Still Chasing a Vibration

[MikeStang 247]

Okay I am still in the process of chasing a dang vibration that I have coming from what feels like the rear end or something.

 

Once you get up to speed at about 50 and up you start feeling a thrumming vibration that is constant and increases with speed.

Its like a deep sound that goes Wuummm...Wuummm...Wuummmm and gets faster the more you speed up... I have adjusted pinion angle, played with Caltracs, swapped shackles Etc....

Car has new 4.5 leaf reverse eye springs, New custom steel Driveshaft that was balanced, 4R70 trans, New tires and wheel that have been balanced 3 times and new rear disc brake kit.

 

So last night I decided to put it on Jack Stands and run the car at speed and see if it would make the noise, so heres what we did.

 

1. Ran car up to 50mph and vibration began very slightly... increased speed to 80mph and vibration was more pronounced, so the problem can be replicated on stands under power

 

2. Removed the Rear tires and installed lug nuts and ran car up to speed again.... vibration still occurs

 

3. Removed Brake Rotors and calipers and ran car to speed... Vibration still occurs

 

4. Checked axle Run out and its almost non existent and axles are running smooth as glass at speed

 

5. observed driveshaft and it is not vibrating or occilitaing and appears to be running smooth as glass at speed.

 

6. ran car up to speed and threw it in neutral and vibration goes away instantly

6a. Revved engine up to speed with car in neutral and no vibration in motor and trans...smooth as silk

 

7. Put car in gear and brought up to speed and placed hand on rear diff and could feel the pulsating vibration in the housing that I can feel in the car....

Gears are brand new and set up by Local fellow with excellent rep and he is a ford guy and rear end does not whine or howl

Housing and Axles are all brand new.

 

Now the only things I can think of are that maybe the Pinion Yolk is slightly tweaked or the new gear set is bad???

OR MAYBE the Pinion angle is a hair off enough to cause the vibration but it sure looks to be spinning damn smooth and straight.

 

Need some help or suggestions here guys.

I have ruled out the Motor and Trans being the culprits so its gotta be driveshaft angle or rear end...

 

Any other tests I can do?

[barnett468 418]

need to know what your tranny angle and pinion angle are.

 

could also be driveshaft balance . i have mine high speed balanced.

 

grab the front yoke and try t wiggle it . if there is much play, you need a trans bushing.

 

might be bent rear yoke . had one in a trans am and i finally figured it out.

 

make sure the exhaust is not touching the body and that it has rubber hangars.

[Brian Conway 264]

I to have spent some time chasing a vibration.  During that chase I had the driveshaft balanced and the ' U ' joints replaced.  They wern't the vibration source. Before getting into the axle/diff. eliminate the driveshaft as the problem. ?  My vibration was a 2 oz. imbalance in the clutch pressure plate.  Brian

[Chelby-Ann 47]

Hey Brian

I went thru the same vibration issue as your having and did exactly the same things you did looing to the root cause.

I finally removed the drive shaft from the yoke after removing the wheels, brakes and rear axels for a second time.

I turned the yoke by hand and found the source of the vibration.

I removed the differential and found that the pinion was not messing with the ring gear anymore after 200 miles.

When I rotated the pinion shaft it felt like I was rolling my knuckles on the table.

Took it to a shop for them to tell me what was wrong.

The pinion bearings that I never replaced when I changed out the gears for 3.55's went bad.

Had them rebuild the diff with all new bearings and seals and that solved my vibration.

 

Good Luck.

[MikeStang 247]

Barnett,

Trans is at 4 degrees down.. Pinion is right at 3.5 degrees down.. Have run the pinion angle from 3 degrees up to flat at Zero and now down to 3.5 and 3.5 is the furthest I have went down and it seems to have yielded the best results

 

 

could also be driveshaft balance . i have mine high speed balanced.

My Driveshaft and U-Joints are all New and are high speed balanced...Shaft was built by Very reputable shop in Houston

 

 

Q. grab the front yoke and try t wiggle it . if there is much play, you need a trans bushing.

A. I had the Transmission bushing replaced when I had the transmission gone through after I busted the case on the trans due to leaving the casting ears on and them hitting the underside of the car. There is no noticeable play at all in the bushing tho... just rechecked it

 

Q.might be bent rear yoke . had one in a trans am and i finally figured it out.

A. How can I tell if the Yolk is bent....Its funny you mention that because My 77 Trans am had this same vibration and I never could figure it out LOL.

My Front Driveshaft yolk is New tho.

Wondering if I don't just get a new Yolk and try it... Can I just unbolt the pinion nut and swap it without having to put a new crush sleeve in and resetting the preload?

 

Q.make sure the exhaust is not touching the body and that it has rubber hangars.

A. Exhaust touches nothing and has rubber hangers... Checked that a few times.

 

Rear end has new gears set up buy reputable builder but bearings were reused from when I did the rear the 1st time with 3.25 gears but he said bearings were fine and I had the vibration b4 the rebuild if I recall

[SA69mach 39]

Remove the driveshaft and yoke from the transmission and run it again.  see if the vibration is in the flywheel/flexplate area, or the transmission.  If you still have the vibration with just the engine and transmission connected, then you can eliminate the driveshaft and all the drive line behind it.

 

If you have it with trans and engine connected, then keep looking and dismantling until you have the problem isolated as much as possible.

 

I guess you have taken off the belts and fan in the engine bay and checked all that end?

[MikeStang 247]

Its not a belt Vibration. Its a serpentine belt and running smooth as glass with no wobble or flex at speed.

Just putting it in neutral accomplishes the same thing as pulling the driveshaft, and when I put it in neutral and bring it up to 4000 rpm's its smooth as silk with no vibration... If I did run the trans in drive with the shaft out it would likely puke fluid out and make a mess not to mention the output shaft is going to free float .

[barnett468 418]

xlnt info

 

if you have urethane engine or trans mounts, they can indice a vibration that you might not feel by simply revving the engine . i had that prob before.

 

as far as the trans and pinion angle go, it will be the smoothest when both the trans and pinion are at exactly the same angle . when you are driving, the pinion is slightly higher than it is when the car is not moving, therefore, I try to set them so the pinion is around 1 degree lower than the trans . this way, if all the parts are in good condition, it should not rise very much at steady speed [hopefully no more than 1 degree] and the slight misalignment at lower speeds will not cause a vibration because the speed is too low.

 

yeah, i did the tires and new drive shaft etc on my trans am because i couldn't see the bent rear yoke by spinning it in gear using a coat hangar on the ground as an indicator, but i just got a new yoke because everything still pointed to the diff and that cured it.

 

a bent yoke is very rare unless someone raced the car or drove it on a motocross track, but it can happen.

 

reading thru everything you did, it is exactly the same thing i do, so i can't think of any other test . you would have o remove the yoke and put it on a lathe and check it with a dial indicator if you wanted to check it.

[MikeStang 247]

It was vibrating like this before I added the adjustable Poly motor mounts LOL.

Trans mount is stock.

I may try to get he pinion angle down on the rear end a little bit more and see what happens.

If I go to the trouble of removing the Yolk I will just replace it with a New Billet unit or something stronger or better LOL.

 

Think I'm going to pull the shaft tonight and put it in gear and see if its will puke fluid out when I accelerate the motor and see how bad the output shaft free floats just to try it.

While its out ill give the pinion shaft a spin and check to see if it feels funny or has excessive slop in it...

Will have to look and see how much slop is to much LOL.

[SA69mach 39]

Might be the output shaft has got a bend or a twist.  Depends on what sort of action and work it has been put through, since it takes a lot of tq and hp to twist a shaft. What is the history on the transmission?

 

Seems the engine is smooth, which is a relief for you I am sure.    As mentioned, hard urethane mounts can induce  a harmonic (which can in turn become a felt vibration) 

Your pinion angles seem good.

 

I hope you don't get a trans puke or out of control shaft.....  Good luck.  Probably worth the effort to isolate the problem.  Maybe smarter to try a new yoke first, but it is your call.  It is not fun tracking down a vibration.

[Cruzzar 22]

I had similar issue with a previous car and it turned out to be not enough contact between the yoke and transmission output shaft.  You should have only about 3/4 inch of extra space when you install the drive shaft into the trans and then slide it back to engage it in the rear end's yoke.  I had a new shaft made(longer) and vibration went away. Just a another possible problem to check out.

[Rsanter 152]

Run one more test.

The test you missed was to bring it to speed and pop it in neutral and kill the engine.

Let the drive shaft and rear end keep spinning and see if the vibration remains.

 

I an suspecting the drive shaft, make sure the Uhoints are properly seated and centered

I know you said it is new but that does not always assure that it is fine

 

Bob

[MikeStang 247]

Driveshaft length is correct.

I have a little less than 3/4" and it has more than enough engagement. The yolk for the 4Runner is very long lol and splined all the way.

 

I pulled the shaft tonight and tried to run the trains, and it didn't puke fluid but the output shaft jumps around to much and would make a racket before you got to 20mph so decided that was a bad idea... With the shaft installed they is no play in it so it's not a tail shaft bushing.

I rotated the rear by hand and it felt smooth as butter and had minimal play in it.

U-joint caps looked fine, all needle bearings were there and looked good and no markings on the cross shafts either.

 

Tossing it in neutral and killing it will be tried tomorrow I suppose, but it's hard to notice when you decelerate... Just tossing it in neutral and leaving motor running when your rolling stops the vibration instantly, but your no longer applying power so...

I even held the throttle in same position and tossed it in neutral...vibration stops instantly and motor revs way up

[barnett468 418]

Driveshaft and trans angle or driveshaft or rear yoke.

[MikeStang 247]

Going to add 2 more degrees of Down angle to the rear end tonight and see if that changes anything.

While I'm under there I will also take a look and see exactly which Rear end Yolk I need and get another one coming I suppose.

 

I don't know of anything in the transmission that could really cause this kind of problem, and with as long as it has been doing it I would think that if it was a transmission problem it would have already failed or broken some parts or something LOL.

when I had it gone through the guy at the shop said everything looked perfect inside and had no excessive wear...

 

I may even consider an aluminum driveshaft, or perhaps an aluminum shaft with a CV joint on one end, which would eliminate ANY problems with drive line angle pretty much no matter what.

 

I just cant help but think that this problem is related to the driveline angles somehow, but there are plenty of guys out there running cars like ours with Reverse eye springs with no issues.... This is really starting to grate on my nerves I know that much... The sad part is there aren't even any shops around here that can diagnose the problem...the one I tried said it was normal and nothing I could do about it :(

[RPM 1,190]

Just in case you're not familiar with these two threads Mike, here's a couple of links. The first link is Mustang Steve who currently has an almost identical problem, but he has a T5, hmm.

 

http://fyi.boardhost.com/viewtopic.php?pid=51320#p51320

 

This second link is about a guy who visits VMF, and the lengths they went to find the cause of vibration.

 

http://www.hotrod.com/how-to/chassis-suspension/1405-1967-ford-mustang-vibrates-during-right-turns/

[barnett468 418]

Going to add 2 more degrees of Down angle to the rear end tonight and see if that changes anything.

 

I just cant help but think that this problem is related to the driveline angles somehow,

 

That should make it worse . Your angles are nowhere near where they should be. Have you installed any dynamat type sound deadening material? 

[RPM 1,190]

6. ran car up to speed and threw it in neutral and vibration goes away instantly

6a. Revved engine up to speed with car in neutral and no vibration in motor and trans...smooth as silk

 

 

 

The fact that the vibration stops after the load on the rear end is removed makes me think it's a pinion angle related problem. Have you thought about removing the exhaust pipes to eliminate them as the issue?

[MikeStang 247]

Barnett the entire inside of my car is Dynamatted....Inside doors, roof, floor, wheel wells, the entire trunk area is also dynamatted as well.

 

RPM I have checked and double checked the exhaust and its bolted at the collectors, runs straight back to an X-Over, then into the mufflers and there is a hanger on each pipe that have the rubber isolator strap that supports the load. the exhaust pipes then run under the axle and out the back on 1 side where there is another rubber isolated clamp... there is no metal to metal contact anywhere, but I may just pull the whole exhaust system out from under the car and go run it just to see since it all comes out in 1 piece LOL...Boy that's going to be loud and fun LOL.

 

Barnett my trans is still pointing down a little further than my rear end is lol. I cant shim the transmission up any more either because the bolts wont be long enough, so that is out of the equation.

I was just hoping to maybe get the rear end pointing down exactly the same amount as the transmission is or maybe a hair more so that when it does rise it will be closer to 0.

Why do you say they are no where near where they should be?

 

 

I will get it up on stands tonight and take a reading near the rear of the driveshaft, then near the front, and then will remove the shaft and check the trans angle and rear angle AGAIN and see what the working angles are.

Right now I have a 4 degree shim under the axle to point the rear down.

[det0326 179]

i have been following your threads on this subject and I know when you say you have tried about everything and that the lower you turn the pinion down seems to help. Barnett is right tho moving it down should make it worse not saying it will but theoretically it should. According to what i know about this your best senior would be since your tranny is 4* down  your pinion should be 3* up.

 

Dave 

[MikeStang 247]

yeah I know the whole equal but opposite angle thing.

So why then do we all shoot for the pinion to be angled down a degree or 2, especially since most transmissions are already pointing down hill.

I have read all about canceling the vibration etc... and even had the pinion pointing up which made it worse

[MikeStang 247]

Well maybe I will flip the 4 degree shim around and see if I can get it going the other way and try it again LOL.

[det0326 179]

One other thought on this Mike. With your car sitting sorta level from the tranny to the rear end is the drive shaft going up or down or pretty much level. To explain more of what I am thinking I know that you have your car lowered and was just wondering how the relationship of the tranny was to the rear end. I guess at some point lowering a car you could cause the tranny to pass the center line of the pinion or be very near level with it. Don't know if this may cause your problem or not.

 

Dave

[MikeStang 247]

Dave the Drive Shaft runs down hill from the trans to the rear end, if I recall its like 2.5 degrees down

[Mach1 Driver 560]

 your tranny is 4* down  your pinion should be 3* up.

 

Dave 

+1