Wheel base difference side to side

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340doc

340doc

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On my 70 Dart the passenger side rear tire is closer to the front lip than the driver side. I wanted to eliminate body panel differences so I measured from center of front spindle to center of rear axle. Sure enough there is almost a quarter inch difference. Front end is all new and rear leafs have solid front eye bushings so I cant blame wore out parts. Would there be any harm in spacing the spring hanger back on the one side to make both sides the same distance?
 
340doc said:
On my 70 Dart the passenger side rear tire is closer to the front lip than the driver side. I wanted to eliminate body panel differences so I measured from center of front spindle to center of rear axle. Sure enough there is almost a quarter inch difference. Front end is all new and rear leafs have solid front eye bushings so I cant blame wore out parts. Would there be any harm in spacing the spring hanger back on the one side to make both sides the same distance?
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Nope !! These cars weren't built perfect. Do what you need to suit your purpose.
 
1/4" is pretty good remember setting caster can move the lower control arms front to rear.
 
That measurement stacks about 6 variabkes into one A to Z length. Spring, eyelet, unibody,cobtrol arm bushing, camber, toe in......how does it track?
 
Go back to your alignment guy. If he has a modern computerized system, he will have your workorder on file, and be able to call it up. Have him check the thrust angle. This will tell him where the problem lies.Only he can determine if shimming the spring is the correct thing to do.
Using the spindles, doesn't tell the whole story. Caster is often split to allow for a no-pull driving experience on crowned roads. Camber may not be identical. If the spindles are at different heights relative to a flat,level floor, and/or the rear axle centerlines are not the same height, the measurement will be off. And the clincher; there is almost no way to set the spindles to be exactly on the same transverse line.
 
Before anything, I would make sure the rear axle housing is in the springs seated squarely since there is some wiggle room to be found there.
 
Every street driven vehicle has thrust angle built into it. Compensates for crown in the road. Drag racers square them for straight launch on a level track.
 
pishta said:
That measurement stacks about 6 variabkes into one A to Z length. Spring, eyelet, unibody,cobtrol arm bushing, camber, toe in......how does it track?
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I've never had anyone tell me it tracked crooked. I'll have to ride behind it. What everyone's saying about the alignment possibly making the difference makes sense. I didn't really notice it until I put taller tires on. I might space it back and if it tracks straight leave it!
 
You can "string it" with a coupla pieces of string. We been doing it trackside for decades to straighten out axles and alignment after a shunt.

Google it, "how to align a car with string", there's a buncha vids etc.


We found member Cannucky's near 1 inch R-rear toe-in using string, (shortened rear-end done incorrectly) then he used shims in the front spring perch to center the rear toe, refering to the string..
 
340doc said:
On my 70 Dart the passenger side rear tire is closer to the front lip than the driver side. I wanted to eliminate body panel differences so I measured from center of front spindle to center of rear axle. Sure enough there is almost a quarter inch difference. Front end is all new and rear leafs have solid front eye bushings so I cant blame wore out parts. Would there be any harm in spacing the spring hanger back on the one side to make both sides the same distance?
Click to expand...

that's not a 100% accurate measurement from the front spindle, toe variance along with other factors will give to different numbers side to side, square the rear up off the body frame holes.
 
AJ/FormS said:
Go back to your alignment guy. If he has a modern computerized system system , he will have your work on file, and call it up. Have him check the thrust angle. This will tell him where the problem lies.Only he can determine if shimming the spring is the correct thing to do..
Click to expand...


This /\ /\ /\


and there is nothing wrong with using the spacers to correct it IF they are the problem and are needed
 
GeorgeH said:
that's not a 100% accurate measurement from the front spindle, toe variance along with other factors will give to different numbers side to side, square the rear up off the body frame holes.
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Yes! Take a rough measurement from the torsion bar crossmember back to the front spring mount. on my E body there was about .25" difference. Now remember this will also move the wheel on the other side. On my car it helped center both wheels, and the car never felt so good.
Definitely take measurement from several spots before moving anything.
 
roccodart440 said:
This /\ /\ /\


and there is nothing wrong with using the spacers to correct it IF they are the problem and are needed
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Alignment will tell you if there is a thrust angle problem, but not necessarily where it is at.
 
You might also try taking a measurement from the body front perch (where the rear spring mounts) to the center of the axle tube. If the car has been owned by someone else and they replaced or moved the rear end they could have put the rear end back in incorrectly. The front of the rear spring mounts against a vertical flat surface which make it easy to measure back to the center of the axle tube. I would think that these vertical flat surfaces are datum points (locating points for the suspension). Unless the car has been in a major accident these spring mount points should be a good place to measure from. When I replaced my rear end I used this measurement to get the rear end perpendicular to the longitudinal axis of the body. When I took the car to get aligned I asked the alignment guy to tell me if the rear end was parallel to the front wheels (axis). He said that it was within 1/64 of an inch, so I guess I did a pretty good job of aligning my rear axle!

Some people elongate the slot in the spring perch (on the axle tube) to move the rear end forward or backwards. If you don't measure from the front perch mount surface there's no way you can get the rear axle perpendicular to the longitudinal axis of the body.

GOOD LUCK!!
treblig
 

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Treblig said:
The front of the rear spring mounts against a vertical flat surface which make it easy to measure back to the center of the axle tube. I would think that these vertical flat surfaces are datum points (locating points for the suspension). Unless the car has been in a major accident these spring mount points should be a good place to measure from.

GOOD LUCK!!
treblig
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One would think that they are datum points from which the car was built on, but some guys post discrepancies here.
 
Every single time I help build a hot rod (on a car that hasn't been messed with) we always measure from the center of the rear wheel axle (using a long metal rod) to the center line of the front cross member. This gets the new front suspension (Mustang II or what ever) parallel to the rear axle tube. If the rear end is not square to the body then the front end won't be square either. I've never had an alignment issue with any car or hot rod that was built this way. I don't know how the factory did it but it you don't have datum points you can't get anything square or perpendicular. Frame alignment shops have books that show all the datum points on all vehicles, they use these datum point to repair/re-align car/truck frames.
My car drives straight and makes turns very nicely so something must be right!!

Treblig
 
roccodart440 said:
True. I'd like to know how much spacer I need too.
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Frame measurements. If your trying to correct thrust angle, you need to know the suspension mounting points are square to each other and to the body, otherwise your trying to shim the rear to match the front, which either end could have some sway going on that is not readily apparent to the eye. If everything outback is square to the cabin and the front is swayed you would introduce dog tracking by shimming the rear, but damn if you can't get pretty decent alignment #'s.
 
Treblig said:
Every single time I help build a hot rod (on a car that hasn't been messed with) we always measure from the center of the rear wheel axle (using a long metal rod) to the center line of the front cross member. This gets the new front suspension (Mustang II or what ever) parallel to the rear axle tube. If the rear end is not square to the body then the front end won't be square either. I've never had an alignment issue with any car or hot rod that was built this way. I don't know how the factory did it but it you don't have datum points you can't get anything square or perpendicular. Frame alignment shops have books that show all the datum points on all vehicles, they use these datum point to repair/re-align car/truck frames.
My car drives straight and makes turns very nicely so something must be right!!

Treblig
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your better shops now have it on computer and measuring equipment that feeds it, you can measure down to 1mm and on late models with only a toe adjustment you need to be on those numbers. Many a day fighting a couple mm's on a frame rack.
 
Here you go...

Treblig
 

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340doc said:
I've never had anyone tell me it tracked crooked. I'll have to ride behind it. What everyone's saying about the alignment possibly making the difference makes sense. I didn't really notice it until I put taller tires on. I might space it back and if it tracks straight leave it!
Click to expand...

If you move the rear axle to change the thrust angle, then to travel in a straight line, the steering wheel may no longer be centered. Since, effectively,the pitman arm is now in a different position than when it was aligned, your toe-in will also be different.
Depending on how far you move it, this may be a non-issue. Or not.
 
Treblig said:
You might also try taking a measurement from the body front perch (where the rear spring mounts) to the center of the axle tube. If the car has been owned by someone else and they replaced or moved the rear end they could have put the rear end back in incorrectly. The front of the rear spring mounts against a vertical flat surface which make it easy to measure back to the center of the axle tube. I would think that these vertical flat surfaces are datum points (locating points for the suspension). Unless the car has been in a major accident these spring mount points should be a good place to measure from. When I replaced my rear end I used this measurement to get the rear end perpendicular to the longitudinal axis of the body. When I took the car to get aligned I asked the alignment guy to tell me if the rear end was parallel to the front wheels (axis). He said that it was within 1/64 of an inch, so I guess I did a pretty good job of aligning my rear axle!

Some people elongate the slot in the spring perch (on the axle tube) to move the rear end forward or backwards. If you don't measure from the front perch mount surface there's no way you can get the rear axle perpendicular to the longitudinal axis of the body.

GOOD LUCK!!
treblig
Click to expand...

Thanks treblig, good idea.
 
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