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Old 04-29-2012, 02:26 AM   #21
bakerjd
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Quote:
Originally Posted by DG_ View Post
I've been reading up on this more on the web and I think after I installed the springs, shocks, phb, and lcas my thrust angle went off spec.
http://www.tirerack.com/tires/tirete...e.jsp?techid=4
I am now wondering if this might be caused by my aftermarket non-adjustable lcas. My car has barely 1000miles on it, so I highly doubt that the frame is bent. I do think that if the aftermarket lcas were a bit out of spec, they may have cause the off thrust angle which in turn caused the strange toe reading.
Would an adjustable lca or uca bring the thrust angle back into spec?
Typically people install adjustable LCAs or adjustable UCA to adjust the pinion angle once the vehicle has been lowered. I would suggest looking into that if you have not already done so. Also, adjust the PHB.
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Old 04-29-2012, 06:07 AM   #22
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As Norm has mentioned before, on a solid rear axle the wheels are not always exactly perpendicular to the centerline of the axle due to manufacturing tolerances,i.e. they can have small amounts of camber and toe.

Hopefully Norm will join in and say if the figures in the charts above are within those tolerances.
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Old 04-29-2012, 01:30 PM   #23
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Pretty sure I was, ahem, wrong.

The axle position is set fore and aft by the control arms, and left to right by the PHB. The universal joints allow the axle to move up and down and side to side without binding. You need both with a stick axle and PHB. I was thinking of the axle/drive shaft as a rigid 'T'. Wrong!

DG, I think you should center your axle in the body. I think everyone has said that from the start, maybe for different reasons.

This is still a bit mysterious, and I for one am glad you posted. I think you may be right about your after market LCAs, but before spending more money I'd find out how the Hunter rig determines toe. The wheels could be parallel, but shifted 1/4" to the right of the rig centerline. I think this could show positive toe on one side and negative on the other.
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Old 05-01-2012, 01:00 PM   #24
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It isn't quite as simple as "PHB affects only axle centering". You have to think a little further outside the box where having a stick axle makes you assume things that aren't exactly true, that in turn tend to limit your thinking.

Let's keep things simple and assume that the two rear wheels are perfectly parallel to each other in plan view (IOW, there is zero point zero total toe).

Turns out that the LCAs are not quite parallel to each other or to the car centerline. So when you move the axle laterally, the arcs that the LCAs follow will push one wheel slightly rearward and pull the other wheel slightly forward. That's exactly how you could have one rear toe at -0.25 and the other at +0.25, and both go back to zero when you move the axle with the PHB adjustment.

What you really should do is center the axle with an adjustable PHB and follow that up with adjustable LCAs to bring the right and left toes down to whatever the best overall setting happens to be. About the two rear wheels being perfectly parallel in plan view earlier ↑↑↑ - I lied (sort of). There is a tolerance on stick axle toe just like there is on anything else manufactured, so there may be a small amount of total toe. If that turned out to be the case, you'd tweak the axle with the LCAs such that both wheels toed the same amount either both in or both out. One of my other cars is a stick axle car with non-zero rear toe, so I know that it happens.


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Last edited by Norm Peterson; 05-01-2012 at 01:07 PM.
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Old 05-01-2012, 03:07 PM   #25
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Thanks Norm.

The axle rotates around the LCA frame mounts when the PHB is adjusted. I'm a bit surprised the LCA lengths could be that different, since the OP bought non-adjustable LCAs. Any theories?
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Old 05-01-2012, 05:19 PM   #26
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It's not that the lengths might be different that makes the axle vary its toe with lateral PHB adjustment, it's that the arcs are different because the LCAs are slightly skew as seen in plan view.

Different LCA lengths would start the axle being slightly toed (think one side toed-in, the other toed-out) when it was perfectly centered.


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Old 05-01-2012, 06:01 PM   #27
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Thanks for all the replies.

So the culprit more than likely is the lcas? The ones I have are J&M lcas from AM.

I have re adjusted the phb with the string method to center the body to the axle. I will purchase an adjustable lca soon. Any suggestions on brand?
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Old 05-02-2012, 06:56 AM   #28
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The LCAs aren't a 'culprit' here, even though adjusting their length is the simplest 'fix'.

If you want to blame anything, it's the plan view skew angles of those LCAs, which have some influence on handling as well as this toe/thrust angle issue. Suspension geometry (particularly in production cars) is always a compromise of some sort, and what we have here is Ford's.


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Old 05-02-2012, 04:43 PM   #29
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Got it. Thanks.
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Old 05-05-2012, 10:44 AM   #30
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Quote:
Originally Posted by Ansibe View Post
Hang on a minute here, guys. I doubt this guy is yanking your chain, even if he is unsure about solid rear axles and PHBs.

As the PHB is adjusted, the drive shaft is pulled to one side, and the wheels naturally point off to one side. It will look like one is toe-in and the other is toe-out.

Your PHB needs to be adjusted with the car's weight on the wheels, with the suspension compressed. The tech may not know that.
Correct.
Only adjustable LCAs would provide you the adjustability to
both center the rear end and adjust toe.
But with the rear end in the OEM side to side location with lowering
springs and an adjustable PHB, the rear end should be neutral in
relation to OEM toe.

When the axle moves up and down during driving, the PHB swings in
a slight arc and the toe specs will vary from fully compressed suspension
to fully extended suspension. A watts linkage will stop this minor
wackyness of the rear end toe while driving...
Sometimes an adjustable UCA is needed to bring the pinion angle back
into spec with lowering springs.

Last edited by 157dB; 05-05-2012 at 10:48 AM.
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