1970 250c?

I just bought a 1970 250C 6 cyl.gas. It runs pretty well except it sounds like its taching out at 65mph on the freeway. Very high rpms. But it seems to shift to all 4 gears. Is this normal? It also has a pretty loud humming noise coming from maybe the drive shaft, especially when you let off the accelarator. Any thoughts?? What should i check out first? Are these common problems on these cars? Thanks for any info, Jeremy

[Mark DiSilvestro]

Jeremy,
If it's shifting through all 4 gears and not slippng, the engine would rev to approx. 3300 RPM. A book I have lists 250/250C engine speed at 100 KM/HR (about 62 MPH) of 3180 RPM with a 3.92 rear axle gear ratio. My book also lists USA versions with a 4.08 ratio which would rev even higher! You should really check yours with a tachometer.
As for humming noises, without hearing the actual sound, my first guess would be wheel or axle bearing or differential gear noise.
good luck, Mark DiSilvestro

Thanks!! I'll check on it.

[cth350]

no wobble, no vibration? Then it's probably not the various rubber bits on the drive shaft. There's a rubber donut at the front and a support bearing in the middle (and in the 114 cars like yours, a rubber donut at the end too).

You haven't owned the car long enough to notice if it's worse in cold weather (right?) The speedometer can make some pretty unusual noises when the cable needs lubrication. Touch the glass of the speedo when the noise is present and see if it changes.

Also, check your tranny fluid level. Consider changing the fluid. If it's burnt and ugly, consider NOT changing the fluid.

-CTH

I dont think its the speedo, Its pretty smooth. Its a loud hum under the car. I just did my axle bearings on my datsun roadster and this does not sound anything like axle bearing noise. Its kind of a whining hum. I think i need to jack the car up and really listen to where its coming from.

[Mark DiSilvestro]

Jeremy,
If not an axle or wheel bearing, there is a center bearing in the driveshaft, or it could be a noisy differential. By the way, some owners of these cars have replaced the original differential with a lower ratio one from a late 70s-early 80s 300D for better highway mileage and more relaxed high speed cruising.
(See previous posts from 'Channel 1') I don't know how or if they regeared the speedometer/odometer for the new ratio.
Happy Motoring, Mark DiSilvestro