'85 Diesel Truck Groaning Noise at 30 MPH in Freezing Weather

[MST3K]

The 'ol 85 diesel truck is making a loud groaning noise at 30 MPH. Under 30, it's fine. I don't see any leaks, and I don't smell anything out of the ordinary.

The noise kicks in right at 30 MPH. I don't think it's the engine itself, though it might've been running a little harsh in the freezing temps. The motor seems to start up ok, as well, we just put in some new Odyssey batteries.

I drove it on Sunday at highway speeds and it didn't make this noise, nothing close to it. But today in freezing weather, when the truck hit 30, the loud groaning or knocking / whirring noise kicks in. It's really loud. If I had to guess it's well over 70 DB. You can't hear anything but the whirring and knocking if you keep on the accelerator.

Probably unrelated, but the speedometer needle jumps from 30 MPH to 70-80 MPH, at the exact same time the groaning starts.

Could this be the front differential? a wheel bearing?

 

[80t0ylc]

..........Probably unrelated, but the speedometer needle jumps from 30 MPH to 70-80 MPH, at the exact same time the groaning starts..........

There's your best clue, so far. I'd say it's your speedometer cable. You can get one at a pick & pull, usually very reasonable. I replaced the one on my '81 just after I bought it. It was cut in half by the front drive shaft that broke loose when PO had it. Hardest part was hooking it up to the back of the speedometer.

 

[MST3K]

There's your best clue, so far. I'd say it's your speedometer cable. You can get one at a pick & pull, usually very reasonable. I replaced the one on my '81 just after I bought it. It was cut in half by the front drive shaft that broke loose when PO had it. Hardest part was hooking it up to the back of the speedometer.

This was exactly right. It was the speedo cable through and through. Truck is alive and kicking thanks to your advice.

 

[80t0ylc]

Glad to hear it's fixed! Thanks for posting your success. Others can benefit later, especially on a search. That's what helps make this and other forums so useful.