Recentering a rearend?

Jimmys66 · Mar 12, 2007

I'm running a set of 255 45 17's on the back of my 66 with 4.75 of backspacing. The driver side Q/P was replaced at some time and now has less tolerance than the passenger side. The tire rubs the driver side but, the pass. side has plenty of room, over 1" of clearance.

This got me to wondering. The Q/Ps are only maybe 1/4" different max. I started to measure things with a tape measure and sure enough the rearend is 3/4" off center to the drivers side. I measured using the housing ends and the frame rails.

I installed the springs correctly, Why would it be out of center? The car hasn't been wrecked in the back(that I can tell, but it did have a Q/P replaced).

How do I correct this problem? I have tried loosening and the bolts and letting the susp. hang but, to get it centered I need to actually force the housing over and then it goes right back to being out of center when I let go. I don't think it's the leafs as this is the 3rd set.

SoCalCruising · Mar 12, 2007

Well, thinking about it, the frame rail locates the spring, and the spring locates the rear end via the spring perch and locator "dowel". So, if that is true, then the frame rail would seem to be displaced. There is always some difference from car to car, but yours would seem to be too much for normal variation. I would suspect that the frame rail was displaced from an earlier accident.

Applejack · Mar 12, 2007

I just installed new leafs in my car and there was enough room between the pin in the leaf spring and the hole in the perch of the axle housing to position it in the center of the car and then tighten the U-bolts.

D.Hearne · Mar 12, 2007

The 77 Comet I just bought, my 89 Ranger and the 68 Merc Monterey I just sold all had the rear offset slightly to the right, not left like yours. The Comet is 1/2" off toward the right, there's 1" difference in fender clearance. My Ranger is not quite as bad but still off. The 68 Merc was as well..None have ever been wrecked.

SoCalCruising · Mar 12, 2007

I will be very happy if I am wrong about why the rear end is offset. It's just that the amount he stated, coupled with the replaced Q/P on that side is very suspicious - at least not knowing if the Q/P was replaced for rust repair vs. a collision. My father's business was an body shop in San Diego and I remember very well the limited equipment available to repair frame damage back in the those days, much less repair a damaged monocoque vehicle. These days, cars are placed on jigs and can be repaired to nearly original dimensional specs. Not so in the old days. Anyway, I'm happy to be wrong about this, if I am.

truck90278 · Mar 12, 2007

Find yourself a good frame shop, check out body shops that do a lot of restoration work along colission damage. Some of these shops have frame equipment that can get you squared away. Not only can they get them close to original, but can frequently get closer to the specs than the factory..Factory work, even on newer cars have pretty large tolerances.

mxmattd · Mar 13, 2007

i noticed the same thing in my 66, only its offset to the right. the passenger side rear occaisionally rubs, but there is plenty of clearence on the driver's side. i haven't measured, but i believe its offset about 1". I have no reason to believe that mine was in an accident either

Jimmys66 · Mar 13, 2007

SoCalCruising said:
Well, thinking about it, the frame rail locates the spring, and the spring locates the rear end via the spring perch and locator "dowel". So, if that is true, then the frame rail would seem to be displaced. There is always some difference from car to car, but yours would seem to be too much for normal variation. I would suspect that the frame rail was displaced from an earlier accident.

You could be right. The only reason I don't think it was hit, is that the QP was replaced with some poor welding skills. The outside body looks nice but I can see every poor weld in the door jam. I would assume that if unrepaired, I'd see a frame wrinkle and if repaired I'd also be able to spot the poor repair.

I've tried to have someone hold the rear centered and then tighen everything up, but it just swings right back to place(or out of place).

So, maybe it is time to send her off the the frame shop. Is this going to be expensive?

Jimmys66 · Mar 13, 2007

Applejack said:
I just installed new leafs in my car and there was enough room between the pin in the leaf spring and the hole in the perch of the axle housing to position it in the center of the car and then tighten the U-bolts.

Where is White Lake? Over by Detriot?

Booksix · Dec 31, 2007

I know this thread is a bit old but did you ever take your ride in to be straightened?

I just lost a wheel on the freeway (attempted theft left me with one locking lugnut and a bunch of other loose ones on other wheels) and now I seem to be overly sensitive about misalignment. I noticed (not the first time but more than ever now that I'm looking for damage) that my rearend also seems to be about 3/4" toward the drivers side.

I was also rearended a few years ago and the car was said to be in spec on the frame straightener. But I'm not so sure that shop was 100% reliable. I'd like to have it double checked/fixed but I'm wondering what the cost would be (a big bill could make the insurance company want to total the car, which would force me to not file a claim and thus cover all the other repairs myself)

69 Rustang · Jan 1, 2008

Interesting thread, I just discovered my car is slightly offset to the right side by about a 1/4" inch last week. I was hoping to get an 1/8" back through "slop" by loosening and reseting. Now I have doubts... I need that 1/8" inch for tire clearance! I may try swapping the left and right leaf springs as I am taking them back out anyway.

Nosboss · Jan 1, 2008

I am with most other people, my car has the rear axle offset to the RH side (passenger). It is more like a half inch. My RH rear tire rubs on big bumps and the drag radials rub on pretty much all bumps... RH side only. My quarter panels are stock with the exception of patch panels on the lower portions.

BTW... HAPPY NEW YEAR GUYS!!!

Booksix · Jan 1, 2008

So no one on here has any idea the rough cost to have a car put on the frame machine and possibly tweaked back into spec in the rear?

Jimmys66 · Jan 1, 2008

Booksix said:
I know this thread is a bit old but did you ever take your ride in to be straightened?

I just lost a wheel on the freeway (attempted theft left me with one locking lugnut and a bunch of other loose ones on other wheels) and now I seem to be overly sensitive about misalignment. I noticed (not the first time but more than ever now that I'm looking for damage) that my rearend also seems to be about 3/4" toward the drivers side.

I was also rearended a few years ago and the car was said to be in spec on the frame straightener. But I'm not so sure that shop was 100% reliable. I'd like to have it double checked/fixed but I'm wondering what the cost would be (a big bill could make the insurance company want to total the car, which would force me to not file a claim and thus cover all the other repairs myself)

My problem ended up being a bad set of leaf springs. I bought a pair of Maiers springs and had planned to do the swap anyways (bad wheel hop).

After we pulled the old(100 or so miles) springs out, we set them on the floor next to each other. Both springs were racked to the left. Not quite sure what happened, Both springs were new but we never inspected them close enough when we installed them to notice.

We bought them from a spring shop in Detroit while at the Woodward dream cruise. My old springs went flat after spending some time at the cruise. We changed them in the hotel parking lot.

Nosboss · Jan 1, 2008

I have the global west springs... I'll have to look at them a little closer to see if that is where my issue is. I just noticed that my driveshaft is closer to the passenger side of the tunnel too so it could be in the springs.

69 Rustang · Jan 1, 2008

Booksix said:
So no one on here has any idea the rough cost to have a car put on the frame machine and possibly tweaked back into spec in the rear?

Most body shops charge about 2 to 2.5 hours/units of labor to set up and measure. Labor rates vary by market, some markets have a separate "frame" labor rate from the "body" repair labor rate. As most labor rates are below $80, would guess it would be under $200 TO MEASURE if you can find a shop that will do it. If in the Bay Area or some other high rate markets a bit more. Pulling any damage would depend on what they find. Keep in mind, with a frame pull, they have to secure the car to the bench somehow which could include using pinch weld clamps. Pinch weld clamps leave marks on the pinch welds when they are done, so you may have other issues to correct later.

The other issue would be having the frame specs, which most regular collision repair shops won't for a car that old. You should be able to visually inspect the undercarraige for unusual looking bends or folds in the rails, floors, and supports and if there is anything major, it will be visible.

chromedog · Jan 1, 2008

my 65 is offset to the left... drivers quarter is about 3/8 inch closer than the passengers. the car took a mild shot to the drivers rear long ago, but still has factory sheetmetal. the impact didnt even damage the outer wheelhouse, let alone the frame rail, so i dont think a collision is the reason. these cars have a hugh factory tolerance, from what ive seen. and, im sorry to say, putting one on a frame machine, even if you had the measurements, is not a good idea. a frame machine is designed to correct damage, not twist, bend, or distort the structure into a different shape. to do this would weaken the unibody, pop welds loose, and literally tear your car apart.

BarnStang · Jan 1, 2008

You can buy new spring perches. CHeck Summit. My local speed shop had a set. Cut the perches off the axel housing. Buzz them smooth with a grinder. Set the rear on the new perches and center. Oh, mark a line before you grind the welds smooth. You willneed to make sure the rotation of the housing stays the same/pinion angle stays the same. Tighten the bolts down and tac weld in place. Pull the U bolts and weld completly. I'm doing this now. (On my list...). THis is the easist way I know to center the rear. Assuming no major structural damage is covered up. THe frame rails would have to be WAY off to movethe rear very much. Unless the whole thing-torque box to the end of the rail was replaced and done so wrong that it was of an inch. Possible. Even if that were the case, I would cut the perches and recenter it. Leave the frame rail intact.

zookeeper · Jan 1, 2008

I was just about to suggest lopping off the perches and re-welding them where you want the rear to end up when I read your post. If the frame rails aren't bent, the doors open and shut fine, I would assume the unibody is close enough for street use and just make the rear axle fit where you need it to be. It's got to be a hell of alot easier than yanking a unibody back into shape (when it probably wasn't square when it was new) or replacing a quarter panel.

65fastbackresto · Jan 3, 2008

A body shop in town

was gonna charge me $200 to check my frame. It was a minimum charge too.

Recentering a rearend?

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