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MG MGA - Alignment

Ok, I've read the archive, I've read Barney stuff, and I've googled some video for the "string" method of alignment.

I have one issue I'd ask clarification for.

As I understand it I set up jack stands and run a string from front to back parallel to the car and wheels.

On a car with the same wheel base on the front and rear wheels I'd set the string at the same distance from the center hub at front and back to act as the base line. Lets pretend its 2".

HOWEVER, because the front wheel base on an MGA is 7/8" narrower than the rear wheel base, I would need to set the distance to the string at the rear wheel hub to 2" and 2 7/16" at the front to have a true base line from the string.

Is this correct?
Tysen McCarthy

This is for aligning the back axle? What do you do if the measurements are not equal (allowing for the track difference as you have indicated)? There is no adjustment to skew the rear axle.
The method sounds OK in principle, but practically you have to project a line off of two points on the rear wheel forward to the front, some 10 ft away, by measuring from a string? This does not sound too precise!
More inportant is the toe-in adjustment.
Art Pearse

Art, its a method of aligning the front end.

See this:

He uses it for toe in, but you can use it for straight alignment.
Tysen McCarthy

Place your jackstands out the front and rear of the car far enough so that you can simply measure accross in front of and behind the car to get the exact same measurement--the strings are then parallel then double check that you are equal distance each side from the hub
and centre up if needed by moving the stands equally and remeasure
I cheat and put the car on the trailer and measure off the trailer---but I know the trailer is spot on
William Revit

Ok the two parallel lines make sense.

However "then double check that you are equal distance each side from the hub" lies at the heart of my issue. From what I understand of Barney's description the front wheelbase is narrower than the rear, so the strings shouldn't be equal distant from the hub.

Tysen McCarthy

Tysen, I think what Willy means is, get your lines parallel first, then adjust so that the lines are equidistant at the rear from the rear hubs and equidistant at the front from the front hubs, then of course recheck they are parallel etc etc.
These measurements at the front have to come from the hub centres of course because you can't be sure the toe is zero yet or where the wheels point
Now to do the toe you have to measure fom the lines to the front and rear of both wheels, 4 measurements in all.
Dont measure to the rim as that is not a machine finished surface. Better to do it at the fattest part of the tyres.
However I think the method is second rate. With 4 measurements there are 4 errors to accumulate.
Much better to fabricate a stand up jig to measure the insides between tyres. I did such and used a threaded bolt to touch the tyres, and no actual measurement is necessary as the jig is transferred from fron to back. It consists of a plank with 2 uprights.
Art Pearse

My coupe isn't on the road yet so you can take this with a grain of salt. Here's what I did based on a YouTube video I found months ago. Make sure the steering wheel is centered. I did one side at a time with a string tied between two jack stands, one several feet behind and the other several feet in front of the car. I used the front and rear edges of the rear wheel rim, moving the front jack stand until the measurement at the front and rear edges of the rear rim were exactly the same. Then go to the front wheel and measure the distance to the string from the front and rear edge of the front wheel. This will tell you which way you need to adjust the tie rod end to adjust the front wheel so the distance to the string is the same for the front and rear edges of the front wheel. The front wheel needs to be able to swivel freely when making the changes to the tie rod end so the tire needs to be on something slick to reduce the twist created by the rubber turning on the concrete floor. Round discs like you use under furniture to slide it easily should work well.

After this, do the same thing to the other side of the car. I figure this gets me close enough to drive to an alignment shop to have it checked and adjusted if needed.

JL Cheatham

This thread was discussed between 12/04/2017 and 15/04/2017

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