Suspension re-assesment - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 15 Old 12-25-2015, 11:18 PM Thread Starter
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Suspension re-assesment

Goals for the car:
Reasonable ride on Michigan roads with handling comparable to a newer Mustang. Able to hold its' own on an open track day and not make me look completely stupid.

Current set-up: '88 LX hatch with stock K member and urethane-bushed FCA's. Bilsteins and MM c/o kit on front with 300# springs. MM CC plates. MM heavy duty RLCA / SN95 RUCA with MM springs, MM PHB, and Bilsteins. Eibach ARB kit. Car has '95 front spindles and Cobra brakes all 'round, FLSFC's and MM STB. (Enough acronyms for you??)

I'm fairly happy with the car. but would like to get an idea of where to go next.

The only thing I DON'T have is the torque arm, and the K member with revised geometry and tubular FLCA's.

Which one would you recommend next? Where is my best bang for the buck??


'88 LX hatch. Mild 331. Full MM suspension minus the Torque Arm, Cobra Brakes. Not as slow as it used to be.
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post #2 of 15 Old 12-26-2015, 07:39 AM
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The rear is the worst end of these cars so since you have already fixed the front some then a TA should be your next move. I think you will be happy.


2003 Azure mach1 5 speed with IUP
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post #3 of 15 Old 12-26-2015, 06:53 PM
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If your budget permits, I agree - T/A next. If not in the budget, then find a rod-ended upper and remove the D/S upper and replace the P/S upper with the new rod-ended one. Get stiffer springs - probably the softer T/A springs sold my MM. This conversion will be a lot less expensive and provide nearly the same level of performance as the T/A. Welcome to the world of PM3L.
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post #4 of 15 Old 12-26-2015, 08:49 PM Thread Starter
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I've been looking at the PM3L as an interim move. Sounds like I need to stop looking and start wrenching.
There will be a power upgrade over this winter. (N/A 331. I'm expecting 325 or so at the wheels.) With that, I expect to need to make some tweaks to the handling. PM3L it is.
"get stiffer springs". Front? Rear? Both? I know the fronts are 300# WITH the coil-over kit. I would have to dig through receipts (or go out and put the car up and find the MM # on them) to see what the rears are.

Thanks for the input!!

'88 LX hatch. Mild 331. Full MM suspension minus the Torque Arm, Cobra Brakes. Not as slow as it used to be.
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post #5 of 15 Old 12-26-2015, 09:23 PM
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You've already got all you need to get some great lap times. If you like the way the car rides save your money on parts and do some track days. The only thing that would make you look stupid on the track is the driver, the parts you have are fine.

While doing the track events pay attention to how the car feels. Does the back end want to come around? Does the front end push in the turns? Look at the track event photos and see how your car looks in the turns and then fine tune the suspension with sway bar adjustments, spring rate changes, etc. to improve the balance.

'03 Cobra-529rwhp, '95R #201, '90 GT w/ IRS, 2015 Focus ST, 2012 GT track car
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post #6 of 15 Old 12-27-2015, 12:01 PM
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Quote:
Originally Posted by Oldbutnew View Post
"get stiffer springs". Front? Rear? Both? I know the fronts are 300# WITH the coil-over kit. I would have to dig through receipts (or go out and put the car up and find the MM # on them) to see what the rears are.
Front rates are fine. Because the PM3L removes most of the rear bind, the rear rates must increase to compensate. As a start, I suggest the lower rated T/A springs MM sells; believe those are 370-430# progressive conventional. Wheel rate will be around 200# average. With the front springs at 300#, front wheel rate will be 270#. The F/R ratio will be about 1.35:1 This is a bit front biased but a good start without sacrificing ride quality.

Once on track the suspension will speak volumes. It will take some seat time to decipher the chatter
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post #7 of 15 Old 12-28-2015, 08:54 AM Thread Starter
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Thanks again for the input. That is exactly the information I was looking for.
As if I wasn't looking forward to the next open track enough already....
Yes, I know I need seat time. I hope it's a lot like riding a bike. It has been about 10 years since I drove anything in anger. Having the car sitting on a reasonable foundation when I show up will improve the experience in every way. I can focus on finding the old mojo instead of fighting a car with big issues.

'88 LX hatch. Mild 331. Full MM suspension minus the Torque Arm, Cobra Brakes. Not as slow as it used to be.
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post #8 of 15 Old 01-07-2016, 08:03 PM
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Panhard bar for fox snap oversteer, stiffer springs,frame stiffening, https://youtu.be/ldrDFD59NQU
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post #9 of 15 Old 01-08-2016, 09:05 AM
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Panhard bar for fox snap oversteer, stiffer springs,frame stiffening, https://youtu.be/ldrDFD59NQU
Agree with chassis stiffening. OP already has the MM PHB. But even if not, the PHB wouldn't help snap oversteer. That is caused by wheel rates going to infinity caused by binding arms and/or rigid springs (= wheel rate going to infinity). PHB controls lateral movement. Preventing binding is one of the reasons it was suggested to remove both uppers and replace with a T/A, or the budget friendly alternative PM3L using sphirical bushings.
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post #10 of 15 Old 01-27-2016, 12:24 PM
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Quote:
Originally Posted by qtrracer View Post
Agree with chassis stiffening. OP already has the MM PHB. But even if not, the PHB wouldn't help snap oversteer. That is caused by wheel rates going to infinity caused by binding arms and/or rigid springs (= wheel rate going to infinity). PHB controls lateral movement. Preventing binding is one of the reasons it was suggested to remove both uppers and replace with a T/A, or the budget friendly alternative PM3L using sphirical bushings.
Dumb question but i'm fairly new to this and a bit ignorant.
With the pan hard bar stopping lateral movement doesn't that stop the binding on the upper control arms? This is from the MM tech site. The Root of the Problem
Solid-axle-equipped Mustangs were manufactured with a four-link rear suspension design that requires the rear upper control arms to do two jobs. One job is to locate the axle laterally. Unfortunately, compromises in the design of the Mustang four-link prevent the rear axle from being precisely located. The axle will shift from side-to-side by up to 2 inches. This inconsistent movement of the rear axle causes a rear-steer effect.

Rear-steer means that the rear of the car is steering itself, without any steering input from the driver. This rear-steer behavior makes the Mustang unstable, and requires corrective action by the driver. This can make the driver feel very uncomfortable, as they do not have complete control of the rear of the car. While that four-link design might be suitable for a commuter car, it cannot provide the handling prowess expected of a high performance vehicle.

The MM Panhard Bar Solution
The MM Panhard Bar adds an aluminum rod as a lateral suspension link between the rear axle and the Mustang chassis. This simple design precisely controls the side-to-side location of the axle to eliminate rear steer. The unstable and unpredictable feeling typically associated with the Mustang four-link suspension is gone, making your car safer and easier to drive!

Why choose a MM Panhard Bar, and not a Watts Link?
There are two good methods of controlling the side-to-side location of a rear axle, a Panhard Bar or a Watts Link. MM's Engineering Team chose the Panhard Bar because it allows a much lower roll center than a typical Watts Link design. A lower roll center reduces the tendency for the inside rear tire to lift and unload during cornering. As a welcome bonus, a Panhard Bar is far less complex, less expensive, lighter, and allows for the use of tail pipes!

Upper Control Arm Bushings
Whether or not your Mustang is equipped with a MM Panhard Bar, it is very important that the rubber upper control arm bushings be retained. This is one application where the compliance of a rubber bushing is a benefit. Retaining the rubber upper control arm bushings is a necessary compromise to achieve acceptable handling. See the Rear Lower Control Arm section here for more information about control arm bushings.

How it Works: The Complex Interactions of a Four-link rear suspension plus a Panhard bar
As the suspension moves, the rigid Panhard Bar causes the Mustang's rear axle to move through a different, and better path than the stock four-link design. This requires the upper arms to physically change length as the suspension moves. Obviously, the metal control arm cannot change length. But its effective length, the distance between the control arm's two pivot points, can change because of the inherent compliance of a rubber bushing. If the ability of the upper control arms to change their effective length is hindered by a noncompliant bushing material, the suspension will bind up, and not move freely. The resulting restriction in the ability of the rear suspension to freely articulate will cause poor handling; the car will have a tendency to oversteer, and it may do so in a sudden and unpredictable manner.

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post #11 of 15 Old 01-27-2016, 06:31 PM
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Originally Posted by MB88LX View Post
As the suspension moves, the rigid Panhard Bar causes the Mustang's rear axle to move through a different, and better path than the stock four-link design. This requires the upper arms to physically change length as the suspension moves. Obviously, the metal control arm cannot change length.
There's your answer, embedded in what you posted.
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post #12 of 15 Old 01-27-2016, 07:15 PM Thread Starter
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Just for the record: The TA springs and adjustable uppers are all in my hands.
Now I just have to get busy putting an engine back in the car and I will be closer to HPDE!!

'88 LX hatch. Mild 331. Full MM suspension minus the Torque Arm, Cobra Brakes. Not as slow as it used to be.
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post #13 of 15 Old 02-03-2016, 04:13 PM
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Quote:
Originally Posted by qtrracer View Post
Agree with chassis stiffening. OP already has the MM PHB. But even if not, the PHB wouldn't help snap oversteer. That is caused by wheel rates going to infinity caused by binding arms and/or rigid springs (= wheel rate going to infinity). PHB controls lateral movement. Preventing binding is one of the reasons it was suggested to remove both uppers and replace with a T/A, or the budget friendly alternative PM3L using sphirical bushings.
I don't know about snap oversteer on an autocross track with lower speeds and sharper turns because I have never done it, but on a road course the panhard bar helped my car immensely. I can get it loose around a corner at 40 mph and feels completely under control as opposed to before panhard was installed. If you ever want to race such as I am you must be aware of mod limits allowed per class such as NASA CMC, all stock suspension points must be maintained although a panhard bar is allowed.
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post #14 of 15 Old 02-03-2016, 08:03 PM
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^^^ I have spun out multiple times on an A/X course. When the car goes into the turn and loads the rear suspension, the upper arms hit bind as they attempt to twist and grow. When this occurs, there is no suspension compliance. The wheel rate goes to infinity and the rear tires suddenly lose traction; the rear comes around pretty fast. Not much can be done except hold on until it stops, or power on and spin it around. I've had this happen with the stock arms and bushings, with the addition of a PHB, and using a PM3L replacement for the uppers. In the latter case, my springs were too soft which caused the shocks to bottom and coil-bind.

One thing has to be kept in mind when adding a PHB to the stock 4-link on a Mustang. The uppers define one roll-center, while the PHB defines another. The two fight each other which is not optimal for handling. Hence, the reason to go T/A only or the PM3L so that only the PHB is defining roll center and controlling lateral axle movement.
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post #15 of 15 Old 02-04-2016, 09:17 AM
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7.29.2 Both GM and Ford cars may also use a Ford 9Ē, GM 12 bolt, or Dana 44 rear axle housing, but the
housing must maintain both the exact OEM suspension pickup points and OEM rear end geometry as the
originally equipped axle assembly.
7.33.2 Panhard bars:
1. Ford cars may add a panhard bar. The bar may be adjustable for length. One panhard bar
mounting point may be height adjustable to allow for leveling of the bar, but the other
mounting point must be of fixed height.
This is from the NASA CMC rule book. I know the TA is best way to go, some racers have used the PM3L but causes damage to chassis in time on a race car. I guess they try to make the cars more equal without going to far.
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