Troubleshooting a driveline vibration

Engine, Transmission & Driveline

  1. CBODY67

    CBODY67 Senior Member

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    Usually, the FSM (downloadable from www.mymopar.com or elsewhere) usually has the speedo drive/driven gear combinations for the particular car and its normal (when built) tire sizes.

    The way I check speedometer accuracy is by doing a mileage check on the Interstate, using the mile marker posts. I would find a generally flat 10 mile stretch and check the odometer accuracy first. You can use a 5 mile run, but a 10 mile run can make up for any speed difference issues, or at least average them out more. 10 miles makes the math a bit easier, but 5 miles can work too. Steady-state cruise at 60mph or more.

    The reason for the distance check is that that relates to the number of revolutions the speedo cable makes, which is a geared situation. The rear speed cup has a bar magnet in it, which turns the front speed cup, which is attached to the speedo needle for speed indication. NO mechanical link between them. So getting the mechanical components correctly calibrated is the FIRST step in speedometer accuracy. Which also relates to the speed indication accuracy.

    Pre-GPS, I'd maintain a steady speed over a flat mile or two of Interstate. 60mph works well, if possible, as 60mph = 60 seconds/mile ("Mile a minute"). 5mph either way, it's a pretty linear relationship, but greater than 5 miles, the timing loses that linearity, by observation.

    I believe you can also use GPS to measure distance too.

    Finding the exact year of FSM might not be important, so long as the model year used reflects the tire size the vehicle came with.

    Just some thoughts,
    CBODY67
     
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  2. WissaMan

    WissaMan Member

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    So the garage called and said the driveshaft is all bent up so he's definitely leaning towards that being the cause of the vibration. He said he knew a guy about an hour away that made driveshafts but he's not sure he's still doing it so I figured I'd ask on here if there's any "sure bet" vendors that are widely recommended -- kind of like how everyone recommended me to ESPO for springs.
     
  3. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Quick Yellowpages search shows two places within 1.5 hours of you:

    Woodring in Hazelton PA
    Home

    Hartman's Driveshaft in Reading PA
    Hartman Driveshaft & Axle

    I know nothing about either place, I just yellow pages searched. Perhaps others here have knowledge of them...
     
    Last edited: Apr 29, 2019
  4. CBODY67

    CBODY67 Senior Member

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    Many driveshaft places also have ties to the HD truck parts industry, at least down here. As in HD truck transmission/rear axle parts, but not all of these parts places to driveshafts.

    Ask if they can/will do balancing OR if they just build the shaft with known "balanced" parts? There's a difference in the end product!

    End result, unless you get a good used one from a salvage yard, the one they build will look nothing like the OEM, other than in length, slip yoke, and u-joints. Usually being out of tube stock that's the same diameter, end to end. Nothing wrong with that, just the different cosmetics.

    You might also check with a larger Toyota dealer. Ours' had to send many out (Tundras and Tacomas) to get rebalanced. Yep, even on a late model Toyota! Less expensive than a new OEM replacement, as they were out of warranty.

    It can easily end up being a $300.00 deal, just for the new shaft, or a bit more.

    Keep us posted,
    CBODY67
     
  5. WissaMan

    WissaMan Member

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    When I picked up the 300 at the garage, I was talking to the shop owner about the driveshaft and he told me they are not all that hard to remove/replace. So when I mentioned that I had a 68 NYer he suggested I try the driveshaft from that car before going through the effort and expense of having a new one made. So we did that yesterday and it made a big difference. There is still some slight vibration at certain speeds but definitely not like before.

    There were a few things we did notice -- the U-joints on this driveshaft don't move smoothly, so they will need to be replaced. Also, while we had the car on jack stands we idled it in gear and watched the driveshaft. To me, it looked like it wobbled a little near the differential. I do know that many years ago on the NYer the U-joint broke and the driveshaft banged on the ground so perhaps that bent it?. Or maybe it's because that rubber in there is deteriorating?

    Also, we noticed the play at the exit shaft and I'd estimate it was around 1/4"
     
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  6. 65sporty

    65sporty Old Man with a Hat

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    So since it changed with a different shaft, I would now have one built for the car.
     
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  7. WissaMan

    WissaMan Member

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    I just watched a couple informative videos on YouTube including this one

    Here's some excerpts from it that everyone may fine useful. Maybe these MPH ranges will vary according to the vehicle but with this other driveshaft the vibration does come and go in the 30 - 35mph range which would seem to point to a wrong joint working angle. Whereas with the original shaft, it came and went at 30 - 35 and also came in at about 55~60 mph which would seem to indicate a wrong working angle and an unbalanced shaft

    upload_2019-5-5_11-6-25.png

    upload_2019-5-5_11-7-36.png

    upload_2019-5-5_11-8-31.png
     
    Last edited: May 5, 2019
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  8. Triple Pickle

    Triple Pickle Well-Known Member FCBO Gold Member

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    I have a 48 Plymouth that had no vibration at all until I went from 2.76 to a 4.10. Now it will jar out your dental work.
     
  9. WissaMan

    WissaMan Member

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    It makes sense that moving to a steeper gear is going to lower the MPH at which all the driveline vibrations occur and if they come and go, it'll move them all closer together. You might also hit some other resonance points with 4.10's that you wouldn't even reach with 2.76's at normal driving speeds.
     
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  10. Triple Pickle

    Triple Pickle Well-Known Member FCBO Gold Member

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    Yup, going numerically higher in your differential will bring any driveshaft shortcomings to your attention real quick!
     
  11. WissaMan

    WissaMan Member

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    I just wanted to give an update on this. With the new U-joints the car feels even better. Perhaps not 100% smooth but very near so. Close enough that I would only notice anything if I was specifically concentrating on it. Originally the vibrations were so pronounced you couldn't help but notice.

    So to sum up this thread, the bent driveshaft was the major cause of the vibration.
     
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  12. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Glad to hear it - and (because in my opinion they're not made to as high a quality as they used to be), you can point the finger at your tires. Unless one is paying big bux for tires, they just don't balance out, and are usually slightly off-round etc... after balancing drive shafts, u joint replacements, tail stock bearing replacement, all needed, I had narrowed things down to my tires. I had my wagon's wheels and tires balanced on a Hunter(?) dynamic road force balancing machine - a long involved (and fairly expensive) process of checking the bare rim, marking it, checking the tire, moving the tire on the rim to offset balance issues between the two, and it made a big difference. Sadly enough, my AC compressor still has a vibration in it at various speeds that mimics a driveline vibration...

    It's always something.
     
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  13. 70bigblockdodge

    70bigblockdodge Old Man with a Hat FCBO Gold Member

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    If you ever need to have a driveshaft made for your car. I would suggest switching to 1350 joints and a straight tube. I know the neck down helps with muffler clearance but, the 7260/7290 u joints are expensive and suppliers made be limited to the worst of off shore junk. 1350 u joints are still popular today made in NA by reputable companies with high mile fleet ties. If a driveshaft causes that much vibes then the yokes are suspect also. So really the only extra you are paying for is the rear end yoke and thet slip yoke, all for a very big durability improvement. My 2 cents.