use. If i had minimal lift it might not be an issue but I have 4" of lift with 6.5 degrees of caster. my adams 1350 front driveshaft is fine for what it's designed for: 4wd at reasonable speeds but it was never intended to be spinning when the vehicle is @ highway speeds.

I was considering getting a solid front axle shaft but when I spoke with RCV they recommended against it unless it's a trailered strictly wheeling rig bc on highway with higher lifts the front drive shaft causes vibrations (what I'm experiencing). with the FAD stuck it's acting like a solid axle shaft thus rotating the driveshaft due to tires moving

That makes it a no brainer. Fix the FAD or pull the driveshaft for your trip.

 

[hjdca]

- had a long drive, noticed some driveline vibrations highway 60+ MPH 1.5-2k RPM (mostly around 1.5-1.6k -- this is a diesel 8th gear)
- shortly after arriving home got a service 4wd light on dash ( i thought this was due a failed repair of the FAD connector harness that broke on trail last yr)
- double checked FAD connect which seems intact
- when I jack up the vehicle can engage 4wd & lockers
- with vehicle jacked up when you push front tires forward it spins the front drive shaft.

My conclusion is FAD failure, likely actuator -- maybe coupler. I don't hear any grinding noise coming from the front axle so less likely think it's shattered.

I've got a big overland trip planned to leave in 2 days so no chance this will be fixed by then...plan is to just drive real slow on the highway to avoid the drivetrain vibrations. Hopefully it holds up....

Has this happened to anyone? Do you think the diagnosis makes sense?

The driveline vibration can be unrelated to the "service 4WD light" on the dash. Most of the time the "Service 4WD light" on the dash is from the Locker sensor in the rear diff. You can clear that by rebooting with your Tazer... Also, keep that rear diff oil clean... It is the metal particals that get into the sensor that make it malfunction.
For the Vibration, I would try decreasing the pinion angle, thus, decreasing the caster, ie. tilt the pinion up a little. Maybe half a turn on all the control arms, and see if that fixes it.

Note: 1350 driveshafts are known to take less pinion angle than 1310 driveshafts and get vibration. So, in other words with the same pinion angle, a 1350 driveshaft can vibrate, while a 1310 driveshaft will not. The guys at Adams will also tell you this.

 

[jnack]

That makes it a no brainer. Fix the FAD or pull the driveshaft for your trip.

pulled drive shaft off front diff and just tied it off to front skid so it's still attached at transfer case & vibration is gone.

gonna put the 4 bolts on once I get to trail since i've got a few hundred off road miles planned & then will plan to get it properly fixed when I get back

 

[jnack]

The driveline vibration can be unrelated to the "service 4WD light" on the dash. Most of the time the "Service 4WD light" on the dash is from the Locker sensor in the rear diff. You can clear that by rebooting with your Tazer... Also, keep that rear diff oil clean... It is the metal particals that get into the sensor that make it malfunction.
For the Vibration, I would try decreasing the pinion angle, thus, decreasing the caster, ie. tilt the pinion up a little. Maybe half a turn on all the control arms, and see if that fixes it.

Note: 1350 driveshafts are known to take less pinion angle than 1310 driveshafts and get vibration. So, in other words with the same pinion angle, a 1350 driveshaft can vibrate, while a 1310 driveshaft will not. The guys at Adams will also tell you this.

the driveline vibration is 100% coming from FAD issue. That may or may not be why I have the service 4wd light. my codes are U1159 Lost Communication with Automatic Sway Bar System & U403: Implausible Data Received From T-Case

The front drive shaft is NOT supposed to spin in 2wd, but since the FAD is messed up it was. When I disconnect the front drive shaft it goes away. My caster is set for excellent road manners with a 4" lift, no sense messing with my alignment when the reality is the front drive shaft was never intended to spin going 65 mph. i'll have to get the FAD fixed when I return from my trip

 

[jnack]

whats the diagnostic code the vehicle is throwing? It is possible it is related to an abs sensor. My truck had a bad abs wire which caused the 4wd service light to pop on. I used my scanner and it told me left rear speed sensor out of bounds. I switched it and everything cleared up.

my codes are U1159 Lost Communication with Automatic Sway Bar System & U403: Implausible Data Received From T-Case

 

[Andy29847]

The front drive shaft is NOT supposed to spin in 2wd, but since the FAD is messed up it was. When I disconnect the front drive shaft it goes away. My caster is set for excellent road manners with a 4" lift, no sense messing with my alignment when the reality is the front drive shaft was never intended to spin going 65 mph. i'll have to get the FAD fixed when I return from my trip

Stock drive shaft?

 

[jnack]

Stock drive shaft?

Adams 1350

 

[Andy29847]

Adams 1350

Thanks for the answer. I'm still running at stock height but I'm looking. I've read that the stock driveshaft should be replaced if you lift over 2" - 3" inches. Then I read where the actual lift many owners get from their kits exceeds the advertised lift. It sure confuses a guy.

I'd guess your Adams shaft has a double Carden joint near the transfer case. Normally with a double Carden drive shaft, you shouldn't have vibration. I am not sure how the 1350 joints affect that. I ran a Tom Woods shaft on the front of my TJ (4" lift). It worked great, but it was a pain to service. The only way to really inspect and service the joints on the shaft was to remove it. FWIW, the center joint of the double Carden can cause problems.

 

[Rusty PW]

The driveline vibration can be unrelated to the "service 4WD light" on the dash. Most of the time the "Service 4WD light" on the dash is from the Locker sensor in the rear diff. You can clear that by rebooting with your Tazer... Also, keep that rear diff oil clean... It is the metal particals that get into the sensor that make it malfunction.
For the Vibration, I would try decreasing the pinion angle, thus, decreasing the caster, ie. tilt the pinion up a little. Maybe half a turn on all the control arms, and see if that fixes it.

Note: 1350 driveshafts are known to take less pinion angle than 1310 driveshafts and get vibration. So, in other words with the same pinion angle, a 1350 driveshaft can vibrate, while a 1310 driveshaft will not. The guys at Adams will also tell you this.

A little correction here on the locker sensors. The metal particles collect around the magnet on the sensor. Not in the sensor. This is easy to clean with a Q-tip. What gets into the sensor is gear lube that weeps in because the sensors are not potted to seal them. The lube inside them ruins them. Here's the thread on potting the sensors.

https://www.jlwranglerforums.com/forum/threads/locker-position-sensor-potting-dana-44.59581/

 

[Rusty PW]

my codes are U1159 Lost Communication with Automatic Sway Bar System & U403: Implausible Data Received From T-Case

Does your sway bar disconnect still work?

 

[chorky]

Thanks for the answer. I'm still running at stock height but I'm looking. I've read that the stock driveshaft should be replaced if you lift over 2" - 3" inches. Then I read where the actual lift many owners get from their kits exceeds the advertised lift. It sure confuses a guy.

I'd guess your Adams shaft has a double Carden joint near the transfer case. Normally with a double Carden drive shaft, you shouldn't have vibration. I am not sure how the 1350 joints affect that. I ran a Tom Woods shaft on the front of my TJ (4" lift). It worked great, but it was a pain to service. The only way to really inspect and service the joints on the shaft was to remove it. FWIW, the center joint of the double Carden can cause problems.

You're not wrong - it is very confusing - especially considering these lift manufacturers can't get their descriptions and numbers straight. Even MOPAR sometimes nets more than advertised lift. But to be fair, it doesn't help that weight is a huge variable. But it would be nice if there could be a more accurate and standardized spec like "3.5" over stock unloaded" or 2" over stock at max GVW" or something..... I also have a double cardigan on my TJ and it's never had an issue in the last 8 years. I have completely neglected to grease it too. But from all the reading I have done it seems the consensus is a new driveshaft will be needed eventually for anything over 2.5" - which is pretty much everything. It's not so much a matter of if, but when. Now larger lifts like 4+ it is kinda needed right away. I have even heard different suggestions by 2 or 3 different and very well known off road shops. So. I think it's one of those things you just gotta plan on doing in the future.

A little correction here on the locker sensors. The metal particles collect around the magnet on the sensor. Not in the sensor. This is easy to clean with a Q-tip. What gets into the sensor is gear lube that weeps in because the sensors are not potted to seal them. The lube inside them ruins them. Here's the thread on potting the sensors.

https://www.jlwranglerforums.com/forum/threads/locker-position-sensor-potting-dana-44.59581/

I thought the new ones that was fixed...in early 2022 or something. Didn't Jeep resolve this by adding filler (potting?)? Maybe I'm mistaken....

 

[Rusty PW]

. I thought the new ones that was fixed...in early 2022 or something. Didn't Jeep resolve this by adding filler (potting?)? Maybe I'm mistaken....

Not that I know of. I potted my sensors on my 2/17 Rubi.

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