What rear gears do you have would be my first question. And are you running posi?

Im going to need your Year, make, Model, Engine, Transmission, modifications before I can properly diagnose your problem...LOL    Id make sure everything is tight with leaf spring bolts. 

Steve69

I had the same problem ...check the lowering blocks for an adjustable"offset" hole or pin...if so when you did a front end allignment it was compensated for...now with the blocks removed you have to recompensate...reallignment....jj

Are they adjustable shocks? one could be stiffer then the other. Or mounted upside down

How is your FRONT shocks?! My wore-out front shocks made my 66 do funny when letting off gas and hard acceloration.
6s6

Did you realign the front after removing the blocks?
What size blocks?

Kar wrote:

I think Jon Richard is on the right path, the front of the leaf spring is responding different with the block removed. The odd thing is, I would have expected more wrap with the block.

Also is there maybe a leaf spring strap missing off on side?

Since it only seems to occur under acceleration, that suggests that either something is changing position or that you are getting more drive from the left rear tire than from the right rear.  If the car is going right, then the differential may be moving counterclockwise (as viewed from the top of the car - right rear tire is more forward than the left rear tire), acting as a rear-steer to the right.  It could also be that the right rear tire is rubbing on something under acceleration - effectively braking the right rear and causing the car to move to the right.

Is there a way that you could have someone (or maybe two people - one to drive and one to shoot video) follow you to watch the rear end while you drive to find out if there might be something you can see to get an idea of the cause?

You sure its not that new high out put alternator pushing all the amps to one side of the car.

Can you create a centerline reference point toward the front on the car, say around the bellhousing? Then measure from the centerline reference to each spring perch. That will tell you if the rearend is square. Using the wheelwells as reference is iffy. Also, I experienced something similar to what you are experiencing when I first got my red car. Turned out that all the suspension bushings were shot and the suspension was wiggling all over the place. I know all your bushings are new, but maybe something is loose? I have run nuts down to the end of the threads on a bolt and torqued them to spec only to find out that what I was trying to clamp wasn't. Since you removed your lowering blocks, are your bolts too long?

I agree with John and Tim that it appears the left wheel is too far back, or the right wheel is too far forward.  Onl;y way to change that is to rework the alignment dowels and holes, so that may be in the future.  I am thinking of ordering a new 9" rear housing (to get rid of the dreaded Versailles housing) after the bash anyway.

Ubolts have plenty of threads showing, so the nuts are not bottomed out. 

I took it to an alignment shop today and we measured the heck out of it.  Even after the alignment, the same problem is there but slightly alleviated.  We even added some caster so I have 4degrees+ caster now.

The driver side wheelbase is indeed longer than the passenger side by 3/8".  I believe this is caused by the caster adjustment in front, and there being fewer shims in the UCA, etc so the front wheel is pulled forward a bit.  There is no adjustment in the rear axle.  I was able to move the axle 0.030 but that is all.

Now that I kow the front end is aligned to spec, I will adjust the bias on the TCP R&P unit.  I can make it steer itself in a left or right circle by adjusting that, so I should be able to dial out any pull.  It is a very simple adjustment, but is a adjust-drive-readjust-drive-readjust type thing, so the lift should get a workout .  If the rear end is not square, that will not straighten it out, though...just mask the problem.

Tomorrow's task...

And to top it all off... The fuel pump flamed out when I was leaving the alignment shop...  So I have to revisit THAT also.  The convertible may wind up going to Illinois if this doesn't clear up.  AndI think next year I may just put the entire car back stock !!!!!!!!

This thought is "way out there" and possibly irrelevant given what you posted above about the alignment but what about that hose that runs from the body to the axle.  The axle is an inch or two farther away from the body now and maybe the line is moving and clinching causing a rear brake to actuate or something.  I suppose the same applies to the parking brake cables.

I dunno, thought of it and figured I'd pass it along.