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4 Wheel Lock in 4WD Auto ?!?!

Invictus

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Good evening,

Last week I was driving into town on the highway. It was quite icy, so I decided to try out 4WD Auto for the first time. To my understanding, if the rear wheels lose traction under load, the front kicks in. Everything was going fine until I turned into a gas station, and that's where my adventure begins.

Making a tight turn, the front end started binding and hopping. All four wheels were in full lock. I made sure it was in Auto and not 4H, so I put it back in 2WD then switched between 4H, 4L, and back to 4A. Same thing happened, all wheels locked up and had difficulty on dry pavement at about two miles per hour, making a turn.

I dropped the truck off at the dealership this morning, and the service shop called me back this afternoon. They said that the rear tires were 5-6 thirty-secondths of an inch more worn than the front tires, which causes the wheel speed sensors to turn faster on the rear than the front, due to tires being a 'much' smaller diameter. Their professional opinion is that I should replace all four tires so that they all match in diameter, and then the wheel speed sensors will then all match up.

Anyone heard of anything like this before?

Any help is appreciated.
 
R

Rob5589

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Sounds plausible. Uneven tire wear or pressure can cause limited slips and lockers to chirp tires or push under acceleration. I suppose the same could happen if there is a difference between the front and rear tire diameters, although I admit to having very little knowledge of the auto 4wd system.
 

spaightlabs

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What kind of tires, OEM or nah, how many miles on 'em, do ya rotate 'em and how often?

If you have 30K on them and they haven't been rotated as often as they should, it's on you imho.
 

devildodge

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Yes, different diameter tires will screw with 4wd Auto. (To include uneven wear with similar tires.) Has been that way since the 70s.

Grand Cherokee owners really had it bad.

That is why most tire places will not replace one tire. If it RWD they will do 2 on the rear instead of all 4, but if it is 4wd...they will usually not do it, they want you to replace all 4.

If you haven't rotated your tires...or like to listen to that Hemi roar at the expense of tire rubber...this is definitely your issue and new tires will fix it.
 

Nomoretruck

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Yes, different diameter tires will screw with 4wd Auto. (To include uneven wear with similar tires.) Has been that way since the 70s.

Grand Cherokee owners really had it bad.

That is why most tire places will not replace one tire. If it RWD they will do 2 on the rear instead of all 4, but if it is 4wd...they will usually not do it, they want you to replace all 4.

If you haven't rotated your tires...or like to listen to that Hemi roar at the expense of tire rubber...this is definitely your issue and new tires will fix it.
X2 to above and its not restricted to Jeep/RAM by any means. I blew out a sidewall on my 1st set of (Ford Edge AWD) Pirelli’s that were down to about 6-7/32nds. The tire shop refused to do anything except all 4, they had printed up warnings taped to their counter for AWD owners. As I was traveling and felt sorta “stuck”, I went ahead on 4 new Pirelli’s. Then I researched the web for my specific drivetrain and yep, most forum posts and other sites agreed that it was not smart to play with differing tread depths, even axle to axle.
Some AWD setups are more forgiving than others so YMMV but mine said “all 4” right in the owners manual. Sigh. That was an $800 rock.
 

Invictus

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Problem solved. I didn't think 5/32" in tread difference would make that much of a difference, but apparently it does. Thanks for the comments guys, got the truck back today and she's all good to go.

I have 23,000 km on the old tires (never rotated) and do about 1/4 of my driving on gravel roads, so that may have played a part in it. I do know that the drive tires (on gravel) will wear quite more than the non-drive tires (front in this case) due to slippage.
 

devildodge

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Why this is a great forum. Many more members here offer help, rather than immediately blaming the truck and FCA.

Glad to hear the truck is performing well after the new tires. Hope these tires with some regular rotation last longer for you.
 

Nomoretruck

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Problem solved. I didn't think 5/32" in tread difference would make that much of a difference, but apparently it does. Thanks for the comments guys, got the truck back today and she's all good to go.

I have 23,000 km on the old tires (never rotated) and do about 1/4 of my driving on gravel roads, so that may have played a part in it. I do know that the drive tires (on gravel) will wear quite more than the non-drive tires (front in this case) due to slippage.
The forum told me that tires can be “shaved” down (tread) to match the existing 3, that would have been less expensive than buying 4 but... something weird in my head about paying $30 to get 1/2 the tread shaved off...

Just edited this reply due to finding this OLD info from Tire Rack on this subject, begin quote:

REPLACING ONE TIRE ON AN AWD CAR?
Thursday, September 30, 2010 by Gary Stanley
Have you experienced a tire failure on a vehicle with all-wheel drive? Unfortunately, the complex systems that deliver power to all four wheels are sensitive to mixing tires with different overall diameters. Simply installing one new tire runs the risk of drivability problems or expensive damage, so you must follow some guidelines when replacing one tire.

Some manufacturers have set perameters for matching the tires used on their four-wheel drive and all-wheel drive vehicles.
  • Audi: As published in their vehicle owner's manual, "rolling radius of all four tires must remain the same" or within 4/32-inch of each other in remaining tread depth
  • Porsche Cayenne: Within 30% of the other tire on the same axle's remaining treadwear
  • Subaru: Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth
Is your make not listed? We strongly suggest checking with the manufacturer directly or replace all four tires.

If the idea of having to replace all four tires sounds too expensive, there is another option: shaving. Tire Rack can reduce the tread depth of a new tire via the removal of tread rubber on a specialized machine that operates as a tire lathe. Prices vary based on how much tread depth must be removed, but is normally about $25 per tire. While shaving off perfectly good tread may seem counterintuative, consider the additional costs of having to replace all four tires (or worse, the driveline damage from mixing tires with different depths!).
You can read more about this in "Mixing Tires."
End of copied information
 
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Deezl

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Much cheaper to rotate your tires every oil change, if not every 5000mi, Guys and Gals

Sent from my SM-G965U using Tapatalk
 

TruckDriver

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The forum told me that tires can be “shaved” down (tread) to match the existing 3, that would have been less expensive than buying 4 but... something weird in my head about paying $60 to get 1/2 the tread shaved off...

This was something I was told to do with an old Scoobie STi I owned, but option two is buy a good tread-depth gauge and go do some burnouts, it's less fun than it sounds, because it doesn't take much slippage to get tires to 'shave' down to the same or near identical depth
 

Nomoretruck

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This was something I was told to do with an old Scoobie STi I owned, but option two is buy a good tread-depth gauge and go do some burnouts, it's less fun than it sounds, because it doesn't take much slippage to get tires to 'shave' down to the same or near identical depth
Ha ha, I can just see me trying to justify this to her... o_O:unsure::whistle:
 

Damion

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Wow a few 32nds isn’t much tolerance for the system. I could see a half inch or better.
 

Nomoretruck

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Wow a few 32nds isn’t much tolerance for the system. I could see a half inch or better.
One of the older Jeep forum.com threads (tire tread depth transfer case problems) was a question about excessive wear when locked in. A poster answered this quote from Tire Rack (admittedly not Jeep):
Quote:
“Some four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.

This necessitates that four-wheel drive and all-wheel drive vehicles use tires that are very closely matched. This is because different diameter tires roll a different number of times each mile as a result of the variations in their circumferences. Tire diameter variations can be caused by accidentally using different sized tires, tires with different tread designs, tires made by different manufacturers, different inflation pressures or even tires worn to different tread depths.

As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile. While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain.

This makes maintaining the vehicle manufacturer's recommended tire inflation pressures and using "matched" tires on all wheel positions necessary procedures to reduce strain on the vehicle's driveline. Using "matched" tires means all four tires are the same brand, design and tread depth. Mixing tire brands, tread designs and tread depths may cause components in the vehicle's driveline to fail.”
End of copied post

Now wether the 19’ RAM diffs operate in such a way as this could be an issue long term, I don’t know. I don’t think 4A operation is an issue as there isn’t anything locked up until wheel spin. If you are driving a long time in 4L with an E-locker then maybe?

I’m not saying this will be an issue at all for the average truck owner unless your tires are severely mismatched in height/diameter. It’s just information.
 

Biga

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A couple 8ths of an inch should not make that much difference. If you inflate your tires the same front to back, your front tires will be shorter anyway because the extra weight up front deflects the sidewalls more in turn making the front tires shorter then the rear.
 
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Nomoretruck

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Lets hope so, based on there not being a lot of griping on forums about blown up AWD transfer cases out there, might just be “marketing”. It’s happened before that an industry is a little “overzealous” shall we say?
 

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