Technical Rear axle not perpendicular to the frame

So I just got my 31 AV8 coupe on the road. I noticed tire rub on the driver’s side rear. I have a triangulated four link in the rear. Luckily I have a friend’s lift available.
So, what would be the best way to adjust the suspension so the axle is at right angle to the center line of the chassis ?
Thanks in advance

 

I was told, and did, triangulate from a common place on each side of the rear axle housing (or brake drum, etc.) to the center point of the front suspension - both sides need to be the same. In my case on a Model A that was the center alignment pin on the buggy spring. I used a laser measuring device I got at a big box store. I have ladder bar rear suspension, so pretty easy to adjust. Worked well.

Is that what you were asking?

John

 

Either the rods are different lengths, or the mounts are welded inaccurately, or something is seriously bent. Determine that by measuring. Then correct accordingly. If it's the rods, cut and weld them all to the same length. If it's the mounts on the frame or rear end housing, and it is a small enough error, you could weld up the holes and re-drill them. Or cut the mounts off and weld new ones on with everything properly squared.

 

You might be needing to remove the body and start over…

 

This was a common issue with GM cars with C clip rear ends. That said, what rear end are you running?

 

First figure out the WHY then re read post 3 as John pretty well hit the how.
I'm not sure that a hoist is going to help a lot unless it is a 4 post with ramps where the car can sit static while you measure and check.
Then the question comes up, is the frame square to begin with? If so there should be matching factory done reference points on the sides of the rails that you can measure from to exact spots that match on the axle side to side.

Now the next question is how far off side to side is the axle? Did you do the OMG I have to have the driveshaft run straight and not at and angle nonsense and move the whole rear end offset to one side in the process?

Possibly does one rear rim have a different offset than the other? I've been there done that on my 48. Bought a pair of wheels as snow tire wheels and got the tires mounted and when I installed them one fit and one was jam up against the bed. On any other rig you would have never noticed but I only had about a half inch clearance on the good side to start with.

 

Personally as stated, I'd use a trammel and first check that the frame is square, checking both lengths and diagonals. Next I'd check that the front axle is square in frame before moving onto rear axle assembly. I'd also check wheelbase on each side between centre of F&R axles. Is the backspacing on each wheel the same? Without seeing car, are rear tyres centred in fenders, are they biased forward or rear in the fender opening(s) and even? I always use reference points that are consistent on each frame rail. Also I'd use a square and check distance between each rear axle flange face to outside of frame rail to ensure that axle is centred in frame. Lots of variables, are upper and lower bars adjustable, you don't want to use all the adjustment to correct any issue(s).

 

If the wheels can accept the heads on an alignment machine have a shop do a 4 wheel alignment setup on it snd print out the specs as to where it is. That will show where it is off and how far. As said, check the frame for square first.

 

Thanks for all the replies. It’s a Brookville chassis and it is square. Measured that before I assembled anything. The rear is a 9”. The rear triangulated four bar mounts were done by Brookville in their jig. I think it’s just a matter of adjusting the bars. My question was more about the best way to go about properly adjust them. What reference points would you use and how to manipulate the rear end while up on a lift. Wheels are new, same backspace. Nothing is bet. Tires are Excelsior radials from Coker. I’ll post better pics later, it’s the driver’s side that’s rubbing

 

Better pics

 

Maybe a coil over issue, the left side looks lower to me. If you got this far with it, I know you can figure this out!

 

Looks like one of my cars. I replaced the original panhard bar with an adjustable one and was able to get the pinion and transmission output shaft in line. Tire clearance is now equal on both sides.

 

I'd measure from the outside of the frame to the backing plate on each side to double check to see if the rear axle is indeed off center and go from there. I know it's a bit late in the game for this, but are you sure the body is centered on the chassis ? Have you accurately checked the wheelbase from side to side ? If everything checks out, the easy out for this is a wheel spacer on the drivers side only and problem solved.

 

Thanks guys, the axle is further forward on the driver’s side. The space between the the tire and the body are unequal both in the front of the tire as well as the back a of the tire.

 

It would be easier to lengthen the bottom bar, but when lengthening the top bar comes into play, that's when angles change way faster for the upper mounting points. You can usually only cheat so much before things don't line up. I would measure wheelbase on each side first and see how far off things are. My guess is the 4 bar mounts are off location on the housing to some degree. Sorry it's not an easier answer !

 

Get you a helper and measure the wheel base. With tires that size it will not take much to move it back into place. Your not the first person who has done this.

 

It’s just an adjustment of the bars, my original question was suggestions for adjusting them while up on a lift.
Appreciate all the suggestions

 

Car looks great, Dean. Hope this issue is an easy fix. My friend who just finished his found (well the body man found) that the driver's side quarter panel was a bit bulged. None of us noticed it until Chris, the body guy detected it. Luckily it was still in bare metal or it would have created a problem ultimately. Chris fixed it and all was well. Hope your solution is far easier to rectify...........Don.

 

Thanks Don, it’s almost ready for a cruise with you Maryland guys !
I‘ll figure it out when it’s up on a lift, to be continued

 

I use a string, like the orange cord used on construction sites. Simply tie it to the back of the body or frame, and wrap it around the sidewall of a rear tire at the center of the wheel. Stretch it forward, just touching the front sidewall of the rear tire, and measure inboard to the frame, just behind the front tire. Do the same on the other side and compare the the 2 measurements. It's handy to have a second person, watch and make sure the string is barely, against the forward sidewall.

 

I use my 4 post lift to get the car off the ground. Makes things a lot easier on this old man. I get the tires and wheels off with 2 stands under each axle holding the car at ride height from the ramps using measurements I took before starting. The first thing is to establish a chassis centerline. Find center on the rear crossmember and drop a bob from that point. Find the center of the front suspension on the frame and drop a plumb bob from that point. There is your chassis centerline. Now find points on the rear end where you can drop a bob equally from centerline on both ends. I use the axle flange. It doesn't have to be on the centerline of the rear end. Adjust panhard bar to center rear end. Then triangulate from the front center point plumb bob to each end of the rear end adjusting the 4 bars to correct any error. You must pay attention to pinion angle while adjusting the 4 bars also. This will get your rear end centered, square and pinion angle set.
To center and square the front, just center the axle with the plumb bob, then measure the wheel base from the rear bobs and adjust as necessary
The front axle is hard to find a spot to accurately measure from. I remove the spindles and use Delrin plugs I made to go in the kingpin bore with a hole drilled in the center. I drop bobs through those holes.
It looks like a plumb bob forest under there when I get all 6 hung.
This is a lot of work but you don't have to do it very often on your hot rod. I will bet that no "alignment tech" can get it any closer with all his fancy lasers. I guarantee my alignment is within a 1/16".
Of course on the front end you need to get your caster and camber correct while doing this.
My background is circle track racing. My method of alignment pretty well ignores whether the frame is square or not. The old saying goes, " It doesn't matter until the wheels go on" is good advise in my book. All my race cars started out with square frames, by the end of the season not so much, but still winning races.
I just finished an alignment on mine.

 

Thanks @Marty Strode and @jaw22w. Good advise and instructions. Will be very useful, much appreciated

 

Ok out of square as your title emplies . Just a matter of creating a triangle by which to compare by as in this sample photo.
Only concern yourself with peak of triangle and end of axle tubes in this illustration for the general points to measure by.

 

That is a great quick way to square the rear. I have done it myself for a quick check. I've even seen it done in the pits. Can also set toe with the strings.

 

Looks like most early Fords, drivers side lean. Pretty common both in buggy sprung and coil over.

 

You learn a lot racing oval track, don't you !

 

You asked how to adjust the bars after measuring.
I'd measure each 4-bar before even putting a wrench on a bolt.
Write it down, then figure out how much you want the driver's side to move back, and how much is needed to move the axle side-to-side and center the gaps between the body and tires.
Look at how much thread is showing on each bar, too. Don't forget the pinion angle.
Then disconnect the left side bars and move the left tire to the right point. Block it in place and check all measurements. Extend the bars and reattach. You may be able to either adjust them in place or just drop one end, extend and install.
Once it's all where you want, measure the bars again and see if both top and bottom bars are the same length.

 

Thanks for that reply, lots of good info. Doing it tomorrow and that was very helpful

 

@RodStRace, got a question, you think I can leave the coil overs on while adjusting the bars ?
Thanks

 

With it sitting on the tires, the main concern with removing the bars is axle twist (springs pushing down on the back of the axle). It 'should be' fine, but if you are concerned, block both tires and maybe cut a length of 2X4 to fit between the pinion and the floor. The right side should hold but it might twist the left side with both bars loose.
If both coil overs are attached to the front of the axle, the reverse applies.
If they are staggered (one front, one rear) the bars on one side and full weight on car should be able hold it steady.
If the bars are truly adjustable installed (left hand threads on one end), you can adjust in place to avoid the disconnect, but expect it to be measure, adjust, repeat until it is where you want.

BTW, what I meant about final bar length is both lower bars similar, both top bars similar. This shows the frame and axle mounts are similar and total length between the frame and axle are similar. Having a frame mount off .25" and the bar off the same .25" to equal out will cause a bit of strange movement during suspension cycling.

You didn't talk about it, do you have a panhard link too? If it's left frame to right axle (common), that can also keep the left side tire tight to the body especially during right turns (tighter in American driving). Make sure it's adjusted to provide best clearance.
Maybe have a buddy hang out each door to simulate body lean and check. You might have to give it a bit more rear height.