Technical 3 days later and vibration still there.

Didn't realize how jacked this was.

I've never liked it after I did it and was in a rush to get car on the road. So finally a reason to correct it and be done.

Other things checked was the tail shaft bushing. That sucker is the way it should be and no slop in slip yoke

 

I didnt see anyone suggest: jack up one rear wheel, turn by hand, listen and feel for bad rear axle shaft bearing, repeat on the other side

 

Three days? my wife's Dart has had a vibration like that since 1985....

 

I will beat the dead horse again. To make a shaft turn smoothly, the joints have to be at the same angle.That is the angle between the trans and the shaft and the angle between the shaft and the pinion. The angles do not have to be opposite. The can both be down. The joints don't care. Think about all the two piece drive shafts. How would that work if the trans end is down and the pinion is up. Which way do you point the middle? You can make a 90 degree turn with a shaft. 45* included angle on both ends.You can turn 45 * horizontally and then turn one end up 45*. All it takes is the operating angles be the same and the phasing correct.
For the OP, I would turn the pinion down and try for 3* included on both ends.
I am a retired board certified engineer so this is the real stuff.

 

He's right, you know.

 

Check this out, it may help

 

That is a move in the right direction.
I know that's going to give you 10* + working angle at the front, ( you're aiming for 3 *) At the rear you could have 10* or 2* depending on the attitude of the pinion. I'd bet if you ran the pinion at an equal angle ( not parallel) but opposite the Trans that you could yet again make an even bigger move towards the target

 

I just went through this. Drive shaft was phased correctly and balanced with perfect angles. New u joints, tailshaft bushing and yoke, axle bearings, drums trued, center section changed to a known good one. Still vibrated. One day, I put both rear tires and wheels on from another car and the vibration was gone. Should tried that one simple thing first.

 

So I checked phasing, and that's spot on... so I don't have to go throw a driveshaft through that shops window today.

Well I wanted to change this anyways and this was a good excuse to do it finally... and if it doesn't fix the issue I know I can at least rule out this being the main cause to begin with. And will maybe save u joints down the road also. But I am going to pull the tires and see this afternoon after slaving at my day job.

Very true, tons better than a 20* and should be better for the life of the joints.. only issue with dropping pinion down to negative 4 is rotating the axle like that the 4 link bars would be out of adjustment and the coil overs would be in a bind... I am honestly thinking of raising the rear 1" to help calm that 10 degree down to about 5 to 6 and we should be golden at that point I would think. I built the car with some adjustment to be had in some areas and Im glad I did it now. Rear can be raised 2 to 3 inches very easily but would need a new panhard rod at 2 or more.


To everyone who has chimed in on my threads.. good bad or indifferent.... I believe a Thanks is in order. So thank you.
Thinking that I don't do that enough and I appreciate all the help.

 

Yeah it's going to require bracket surgery, but that's easier than cutting the car apart.

 

Absolutely. Look at 60's and 70's Cadillacs. The trans and differential are both pointed down to achieve a low tunnel. But you need a CV at both ends as Cadillac used.

The diagram above makes it clear, yet the angles and wording muddy it up a bit. All you need is parallelism of the crank/trans and pinion centerlines. Going on about his angle here and that angle there confuses many people. Just get them parallel in all planes.

Cosmo

 

Yes, the reason they are called Constant Velocity Joints is because they do not suffer from the variable velocity of U-joints.

 

Back in the day, I bought a brand new 67 GTO that had a vibration at just over 65 MPH but no vibration when stopped and revving the engine. Eventually it got bad enough where it vibrated just revving the engine. I thought it was a bad water pump and took it to the Pontiac dealer who said it wasn't the water pump and the vibration was caused by the torque converter. It was under warranty so I didn't care what they did. After a week or so the converter came in and dropped the car off for replacement. When I went to pick up the car it wasn't ready. The converter was replaced but they were now changing the water pump. I said to the Service Manager I guess the water pump was the problem all along. He said no there was nothing wrong with the water pump but they were changing it as a precaution. Yeah, right.

 

So. Finally the rain stopped. So drive time. Vibration has gotten less but changed the feel. Went to tire shop. Rebalance later. Looked at all 4 when spinning and all 4 have some runout it seems. Looks like going to have to drop some money on tires again. Been wanting to change wheels anyways. So here is a reason to spend money for upgrades I guess. Haha.

 

From the picture the yoke should go father into the trans.

 

I wish man. 727 the output shaft is behind the tail shaft seal. .75 from bottoming out. The yoke is long as hell and goes in quite a ways so no stress there.

 

What do you want the problem to be ?

Swap wheels and tires with a budy for a test. See if his car vibrates with your tires and see of your car stops Vibrating with his tires -stops or at least changes.

It makes no difference to me how you spend your time or money, that being said I'd like to see you get it worked out and recieve the help you asked for.
Its pure folly to chase the obscure and fine details when there's a blairing and obvious fundamental flaw in the Ujoint working angles. If you want to put 3,4 or 5000 rpm thru a u joint it needs to be around 3* working angle. If you must to run 10* angles without a vibration keep the drive shaft Rpms under 1000.


Here's a little story that happened to me. I had a car that developed a vibration that came on at highway speed. It wasn't earth shaking but it would be really unpleasant for a length of time. I started with all the usual crap, completely flustered and discouraged I sought the help of a couple older wiser guys. They said well lets go for a ride and see. 3 jumped in my rag top Gto and off we went. The damn thing was smooth as glass and no vibrations. These guys are questioning my sanity and say there's nothing here. We get back to their hang out and start talking about this. So long story short ,,, 3 guys weight changed the rake of my goat lowered the rear, corrected the angles and the vibration went away. Take the guys out and vibration was back. I had some saggy springs up front, some air shocks in the back. Their weight leveled the car, leveling the car changed the angle of the engine, and the angle of the drive shaft enough to eliminate the vibration.

There were some of the twist in coil spring boosters I'd recently removed, and a few more ponds of air in the shocks I'd just added and mysteriously a vibration presented itself.

 

Just for the record... I mess with Jeeps and short wheel bases can make for some serious u joint angles around 7 degrees or more. This creates some drive line vibration but a lot less than you might think. Not saying it's something that should be done if it can be avoided.

 

stubbsrodandcustom, It looks like you can tip the differential down by adjusting your 4 link, this will eliminate the severe angle at the rear. Can the trans be raised anymore? Early 90's Dodge trucks had a similar problem like Vicky ^describes above. You either set the pinion angle for towing or near empty, not both.

 

Im already maxed at trans... Raised it up an inch off the crossmember now and there is no way it will go any higher... cant drop motor any more also... That inch made a huge difference... Going to give the pinion angle a full check now that's its been driven anyways.

31Vicky Yeah Im going to see if anyone else I know has the same bolt pattern.. most of my guys are 5 on 4.75 or 5 on 5 from what I have seen. I do have a set of tires that were on my pops 58 ford that I may toss on just to see... they are a smaller tire than the rear so may have to be careful with that. I have fought weird things through the years..

Maybe I am crazy but when cold and first driven... its hardly noticeable... Warms up presents itself more it seems. The intensity is there when it warms up... Not feeling anything through the shifter now.....just feel the motor through the shifter.

At 65 when this problem starts... Im turning 2100 to 2200 rpm roughly...

 

So Have been slowly working things out.. driving the hell out of it lately. Still have a little vibration but tons better.

After the last tire balance job I watched the tires for shake and run out.. 2 tires have some extreme run out, one has a shake to it also. BUT I will say this, After getting pinion angle and driveshaft angle adjusted... The problems have almost all gone away... think the only vibration I have left is all in the tires. So a set of BFG silvertowns have run out.. even a BFG radial ta has it too. So be cautious on your tires and watch them spin on the balancer... Now to figure out what tires to swap to next... Looking at doing wheels and tires at the same time I think.

Figured I would let yall know that we have it licked pretty much.. I know I have seen many threads where people never respond to what was the fix. Thanks to everyone who was here to help.

 

Identifying the "frequency" of a vibration will pretty quickly rule out ( or rule in ) which component(s) are likely suspects. The vibration frequency of wheel/tire issues and non-FWD driveshaft issues is quite different.
For instance, at 60 mph the wheels and tires are spinning about 800 rpm, and depending on axle ratio the driveshaft is spinning about 3000 rpm. (Driveshaft phasing or poor angularity causes vibration at 2X driveshaft rpm, or about 6000 "rpm" ( cycles per minute).

Attached is a vibration measurement I made on my old RWD Volvo's steering wheel running on the highway.
I could "feel" vibration in the steering wheel at that speed.
Because there is a "spike" visible at ~ 900 cpm/rpm ( the wheel/tire rotating speed) I will be checking the tires for runout, and if that is OK getting them balanced. It is also possible that loose suspension components could be allowing the wheel/tire to move/shake more than it normally would.
I did not consider doing any work on the driveshaft since the vibration is not at it's running speed of ~ 3400 cpm/rpm.
==============

For under 30 bucks it is possible to buy a mechanical vibration driven tachometer.


5;00 to 5:20 basic principle ( wild vibration at "resonant frequency" of extended wire)
7:45-8:10 actual use 2200 rpm/cpm
8:40 - 9:20 actual use 3600 rpm/cpm

It looks like a useful substitute for a fancy electronic spectrum analyzer.

 

It has been suggested several times, so now that you have gotten close to solving problem, put a new bushing in the tailshaft. It would be nearly impossible for it not to have been worn beyond tolerance.

 

From the picture I would say your driveshaft is too short. Which for sure will cause a vibration at speed.

 

In most leaf spring apps the pinion angle is close to level or a little down. They will lift under acceleration.

 

You mentioned the tires running out. It may be worth having them shaved to rule them out. Any 4 x 4 truck shop or truck alignment shop should be able to handle it.

 

Length has nothing to do with it, it's all placement and angles.
Which if you see stubs has corrected the problem by correcting the working angles, not the length.

 

check the harmonic balancer!