Suspension Kit (Grab-a-Trak)

[wrobinson]

I need some input from you guys. I have been looking at purchasing a Grab-a-Trak suspension kit for my son's 1973 Mach 1 build. The car will be more of a daily driver than a weekend warrior. I also have reached out to Ohio Mustang for a quote for suspension kit. The car has a EFI 351C with AOD and 3.25 rear gears. We are running 17" American Racing Torque Thrust D's. The brakes will soon be upgraded with a MustangSteve kit for 12.5" front discs and 11.75 rear discs.
Questions:
A. Use polyurethane bushings or not for performance daily driver?
B. What size front sway bar 1.125", 1" or factory bar?
C. What rear spring 4.5 leaf or 5 leaf with reverse eye?
D. Should we upgrade rear sway bar or use factory 1/2" bar?

 

[tony-muscle]

What I would do for normal driving with spirited bursts:
-PUR only on sway bar bushings
-Front sway bar: 1" would be okay for most driving if you already have it; 1 1/4" if you are in track or if you need to buy one (match with larger rear)
-Rear: 4.5 springs; keep 1/2" bar in rear unless you upgrade the front to 1 1/4", or unless you don't have any and you need one.
-Find a good set of shocks like Bilstein.

I believe the above is a good combo for a spirited driven machine, but all depending on your budget and the spirited/street combo you want.

 

[wrobinson]

What I would do for normal driving with spirited bursts:
-PUR only on sway bar bushings
-Front sway bar: 1" would be okay for most driving if you already have it; 1 1/4" if you are in track or if you need to buy one (match with larger rear)
-Rear: 4.5 springs; keep 1/2" bar in rear unless you upgrade the front to 1 1/4", or unless you don't have any and you need one.
-Find a good set of shocks like Bilstein.

I believe the above is a good combo for a spirited driven machine, but all depending on your budget and the spirited/street combo you want.

Thank you so much for your input.

 

[jpaz]

No real need for the change to rear disc brakes either.

 

[Stanglover]

PLEASE do NOT buy Grab-A-Track rear springs, They are garbage and will be too high. These are what I put on my car; 4.5 leaf, standard eye. They were 1 1/2" too high. I used lowering block initially, but only as a temporary solution. I had them de-arched at a specialty spring shop, but they started to reverse bend soon after.
In my research, I found that many aftermarket manufacturers do NOT use proper spring steel. I found reference to a steel known as 4140, which is a pre-hardened tool steel and I'm pretty sure this is what GAT's are likely made of.
There are other good spring manufacturers in the US, BUT I highly recommend you buy springs from Eaton Detroit Springs. Do it once, do it right. Eaton will suggest the best springs, front and back, for YOUR car. Trust me on this.

 

[tony-muscle]

Be aware of what Geoff is saying about springs. I bought the Maier 4.5 leaf springs and they are amazing - great ride and awesome traction. However, they are expensive, but you pay for what you get. These springs will lower the rear about 1/2". If you don't want it lower just use longer shackles.

 

[Lazarus]

I have a GAT suspension in my 72. Been very happy with it. I mostly avoid poly bushings due to their squeaking. There was one place I used poly because of durability but I cannot remember where.

I went with the 4.5 standard eye rear leaf springs and they were definitely high at first but settled nicely after some driving and time (though I do kinda like a rake anyway on a musclecar). I have seen some folks on the site have some trouble with the leaf springs in that kit, being inconsistent left to right, so maybe I got lucky or they got unlucky...

The thicker sway bars are better than stock, but should have a proportional rear bar installed to avoid the feeling of a super tight front but wobbly/fishy rear end. The front should be slightly stiffer for safety reasons. Online consensus seemed to be roughly a 1/4” difference front to rear; i.e., the 1 1/8” bar should have a 7/8” rear sway bar, the 1” bar should have a 3/4” rear bar. If yours has a factory rear sway bar, it’s probably easiest to get the 1 1/8” front in the kit and the Addco stock replacement rear bar, which is 7/8”. A new 1 1/8” front bar and a 50 year old, metal-fatigued 1/2” rear bar is probably a mismatch.

Mine didn’t have a bar in the rear already, so I bought the addco rear bar for cars without stock rear bar. That addco model is 3/4”, and I got the GAT with 1” front bar.

 

[droptop73]

I used the GAT 1-1/8" front and 3/4" rear sway bars and am happy with the handling. I believe the GAT rear sway bar is not a replacement for the OE bar, it mounts differently. If the stock rear springs are not worn out use them, there is no need to replace if they are not sagging same with the front springs. Don't use polyurethane anywhere except the sway bar. I really like the Global West high durometer strut rod bushings they are pretty reasonably priced.