First, did you shorten your driveshaft and was it balanced?  Does it shake at 65 in 4th and 5th gear equally?  Is the vibration worse when accelerating up to 65, dwelling at 65, or decelleration down from 65?  Does it get worse going beyond 65?  If it is speed related at only this speed it tends to point to a resonance issue that may be related to driveshaft balance, engine balance, or wheel balance.  The wheels are turning a lot slower than the driveshaft so by feel determine if the vibration is low frequency, at engine speed when in 4th gear (1:1) or at twice engine speed since misalignment of driveline angles typically produces vibration at two times driveshaft speed.  If you have messed with your exhast system, it is easily excited by the driveline and can shake heavily at certain speeds.  If you shortened the driveshaft, how far is the yoke into the transmission.  If you didn't shorten it, are you bound up because the shaft is too long?

Next, get a digital level for about $29.00 - Sears has one - I have had poor success with the $5.00 angle finders but maybe that's my luck.  Lift the car front and rear and support it under the rear axle to preserve the correct axle position.  Take the level and measure the angle of the engine/transmission.  I find that holding the level along the valve covers works pretty well.  If the car is at its normal level, it will be pointing down in back between 3 and 6 degrees.  Next, measure the angle of the rearend.  The car has to be in the same position when you measure the axle and the engine so you can compare the two angles.  The pinion should be pointing up but the angle is what we need to know.  You can measure the angle on the bottom of the axle housing but make sure you orient the level so it is pointing front to back as a slight twisting from front to back can give you a false angle reading.

Next, for now, measure the angle of the driveshaft and although it may no be needed now, measure from the floor to the center of the rear and front u-joints and the distance between the u-joint centers.  These measurements may be needed to plot out the combined angles.

Before you do anything, post all the angles and then we can figure out what to do.  One problem with some of the T-5 conversion crossmembers is that the set the driveline angle down to 6 degrees and it no longer matches the rearend.  If you move the pinion to match your u-joint angles can be too large so you have to figure out an optimum move.

MWN - hope you do not mind, I like to jump into this post as I too am having driveline vibration problems. 

I have a vibration problem that has gotten worse recently.  There is a steady vibration that starts to get worse at about 60 MPH and increases to about 70 MPH where the intensity decreases, but doesn’t disappear.
If I step in on the clutch or just lift off the gas, between 60 & 70 MPH, the vibration continues, but changes intensity slightly.
I have 9” rear w/3.89 and a new WC T-5, about 4000 miles on the combination, I had an aluminum driveshaft that I brought to my local driveshaft shop and was told it was bent.  I purchased a steel unit, that was balanced, and new u-joints.  This seemed to help, but not eliminate the vibration.  The rear axles have new bearings, and the center section has all new equipment (w/about 4000 miles).
The driveshaft is 50” long, u-joint center to center.
I have a protractor level and took the following measurements as GPatrick suggested.
Valve cover – 4 degrees down in rear.
Driveshaft – 3 degrees down in rear.
Rear End housing – 3-4 degrees down towards the front.
This vibration got worse recently after I replaced the two exhaust system u-bolt clamps at the rear of the H-Pipe with “band clamps”, to allow for easier transmission removal.
Any assistance is appreciated.
 

November 2014 issue of Car Craft on page 80 has a article on Driveline Vibration.  They say in there Tremec has a Iphone Driveline Angle Finder App that is free. 

Steve69

Last edited by Steve69 (11/01/2014 8:54 PM)

When you lower it, the angles may change again so I think shims would be a good short-term solution and if they don't work, it is an inexpensive trial and error.  I would try to lift the pinion by 3 degrees which would take it to a pinion up angle of 2 degrees to allow for spring wrap.

A driveline misalignment can put high stresses on u-joints but I don't think you case is extreme. While installing the shims, check the u-joints to make sure they look and feel OK and if they can be greased it would be a good time to give them a shot.

An additional angle that can come into play is centerline offset of the differential.  Is the 57 Ford rear centered?  If the pinion is offest you need to include that angle along with the vertical u-joint angles to ensure that the u-joints are opperating within limits.

Summit seems to have a good collection of shims - both angle and width.  I have search a few other posts and they suggest that the pinion be set 1/2 degree from the engine/transmission but with your gearing I think 1 degree may be better.

Let us know what you find out.

In the Tremec installation instructions it discusses the rear crossmember and states that it cannot be a cantilever design.  Several of the aftermarket crossmembers I have seen simply move the mounting plate for the trans mount rearward which effectively does create a cantilever since the weight of the transmission is not carried through the mount and into the centerline of the crossmember.  With the stock Mustang mount with the original transmission you can see that the mount is nearly centered over the center of the crossmember.  The cantilever design in some mounts can be pretty weak torsionally (twisting) and this may lead to a reduced natural frequency of the engine/transmission on its mounts - in particular a "pitching" or "rocking" motion of the motor and transmission or a vertical shake at the back of the transmission.  Take a look at your crossmember design or take a picture so we can see how it supports the transmission.

Lift the car under the rear axle and support it.  Get it high enough so that you can crawl under the car to check your exhaust system.  Lightly place one hand on the exhaust system in front of the mufflers so that you are not bracing the pipes.  Using the heel of your hand, impact the exhust system at multiple locations and feel the response with your hand.  You are performing a low-tech bump or impact test which is effectively the same as ringing a bell.  Feel the vibration frequency/frequencies of the exhaust system when it shakes at its various natural frequencies and compare to what you feel in the car when the shaking is bad.  This would help to explain a speed sensitivty at a particular MPH range.  But, this diagnosis doesn't help with vibration that is present at all speeds.  Regardless, you did mention that it got worse after changing clamps so this may be related.

When the driveshaft was shortened, was it balanced as well?  Most shops will balance automatically when modifying the shaft but it is stll good to check.  Also, a few weeks/months ago I think there was someone on this site that found that one of the weights had fallen off the driveshaft.

For your angles, please confirm your rear axle angle and that the pinion is indeed pointing up.  If it is pointing up, the angles don't look too bad - if it is pointing down as Bob found, you will have vibration through all speeds.  Were the perches moved on the axle when swapped into the Mustang or did they have the correct angle?  Also, is the pinion centered or is it offset to the side.  You have about a 2 to 2.5 degree u-joint angle just looking at the vertical readings.  If it is offset to the left or right the total angle would have to be computed.

Another question is does the vibration change with car load?  Is it worse with 4 people in the car or if you have a heavy load in the trunk.  The change in ride height will alter the angle of the pinion slightly and can make a drivetrain angle problem worse or even better in some cases.

Back to tire balance suggested in a post above - add to that out of round tires.  If your car sits for extended periods it can cause the tires to become square.  Sometimes after driving they will become round again but sometimes they will take a set and regardless of balancing, the car will shake at all speeds and get worse at higher speeds.  I had a tire on my Porsche that went square and only replacement cured the shake at 75 MPH on the interstate.

It would be helpful if you could describe your problem as low or high frequency which helps to determine if it is driveshaft balance, alignment or tires.

Maybe I am over simplifying, but since the rear axl flange is up and shy of a couple of degrees, couldn't I loosen the U clamps and or shackles, then use a jack to dial in a degree or two?
Thank you

Ok, looks like Summit has Competition Engineering Two Degree Wedge Plates C7025. I think two degrees may be enough, but in case I still have vibration will an extra set and four degrees hurt?
Thank you

MustangSteve wrote:

Posted for MWM

What are you showing in your pic MS?   Just currious having a vibration problem also.   Thanks Steve69

GPatrick, thank you for your input, I think I'm on the track now.  I will check the centering/offset of the drive shaft.  It will be a few weeks before I can get to installing shims, etc., but I will post the results.

Note that if one Googles "leaf spring wedge shims", or "leaf spring shims", several venders will come up.  Most of these venders cater to the 4-Wheel people, and some offer custom degree shims based on your specs.  One item I'll note is that as these shims will mount on top of the spring, your need to account for the center bolt that clamps the spring together as it also centers the spring to the housing perch.  Some of the venders offered a replacement bolt with a longer head to make up this difference, some shims will use this bolt to hold the shim in place.  In any event, anyone planning to install shims must take this bolt into account.

MWM - once again, thank you for your post, hope you don't mind me jumping in.