Unpredictability

[Department Of Boost]

Sounds like rear control arm issues. Mostly the LCA’s. Most aftermarket LCA’s bind quite a lot. A binding LCA will “wrap up” as you load the suspension. When you loose traction all of that “wrap up” (or wind up) instantly and violently comes unwound. Next thing you know you are very sideways with almost zero warning.

I’ve run through 5 sets of LCA’s to find some that broke away predictably.

 

[SoundGuyDave]

I’ve run through 5 sets of LCA’s to find some that broke away predictably.

Let me guess.... Rod ends? Any other bushing is going to have some wrap-up effect.

 

[sheizasosay]

I've had 3 sets and I am sticking with J&M Street Extreme's. Rod ends are too loud and when compared to the street extreme's....unless you can articulate that joint past 10 degrees, then I can't understand why a rod end would be used on a dual-purpose car. There is zero bind up until that point....and that's a hella long way. Hell, I'm not even sure I would change them out on a track dedicated car.

A poly/poly UCA can do you wrong too.

 

[braupe]

Everyone here is making good points. Something else to consider is the solid rear axle. By design its not perfect. (not garbage, but not IRS). In theory with all of the possibilities for wind up to occur, or wheel hop, or even a random bump, one wheel can be disrupted, and cause the other rear wheel to follow suit. Meaning that on an IRS car one wheel can get stupid, while the other wheel helps keep the rear end in line.

I would say that I have the driver mod, but I have been doing stupid things in different cars for along time. A live axle car always seems to be less settled in the turns than an IRS car ( I am speaking in general terms here). And yes, mastering a live axle car is work, but its fun, and rewarding.

Like someone wrote in a previous post, our mustangs a kind of point and shoot machines. Decent in the corners, but no miata.

 

[Department Of Boost]

Let me guess.... Rod ends? Any other bushing is going to have some wrap-up effect.

Close, I'm running the J&M Exteme's now. They are fantastic. You can play with the traction/sliding "line" all day long and as far as I can tell there is no more NVH than stock.

 

[DILYSI Dave]

I wonder if the axle is bent. Toe out would make it a handful.

 

[Whiskey11]

I wonder if the axle is bent. Toe out would make it a handful.

FWIW, I've seen a few alignment sheets where the rear axle on the S197 is toed out from Ford. I wouldn't be surprised if it is toed out a little. How much though is a different story. I can't even remember my toe out...

 

[Philostang]

Hmmm...I seem to recall the last time I did an alignment on my car (late last season) I was getting toe out readings on the rear driver side. In all honestly, it was late, I was rushed, so I chalked it up to the "mental feebleness" of the hour. I haven't had a chance to come back to it.

I'm going to be re-aligning the car in a week or so. If the rear is out, what would the options be to address it? I mean, I know "a new axle" is one option, but I'm wondering if there are others out there that I may not know about.

Best,
-j

 

[Norm Peterson]

There are methods for "adjusting" toe and camber on solid axles using either heat or a large press. Rehagen Racing could probably do this, and a circle track shop that sets up asphalt race cars would probably also be a safe choice. I've heard of a couple of cases where individuals did this sort of thing on a DIY basis, but it's definitely not a job for the faint of heart.


Norm

 

[sheizasosay]

There are methods for "adjusting" toe and camber on solid axles using either heat or a large press. Rehagen Racing could probably do this, and a circle track shop that sets up asphalt race cars would probably also be a safe choice. I've heard of a couple of cases where individuals did this sort of thing on a DIY basis, but it's definitely not a job for the faint of heart.


Norm

I would think a collision shop would be able to do it .


Sent from my iPhone using Tapatalk

 

[Chim-Chim]

if it has the stock lsd in it, you really need to check it. mine went out at 35,000 miles, and it makes it a huge handful to drive

This. When I replaced my stock lsd with a Trutrac it was a huge change in predictability in breaking the rear loose. You can rebuild the stocker with new clutches (a temporary fix with your power levels), or swap in a better lsd. The difference in handling predictability, mostly in aggressive corner exits, was way more noticable than new lcas with rod ends AND lca relo brackets combined.

Grippier tires and improved LCA geometry, while good things to address, won't address the root of the problem and in some ways make it more difficult to deal with. It just makes it more abrupt and unpredictable when you get one tire fire.

 

[Norm Peterson]

Could be, but I'm thinking if you have a race shop so the job, you'd have the opportunity to have the axle decambered half a degree or so per side at the same time. Normal repair shops might not be willing to do that.


Norm

 

[Kobie]

Could be, but I'm thinking if you have a race shop so the job, you'd have the opportunity to have the axle decambered half a degree or so per side at the same time. Normal repair shops might not be willing to do that.


Norm

Wouldn't this just KILL the rear tires on a solid axle car?

 

[Norm Peterson]

In small amounts, not at all. In fact, a small amount of negative rear camber is actually beneficial where corner-carving is concerned. First, the entire axle "cambers" slightly, due to differential tire compression as the inside tire unloads and the outside tire picks up that load. This effect is roughly 1° per lateral g. Second, tires grip best when running at a small negative camber, which I suspect is due to tire distortion reasons.

The limiting factor probably isn't related to tire wear anyway. but to the misalignment 'tolerance' in the axle shaft/side gear splines. Up to about 1° total (considering the resultant from toe and camber) seems to be, ummm . . . tolerable . . . unless you see barrel-shaped half shaft splines in your axle's future.

The car below ran for nearly 20 years and over 100,000 miles with -0.5° camber and nearly that much toe-in on each rear wheel, or almost 0.7° total angular misalignment per side. It was a junkyard-sourced axle purchased as an emergency repair while several hundred miles from home, so it was a case of taking what was available. But I never had a rear tire evenness-of-wear problem during the years that I was autocrossing the car or during the years that I was not.

It has crossed my mind more than once to decamber the Mustang's axle a similar amount.


Norm

 

[Philostang]

That was my next question - so you can get away with -0.5° camber without those barrel splines? Well, if I end up having the axle worked on, I'll seriously consider this. I just wasn't sure how much I could do before needing different axles.

 

[Department Of Boost]

Correct me if I’m wrong here but wouldn’t “barrel” shaped splines be useless on a 8.8? You would be re-angling the outboard flanges, I don’t see how different splines at the diff would do any good?? Unless maybe you had the entire tube angled and not just the ends??

I’ve seen 9” full floater rear ends set up with angle in them but they have a floating axle which is splined at both ends.

 

[Norm Peterson]

With the 8.8 or any other axle not modified at the ends to allow misalignment between the wheel and the half shaft - no matter how you decamber the wheels, you're introducing that much angular misalignment between the half shafts and the side gears, whose orientation is fixed. Although it probably wasn't the original design intent, tolerances and clearances in the splines lets you get away with a little misalignment before they start binding. Barrel-contouring the splines opens up the clearances at the face surfaces of the side gears without making the basic fit of the half shaft/side gear too sloppy and allows for greater misalignment . . . more than likely coming at some cost in durability.

That's about as good as I can explain it - I'm really a structural guy.


Norm

 

[Department Of Boost]

Maybe I didn’t write that correctly.

If you lets say decamber a 8.8 by angling the flange end of the axle I would think that you would have a lot more to deal with than a misalignment at the splined end of the shaft. You would have a shaft that would in theory be pointed below the female splines in the diff. My rough calculations say that the axle would be pointing to a spot roughly 10-12mm below the diff. That shaft is not going to slip into those splines.

The only way I see it working is if you decambered a 8.8 by angling the entire tube at the point where they press into the rear end housing. And that seems a bit sketchy.

 

[frank s]

Seems to me the Herb Adams Pontiac raced in the early Trans-Am had a couple of degrees negative in the rear, accomplished by simply bending the axle housing. The standard tolerances allowed it to work without ill consequences. I wonder if modern manufacturing and metallurgy will have tightened the clearances so that simple won't apply any longer.

I know of one fellow in the Midwest who is reputed to add a degree of negative by chaining the center section to the floor, heating a spot on the axle tube while the axle end is jacked up. I haven't seen it, so my belief is suspended.

 

[Norm Peterson]

Maybe I didn’t write that correctly.

If you lets say decamber a 8.8 by angling the flange end of the axle I would think that you would have a lot more to deal with than a misalignment at the splined end of the shaft. You would have a shaft that would in theory be pointed below the female splines in the diff. My rough calculations say that the axle would be pointing to a spot roughly 10-12mm below the diff. That shaft is not going to slip into those splines.

The only way I see it working is if you decambered a 8.8 by angling the entire tube at the point where they press into the rear end housing. And that seems a bit sketchy.

If you're trying to avoid tweaking the tubes and are limiting the mods to the axle ends, you can't just angle the wheel bearing without also offsetting them vertically. My guess is that anybody who could DIY this task probably does it once in a while in his day job.


About -1° is what I keep hearing is the maximum negative camber you can reliably expect to get away with before the splines at the side gears start needing attention. More is probably possible in many cases, but you won't know how much more would still be OK or for how long until you find out how much is too much.

One or two people with 3rd or 4th gen F-body cars have used variations on the heat + force method mentioned by Frank. IIRC, it took more force than anticipated even with acetylene heat. Reportedly, somebody there even discovered that slightly more than -1° stick axle camber was officially acceptable for those cars, though I've never seen separate confirmation.


Elsewhere, I've seen a picture of the rig that is/was used to adjust camber on Class 8 trucks. Basically this contraption is a couple of large jacks and a couple of beefy straps that can be moved laterally in a beefy channel. Operator "feel" is probably important.


Norm