For its time, the suspension used on the aero Fox Cougar and Thunderbird was unique in that the majority of parts did not interchange with other similar Fox-chassis vehicles of the era. The middle-of-the-road 104" (264.2 cm) wheelbase had a lot to do with that, adding some weight to the car and therefore requiring heavier-rated springs than the 100" (254 cm) wheelbase Mustang, while the 102" (284.5 cm) wheelbase Mark VII had its own unique suspension components due to the air ride.
Fortunately for us, with the passage of time Ford used a lot of parts engineered for our cars on other vehicles, with the most prominent being the 1994-98 Mustang (SN95). This means a good supply of factory and aftermarket replacement parts for us. We'll explain below what interchanges and what can be substituted safely.
Please note that, by now, a majority of these parts are only going to be available as aftermarket pieces through parts stores. Ford dealerships usually do not carry most of the components listed below. Sometimes you can luck out and find some NOS or good used parts on eBay if you're diligent enough. Ultimately it would be great to rebuild the suspension using new Ford parts but we think that ship sailed a long time ago, so aftermarket is going to be your best bet. At least you can still get most everything—we have to count our blessings!
The front control arms used on 1983-86 Cougars and Thunderbirds were originally produced by Rockwell in either their Newton Falls, OH or New Castle, PA plants. They are 100 percent identical to those used on 1979-93 Fox Mustangs (and 1979-86 Mercury Capris), which interchange with no issues. You can usually purchase them with bushings installed, and with or without ball joints. For correctness, it should be purchased without the ball joint, or you can remove the new ball joint once you get them. That way you can run the correct ball joint (see below) even though Fox Mustang-style ball joints will work fine.
The OEM ball joints used on our cars were "sealed for life" and did not require lubrication, but if the factory seal failed then they would leak fluid and cause premature joint failure. We had that happen a few times and take it from us, that is not fun. Be sure to inspect the seals on your factory ball joints and tie rods on a regular basis to make sure they're not leaking. You should be able to get a similar-type replacement ball joint or tie rod new should you desire them again. (We've had better luck with the non-factory, but greaseable, style on our cars). By the way, Fox Mustang/Capri ball joints were identical but with factory grease fittings. The SN95 ball joints are metric and aren't long enough to fit into our spindles.
The modified Macpherson front struts were initially unique to our cars, since the point of maximum deflection (a.k.a. the "sweet spot") was a bit longer in travel versus a Fox Mustang. Therefore you can still get specific struts for our cars brand new. However, sometimes parts books will interchange a 4-cylinder Fox Mustang strut with our cars, since the 10" (25.4 cm)brake spindles are alike. You could technically use this strut since it's close in spec to ours, but we prefer our own specific strut just to make sure the ride quality stays at the consistent levels that we expect.
Since the Mustang got a bit larger with the SN95 platform, it's been reported that a 1994-98 Mustang strut can be used safely in our cars. Physically its compressed and uncompressed lengths are very, very close to our cars. The only caveat: a spacer will be needed between the strut and spindle, since our spindles are thinner compared to the later Mustang's thicker mounting point. Sometimes new struts will come with spacers (washers) or you can make your own. Other than near compatibility, we don't see any advantage to using these struts when perfect stock replacements are still available for our cars.
New strut mounts are available for our cars and may in fact be the same used throughout other Fox vehicles. We had no problem getting them for one of our cars not that long ago.
The factory front sway bar for non-turbo cars was 15/16" (2.38 cm) and interchanges with a 4-cylinder Fox Mustang (and possibly other, earlier Fox vehicles). For the XR7 model, the sway bar was 1-5/16" (3.33 cm) and identical to those used on the Turbo Coupe and 1986-93 Fox Mustang 5.0L V8 cars. In either case, our end link kits seem to be a bit longer than those used on Mustangs so be sure to get the correct kit. Stock end link and sway bar bushings are rubber, but we've learned from experience that replacing all sway bar bushings with urethane will greatly increase handling and also last a lot longer.
The factory front springs, initially made by TRW, were tailored for each engine and overall weight of the car with options. Initially there would have been a tag affixed to each spring with a code; that code could then be cross-referenced in dealer shop manuals to reveal the spring rates. The driver's door tag also has spring codes listed directly next to the transmission code in the lower righthand corner of the tag (see reference photo here for example) which can also be used to decode the spring rate. Over time, some of this information has been homologated into general purpose replacement aftermarket springs, since the variations were so close to each other from the original Ford specs. Therefore, in the aftermarket you will find only a few different styles instead of the myriad that Ford installed from the factory.
Aftermarket replacements will come in two styles: constant rate and variable rate. These cars never had variable rate springs out of the factory. If you would like to try them, that is fine. To be more technically correct the constant rate springs should be used. Either kind should get the car's ride height very close to factory specs; be sure to take before and after measurements and photos to double check, as sometimes springs can lower the car unexpectedly.
That being said, we do like the MOOG brand, as they seem to be the closest to factory in quality, but any good name brand is fine so long as you get a decent warranty with them. Most springs are sold in pairs for convenience.
MOOG front spring information (stock ride height, constant rate):
Since the SN95 Mustangs are closer in size and weight to our cars, there has been a movement as of late to use springs from those cars in ours. The general consensus is that they do indeed work, but V6 and V8 Mustang factory springs lower the car a bit (sometimes 1" (2.54 cm) or more). The V6 convertible springs are higher rate and seem to do a better job in keeping the stock ride height for our cars. We at COOL CATS have not tried these springs and have no experience with them. From what we've seen, there's a lot of experimentation going on and there is no clear-cut formula for which spring to use in which car. If you're a tinkering type, there's some information on the message board here that may help you; otherwise it may be wiser to stick with Cougar/Thunderbird springs.
As far as interchanging goes, you can generally use a 1987-88 Cougar/T-Bird spring with no issues. They are a bit different but not enough to affect ride height or quality. These are the only known Ford direct interchange springs.
New spring isolator kits are available; you'll probably have better luck ordering them for a Fox Mustang. Replacements are generally urethane but they last a lot longer than stock rubber. Places such as LMR carry Mustang-based kits that can be used for our cars with no issues.
The rear upper control arms used on the Cougar/T-Bird Fox chassis were unique to the cars (1983-88). Center-to-center of the mounting holes measures 10.25" (26cm). They are longer than those used on Fox Mustangs by about an inch. However, a GM 1968-72 G-body upper control arm is within 0.040" (0.10 cm) of our uppers and fit quite nicely. We haven't heard whether SN95 uppers interchange.
Similarly, the 1983-88 rear lower control arms are longer than a Fox Mustang by about 0.75" (1.9 cm). They measure 18.2" (46.2 cm) from center to center on the mounting points. While we've heard of the Mustang lowers being used (and we've even used them ourselves long ago), you must check the pinion angle to be sure it will not bind up the rear axle. A pinion angle from 0 to +4 degrees is acceptable; otherwise, don't use it. We are not aware of any other lower control arm that directly interchanges.
The rear shocks for our cars, again, were unique. New shocks are available without issue. It may be possible to use an SN95 rear shock as well; that has not been verified. Fox Mustang shocks are too short.
If you have an XR7 (or Turbo Coupe) with the rear stabilizer ("quad") shocks to help with rear lateral deflection, you can still get them new but they may not be listed for your car. Instead, search for a Fox Mustang GT or LX 5.0 car and you'll find them. The framerail brackets are unique to our cars and do not interchange with any other vehicle.
Most (read: V6) cars did not have a rear sway bar even though the provisions are there to mount one. The V8 cars had a very thin (~ 1/2"/1.25 cm) bar. The XR7 and Turbo Coupe got a thicker 13/16" (2.06 cm) bar that was identical to those used on 5.0L V8 Fox Mustangs.
The rear springs used on 1983-86 models were a little underwhelming from the factory. This is due to the longer overhang and trunk area on these cars. The constant-rate springs generally had a difficult time keeping the back of the car at a consistent height, especially when it was loaded down, and the cars appeared to "sag" after awhile, even with the trunk and back seat empty.
You can directly interchange rear springs from 1987-88 Cougars and T-Birds, as their revised spring rate helped keep the back end at a better ride height. They will give a factory-style ride without sacrificing practicality. Aftermarket replacements list the same spring for all 1983-88 cars anyhow and seem to be available only in constant-rate.
MOOG rear spring information (stock ride height, constant rate):
An interesting alternative spring is a heavy-duty variable-rate version known as a cargo coil. We've been using cargo coils since the mid-1990s and love them. They solve all of the problems with these earlier cars without sacrificing ride quality. The more weight in the trunk (or back seat), the more these springs try to push upward. They are well worth the money and effort to hunt them down. While not technically "correct" for judging, this is one case where solving a glaring problem and handling situation can be more important than factory correctness. The old MOOG p/n was CC823 (spring rate 340 lb/in, load 808 lbs.); it has been discontinued but we've found them on eBay and Amazon before. If you're not going to have a lot of weight toward the back of the car then you're probably better off with standard, constant-rate replacements.
The 1987-88 Cougar and Thunderbird have revised, longer front control arms that are 100 percent identical to those used on 1994-98 Mustangs (all engines) and the Fox-based Lincoln Continental (1982-87). They will interchange with no issues.
Just like the earlier cars, the 1987-88 ball joints are available new. See the 1983-86 info above for more information.
Specific front struts for the 1987-88 cars are still available brand new. Again, it should be possible to use an SN95 strut.
New strut mounts are available for these cars as well.
All 1987-88 3.8L V6 and non-XR7 5.0L V8 cars got the thinner 15/16" (2.38 cm) front sway bar, while the XR7 model (and similar Thunderbird Turbo Coupe) got the thicker 1-5/16" (3.33 cm) sway bar.
See the information on 1983-86 cars above. You can generally interchange 1983-86 front springs in these later cars with no issues. Again, those are the only known direct interchange springs.
Just like the earlier cars, the rear upper control arms are unique to the Cougar/T-Bird Fox chassis. You can use uppers from an earlier car with no problem.
The rear lower control arms are unique to the cars. Earlier lowers will interchange.
New shocks are available for 1987-88 cars without issue. There was a very slight difference in length vs. the 1983-86 cars but one of those shocks can easily interchange.
Same as the earlier cars (see above).
See the information for 1983-86 cars above.
The rear springs for 1987-88 cars were thankfully revised from Ford to allow for more weight in the trunk. We think this had a lot to do with the new trunk pan, which moved the spare tire to the driver's side of the trunk well. Regardless, these springs were much better in performance and keeping a consistent ride height.
You can directly interchange the older 1983-86 Cougar/T-Bird springs should you desire to.
Otherwise, the same information for 1983-86 cars above concerning aftermarket replacement springs applies to 1987-88 cars. Same goes for the spring isolators.
For a lot of the components listed above, you may be able to reuse your control arm but replace the bushing instead. That is very common as these cars age, and if your control arm is still in good shape then it makes more sense to just change the bushing out. Keep in mind that, no matter what control arm you have, the bushings are pressed in and can require the same for removal and replacement; however, some replacement kits provide just the bushings for reuse in the factory shells. The bushings themselves are identical to those used in corresponding Fox Mustangs. For example, the rear lower control arm bushings for your car and for a Fox Mustang are all the same size and can interchange perfectly, even the oval ones. You can also get the (pain in the backside) rear end upper control arm bushings. Stock bushings are rubber throughout the car. If you want to upgrade to urethane or Delrin, that is your call but be prepared for a slightly harsher ride quality. You can find stock-style bushings at parts stores or online, or sometimes through Mustang parts sites such as LMR, Fox Mustang Restoration, and CJ Pony Parts.
If your suspension bolts need replaced, again, Fox Mustang bolts will work. See the Mustang sites listed above to find them. We are not sure about SN95 bolts as they may be a different length or style.
Most of the rubber components do not have a provision for lubrication. The best time to do that is when it's all apart, and be sure to use a grease that is waterproof and will cling to the surface well. You really cannot easily grease up any suspension components with them still on the car.