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Discussion Starter #1
Hi All,

With AutoX starting in a few months, I'd like to get some more work on the mustang to help it handle better this coming year (year 2 of doing autoX).

Every event I went to, they do the car inspection and they go about yanking on all 4 tires. The front end is solid. I have updated to poly bushing from MM when I upgraded to 13inch / 5 lug setup.

The rear end is not the same, it is original rubber and it moves like crazy. The newer guys usually call over a more senior guy to have them explain that 20 year old mustangs 'do that'.

So my question is what effect does this movement / play cause in autoX and overall performance handling.

The rear end is already 'off' by about 1 1/2 inches to the passenger side, I was hoping that upgrading the upper / lower control arms to units with poly bushings would help straighten this out.

The car is mostly stock. I upgraded brakes last year and went to 5 lug with some 17x9 rims to fit those and get a bit more meat to the ground. This is not a daily driver except on Fridays and track days.

Thanks for an advice.
 

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Discussion Starter #3
I think I'll eventually get to that point (and I would like to), but considering that my rear suspension is stock, wouldn't it be more productive to address the other components first (springs / shocks / control arms)?

Would upgraded / poly control arms help in stiffening up the side to side play of the rear end, or is this really what the panhard bar is for?

Also from what I understand, having a panhard bar requires a TA? Or is that me mis reading MM website?

Thanks again!
 

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A TA isn't required to run a panhard bar, however they work best together. I ran my panhard bar for nearly two years with the stock upper control arms before getting a TA.
 

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Hi All,

With AutoX starting in a few months, I'd like to get some more work on the mustang to help it handle better this coming year (year 2 of doing autoX).

Every event I went to, they do the car inspection and they go about yanking on all 4 tires. The front end is solid. I have updated to poly bushing from MM when I upgraded to 13inch / 5 lug setup.

The rear end is not the same, it is original rubber and it moves like crazy. The newer guys usually call over a more senior guy to have them explain that 20 year old mustangs 'do that'.

So my question is what effect does this movement / play cause in autoX and overall performance handling.

The rear end is already 'off' by about 1 1/2 inches to the passenger side, I was hoping that upgrading the upper / lower control arms to units with poly bushings would help straighten this out.

The car is mostly stock. I upgraded brakes last year and went to 5 lug with some 17x9 rims to fit those and get a bit more meat to the ground. This is not a daily driver except on Fridays and track days.

Thanks for an advice.
You better check the rules for your class before you start doing stuff. Having said that a PHB is a huge improvement even with stock CAs.
 

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I think I'll eventually get to that point (and I would like to), but considering that my rear suspension is stock, wouldn't it be more productive to address the other components first (springs / shocks / control arms)?

Would upgraded / poly control arms help in stiffening up the side to side play of the rear end, or is this really what the panhard bar is for?

Also from what I understand, having a panhard bar requires a TA? Or is that me mis reading MM website?

Thanks again!
As noted above a PHB can be used with the stock 4-link, but ...

The stock uppers are trying to do two jobs at the same time: (i) lateral axle control and (ii) preventing axle rotation. To do these two jobs, the upper arms and bushing must twist/deflect. Adding poly to this mix causes more bind than already exists. Leaving the stock-design uppers in place and adding a PHB to the mix creates a conflict between the uppers and PHB for lateral control of the axle. It's better but not optimal. The solution is removing one or both of the uppers completely. This would require a PHB/Watts Link for lateral control and the T/A, PM3L or true 3-link for rotational control. When this is done the rear suspension is transformed.
 

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Discussion Starter #8
You better check the rules for your class before you start doing stuff. Having said that a PHB is a huge improvement even with stock CAs.
I don't really race for class. My brother has a 350z (stock) and we race on weekends for bragging rights, it's what keeps it more than fun for now.

He's been doing it for 3 years, last year was my first and I was able to get within 2 seconds of him by the end of the season (it started with a 10 second gap on my first runs).

So really I'm trying to beat him with a old mustang vs his newer 'expensive' car. :)

poly bushings in the uppers is a definite no-no, all poly in the lowers is also a no-no
I see. I had always thought we wanted to stiffen up things from original factory rubber. But after this comment I started digging around MM and found out that isn't exactly the case. Thanks for the info.

@qtrracer - thanks for the detailed explanation that explains a lot in a short paragraph.

I'll get to searching for more info on the binding effects of the rear end. Thanks all!
 

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I guess the "moving around alot" is a subjective measurment but I would thing you wouldn't get that much movement from rocking the car by hand unless the bushings were in bad shape.

I'd also wonder about an inch and a half of variance from side to side on the axle, I know some is allowable but that seems a bit much.

I'd do this:

Check all the bushings by removing the parts and inspecting the bushings close up.

Check your torque boxes for distortion.

If everything checks out, it's up to you, do a set of springs and shocks/struts and whatever else you want (LCAs- ones meant for the track, PHB, TA) or can afford.

I used my car with stock LCAs (good, stock bushings), stock UCAs (good, stock bushings), stock swaybars, stock front end with just lowering springs and Tokico shocks/struts for 4 years and it wasn't the fastest thing around, but it was safe and handled better than stock. Once my driving got better and money became available, I put a better suspension under it (and am still in process of finishing that job- TA going in this year).
 

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Just one person's opinion, but the MM PHB was the best mod I made on the car, as far as feel on the street (a shifter was the best).

Really didn't help my times much in autocross, but it FEELS so much more solid and predictable.
 

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Leaving the stock-design uppers in place and adding a PHB to the mix creates a conflict between the uppers and PHB for lateral control of the axle.
I've seen that before, but I don't understand.
I mean, on a four-link WITHOUT the PHB, the uppers must be working like a SOB to help keep the axle in place.
The PHB keeps the axle from moving side-to-side hardly at all, so how does that mean MORE work for the uppers or push them outside the range they were designed to handle?
 

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I've seen that before, but I don't understand.
I mean, on a four-link WITHOUT the PHB, the uppers must be working like a SOB to help keep the axle in place.
The PHB keeps the axle from moving side-to-side hardly at all, so how does that mean MORE work for the uppers or push them outside the range they were designed to handle?
It has to do with roll centers. A roll center is the point in space about which the body tries to rotate when leaning in a corner. Both the front and rear suspension have roll centers, but we'll just talk about the rear.

The roll center is defined by the geometry of the device used to locate the rear suspension laterally. In a factory Mustang, this is the upper control arms. they define a roll center well above the axle centerline -- usually about 12-18" above the road surface.

A Panhard bar's job is to locate the axle laterally, too, so it defines a roll center too. It is, for the most part, where the bar intersects the centerline of the car -- generally 8-10" above the road surface.

Notice that the two roll centers are not the same. This means as the body rolls, the upper control arms and the PHB both tri to make the body roll around different points and they ending up fighting each other and binding up.

When the two bind, roll resistance goes way up, the same as if you had stiffer springs or a bigger sway bar. The stiffer a suspension is, the less grip it has, so when it binds, it looses grip. That results in snap-oversteer when the rear suspension binds up. Not a Good Thing.

Binding also puts ENORMOUS loads on the UCAs and the PHB. Generally the busings of the UCA's end up getting torn up over time.
 

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Discussion Starter #13
@MJ91GT

My passenger side tire is dead even with the fender lip. The drivers side is off by about 1 1/2 inches. So I guess 3/4 inch is probably more accurate of a measurement.

@gt40mkII

So with what your saying, should I wait and to a TA and PHB at the same time to avoid that type of conflict? If we where to do the PHB, would we likely not see much improvement on handling?

I do only autoX at this point, would I be seeing snap over steer in that type of driving or would it be more prevalent in road course type of driving.
 

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This is what u want:

MM XD LCA
MM Panhard bar
MM Torque Arm
UPR lower torque box reinforcements

(i hope u already have good subframe connectors)
 

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It has to do with roll centers. A roll center is the point in space about which the body tries to rotate when leaning in a corner. Both the front and rear suspension have roll centers, but we'll just talk about the rear.

The roll center is defined by the geometry of the device used to locate the rear suspension laterally. In a factory Mustang, this is the upper control arms. they define a roll center well above the axle centerline -- usually about 12-18" above the road surface.

A Panhard bar's job is to locate the axle laterally, too, so it defines a roll center too. It is, for the most part, where the bar intersects the centerline of the car -- generally 8-10" above the road surface.

Notice that the two roll centers are not the same. This means as the body rolls, the upper control arms and the PHB both tri to make the body roll around different points and they ending up fighting each other and binding up.

When the two bind, roll resistance goes way up, the same as if you had stiffer springs or a bigger sway bar. The stiffer a suspension is, the less grip it has, so when it binds, it looses grip. That results in snap-oversteer when the rear suspension binds up. Not a Good Thing.

Binding also puts ENORMOUS loads on the UCAs and the PHB. Generally the busings of the UCA's end up getting torn up over time.
I have to replace my diff side UCA bushings twice a year and the UCAs every other year.
 

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When the two bind, roll resistance goes way up, the same as if you had stiffer springs or a bigger sway bar. The stiffer a suspension is, the less grip it has, so when it binds, it looses grip. That results in snap-oversteer when the rear suspension binds up. Not a Good Thing.

Binding also puts ENORMOUS loads on the UCAs and the PHB. Generally the busings of the UCA's end up getting torn up over time.
So remind me again why I installed a panhard bar? :confused:
 
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