Scraping sound from rear of vehicle when turning slow

70’s Ford 4x4 truck. I’m getting a very noticeable — but intermittent, doesn’t happen every time – metallic scraping sound when turning right at slow speeds. Coming from the rear of the vehicle. Like in neighborhood driving. No unusual sounds when going straight. For the past week the problem seems to have gone away, so I’m playing this one by ear. Hopefully whatever it was has gone away. But I’m ever the worrier.

when it happens, it sounds like if I dragged a big sheet of metal on the road behind the truck. I’m sort of suspicious this sound is from the rear limited-slip differential. Could it be the diff clutches are corroded? Coming loose from their moorings? A differential bearing on the fritz?

Are you in 2 or 4wd, suggest not 4wd

When was the last time the rear diff fluid was changed?


Ford limited-slips are called “Trak-LoK”. If your truck has Trak-Lok it requires an additive to the diff oil to lube the slip clutches. You can get a tube at any parts store and throw it in for less than $10. (Be careful, it smells really bad and clings to you skin for days!!) If that stops the noise then you have your solution.

The intermittent scaping sound from the rear of the truck while turning at slow speed is heard in 2WD. I didn’t try it in 4WD. The rear diff fluid was last changed about 6 years ago. I did check the level about a month ago, while doing a general under vehicle inspection and lube, and the level was full to the fill-port, ok. From the look of the fluid, it also appeared ok, same viscosity and appearance as new fluid. Truck not driven many miles, maybe 3-4K per year. I’ll change out the fluid w/fresh, and put in a new dose of additive. I already have a spare bottle of it. Hopefully that will help, and if not, no harm done, as it is time for a fluid change anyway.

Has anyone here ever experienced this problem? Maybe there is some rust in there that is causing the noise? It almost sounds like there is a small pebble in there that is sometimes getting caught between moving surfaces. I drove it yesterday, and it continues to be silent. So maybe whatever was causing it was ground up and sitting at the bottom of the diff case. Thanks to all for the good comments.

Don’t know about Fords, but I had limited slip in my diesel Olds. They didn’t put the additive in at the factory and you’d get a very serious sounding clunking noise on a slow speed sharp turn. You put the small bottle of whale oil in labeled as some kind of GM additive and drove it in a figure 8 a few times and no more clunking.

The truck also has that clunking noise when turning at slow speeds, especially when being driven for the first time after it has been sitting for a week or longer, then it quiets down after a little driving about, but that is all normal for the early 70’s lockers. It has the Ford additive in the current fluid. I put it in myself, when I changed the fluid 6 years ago. The scraping sound is a new one.

"The intermittent scaping sound from the rear of the truck while turning at slow speed is heard in 2WD. I didn’t try it in 4WD " — Does not matter. The rear diff is always being used, and if it has Trak-Lok then it’s also always being used.

Put more Trak-Lok fluid in. It sounds classically like grinding slip clutch plates. When you put it in, drive forward and backwards in sharp circles several times slowly.