News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

Good news - Tailshaft Vibration is no more

Started by Bruce Reynolds # 18992, January 21, 2005, 06:32:04 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Bruce Reynolds # 18992

I have some good news to share with you all.

The vibration that I have experienced in my 60 CDV has finally been solved.   No, I havent sold the car.

It was still there, after replacing the universal joints, motor, transmission (back to 390 and Hydro from 454 and TH400), diferential ball joint (slightly improved it), front lower ball joints, and a lot of other stuff which had nothing to do with it.

I shimmed the centre bearing up 10mm, or just under 7/16", and voila, vibration 99percent gone.  I then raised it up another 1/8", and it went completely, but during the test drive, the tailshaft cross was just touching the tunnel roof at a decent bump in the road.   So, back to the 10mm thick piece.   I can live with it now.

From consultations with a transmission shop friend of mine, it turns out that it has the dreadded "Volvo" symptom, where the springs sag with age, and the driveline angles change.   It doesnt take much, but a couple of degrees is all it takes.   All the Volvo fix it to shove in a couple of spacers, so if it was good enough for a Volvo, then backyard engineering will suffice for me.

Bruce,
The Tassie Devil(le),
Smooth 60 CDV.

P.S.   Now back to trying to keep the wheel caps on.

Randall A. McGrew #17963

Congratulations!  Those kinds of things can drive ya nuts.
Glad to hear you did not have to sell the old girl.

Ed Mobley

Bruce and I have been chatting over the past couple of weeks on this issue as I too have some vibration.  In my case, my rear engine mount has collapsed about 1/2" with age as measured against a new mount.  This too will affect the drive shaft angle.

Im hoping that one day I can find that tool that Cadillac produced to measure the drive shaft geometry - that way there will be no guessing.

Regards,

Ed


Robt.Vonheck -via SunDiego Calif.

Bruce:  -so lets see, you essentially raised the transmission/output-shaft(and therefore the front UV-joint) slightly, and discovered that eliminated the chronic-vibration! Excellent, as you probably know, that means that you can alternately lower the nose of her differential;  --owing that the axis of both the trans. & differ. must absolutely be parallel (albeit not necessarily pointing at eachother)!  In other words, it does not matter what the angle of the driveshaft is, in so long as the said trans. & differ. shaft-axes are precisely "parallel".  Nowthen, using this requsite guide-line, --one needs to preferably use an adjustable/Bubble-level to determine if the two said axes are indeed parallel?   Drive-line repair-shops always have one of these special Levels at the ready, and it is merely set against the usually flat-bottomed pan of the transmission where it is adjusted to "zero", --and then up against some flat portion of the differential (that is seen to be parallel to the input-shaft); --again, placing it against the driveshaft is a waste of time, as that angularity means nothing).  One can also place the Level against the forward-most and aftward-most portions of the two UV-joints, -but doing it that way is rather best left to an expert.

Bruce Reynolds # 18992

Gday Robert,

Well, the Engine Mounts are new, the Transmission Mount is like new and good, the Rubber Centre Bearing Mount is good and undamaged, the Universals are new, the Top Diferential Ball Joint is new, the Tail Shaft rear tubing is original and the front tubing has been remade to accommodate the Cadillac front yoke to original specifications, and the Chassis isnt bent, twisted or cracked.

So, the only thing that can cause the diferential pinion angles to be out of alignment to such an extent has to be all the rear suspension bushes, and coil springs.

Well, having said that, all the bushes appear to be in good condition, and the mounting bolts are centred in the bushings, and the lower control arms are straight.

As I said in the initial posting, the replacement ball joint only managed to alter the alignment by .5 of a degree.

And, there are already two shims in front of the lower control arms.

I am aware of the necessity for correct phasing of the tailshaft/s as I am particular in this area when previously building cars from scratch, I am a Drag Racer and Hot Rodder, and have never experienced these problems in a car that is so like it came out of the factory.

When it had the 454 and TH400 in it, (It was in place when I purchased the car),I was aware of the alignment problems and as I was going back to the 390 and Hydro I thought that it would solve it, but to no avail.

Now I know the problem, I will eventually replace all the rear bushes, and in 2008, I will pick up a pair of new Coils, as I dont want to leave the riser in place, even though it is solid.

Bruce,
The Tassie Devil(le),
60 CDV.


Rhino 21150

I had a similar vibration in my 76 Delta Royale. I didnt think much about it. When I put a trailer hitch on it I also added air adjustable shocks in the rear. I noticed the vibration went away when I pumped up the rear to level the back with the trailer on it. It never occured to me that this may have fixed your problem.
I thought the vibration went away when I put new springs on the rear (coils), which I did at a later date. It was the shocks.
I may have to put adjustables on the front too. It is so much fun to raise and lower the car!
BTW, the shocks are Gabriel, $60US per pair from Auto Zone. The springs were from Whitney, $38US per pair.

Robt.Vonheck

-woops, my client-phone rang before i had a chance to review my explaination (which turns out info. you already knew);  --but please note that where i said "you can alternately lower the nose of her differential" (NO that would actually exacerbate the problem) i should have instead stated: "alternately raise the differentials-nose instead of raising the transmissions-tail" --which also means that perhaps you might elect to elevate both said portions but just half as much, so as to possibly avoid the tunnel-interference situation you encountered during body-jounce.  Additionally, we should note that settling of the rear-springs (ie: ride-height)does indeed tend to create the subject out-of-parallel vibration condition because the eng./trans.-mounts are thereby effectively pitched-downward at the trans./tail-shaft, even if in perfect condition!  At any rate, hopefully you put your finger on this pesky problem before likewise damaging the new UV-joints....   ~Bob vH

Bruce Reynolds # 18992

Robert,

I have only raised the centre of the two piece tailshaft, which actually is the same as lowering the diff pinion.

Funnilly, the car sits level when parked, so I must have collapsed front and rear springs.

Bruce,
The Tassie Devil(le),
60 CDV

Mick

Hello Bruce.
Congratulations on solving the vibration.
What is your opinion on the differential input flange aiming down instead of upwards closer to in-line with the rear driveshaft?
My very hard-head refuses to believe that aiming down is the optimal or correct way. It forms a senseless nasty angle against all common sense.
Mick

Mike #19861


  Funny, I would not have related this to your vibration problem. It does make sense, since the rear shaft is quite a bit shorter than that of a car with a single piece shaft, the more the spring sag in the rear, the sharper the driveline angle as compared with a longer shaft.

 Good diagnosis, Bruce!

 This could also be a real problem in the Cadillacs from the 60s and 70s. If you look at a plan veiw of the angle of the engine, drive shaft and pinion angle, you will see that they are quite severe. The reason for this is to give a relatively flat floor and low transmission hump. The engine is placed far forward in the chassis, with the angle to the rear quite sharp. The driveshaft remains low and the arc at which the rear axle travels keeps the pinion pointing in a downward position. This would be far too much for conventional u-joints, so Double Cardon joints are emplyed. They are essentially 2 u-joints close together in phase. They split the angle between the two of them, and cancel out each others vibrations. They do tend to be pretty forgiving to angles beyond the 15 degree critical limit of conventional u-joints.

 But, if and when the rear springs begin to sag, as they almost always do on these heavy softly sprung cars, the angle does increase. It can further increase with added weight in the rear and/or when the car travels over dips and humps in the road. Momentary vibrations can be felt as the driveline goes past the critical angles.

 I noticed this in my 70 Fleetwood when there was a load in the rear before I fixed the ALC. Now, with the correct rear ride height maintained, there is no vibration at any time. I do get a vibration in the Caprice with a load in the rear as well. It occurs to a lesser extent with the 86 Fleetwood. I hope to install ELC in that car at some time which will eliminate that problem.

  Mike


Bruce Reynolds # 18992

Gday Mick,

When dealing with universals and tailshafts, there is an engineering practice called "Phasing" which dictates that the centreline of the out-put shaft, be parallel with the centreline on the input-shaft, but must not be directly in line.

This is to allow for the up and down movement of the suspension, and allowing the rollers inside the universals to be turning all the time within the universal cups.

If the universal is straight, then the needle rollers wont turn, and will eventually disintegrate.   A totally "In-line" operation uses Bushes instead of roller bearings.

With the two-piece tailshafts of the "X" frame cars, other angles come into play.

Now, by having an angle on the diff, facing slightly downwards, as one accellerates, the natural tendency is for the pinion to try and rise up as the vehicle is trying to move forward.    If this rise is too far, then the "phasing" will be even further out.   So, as you can read into this, my suspension bushes must be too loose, even though they appear to be good.

In a drag race vehicle, this angle is retained by having a solid mounted rearend, or using Ladder-bars to optimise traction.   In a street application this isnt practicle as the average car has to go around corners and the owners demand a smooth and maintenance-free operation.

Hope this helps you understand.

Bruce,
The Tassie Devil(le),
60 CDV

Bruce Reynolds # 18992

Gday Mike,

Thinking backwards over the whole vibration occurrences, when the vibration readed its ugly head, it was only when taking off, and between 5 and 15 mph.   This is when there is most strain on the suspension bushes and the diff is trying to wind itself up into the floor.

And, when it occurred, the extreme left front of the car would shudder and shake, meaning I could see the front of the mudguard shuddering.   Plus, the diff felt like it was shudding and the exhaust was doing the highland fling.

So, the only thing I can put that down to is the fact that if one continues a line forwards through the "X" member of the Chassis, it nearly comes out at the left front corner of the cars bodywork.

But, when viewing the take-off from outside the car, with my son driving it, and he could feel the shuddering, I couldnt see the car doing anything unusual, but moving off as it went past.   Maybe the vibrating was in phase with the vision that my brain was absorbing at the time.

I even laid on the ground as he went past, and nothing was visible.

But, boy, am I glad that Yann and Gita dont have to experience the vibrating when I pick them up from the airport at the end of March.

Bruce,
The Smooth Tassie Devil(le),
60 CDV

Mick

Thanks for your patience, Bruce.

I do understand the need to have the universal joints forming an angle to ensure the needle rollers exercise some degree of turning when the driveshaft spins.  That could explain the angle between the center support and the rear driveshaft section; and the sharper angle between the rear portion of the driveshaft and the differential.

That sharp angle with the differential aiming downwards diminishes at acceleration but increases at deceleration, but never get to 0º.
If the differential was more in-line with the rear driveshaft section, the angles would vary ± from 0º in-line instead of only downwards

I do understand the phasing of universal joints respect to each other in a single shaft to behave as closely as "constant velocity joints" as possible.

But, the front section of the driveshaft is my nightmare. The angle between the transmission tailshaft and the front section of the driveshaft is minimal, can never be parallel to the rear section of the driveshaft as some publications suggest, and does not provide much needle rollers turning.

In relation to transmission mounts, the dilemma is:
Soft rubber mounts can allow the tailshaft to shake somewhat and isolate its vibration to reach the chassis.
Hard rubber mounts can transmit the vibration to chassis and felt everywhere...Or hard rubber mounts do not allow shaking because the transmission is firmly held that way ?

Mick
1961-6239 + 1962-6339