5.0 Mustang & Super FordsHow To Drivetrain
Power Steering - Steered Straight
'79-'04 Power Steering
Fine, you say, I now understand how the spool valve works, so what's the big deal? Well, after that, what matters is the exact shape of the edges of the grooves in the collar and lefthand shaft. And when we say exact, brother, we're talking small--like, so minute you need a magnifying glass to see 'em. These edges are not simple 90-degree cuts, but a series of steps. The more intricate the steps, the more nuanced the control over the power steering fluid flow.
As you can see, Ford's chassis engineers can fiddle with the T-bar and the porting troughs in the spool valve (along with a bunch of other stuff) to adjust the steering feel. You cannot. It takes far too many specialized, accurate fixtures and machine tools to cut and assemble a spool valve, so no shop is going to file a few grooves and make a magic spool valve.
What you can do is swap steering rack assemblies. From the advent of the Fox Mustang in 1979 until 2004, Ford made just a few major changes in the Mustang steering rack. Save for the steering input shaft, all Fox and SN-95 racks are direct bolt-in replacements for each other, for example. And that steering shaft difference can be accommodated easily enough with aftermarket parts, which we'll get to in a minute.
Chuck Schwynoch at Maximum Motorsport characterizes the Fox power steering rack as having a slightly notchy or on/off feel due to simple machining on the grooves in the spool valve. He prefers the SN-95 rack, which he finds has a more linear response.
Also worth noting are early Fox racks which were sourced from TRW. These are easily identified by their construction: aluminum castings at each end and a steel tube in between. After the TRW racks were phased out in the mid-'80s (there's no hard date for when TRW racks quit showing up), Ford built its own racks in-house. These all use a single aluminum casting.
Generally speaking, Chuck figures Ford paid more attention to the feedback the car gave the driver as the Fox/SN-95 chassis was in production longer, and therefore it's the later SN-95 cars that are preferred.
Chuck's top choice is the '00 Cobra R rack. Apparently some of the massaging these racks received at the factory was not suitable for mass production, but with just 300 Cobra Rs built, this wasn't a problem for Ford. What is a problem for us is that few Cobra R racks were made--just enough for the production run and a few service parts, and those have all been gobbled up. In fact, Maximum Motorsports bought the last 12 of these steering racks it could find and has put all of them into service. So, the '00 Cobra R rack is the one to have, but is unobtainable.
Using the same valving code as the '00 Cobra R rack but carrying a different Ford part number are the '99-'01 and '03-'04 Mustang Cobra racks. Maximum isn't sure if the valving is precisely the same as the Cobra R racks, but it's close. Definitely a desirable steering rack assembly.
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If a Cobra rack isn't available, Maximum recommends the '02-'04 Mustang GT/Mach 1 rack. And if that proves impossible to find, the next choice is the '99-'01 Mustang GT/Bullitt assembly. We'll also note Maximum doesn't sell steering racks, save for the Flaming River manual rack assembly for those wanting manual steering.
At the risk of repeating ourselves too many times, you don't need to change steering racks on a plain old daily driver Mustang. Leave this trick for serious hobby and track cars.
For the majority of Mustang owners, the bang for the buck come with paying attention to the tie rods and outer tie-rod ends. Both inner and outer tie-rod ends wear, and replacement is the cure. Likewise, if you've lowered your Mustang, offset rack bushings may be useful, but a bumpsteer kit is likely an even better purchase.
Leaks are not a common problem with Mustang power steering racks, but sometimes the Teflon seals under the pump-to-rack line fittings need replacement (often because they were lost or damaged during rack maintenance).
The spool valve, rack, pinion, and input shafts appear bulletproof and should not require maintenance, but if someone has been banging curbs with the front end and the interals are out of whack, then the rack assembly should be replaced.
The rubber bellows at the end of the steering rack are important as they keep dirt out of the precision internals. We'd be suspect of a rack assembly with torn boots.
Power steering pumps are beyond the scope of this article, but if you have one that doesn't hiss like a mad cat, you're fine.
The bottom line: Fox drivers looking for increased precision should consider upgrading to a later SN-95 steering rack assembly and matching steering shaft, and everyone should keep ahead of tired tie-rod ends.
Horse Sense: Keep in mind the typical wear points in the Mustang steering are the inner and outer tie-rod ends. These are normal maintenance items at anything around 100,000 miles, and if your Mustang is wandering or has notchy steering, they are the first place to look.