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Discussion Starter #1
I put my cobra into the alignment shop yesterday and one of the discoveries is that the rear end (9") is toed out 3/32 on one side and 1/32 on the other. The alignment shop suggested I should get this fixed.

I called the local rear-end specialists in the area and they don't think I should worry about this, stating that I'd never notice it, and it's a non issue. They correct housings using the heat-and-quench method to shrink the metal and can't get it any closer than this.

I then called a race car fab shop in the area and they suggested it's not a big deal, but if I really wanted to get it fixed, they'd use a frame machine and literally bend/tweek the housing in the car to fix it.

Anyone here an expert on rear toe? How big of a problem is this really considering this car will trap somewhere around 140-150mph.

Byron
 

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Where was that measurement taken? at the axle centerline?
 

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they didnt give you the toe numbers in degree's? I have never seen toe measured in 32nds. I have worked in a few front end shops. Never have I seen a machine that measures in 32nds. But if this measurement is from the center of the axle it wont be a big deal.
 

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Discussion Starter #5
I'll ask

Since it's a distance measurement, I'm assuming it's the distance from the center of the axle housing to some point on the leading edge of either the wheeel or tire or perhaps some predetermined distance from the center of the base circle of the axle. I guess this is important. If it's 3/32 out 1" from the center of the axle, that's pretty severe. If it's 3/32 out 30" from the center of the axle, it's a who cares.

But no, it's not in degrees, it's in 1/32nds of an inch for toe.

Caster/camber are in degrees.
 

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Discussion Starter #6
Toe measurement

I just talked to them on the phone. Toe measurement is taken from the leading edge of the rim relative to the trailing edge of the rim. And, both of those measurements are taken relative to a reference plane drawn 90deg from a line drawn through the center of the "ideal" axle housing.

So, given that my rims are 17" diameter and my largest toe out is 3/32 on the drivers side, that's .094" toe-out of the front edge relative to the rear edge, or .047" (half that) from the plane to the leading edge of the rim.

If you want it in degrees, the base of the 17" rim has a 53.38" perimeter, so a close approximation is .047/53.38" or .0008degrees. Maybe that's why they don't measure it in degrees; that sounds like fly **** to me.

Anyway, according to race shop #2 who I contacted to potentially correct this axle housing problem, my 9" wheel backspacing will create more toe-in pull than the axle housing will create toe-out pull, so this is indeed a fly **** distraction and I should move on to bigger and better concerns.

If anyone here disagrees, please let me know. Otherwise, I'm going to ignore this problem and get on with life.
 

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Re: Toe measurement

ByronRACE said:
If you want it in degrees, the base of the 17" rim has a 53.38" perimeter, so a close approximation is .047/53.38" or .0008degrees. Maybe that's why they don't measure it in degrees; that sounds like fly **** to me.
At 3/32, I come up with .6 degrees on a 17" rim, if it is measured from the center to the outside diameter.
 

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It is common for rear ends to be toed out that amount.On oval track cars it is a very important adjustment.Toe out makes a car loose on corner exit.I have used the heat and quench method many times and if I were racing for money I would fix it.
 

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The concern I see with fixing it is, I doubt very seriously this housing is a 'floater' as we use in oval racing. Heat and quench is very effective as I used to do it to our housings. This is possible without adverse effects because of the use of 'crowned' axels. The problem using this method on a finshed stock style housing would be the possibility of putting the axel bearings in a bind causing premature wear. Granted there is some play in the axels, but the amount in this case is unknown.
 

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80cobra said:
they didnt give you the toe numbers in degree's? I have never seen toe measured in 32nds. I have worked in a few front end shops. Never have I seen a machine that measures in 32nds. But if this measurement is from the center of the axle it wont be a big deal.
While todays modern computer alignment machines make references to toe in/out in degrees, many, many, years ago (before wiz-bang computers were dirt cheap) figuring toe in/out was easier referenced with a very special analog measuring device in fractional increments......a tape measure (LOL).

While 4/32" (1/8") total combined rear housing toe out might sound like a lot, the adverage 9" housing without a back brace will flex/bow foward that much (and more) under load (like a launch with slicks). Lack of a back brace + sticky slicks + nitrous can equal a bent housing with a bunch of toe-in after a while.
Because of this I feel that Ford must build in some small amout of toe-out on purpose because almost every 9" housing I have messed with had some amount of toe-out from the factory. I wouldn't really worry about it unless you start seeing un-acceptable rear tire wear that can be blamed on the toe-out.

On a side note, letting the adverage alignment shop talk you into a "4 wheel" wheel alignment on a "street/strip" or "drag only" car could be asking for trouble because some race cars need pre-load to launch straight. The pre-loaded rear suspension & chassis could throw off the computers readings and tell the technician the wrong adjustments to make at the front wheels.
 

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I limited myself to 2/32 each side toe in to aviod bearing problems.
 

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Discussion Starter #12
Thanks

Thanks for all the information. Rear tire wear due to right-pedal effects will far outweigh any wear problems from toe. The loose rear might be noticable on corner exit; I am going to road race this car. If I can feel it, I'll search harder for a shop that can fix it. I made calls yesterday and found noone that can fix it. If I do it myself, I'll have to build a jig and all...it'd be an ordeal.

Merc460: How did you get that measurement? Do you realize that the measurement on this machine is the front edge of the rim relative to the rear? It's not the front edge relative to the center-line. I did forget to multiply by 360deg; so you're right...my calculation was wrong. But, if I do it over, I end up with .32deg not .6. I think you might have thought the 3/32 measurement was from the center-line to the front edge of the rim, and it's not...it's half that.
 

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I don't think it matters really....



Right angle triangle:
side one) 8.5" (17/2)
side two) .046875 (1.5/32)



Inverse tangent (rise/run) = degrees

tangent^(-1) (.046875/8.5) = .316*

Have a good day!
Michael
 

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Re: Thanks

ByronRACE said:
I think you might have thought the 3/32 measurement was from the center-line to the front edge of the rim
Hey, I had to use my toes on that one. :lol: Yes, I didn't know that's how that machine measured it, which is why I said "if it was measured"
I say just run it, not enough to really worry about.
Was this alignment on the 'thrust' line or the 'center' line of the car?
 

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Discussion Starter #15
Measurement

It was referenced to a plane drawn 90deg relative to the center of where the rear axle should be. So, basically, centerline of the car I'd assume.

In any event, I think we've beat this to death and I'm happy to let it go.
 

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Re: Measurement

ByronRACE said:
It was referenced to a plane drawn 90deg relative to the center of where the rear axle should be. So, basically, centerline of the car I'd assume.
I asked only because I think you would be much more pleased with a "thrust line" alignment. The front wheels are lined up on the rear axel's thrust line. A more accurate alignment. :wink: Most shops just do a center line job which is close but not exact. :)
 

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Discussion Starter #17
Hmmm.

Well in my case, I'm not sure I'd want the front aligned to the rears thrust line.

The front is also aligned to the same plane...

So relative to that plane and to eachother, both and front and the rear are as close as they're going to get unless I bend the rear housing.
 
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