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Groaning noise when turning

I bought a 2003 Ford F-150 4x4, the 7700 series which I have heard called the “Heavy Half Ton”. It has the 5.4L Triton V8 but a GVWR of 7700 lbs. a 3/4 ton suspension, tranny cooler, and a 3.73:1 limited slip rear differential. It has about 155K kms (I am living in Alberta, Canada at the moment).

I have two problems that may or may not be mutualy exclusive? The main issue is when I am going from a dead stop to a left or right hand turn there is a horrible groan that comes from the rear end of the truck, but stops as soon as I am going straight. It is intermittent when the vehicle is cold or first running after being stopped for awhile (sometimes it will do it sometimes not). but if I have been driving for some time it will always make the noise on low speed turns.

I suspected that it was the rear differential clutch pack was sticking, and on inormation from a gear-head friend, drained the rear-diff oil and replaced it with manufacturers recomended synthetic diff oil and put in one bottle of an additive to lubricate the clutch pack.

It made no difference!?! And the sound seems to be getting worse?

Also, and this may or may not be related, there is a squeaking noise coming from what feels like the U-joint when I go in reverse? It only happens in reverse and it is getting louder too.

I had a Ford dealership quote the clutch pack at ~$300 CDN and the labor at ~$400 CDN. Also they priced the U-joint at about $50 CDN and the labor at about 1.5 hrs.

Does this seem like the right solution to these issues? Replacing the rear diff clutch pack and U-joint? And are these prices fair-ish? Is there anything else that this could be?

Any help or advice would be greatly appreciated.

They’re both possible causes, but I’d be very relictant to spend that much cash without first trying to determine if those are the actual sources of the noises. There are other possibilities. Groaning could be as simple as a bushing or spring shackle, the sqeaking could be a simple carrier bearing.

Have you had this on a lift yet?

Once just before I bought it, but the only thing I remember that mechanic saying was that the ball joints (in the front?) might need replacing soon? I asked how soon was soon and he said in the next year or so?

I can ask them to check for these other issues as well, I am just wondering if those are the most likeyl causes, since the symptoms are very repetable and only under very specific conditions, i.e. reverse and turning from a stop?

Are you sure that groan isn’t coming from that ball joint? Sound does travel.