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Discussion Starter · #1 ·
I have a 2003 F-250 with the 7.3L. This last week I was towing our camper up to the camp spot about 2.5 hours from home. All was well then the last 15 miles or so it started.

On an uphill grade and only on turns left and right there was a horrible shift in the rear axle and popping noise. It never happened on flat turns or down hill just uphill. We got off the pavement and started up the hill to camp and still same thing.

The next day I drove into town (about 20 miles) without the trailer and never noticed any popping or shifting so I figured it had something to do with the trailer. Then on the way back, once we got off the pavement the symptoms returned. Uphill only on turns, popping and shifting. Like the axle shifts a couple inches one way or the other.

Some Google searching suggested it might be the clutches in the limited slip so I went back to town and changed out the gear oil with new synthetic 75W-140 and a bottle of friction modified (in the parking lot).

Drove back to camp and it was not as bad but did happen again. Then we came home yesterday towing the trailer. Not till we got off the interstate did it start to happen, uphill only on turns.

So it seems it does not do it when the axle fluid is cold but happens once it gets good and warmed up.
Any suggestions?
 

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if this is not a new to you truck and this issue just popped up I would eliminate the limited slip diagnosis ( but not eliminate the rear end altogether )

they do not behave differently with a trailer and if anything they don't just start working aggressively with age


first thing i would do is a tighten and torque ( put a wrench on the u bolts / and other associated fasteners and look at each leaf of the springs for breakage/ shifting

also look at the axle pad to spring surface for any noticeable movement

now if you could elaborate on the diagnosis of "shifting" that may help others figure this out
 

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Discussion Starter · #3 · (Edited)
if this is not a new to you truck and this issue just popped up I would eliminate the limited slip diagnosis ( but not eliminate the rear end altogether )

they do not behave differently with a trailer and if anything they don't just start working aggressively with age


first thing i would do is a tighten and torque ( put a wrench on the u bolts / and other associated fasteners and look at each leaf of the springs for breakage/ shifting

also look at the axle pad to spring surface for any noticeable movement

now if you could elaborate on the diagnosis of "shifting" that may help others figure this out
Thank you for your response.

I have owned the truck for about 3 years now and have never experienced this.

In terms of "shifting" it feels like the whole *** end of the truck literally shifts a couple inches one way or the other depending on the turn. This happens at slow speed (less than 5mph) and greater speeds like 20-30. I cannot say I have noticed it at 50+.

I looked underneath and did not notice any broken/shifted components but without knowing what to look for I could have easily over looked something. I will go back and inspect again.

I have verified u-joints are solid and no slop in the drive shaft. I lifted each rear wheel off the ground and wiggled/lifted/pulled on each tire to see if the axle or bearings showed movement which they did not.

One thing of curiosity is it does not happen when the axle is cold, I made many firewood runs while camping (driving around looking for wood near camp) and never noticed it. It seems to require some 20-40 miles of run time before this starts to happen and again, only on uphill turns. The more sharp the turn, the worse the pop. Almost reminds me of the detroit locker I had in a Jeep years ago. It happens on pavement and dirt so it's not a binding thing like the detroit locker would do.
 

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maybe drop the diff cover ( clean it well before so you can save your new oil ) and take a peek inside maybe it does have other than a clutched OEM LS ?)

but the shifting feel has me more concerned and focused on the springs/spring pad locating dowel, leaf ,hanger etc

however, none of those should go away with temperature increase
 

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Discussion Starter · #5 ·
maybe drop the diff cover ( clean it well before so you can save your new oil ) and take a peek inside maybe it does have other than a clutched OEM LS ?)

but the shifting feel has me more concerned and focused on the springs/spring pad locating dowel, leaf ,hanger etc

however, none of those should go away with temperature increase

When I changed the fluid in the parking lot I inspected the spider gears, etc. Nothing "looked" damaged, there were no broken pieces or chunks in the bottom of the pumpkin. There was some metal grit in the oil, I assume from clutch wear. Wish I had taken a picture now, I do not know what the OEM LS clutch packs look like to compare.
 

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Discussion Starter · #6 ·
Having drove around for the past few days I am unable to produce the pop and shift of the rear axle. Is it possible the new friction modifier takes awhile to soak into the clutches? So confused.....
 

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it does take a while for the additive to migrate inside the clutch packs and coat the friction surface. a few figure 8's are helpful when trying to get the modifier dispersed in a hurry
but to revisit the original issue the limited slips don't usually just start working more aggressively for no reason

and a "pop and shift" is not a typical LS complaint a "Chatter" while turning is a typical complaint of a LS that could use some additive
 
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