Driveline producing harmonics.

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Feb 12, 2002 | 11:20 AM

petem

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Driveline producing harmonics.

My '76 F250 4WD is generating a slight ringing sound at freeway speeds at around 2500 rpm. I thought it was air whistling, but it disappears when the engine speed is changed. Could this be coming from one of the driveshafts?

Feb 12, 2002 | 11:24 AM

Ford79

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Driveline producing harmonics.

Could be a u-joint. When they dry up, they tend to make a whistle/ring/chirp type sound.

Feb 12, 2002 | 09:01 PM

thelonerangerxlt

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Driveline producing harmonics.

Pete, make sure the driveshaft(s) are in phase. The u-joint caps must be aligned with each other, (in a straight line, viewed from front to back).

Feb 13, 2002 | 11:54 AM

petem

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Driveline producing harmonics.

Great-thanks for the advise. I not quite understanding the driveshafts being out of phase. If the u-joints caps are not aligned correctly, is it because the yokes are damaged or distorted? pete

Feb 13, 2002 | 09:01 PM

thelonerangerxlt

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Driveline producing harmonics.

Hi Pete. The mis-alignment of the u-joint caps, looking along the driveshafts, is called "out of phase". This condition is caused by the slip joint being put together with the splines being one (or more) splines off from where they should be.

I'm not sure of your set-up, with the 2 driveshafts. But you will have at least 1 slip joint; on the rear-most drive shaft. You may have another where they meet up. Just make sure that the u-joint caps line up with each other. If you pull a string tight between the caps, the string must be exactly parallel to the drive shaft length.

Hope my explaination is not too confusing.

Feb 14, 2002 | 12:14 PM

petem

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Driveline producing harmonics.

Ahhh-ok. I think I got it. I will check that. Actually my truck has three driveshafts-all with slip-splines and three u-joints per shaft. A lot of variables. Thanks again!