1971 CDV - Vibration at HWY speed under load

[impalamansgarage]

Excellent information.

Let me review what I've done to the drive line and suspension:

- All four rear trailing arms have new bushings. Recently replaced.
- New shocks. I used Monroe OEM Spectrum (http://www.monroe.com/en-US/e-catalog/5815)
- Transmission mount as well as engine mounts are new.
- Transmission rebuilt (smooth as silk)
- Tried new rear springs but went back to original springs.

Let me talk about springs for a minute. I actually ordered the "heavy duty" springs listed on rockauto.com for this car. It was a mistake. While they were visibly shorter that the stock springs, they were much stiffer. The result was a Cadillac which looked like an early 70s hot rod. Remember when hotrodders would stick the rear end of a Camaro or Mustang high in the air?  Anyway the rear of the car was very high..... several inches in fact. I decided to test drive it like that and low and behold NOTHING happened. The vibration remained. I reinstalled the stock springs and the car sits nice and level.

Now am I correct in assuming that those stiff springs changed the driveshaft angles? I would think that as the rear of the car goes up, so would the transmission tail housing. Thus the angle at both the trans and at the pinion would be greater. Furthermore as you accelerate it would be less likely
for the driveshaft angles to be minimized.

What does this situation tell us? Comments welcome.

["Cadillac Kid" Greg Surfas 15364]

The change of elevation (of the pinion) is spread through the 4 u-joints in the 2 carden joints and each u joint "sees" 1/4 of the change.  That is actually less than what occurs when the car goes over a stiff bump.
Greg Surfas

[savemy67]

Hello Impalaman,

I am not understanding something in your most recent post.  The post stated that the new springs were visibly shorter than the stock springs, yet the rear of the car was higher when the new springs were installed.  Assuming that you are referring to the free height when noticing that the new springs are visibly shorter, this would imply that the loaded height of the new springs was much greater than the loaded height of the stock springs, further implying that the stock springs are so soft that they are compressing several inches more than the new, shorter springs when loaded.  Without knowing the free and loaded height of the springs, the only conclusion I can draw regarding the springs is that your stock springs are so worn out that they are just barely able to keep the car (without any payload) at a level height.

You are correct that taller installed rear springs would change the angle of the transmission output shaft, since the transmission carried by the frame, and the taller springs would elevate the frame in the rear. However, if my geometry is correct, the angles will decrease (when measured at the bottom of the shafts) - the decrease being relative to 180 degrees.  The angles would be moving away from axial alignment, so one would intuit that vibrations might get worse.

Without knowing the baseline angles, or the spring height measurements, or the frame status, it is difficult to make any hard and fast conclusions.  If you want to spend some money, I would suggest purchasing a good inclinometer.  Find a dead-level parking place for your car.  Remove the driveshaft and place the inclinometer on the face of the transmission output shaft and pinion flange.  Subtract 90 degrees from these measurements to give you the +/- degrees from level.  Replace the driveshaft and measure its angle.  Do the math and see if the angles are within specification.  I think it should be 1 to 3 degrees.

Your post stated that you have new trans and motor mounts.  While I don't think the '71 the Cadillac rear suspension is adjustable, the transmission mount is adjustable using shims.  Given the age of your car, you probably have no way of knowing if it came with shims from the factory.  Measure the angles to see if shims might help resolve your vibration issue.

Respectfully submitted,
Christopher Winter

[impalamansgarage]

I have a photo of the two springs side by side that I can post later. The new heavy duty spring was made out of noticeably thicker rod stock. I compared
the two with calipers and the difference was substantial. As such, while the older spring was taller, it's thinner material has a softer ride. With the stock springs in place
the car sits level.

With the new heavy duty springs in place, the rear of the car sat quite a bit higher due to the extra thickness of the steel, regardless of the fact that the spring was shorter by about an inch or inch and a half.

In addition to checking drive shaft angles , which I plan to do very soon, I purchased a Steelman Wireless Chassis Ear. I plan to place wireless microphones around the chassis in an attempt to determine the point of origination of the vibration.
https://www.amazon.com/STEELMAN-97202-Wireless-ChassisEAR-Diagnostic/dp/B00123J79O

My factory service manual contains ride height measurements I can take as well. Now all I need is the time.

[impalamansgarage]

I used an inclinometer on my smart phone.

Trans tail is tilted 5 degrees downward.
Driveshaft tilts downward toward the ground at 1 degree.
Pinion flange is tilted downward toward the ground at 7 degrees.

[impalamansgarage]

Hanging threads are annoying, much like this problem has been. Long story short, the car has been normalized. Stock
springs were reinstalled.

A while back I bought a Steelman Wireless ChassisEar.
https://www.amazon.com/Steelman-60635-Wireless-ChassisEAR/dp/B07K3XZR7R

I recommend this gizmo.

I used this device to search for the noise while making multiple test drives and changing
the position of the sensors.

Finally I placed one of the sensors on one of the flanges on the pinion housing.

Once I reached the problematic speed and torque situation, I was able to hear that the problem was coming
from the pinion housing.

I don't have the tools to rebuild the rear end so I plan on taking it to a shop to have that done before too long.

This problem was very difficult to diagnose. It only occurs above 45mph under load.

It is speed and torque related.

Examples:
If you romp on the loud pedal out on the highway to pass someone, it gets REALLY loud.
Going up a slight hill at any speed above 45 will make the noise.

I suspect one of the bearings in the pinion is at fault. Regardless I'm taking to a pro to fix.

Cheers everyone.

[chrisntam]

Like a dog on a bone, you won't (and didn't) let it go.

Great to hear you've narrowed it down and thanks for the recommendation of the noise locator!  Well done.  I bet that tool can be pretty handy.

[TJ Hopland]

Interesting.  So the jumper cable looking clamp must contain a contact microphone?  And that style of clamp must just be the most universal type of clamp they found?    These days you would think you could also get a camera and display in the same size packages for double the diagnostics.

[impalamansgarage]

Indeed. Camera tech is everywhere now. Adding cameras to this tool's capabilities would be pretty awesome.

[impalamansgarage]

So I let this project sleep for quite some time while I restored my Mercedes. LOL.... sorry guys.

HOWEVER .... the time has come and I am right in the heat of the battle rebuilding the rear diff and
pinion on this 71 Deville. I now know why (in my opinion) you don't see these cars on the roads
like you do other classics. The rear ends on these early 70s are somewhat of a more rare beast.

I have never rebuilt a rear diff or pinion before so keep that in mind.

At the expense of preaching to the choir, here are my observations:

- This pinion and carrier on this car was LOOSE..... and I mean LOOSE... as in NO PRELOAD.
- This had to be causing the vibration.
- All of the bearing races I removed from this rear end had visible chatter marks. You could not feel
them with your finger nail but you could see them.
- NO ONE makes a pinion crush sleeve for these cars. I cannot find one anywhere.
- NO ONE makes a pinion bearing spacer either.
- Again I am talking about the early 70s Devilles.
- These rear ends use a straddle type pinion which is somewhat similar to the GM truck 14 bolt 10.5.
https://www.youtube.com/watch?v=y3sXMW1CMVs&t=69s

Resultant plan of action:
I decided to go with a bearing spacer and shim stack because of the lack of parts availability.
At least if I have to disassemble the pinion again, I could put it back together and not worry
about finding a crush sleeve. The inner pinion bearing is an HM89449 so I looked at other vehicles on RockAuto which also use that bearing as their inner pinion bearing. Logically any crush sleeve or bearing spacer for vehicle X should match the ID that I need for my car. Also since crush sleeves are 100% vehicle and/or application specific, finding an exact match for length as well as ID was a very long shot. So I decided to find a vehicle for which the inner pinion bearing was an HM89449 AND there was a recommended bearing spacer and shim kit available. The idea here is that it should be possible to cut the spacer down to the length you need.

I found that a 1974 Chevy K10 truck used the HM89449 inner pinion bearing and that pinion bearing
spacer kit "USA STANDARD GEAR USA55046" was available.
https://www.rockauto.com/en/moreinfo.php?pk=4031406&jsn=726

This spacer has a very slight taper on it so that it mates nicely with the HM89449 inner bearing and the
M88048-A outer bearing.

I had the original crush sleeve which came with the car and it was .701 in length. I took the new spacer to a local machine shop and had them cut it down to .701 on a lathe on either side of the taper to retain the proper bearing mating services.

The pinion preload on these cars is 22 to 30 inch pounds.

So right now I have finished a long process of tweaking the spacer and shim stack to obtain preload in the mid 20s (24, 25 etc...)


I ended up using a rotary hand sander in my bench vise to trim down the spacer to .675 in length. I then added a .014 shim stack to get .689 total spacer length.

This gave me the preload I needed. At this point I still need to finish rebuilding the carrier assembly as it is now completely apart as well.

I just wanted to stop by and talk about what I found and the progress made. The stupid pandemic slowed things as well.

It's clear to me now that parts availability for the rear ends on these cars is a big part
of why you don't see many of these cars on the road.

Try searching for a crush sleeve for an early 70s Deville. Let me know what you find.

If you feel so inclined you can check out the videos I made on getting rid of the vibrations in
this car over on my Youtube channel. Look for Impalaman's Garage. I have a play list entitled "Finding Resonate Drivetrain Vibrations".

Cheers.

[impalamansgarage]

The vibration is FIXED!

AFTER 7 YEARS !!!!!!!!

This car was defective from the factory. After discussions with a local classic car restoration company (Impatient Creations - https://impatientcreationsinc.com/) and discussions with PMT Fabrication (https://pmtfabrication.com/) I have found that the pinion angle was wildly off.

I replaced the stock rear trailing arms with adjustable ones from PMT fabrication and fixed this issue finally.

The driveline working angles were wildly off. Below 45 or 50 mph it was ok to drive but anything above that was horrible.

I've documented my findings with the driveline geometry here:
https://www.youtube.com/watch?v=Vnt7fvkIrtI

That is the last video in a series I made. The last two videos document my findings in the driveline geometry.

I personally believe that this car was assembled incorrectly at the factory. I do not believe that the trailing arm mount points on the rear axle were welded in the correct spot.

I did rebuild the differential as noted in the previous post but this did not correct the problem. Hope this mess helps someone.

[scotth3886]

This 9-page thread is hugely helpful. 

I've been after a similar issue in my 66 Fleetwood since I've had the car.  I've done everything except pinion bearing and the two bearings in the rear of the tranny.  I never thought of replacing the rear trailing arms and didn't know there were adjustable ones avaiable.

My noise manifests itself as a road speed related vibration but isn't.  It's noise only. When I'm driving with the windows down, it's not there.  I don't really notice much until I'm over 85 or 90 and then it's more of a buzzing sound.   However, the driveline isn't as smooth as it should be for a Cadillac as it feels a bit gritty or granular. 

I've had many B and C body GM cars in my life and have never experienced this before.  I've worked at a new car Cadillac dealer during the period when my 66 was a new car and then an Olds dealer after, also here in Columbus, but in the parts dept at both dealers.  I drove many of these C-body cars but don't recall ever experiencing such a thing.

Never thought of trailing arms though.   

[impalamansgarage]

Howdy Scott. Glad to know someone is reading this thread at least. LOL

Might want to measure your driveline angles. You never know. I used a magnetic digital angle finder from Lowes. Works well.

[scotth3886]

Howdy Scott. Glad to know someone is reading this thread at least. LOL

Might want to measure your driveline angles. You never know. I used a magnetic digital angle finder from Lowes. Works well.

I have one of those that I've used to set the rake on my electrostatic speakers, which are a real bitch to position optimally.

I've tried so many things that I can't remember if we checked those angles or not.  I remember that we talked about it, but at age 80, I'm not sure what we did about it. 

I have a talented mechanic at a nearby Chebbie dealer who helps with it. 

I live in a geezer HOA of single-family homes that are fairly close together, so my compressor and air tools are highly frowned upon.  So if it's going to noisy, I have to take to the dealer.

[klinebau]

I thought with the double cardan joints on each end of the driveshaft that the angle was not that important.  I suppose if it was extreme, then it might be a problem. 

[scotth3886]

I thought with the double cardan joints on each end of the driveshaft that the angle was not that important.  I suppose if it was extreme, then it might be a problem. 

I thought that's the main reason they used them.

[The Tassie Devil(le)]

Congratulations on letting everyone know what the solution was.

When I was chasing a similar problem in my '60 CDV, it turned out to be the upper Ball Joint that was totally worn out.

Bruce.

[impalamansgarage]

Here are the old and new measurements for reference:

Angle Measurements Before adjustments:
Engine/Trans  6.5
Drive Shaft  1.8
Pinion        8

Engine/Trans/Drive Shaft Working angle: 4.9 (6.5 - 1.8 )
Drive Shaft / Pinion Working angle:    9.8 (1.8 + 8 )

Difference: 5.1


The difference between your working angles should be less that 1 degree as you know. Also with a typical
single u-joint style drive shaft, the measured angle needs to be 3 degrees or less. The way
these cars are put together makes this impossible. Thus GM used double cardan on each end in a W configuration. So that 4.9 degree angle at the trans is actually OK since it gets cut in half by each
side of the double cardan. (in my mind....)

Changes:

I took a lot of that up-tilt out of the pinion with the new adjustable trailing arms and now
the angles are:

Engine/Trans  6.5 (unchanged for obvious reasons)
Drive Shaft  1  (changed be default when I adjusted the pinion)
Pinion        4.5

Engine/Trans/Drive Shaft Working angle: 5.5
Drive Shaft / Pinion Working angle:    5.5

Difference in working angles is basically zero. (Assuming a $30 Lowes digital
angle finder can provide less than half a degree of accuracy is a bit silly but oh well.)