Independent Rear Suspension (IRS)…to do or not to do?

When I first got my ’91 LX, I knew it wasn’t going to be an ordinary LX.  And I knew it wasn’t going to be a drag racer either…been there, done that and the nearest track is 2hrs. away.  I’ve always had a passion for open road racing, I once owned a ’86 SVO Mustang and loved the handling, braking and balance characteristics.  A few years ago I discovered autocross racing and immediately got hooked.  The NYR-SCCA, MetroNY-PCA and BMW-CCA all hold autocross events at Nassau Coliseum and Tobay Beach.  Anybody can start racing.  See my AutoX Checklist page for info.

Instantly my LX got modified for road racing.  As you may know if you have followed this blog, much has been done to increase braking and handling aspects of my car.  I even did work on the factory solid rear axle (SRA).  But, I’ve always wondered how the car would react to a independent rear axle (IRS).  The factory 4-link suspension in the foxbody is very poor and needs a lot help.  To remedy this, I installed a Maximum Motorsport pan-hard bar and torque arm, which made great improvements on the handling and grip.  I was very happy with the results, but I couldn’t help researching the forums on the IRS swap.  It took a while, but one day I came across an IRS on eBay that suited me perfectly.  It had everything done to it that I wanted, plus was a 2003 with 10K on it with stock 3:55 gears.  The only work needed was control arm bushings.  The IRS did not sell on auction, so I contacted the seller and we made a deal I couldn’t refuse.  One week later he IRS was delivered.

eBay Ad

IRS’s generally go for around $1000, you can get them cheaper and some go for more.  I was actually thinking of going the cheap route and rebuilding everything, but parts and labor are so expensive, it just didn’t save me anything.  I had found a ’99 IRS on Craigs List in my area for $500, and I could of probably talked him down to $400  For anyone else thinking of doing this swap, it’s best to replace all the rubber in the IRS while it’s out.  You’ll get the most out of the IRS with new urethane and delrin bushings.  To go through all the work and expenses and install a stock IRS, is just not worth it.  The Maximum Motorsport kit is $800, then there’s braces, shafts, etc..  And we haven’t even got into the pumpkin yet.  My IRS had low miles and was a 2003, so it comes with 3:55 gears, like the ’04.  The 1999 IRS for cheap came with 28 spline axles and 3:27 gears, that I would have to change, along with the posi unit, possibly the spider gears, etc..  More expenses, and more work.  Try and find one that someone already did all the work to, make sure its done right.  Because once it’s in, it’s a pain to get out.


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