captainron19

I Have a 2005 F150 V8 FX4

Lately I have been hearing two strange noises from my the rear of my vehicle and not sure if they are related or not.

1. When at a stop and begin to move while making a sharp turn (either left or right) it seems as if the rear of my vehicle is vibrating a bit (almost as if the tires are having trouble getting traction)

2. This noise does not happen often but on some occasions (maybe once a week) I hear what sounds like a chain dragging under the truck. I would not classify it as a grinding noise but it sounds like metal on metal and like I said sounds like a chain dragging. Checked the undercarriage and nothing is loose or hanging that i can see. I think I did troubleshoot it to the point where it appears to happen when driving up a steep incline. I do not think it is transmission related because it doesn't suddenly stop if I give the truck more gas or even let off the accelerator. The sound only lasts for a few seconds and then stops.

Any thoughts?

BensKingRanch

How many miles on the truck? It could be a lot of things. When is the last time the rear diff fluid was changed or even checked? What all did you check under the truck? Brakes? Diff? Exhaust?

BensKingRanch

Does that noise sound more like a rattle? Possible under light load, like when you are just getting going?

captainron19

Truck has 64k on it. The rear diff fluid was changed approx 1 month ago when I took it in for an oil change.

captainron19

Yes it sounds like a rattle but does not happen when I just begin moving.... last time it happened I was on the highway going about 60 and like I said i think it is happening when going uphill

BensKingRanch

Lets start with the rear end. Did the issue start after the fluid change, or before? Did they put in a friction modifier additive in the diff?

The "rattle" could be several things, I just had a rattle in my work truck, it ended up being the cats coming apart on the inside. You can get under the truck with a rubber hammer or block of wood and knock on the exhaust and see if you hear it rattle, that'll let you know if something is loose and that's a starting point at least.

captainron19

Come to think of it it was non existent before the oil change when they changed out the differential....think I will be taking it back there and have them give it a look over..... thanks on the tip for the rattling noise.... will look into it further.

BensKingRanch

There is a friction modifier (additive) that you are supposed to mix with the differential fluid on a limited slip rear end, If it is not included the rear end can "slip" or chatter on sharp curves. They should have put it in, and if they didn't you can get it at any parts store. It's called "limited slip additive" or "friction additive". It comes in a small tube. Try that, or make the shop add it

BensKingRanch

Any luck?

captainron19

Thanks for the follow up...was away from the computer for a few days. Well Some progress..... the vibration feeling from the rear seems to have dissipated. Took it to the shop where I had the differential fluid changed - they informed me they have the friction modifier fluid already int he oil but he added a little more of it and told me to give it a couple of days and like I said it improved.

But now the rattle sound from underneath is the troubleshooting problem. Like I said it happened rarely (mostly when going uphill). Yesterday I took my boat out and while I was trailering it the noise happened much much more frequent (most likely due to the extra load from the boat) It didnt just happen when going uphill but also on level ground.

Again it doesn't occur when the vehicle shifts and the rattling noise goes away the second I let my foot off of the accelerator. Working at my fire station today and our mechanic is on duty. We just removed the drive train to inspect the u joints. He said everything looked ok and we replaced it. He just took the truck for a spin and I told him to go up the hill near our firehouse where I hear the noise every day when I leave work. He took it up the hill twice (once at normal speed and again with giving it a lot of gas) and the noise would not re-occur for him (GO FIGURE)

Gonna hook up the boat tomorrow and take it out with him with a load on it to see if we can get it to reproduce the sound.