wheel bearing noise or pinion bearing noise ?

[grasshopper]

Hi all. I have a noise coming from the back of the car ..76 (Spider). Its a whining or humming type sound. I can hear it when i am going really slow or when i am going fast. Gets higher in pitch as i go faster. It does not seem to change when i put load on either side. Can it be a rear wheel bearing making this noise ? I am really hoping it is not diff related. Anyone have this problem before that can offer some insight ? Thanks.

[18Fiatsandcounting]

I have not had any experience with this recently in a Fiat, but I have had issues with my other cars. In my case, the front pinion bearing in the differential was more of a whine or hum while at speed, while the rear wheel bearings were more of a rumble or clunking at low speed (in severe cases).

So, I hate to say it, but it sounds like it could be the differential, likely the front input bearing. But, before going too much further, I'd put the rear axle solidly up on jack stands, remove the rear tires, remove the brake calipers and try to move both rear axle flanges up and down, side to side, in and out. If no movement there, then try the same on the input to the differential.

By the way, the first thing I would check is that your differential has enough oil in it. If it is really old, it might be worth just changing it out and seeing if that helps. Make sure you use the EP (extreme pressure) oil.

-Bryan

[grasshopper]

Thanks Bryan. To make matters worse, i have a 124 Sport Coupe with the same issue ! lol I know for sure that the Coupe had the wrong oil in it for several thousand miles. I had the gl 1 in it. Now both have HP oil. Looks like it will be a long winter working on the cars.

[18Fiatsandcounting]

Ahhh, Grasshopper, yes, you must use one of the EP oils for the differential (not the transmission). GL-4 or GL-5, 80-90W. Anything else and you'll have a problem over time.

-Bryan