Scott Gibbs

39 Zephyr 4 door Severe Vibration between 30 and 35 MPH

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I am a relatively new owner of a very nicely restored 39 Zephyr 4 door sedan.  The odometer shows about 50K miles but I think it is a replacement unit so the car likely has more miles on it than shown.  The car runs and drives great but it has a very strong vibration at between 30 and 35 MPH when accelerating.  If you take your foot off the gas it stops as you coast and it is gone above 35 MPH.  I am thinking it is the universal joint in the enclosed drive line as the vibration is similar to what you get in on open drive line that has a bad universal joint.  It seems to be a pretty big job to replace the universal so I'm looking for a way to be sure that is the problem before I proceed with dropping the rear end to get at the universal joint.  Any suggestions about diagnosing the problem will be appreciated.

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I would check the tires for flat spots or an out of round condition. If they seem OK rotate the tires using a 4 wheel rotation chart.

 

The enclosed U-joint are very durable. If the tires do not solve the problem, you can try using some John Deere Cornhead grease in the u-joint. If this reduces the vibration, remove the cover from the u-joint and look for signs of wear or loose bolts.

 

You should also raise the car on a hoist and use a stethoscope to check for noises in the drive train. You may have a loose drive shaft collar at the pinion gear or a center bearing that the rubber has deteriorated.

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Thanks for your advice.  I had the front tires rebalanced with no effect but not the rear yet.  I haven't figured out how the rear fender skirts come off.  Is it just a matter of rotating the chromed bolt head as shown by the arrow on it.  Are they hard to get back on?  I have been a little timid working on this car.  It is significantly different than my 40 Studebaker Commander or 32 Pontiac  Business Coup.  I have to confess I've never owned a Ford product before.  My Dad and Uncles were GM and Chrysler guys.  I've driven the same 1977 M-B 240D since I drove it off the show room floor in July of 1977 as my daily driver.  I have been able to do all the work it has needed myself.  The clutch lasted 29 years.  I took me a few days to change it but it really wasn't a bad job.

 

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Look at engine mounts, the rubber shrinks and engine sits metal to metal....

I read your message as noise worse when torque is applied...Ujoint is poss, Ive never seen one fail,

My issue is loose driveshaft collar at diff...not easy fix...my feel is when releasing throttle ...

yours on torque  / accel...Vibration, or noise or feel...how bout faster...wheel shake?? thump in brakes....??

balance on rear tires would have to be pretty bad to fell at slow speed... like bad tire wobble...

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Thanks for your help.  You suggest several things I can check that I haven't thought of.

  I'll be sure to let you know what I find out.  Thanks again.

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There is no noise with the vibration, just a mostly horizontal shaking.  The more I think about it, it feels a lot like a tire wobble but its odd that it is speed sensitive.  After I run the rear with the wheels off the ground, I'll check to see if I can tell how loose the front end king pins, etc. are.

Re the collar at the rear end, the rear end shift to the higher gear is very smooth and quiet.  There is a noticeable "clunk" of the shift from high ratio to low.  Anyone know, if this difference is normal?

Thanks

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So it sounds like you have a Columbia two speed rear axle in the 39?  You have been holding out on us Scott,  that's OK they were an optional extra.  Those overdrives have a lot going on in them. I don't know about horizontal shaking but mine had a rumble from around 40 MPH. in OD after I rebuilt it!!  Changed oil to" Pink Shock Proof" racing  oil, and it gradually lost its rumble and runs smooth now. Does "clunk from high to low ratio though so I always change down as Im pulling up to stop. Not game enough to change down at speed!  Does any one out there know if its safe to change down at speed? or what the procedure is? 

Edited by 38ShortopConv. (see edit history)

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