At my wits end: Need help with driveline vibration

[AR67GTX]

I should have mentioned it earlier but a lot of transmissions and differentials have a place on them that is either cast or machined to be parallel to the pinion in case of the rear, and the tail shaft in case of a transmission, useful to set an angle finder on. I have a Chevy, a Ford and Mopars so I can’t remember the particulars of each but those areas make it easier to place an angle finder than trying to use the yoke u joints themselves.

 

[HawkRod]

Good to hear you got some positive results..... And a suggestion... I'm sure you noticed as you added shim the locator pin loses projection & with 6 degrees it's probably pretty short... After your road trip I'd suggest cutting the perches off the housing & re-weld them in the correct orientation....

I think I would have had a major problem if I had standard locator pins. When I adapted my 73 ISO suspension to get rid of the rubber bushings, I made tall adapters that fit on the locator pins. The adapter, in turn, locates the top plate. Because the adapters were quite tall, everything still indexed in very nicely and are kept in the right location. So bottom line: I got lucky and it all worked well even with 6* of shims.
As a repeat, here is the adapter on the locator pin. You can see how the adapter, in turn, locates the bracket that the axle sits on and engages into.

Here is the adapter on the pin.

I'd like to say I engineered it to handle 6* of shims, but I only assumed I might put small shims in. But I'll take luck the few times it happens!
Anyway, here is a link from my other thread that has more pictures of their design and fitment. https://www.forbbodiesonly.com/mopa...-roadkill-style.213411/page-16#post-912206595

Having said all that, I fully agree I should reweld the perches in a better location when I get back. I will probably also then change the perches to the older style with smaller locating holes so I can discard all the crazy brackets.

 

[qkcuda]

Way to go Hawk. Glad you got it solved. Have a great trip.

 

[1STMP]

Sliding into a curb? Rough driving? Perish the thought. I never would have done that in my teenage years!
I guess checking the housing is next. But I don't have to tool to check it, so not sure how to verify it is good (or not).


Only thing I can think of is phasing of the driveshaft. In other words, if the U joints are not exactly 90 degrees from one another. But I don't know why keeping it in the same orientation matters unless the pinion can somehow nullify that. Quite frankly, some of this crap is like voodoo.


So there are several comments about my housing and questioning the straightness. There is a special tool to check this, and I don't have one. I have not checked it, and I'm not quite sure how to go about doing so without the special tool.

A contractors laser level can tell if your
housing is bent. Mount it on one of your axle
flanges and point it to the same point on the
other end. It will become very evident if
something is out of wack. (Know this from
many years of owning Jeeps and miles upon
miles of rough terrain beating up axle
housings). You can also place it on the axle tube
at 90 degree intervals. If your housing is
bent you'll have the laser pointing at odd
angles.
Another item you may want to check is the
flex plate on the torque converter.

 

[tommytunes]

tires or prop shaft out of balance.

 

[Old Sparky]

I don't know if this will help but I had the same problem on my 4x4 and it turned out that the drive shaft was assembled wrong....take the shaft out and turn it 180 deg. and put it back in and try it....if that's not it take it out and change one or both of the uni's 180 deg. one at a time. For some reason it mattered how the shaft was assembled and how it was installed in the vehicle.....cured my problem....later I found out it was mentioned in the service manual as well. Seemed rather silly to me but it worked....might only be relevant to a 4by tho...??? Good luck

 

[Grant McLeod]

Potholes are a pa issue, hammer mark on a front wheel bearing ?

 

[zyzzyx]

Hawk, where are you? Ready, set, ???

 

[axxmann]

Some of you may have been following along with my HawkRod RoadKill restoration thread and read about this. I am also trying to leave in a couple of days on a cross country trip and really want to get this fixed. I am posting this here to try and get broader viewing in case there are some good ideas I have not yet tried.

Car specs:
1973 Plymouth Road Runner. Factory 340, 727, 3.55 sure grip car. Car is fully equipped, still has it's factory A/C, so it weighs in at around 3900 pounds.
Currently the car has a 340 based stroker displacing 416 cubic inches. I have also added a Gear Vendor's Overdrive.

Issue:
The car has a harmonic vibration that occurs around 60 MPH. An important note is that this vibration has been there since I "restored" the car in the mid 1990s (read - low budget fix it up).
I have tried almost everything to address it. I have

• Rebuilt and rebalanced the engine (now twice - even a completely different engine). The 415 inch stroker engine that is now in the car is a balanced and blueprinted engine and is 100% different (including the block) to the previous engine with no change in the vibration issue.
• Put in two completely different transmissions. I have put two completely different transmissions into the car. Vibration did not change at all, regardless of which transmission was in the car.
• added a Gear Vendor's overdrive. Adding this GV O/D did not change the vibration at all. No change when adding it.
• Balanced the drive shaft (now twice because it has been shortened for the Gear Vendor Overdrive). In other words, I had it balanced before the overdrive to try and solve the issue, with no change. After the overdrive install it had to be shortened and was balanced again. No change to the vibration.
• Tried a completely different rim and tire combo on the car. I moved all four rims and tires from my 70 (that is smooth as silk) to this car. No change in the vibration.
• I swapped brake drums from my 70 (that is smooth as silk) to this car. No change in the vibration.
• I had a slightly bent axle. I bought two new axles from Dr. Diff and installed them. No change to the vibration.
• I swapped the3.55 rear differential with the one from my 70 (that is smooth as silk). No change in the vibration.
• AND I have tried to shim the rear end up and down to no avail.

There are two elements to the vibration:
(a) At around 60 MPH, there is a harmonic vibration. This vibration oscillates in a rhythmic pattern. Tough to describe in words, but rrrRRRRrrr... rrrRRRRrrr... I would guess the harmonic is maybe 70 to 90 cycles per minute (each rrrRRRRrrr cycle). This vibration has been there since the mid-90s when I "restored" the car.

(b) When accelerating slowly, no issue. When accelerating hard, there is constant hard vibration. This vibration is fairly new since I have been playing with driveline angles to try and fix issue (a). This vibration occurred when I shimmed the rear of the transmission up too high. I since have removed those shims, but then I removed the ISO suspension and that has dropped down the axle and I assume has created the issue again. After measuring driveline angles, I added 2 degree shims to shim the pinion down 2 degrees. No appreciable change that I can feel.

Current driveline angles (measured without the car itself level, so only the difference between the readings really matter). I used a digital level and rear suspension at drive height - I held the car off the ground using jack stands on the axle.

• Engine/Trans (measured at the front pulley with a square). 0.6 degrees UP
• Rear Pinion (measured by putting straight edge along back of pinion). 2.7 degrees UP

So this meant there was 3.3 degree difference between the two. All I have read states these should be the same angle. So I added two degree shims to shim the rear DOWN. This should have given me around 1.3 degrees difference. Still no fix.

I truly don't know what else to try. If anyone has any plausible ideas I'd love to hear them.

Thanks in advance,

Hawk

I have been getting a different vibration than the one I just dealt. It ended up being the driver side header rubbing on the driver side torsion bar. We forced the exhaust over and got more clearance and the vibration is gone. Good luck.

 

[1963JAM]

I am chasing the same highway speed vibration on my 66 Satellite. My vibe happens sporadically between 65 and 75 mph. Having read the previous responses and purchasing a magnetic protractor and following the Spicer Driveline Angle Calculator recommended in someones post, I have 1.5 deg at trans and driveshaft and 4.6 at differential and driveshaft. I am learning from these posts less than 3 is desired. Has anyone used angle shims to correct this? Should I start out with replacing the rear shackle bushings first then check again? Will the shim keep the rear end properly positioned on the leafs? I went to two reputable drivetrain shops this morning and got puzzled looks from mechanics when I asked them about correcting this driveline angle at the differential.
The leafs and bushings could be original to the car for all I know.

 

[Tony Tee]

Aren't there specialists that can pinpoint vibrations with fancy equipment . Like a aircraft companies or A&P mechanic that works on helicopters? Just thinking?

 

[1 Wild R/T]

Aren't there specialists that can pinpoint vibrations with fancy equipment . Like a aircraft companies or A&P mechanic that works on helicopters? Just thinking?

I don't know about any specialists per say but there are definitely techniques and tools for NVH (Noise/Vibration/Harshness) diagnosis...

I've known a few techs with this..

Amazon product ASIN B07K3XZR7R
I've been to a training session where they had this... But I don't know anyone who's gonna actually buy one so they can fix a vibration easy/faster/cheaper on a customers car... If you want to buy it I'll teach you how to use it....

Portable Wired Vibration Analyzer - DigivibeMX M20 (GX400) – Erbessd Store

 

[Cincy Kid]

I had exactly the same issue, but, only after I installed the Gear Vendors O/D. The fix? (As long as your angles Trans/Driveshaft/Pinion are correct) Had to have another driveshaft made that allowed more yoke to grip on the spline. Call Gear Vendors & they will help you, mine was made (originally) about 1-1/4" too short. When I reached 60mph tons of vibration, as the yoke was not fully engaged into the spline. New driveshaft 1-1/4" longer, (this is a critical issue with the O/D, the driveshaft has to be a bit longer going into the tailshaft & onto the spline) problem solved....

 

[1963JAM]

I had exactly the same issue, but, only after I installed the Gear Vendors O/D. The fix? (As long as your angles Trans/Driveshaft/Pinion are correct) Had to have another driveshaft made that allowed more yoke to grip on the spline. Call Gear Vendors & they will help you, mine was made (originally) about 1-1/4" too short. When I reached 60mph tons of vibration, as the yoke was not fully engaged into the spline. New driveshaft 1-1/4" longer, (this is a critical issue with the O/D, the driveshaft has to be a bit longer going into the tailshaft & onto the spline) problem solved....

After talking to some fellow FBBOs at Carlisle, I checked my trans slide yoke play for just what you’re saying. I have 3/4” play/slide at trans slip yoke. Also checked slide yoke for any wear but saw none.
I’m still chipping away at the stone (the vibration). Seems a new set of motor mounts helped with ridding more of the vibration. Old mounts looked fine but new mounts did get rid of more bad vibes.
So far I’ve surface balanced tires, balanced drive shaft, added 2 1/2 degree shim at axle spring mount, and now motor mounts. Next I’m chasing slight shake in steering wheel. Pitman arm joint has a little play. I’ll see if tightening up joint takes care of that.
This whole bad vibe chase of mine was mainly in the seat and floor, but the above mentioned replacements is making ride smoother.

 

[JoePole]

I have also been fighting the bad vibration blues for a couple of years now. Mine started after a gear swap to 3.55's however it was probably already there. Checked pinion preload, runout and gear contact. Was really noticeable from 55 mph plus and present under load and coast. Found bad front u-joint and replaced both. Then tried hose clamp balancing on driveshaft. Swapped my factory trans mount with another one and helped moving the vibration to 60+. Installed poly mount and it got really bad! Swapped back to original rubber mount. Did a planned 360 Magnum swap Added back my rear 904 tailshaft weight. Maybe got a little better. Measured driveline angles and added 4 degree shim. Got much better but gets worse but tolerable at 65 plus. Still searching.......

 

[Tony Tee]

Not sure if this has been mentioned? The alternator spins at double the speed of the engine. It could be out of balance as well.

 

[JoePole]

Something to note is that when I did my engine swap I found a broken converter mount hole on the flex plate and a crack in another. I am assuming that it was caused by the vibration so beware.

 

[1963JAM]

Something to note is that when I did my engine swap I found a broken converter mount hole on the flex plate and a crack in another. I am assuming that it was caused by the vibration so beware.

Good suggestion. I’ll spin the crank and inspect that as well. Thanks

 

[1963JAM]

I have also been fighting the bad vibration blues for a couple of years now. Mine started after a gear swap to 3.55's however it was probably already there. Checked pinion preload, runout and gear contact. Was really noticeable from 55 mph plus and present under load and coast. Found bad front u-joint and replaced both. Then tried hose clamp balancing on driveshaft. Swapped my factory trans mount with another one and helped moving the vibration to 60+. Installed poly mount and it got really bad! Swapped back to original rubber mount. Did a planned 360 Magnum swap Added back my rear 904 tailshaft weight. Maybe got a little better. Measured driveline angles and added 4 degree shim. Got much better but gets worse but tolerable at 65 plus. Still searching.......

Interesting that poly mounts made it worse. That info saved me a few dozen dollars.

 

[Cincy Kid]

After talking to some fellow FBBOs at Carlisle, I checked my trans slide yoke play for just what you’re saying. I have 3/4” play/slide at trans slip yoke. Also checked slide yoke for any wear but saw none.
I’m still chipping away at the stone (the vibration). Seems a new set of motor mounts helped with ridding more of the vibration. Old mounts looked fine but new mounts did get rid of more bad vibes.
So far I’ve surface balanced tires, balanced drive shaft, added 2 1/2 degree shim at axle spring mount, and now motor mounts. Next I’m chasing slight shake in steering wheel. Pitman arm joint has a little play. I’ll see if tightening up joint takes care of that.
This whole bad vibe chase of mine was mainly in the seat and floor, but the above mentioned replacements is making ride smoother.

Gear Vendors recommends a maximum of 5/8” play at the trans slip yoke