Differential whine

[JohnB27]

So I'm getting my recently acquired '66 FHC sorted and have been taking it on longer drives and slowly expanding my "Radius of confidence" with it. It's running quite nicely now, but one thing that is a little bit of concern is a fairly loud whine from the differential while under load. It feels fine but I'm just wondering if this is indicative of impending problems or just the nature of the beast. I don't recall a whine this loud in my old '67 OTS, but that was years ago, plus I almost always had the top down so wind noise was much more prevalent. Maybe I'm just not used to the cabin quietness of a FHC? What is the forums experience?

I'm thinking of replacing the gear oil with Redline MTL and seeing if that helps.

[Mark Gordon]

I think that most fuel and oil additives mainly benefit the manufacturer's bottom line. Redline products are an exception. When I got my car, the second gear synchronizer was allowing the gears to grind unless I made the shift very slowly. I drained the gearbox and added MT90 and the result was almost like rebuilding the gearbox. I think that you would be wise to drain the diff and add MTL. Periodic changing the oil is good maintenance practice anyway, so what do you have to lose?

[Moeregaard]

I could hear the final drive units in both of my coupes. It was never intrusive, but I knew it was there. I ran 1E30036 for sixteen years and never noticed a change in sound. My guess is that you don't have a problem, but an oil change might quiet things a little.

[chrisfell]

Mine whines. It whined when I bought the car. After 50,000 miles, it is still making a noise. There are speeds when the noise is worse, and speeds when the noise is less. I drive at the latter speed. It is worn and could do with a rebuild, new crown wheel and pinions, new bearings and seals, re-shim to align the teeth correctly, nice coat of paint. Of course, while the cage is out the rear brakes could do with new seals and rubbers, the fluid lines cleaned, rubber ones replaced, and all the suspension bushes and bearings replaced.

Or I could leave it for another 50,000 miles and drive the car at speed where the noise is less. I bought my car to drive so I will probably leave the axle be.

[Moeregaard]

I wouldn't worry about it unless you find metal bits when you change the oil. Out of curiosity, does your car still have the 3.54:1 ratio?

[JohnB27]

Thanks for the advice. I'll not worry about it and replace the diff oil with MTL.