1999 Cobra Rear Suspension "Traction Bars"
The 1999 Cobra with IRS has many bushings in the upper and lower control arms as well as between the IRS subchassis and the Mustang unibody. All of these will deflect under load and some of them may contribute to the wheel hop inherent in the IRS design.
Stiffer springs and shocks have reduced the wheel hop in my Cobra to
a tolerable level. I cannot take the time to remove and measure all
the bushings and have stiffer ones made on my own. So I decided to
try an inexpensive experiment to see the effect of limiting the fore and
aft motion of the IRS hub by adding a metal bar link between the lower
control arm and the chassis. This link would resist motion fore and
aft due to the normal compressive deflections in the suspension bushings.
The stiffer springs and shocks minimize the vertical motion in the suspension.
Note that these traction bar parts and pieces are intentionally weak to prevent possible damaging binding of the suspension. The link bolts can only be tightened down at a drag strip, and must be loosened when driving to and from the drag strip and at all other times when not on a drag strip. DO NOT USE ANY TYPE OF PINNED OR RIGID LINK ON A STREET OR ROAD RACE CAR. Binding suspensions will break parts!!
The bars were made from 1"x1" mild steel square tubing. The brackets were made from 1-1/2" x 1-1/2" angle. The bolts are 3/8" with nuts having nylon inserts to keep them from vibrating loose. Use washers everywhere. The long bars have to be bent slightly in a pipe bending machine to clear the exhaust (about a 2" offset).
The rear clip was first bolted to the frame rail and lined up, then the car was driven to a muffler shop where the clips were welded. The frame material at the rear is a very tough alloy that is very hard to drill.
The rear clip is slotted to allow the bolts to be loosened and the bar to move so that there is no bind without completely removing the bars. When I first installed the bars, I put some grease on the washers and did a couple of burnouts. The grease indicated that the bar moved about 1/2", which meant the wheel moved significantly fore and aft when there was only very minimal wheel hop.
The front clip only has bolt holes, no slots. My installation was easy because I have the IPS/HAL shock brackets that move the shock up out of the way. With a stock shock, there will be some different clearance problems than I have with my shocks. You will have to make a bracket that you can get bolts in and out of easily and clear the shock body and the tie rod and still have the square tubing clear the tail pipe.
You must also be very careful when lifting the car with the bars in place because the rear suspension will drop when the car is lifted by the chassis and the bars will come down on the tailpipe and the tailpipe hangers will be stretched while they support the wheel and tire. Unbolt the bars before jacking up the car by the chassis.
So far, as of 6/11/00, I have run the bars with the bolts snugged up in the slotted rear clips during the last three drag strip sessions. The last two session have been with M/T ET Streets, size 26x11.5x16. There has been no noticeable hop on launch at up to 4500 rpm with 4.30 gears except for one minor jolt on the 1st-2nd shift. I have not run the slicks with the bars loose, however, so I have not quantified how much of a contribution the little bars have made. I like them a lot, however.
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