Drive Train Vibration

[Dan Hiebert]

Our D24 gets a vibration increase as the speed increases or decreases through 30 mph.  Since the (original) speedo shows 5 mph increments I can only nail it down to always through 30, beginning on the way up between 25 and 30, and on the way down between 35 and 30.  Does not matter whether I am in 2nd or 3rd.  I do not think it is the engine and drive train up to the clutch, since I can rev it in neutral from idle up to about 3K with no excess vibration.  I initially wrote it off to a bent rim that was on the car forever, but I replaced that a couple years ago and the car still does it.  It's a whole car shaking vibration, noticeable, but not severe.  If I'm not in that vicinity of 30mph the car runs like a sewing machine, noisy but smooth.  It has done this as long as I can remember.  I put a new clutch in it about 30 years ago, that was the last time I had any part of the drive train apart, and I have absolutely no recollection if it did this before then.  I have never fiddled with the ball-and-trunnion joints.  I have suspicions but want to get you'un's thoughts.

[Doug&Deb]

Servicing the u-joints wouldn’t be a bad idea. Also, when changing the clutch if you didn’t get the driveshaft on exactly how it came off that could cause a problem. It’s best to mark the orientation front and rear before removing it. Try removing the front of the shaft from the trans and rotating it 180 degrees. If that doesn’t help then try doing the same on the diff side. 

[Ivan_B]

If the vibration happens while driving, it is likely something that rotates while driving. Check tires and driveshaft. Both should be balanced. Tires should be also checked whether or not the rims are straight.

To DIY this, I would first take the tires to the shop and confirm they are within specs. Driveshaft is a non-DIY item, unfortunately, but you can also take it off the car and take it to the balancing shop. And yes, it must be installed the same way it was at the factory. So look for some paint marks on the flanges to see if they still match.

 

Also, just in case, check your exhaust to make sure it does not bang on the frame, etc., while shaken

[Sniper]

3 minutes ago, Ivan_B said:

Driveshaft is a non-DIY item,

 

Actually, it is. 

 

https://www.demandaam.com/technical-support/aam-technical-tips/driveshaft-balancing

 

Once you pull the driveshaft off to get it balanced and factory setup is moot.  But since it can only go one one of two ways try the other position and see if it makes a difference..

 

 

 

 

[Ivan_B]

7 minutes ago, Sniper said:

Actually, it is. 

Did not know that, good to know

[Sam Buchanan]

3 hours ago, Ivan_B said:

And yes, it must be installed the same way it was at the factory. 

 

Why is that?

[kencombs]

30mph is a very low speed for a driveshaft vibration, at least in my experience.    To help isolate it I'd try these things.

 

1. put the rear end on stands so that it is supported by the springs, not hanging.

   Remove the rear wheels.

   Run the car in gear up to and past 30 and see what you feel.

   Any vibration would point to the driveshaft, but not necessarily balance.   Bad ujoints, a ball and trunion whose trunion is not centered, or even just dry joints can cause it.

 

If not vibration at this point put the wheels on and repeat. 

 

If that doesn't reveal and issue, see if you can find a front end shop with one of the old on the car balancers.  They will reveal exactly which corner is causing the shake.

Slightly bent wheel, tires out of round or otherwise distorted, brake drum out of round etc will all show up with that test.

[DJK]

21 hours ago, Sniper said:

 

Actually, it is. 

 

https://www.demandaam.com/technical-support/aam-technical-tips/driveshaft-balancing

 

Once you pull the driveshaft off to get it balanced and factory setup is moot.  But since it can only go one one of two ways try the other position and see if it makes a difference..

 

 

 

 

Sniper, that was a similar fix on Nissan vehicles years ago. Spinning the driveshaft at speed and holding a piece of marker crayon to just touch the high spot of the shaft, then adding a hose clamp with head  opposite of the crayon mark, would correct a vibration concern.

[rallyace]

A couple of things that the answers above did not clarify. First, the driveshaft is subject to phasing. A universal joint is not a constant velocity joint. When both ends are in phase they will amplify the velocity change. Putting them out of phase will negate the difference. Look up 'double cardan joint' on the internet for  a technical explanation. Now, balance is another thing. The third thing to consider is that with the trunnion type joints, the pin must be exactly centered. If you have any wear in the trunnion cup the shaft will not be centered and balancing is next to impossible as the shaft will shift slightly from side to side on every rotation of the shaft. At 30 MPH your driveshaft is turning about 1500 RPM. Proper balance is necessary. I gave up trying to get my trunnion type shaft balanced and had a truck driveline shop make me a new one with Spicer universal joints. It cost me $300 which I consider to be well spent money as the new universal joints can be found in just about every auto parts store.

[Sniper]

Phasing is built into the driveshaft, nothing you can do about it short of cutting an end off and redoing it.  Unless you have a two piece setup with a built in slip joint, which isn't the B&T driveshaft.

 

You used to be able to get NOS housings and all the parts to rebuild as a kit for the B&T setup, not sure if you still can.  But at this point you are approaching the cost of a conversion driveshaft.  I know just the housing is $105 on ebay, I think Bernbaum's has the whole kit for $200. 

[Ivan_B]

On 9/3/2023 at 8:29 PM, Sam Buchanan said:

 

Why is that?

No idea, but this is stated in literally every single instruction manual when removing the driveshaft. I suspect that this is because it is balanced on the vehicle, before, or due to the expected cumulative wear of the associated components. Putting it the same way back in is expected to keep the existing balance. Of course, if you balance it off the vehicle, this does not apply.

 

7 hours ago, DJK said:

Spinning the driveshaft at speed and holding a piece of marker crayon to just touch the high spot of the shaft, then adding a hose clamp with head  opposite of the crayon mark, would correct a vibration concern.

I don't believe that evening-out visibly bent shaft is quite the same as balancing. Not sure about driveshafts, but you can turn your wheel rim + tire with a dial indicator and position them appropriately to even-out the combined circumference, but this is not the same as balancing which requires either a special machine or at least a spinning cone

[Sam Buchanan]

26 minutes ago, Ivan_B said:

No idea, but this is stated in literally every single instruction manual when removing the driveshaft. I suspect that this is because it is balanced on the vehicle, before, or due to the expected cumulative wear of the associated components. Putting it the same way back in is expected to keep the existing balance. Of course, if you balance it off the vehicle, this does not apply.

 

Not the case with our cars. Sniper alluded to this in a post above when commenting about driveshafts that have splined slip joints that can be pulled apart and reassembled out of phase. But that isn't the case with the trunnion driveshafts that came on old MoPars. It isn't possible to get the trunnions out of phase because the housings are welded to the shaft. This is another case where "conventional wisdom" doesn't apply to our old cars and why we need to be familiar with the unique aspects of these cars before making blanket statements.

 

After the flywheel and clutch have been serviced/replaced the "factory" balance is long gone....and I suspect the driveshafts were balanced prior to installation on the chassis (balancing an entire drivetrain would be quite the process....LOTS of moving parts). But if someone wants to mark and index the driveshaft prior to removal that certainly won't hurt anything.....but it will only reinstall two ways (well, maybe four if swapped end-for-end...)  

 

Just for educational purposes here is the trunnion-style driveshaft which isn't remotely similar to modern driveshafts. Notice how variations in length is accommodated by the springs inside the joint instead of the modern method of splined slip joints. And also the infamous wickedly difficult to install boots!  ?

 

 

 

Edited September 4, 2023 by Sam Buchanan

[Dave72dt]

I haven't researched the idea but how would a driveshaft be balanced on a vehicle?  I understand checking runout, both on and off a vehicle.  Too many varibles in trying to balance an entire drivetrain at once and attribute it all to a driveshaft.

Edited September 4, 2023 by Dave72dt

[Dave72dt]

Because the vibration is occurring at two different speeds depending on loading or unloading of the diff, I'd look carefully at the rear joint, pinion angle and pinion bearing.

Edited September 4, 2023 by Dave72dt

[Ivan_B]

41 minutes ago, Sam Buchanan said:

Not the case with our cars.

Good to know, thanks. I did not even look at it, since mine is working as expected... Just assumed it was the standard U-joint

37 minutes ago, Dave72dt said:

I haven't researched the idea but how would a driveshaft be balanced on a vehicle? 

The only way I know is to use a vibration meter, measure vibration at different spots and playing around with the weights. Apparently, you can do the same without the meter, by just listening what happens. Not sure how effective that would be for an average DIY guy, though ?

[Dave72dt]

I've used vibration sensors spin balancing front tires on a vehicle before.  That usually only includes wheel, tire and hub/drum.  It doesn't work on a drivetrain on a vehicle.  that would include the driveshaft, either tire and wheel or both, those hubs/drums. axles and gears as well as any bearings that may or may not be in good condition, a process that would not be very efficient on an assembly line, repair shop or DIYer.  I'm guessing the factory did a runout and balance off the vehicle and then installed them.

[kencombs]

9 minutes ago, Dave72dt said:

I  I'm guessing the factory did a runout and balance off the vehicle and then installed them.

More likely that the shafts were built up in a totally different production line and shipped to the factory.   That's the way most things are today anyway.  The 'factory' is a assembly point and actually makes very few 'subassembles'.    May have been different in the 40-50s as business were more vertically structured.   Like Ford and there lumber business to turn logs into car parts.  Even started the charcoal thing with leftovers.

 

Back in the day I knew a guy that used one of the Mopar programs where you could go the assembly plant and pick up your car to save shipping.  This was is the mid 60s that I knew him and this had happened years before I think 55 or so.   He was amazed at the speed even then and lack of testing before the vehicle was started and driven to the storage lot.

[Dan Hiebert]

Thanks, everyone, for the responses!  You'uns are validating my suspicions as to what to look into, mainly the driveshaft and its components.  Especially in light of my self admitted lack of regular maintenance on it.  I know when I had the driveline apart many years ago that I did mark everything so I could put it back the same way it came apart.  I could tell that a PO had the driveline apart at one time, but there was nothing marking the component alignments.  I'll take the opportunity to look at the rear end, too.  

[Sniper]

5 hours ago, Dave72dt said:

I haven't researched the idea but how would a driveshaft be balanced on a vehicle?  I understand checking runout, both on and off a vehicle.  Too many varibles in trying to balance an entire drivetrain at once and attribute it all to a driveshaft.

 

The link I posted tells you how

[DJK]

16 hours ago, Dave72dt said:

I haven't researched the idea but how would a driveshaft be balanced on a vehicle?  I understand checking runout, both on and off a vehicle.  Too many varibles in trying to balance an entire drivetrain at once and attribute it all to a driveshaft.

 Spinning the driveshaft at speed and holding a piece of marker crayon to just touch the high spot of the shaft, then adding a hose clamp with head  opposite of the crayon mark, would correct a vibration concern.

[Dave72dt]

I've done the hose clamps in the past when I was building my own driveshafts and could never get the hose clamps tight enough to stay permanently in place.