4-to-5 Lug Conversion

For All 1983-88 Cougars / Thunderbirds

Page Revised: 10 May 2019


Article by
Eric Dess

While's there's technically nothing wrong with the stock 4-lug bolt pattern on your Cougar, if you ever want to upgrade rims then you're in for a shock: it's getting more and more difficult to find new, aftermarket 4-lug spec wheels for our cars. Even some older factory 4-lug Ford rims are getting tough to hunt down. And pricing (with shipping) can be a deal-breaker sometimes. You may yearn for something that is a little more modern—more "normal". Enter the 5-lug conversion.

There is a whole new world of possibilities for rims when you have a 5-lug pattern. For example, just about any 1994-2004 Mustang rim will bolt right up with no problem. Or if you're going retro, a set of BBS 16" spoked Mark VII rims look sweet. The choice is yours—if you've already found that perfect rim, but need to swap to 5-lug, then this is the section for you.

For our vehicles, Ford uses the 5 x 4.5" bolt pattern on almost all of its late-model 5-lug rear drive vehicles. The only exceptions, ironically, are the 1989-97 T-Bird/Cougar and 1993-98 Mark VII, which use a very unusual FWD 5 x 4.25" pattern (from the Taurus, Sable, Continental and Windstar). While Panther platform (Crown Vic/Grand Marquis/Town Car) wheels have the correct pattern, the offsets are too great to make work without a lot of reconfiguring.

Physically changing the front over to the 5-lug pattern can be rather simple (10" rotor) or more complex (11" rotor, 13" rotor), depending on your preferences. The rear, however, is going to require axle work at the very least, along with the requisite brake work. This can be a daunting task for the uninitiated so if you're a bit apprehensive, have a professional do the work for you.

Also, please keep in mind that there are many ways to achieve a full 5-lug conversion. There is no single "right" way to do it, simply because there are a lot of different parts from which to choose. We hope that this section helps demystify the situation and inform you of your choices so that you can make the best decision for your purposes.

Generally speaking, the front will likely need a spindle change along with the new 5-lug rotors. Out back, you will need to change the rear axle shafts at the very least. Going from drum to disc will entail a lot more work and parts. It's possible to just swap in the entire 5-lug rear end to solve that issue.


Stock Rotors (10")

Until recently there really wasn't a pre-made bolt-on solution for 10", 5-lug rotors. Not long ago we were contacted by Brian Portez of Complete Brake Service in Columbus, OH. Brian says that his company has 10" 5-lug rotors for the Fox Cougar/Thunderbird (and 4-cylinder Mustang) in stock. This is about the only place that has come forward about these rotors and the only place we've ever heard that carries them. They'll even ship the rotors anywhere. The price (around $60/each US) is very competitive. You can visit their website or you can call 1-800-581-2339 (locally 614-221-4888), and ask for Brian.

Jason from FL writes: "Just installed the 5-lug 10 inch rotors. Fit was perfect, quality seemed excellent. Price was good at $129.00 U.S. plus shipping. I got rotors, new inner and outer bearings, seals and dustcaps. Shipped to my door in 3 business days. Thumbs up from me!"


Fox Rotors (11")
11" 5-Lug Rotors

If you have already upgraded to the 11" rotors then the only direct swap 11" 5-lug front rotor will be from the Lincoln Mark VII (~10 49/64"). Keep in mind that most Mark VII's had ABS brakes, which means that an exciter ring was part of the rotor hub. This increases the cost of the rotor; however, you should be able to find a Mark VII rotor for a car without ABS. Also, you will need at least a 15" rim to clear the brakes. (If you haven't upgraded to 11" Fox brakes but are planning on doing so, see the information here). Also, you should know that with the dust cap on, the center caps of certain wheels may not fit properly over the Mark VII rotor (in particular, the popular factory Torque-Thrust style rim). The rims affected tend to have very small (under 2") center caps. To resolve this, most people run without the dust caps and/or center caps. Just an FYI in case you were planning to run those rims.

SN95 Mustang Rotors (~11")

Since the Fox 4/SN95 Mustangs use a modified Fox suspension up front, you can use that car's braking system on your Cougar. What you have to understand is that it's a little different than what's on your car. In 1994 Ford opted to use the hub-type system on the front of the Mustang, meaning that the rotor does not have studs, but rather holes to slide over the hub that's bolted to the spindle. It's not that major of a difference but it does mean that you're dealing with different parts than what you're probably used to. However, you will happy with the relative ease of installation and assembly, and the comfort of knowing that you have a more modern system on your car.

The biggest advancement with Fox 4/SN95 Mustangs is that they all have comparatively large rotors from the factory, roughly 11" in diameter. Again, you will need at least 15" rims to clear the braking components. You can use the following parts:

Spindles: Any 1994-2004 Mustang can provide the spindles. However, there is a difference between the two major styles. In relation to the standard Fox spindle, the 1994-95 Mustang spindle moves the ball joint 20mm forward, 27mm outward, and 1mm down. The wheel center moved 17mm forward, 23mm outward, but is the same height. The outer tie rod end is moved 20mm forward, 41 mm outward, and 4mm up. The second style is the 1996-2004 Mustang spindle, which compared to the earlier '94-'95 spindle, has the lower ball joint moved 1mm rearward, 5mm inward, and 2mm down. The wheel center also moved 1mm rearward, but is the same width and height. The inner tie rod end is the same fore/aft and width, but moved down 28mm. This may all sound confusing, but in a nutshell, the 1996-2004 spindles lower the point where the tie rod attaches by about 1", and also pushes the spindles out slightly. Essentially they're meant for lowered cars. They are more conducive for performance driving (autocrossing, etc.) but will require slightly modified alignment settings, caster/camber plates, and a bump steer kit. They also have a revised casting that will allow for larger 13" Cobra brakes later on, should you choose to do so. The 1994-95 spindles work perfectly well with stock caster/camber settings on a Fox Cougar/Thunderbird at stock ride height. Again: non-lowered car, 1994-95 spindles. Lowered car, 1996-2004 spindles. Do not mix 1994-95 and 1996-2004 spindles on the same car! You must get a matching pair.

Calipers: Any 1994-95 or 1996-2004 Mustang can provide the calipers, so long as they match the rotor size (see "Rotors" below).

Brake Lines: It may be possible to reuse your front rubber brake lines, but if not, then 1994-2004 Mustang ones can be used.

Bump Steer Kit

Tie Rods: You will need to change at least your inner tie rods to SN95 (1994-2004 Mustang) specs. You can try to use SN95 outers first, but most people report having to change the inners as well. If you're lowering or have already lowered the car, you should go with a good quality bump steer kit in place of tie rods. Jeremy writes, "Fox inner/outer tie rods have SAE threads. SN95 inner/outer tie rods have Metric threads. If you go with SN95 brakes you must change both inner and outer."

Ball Joints: You will need to change ball joints to SN95 specs. If you're keeping the stock ride height, the stock SN95 pieces are fine. Otherwise we'd highly recommend Steeda's X2 ball joints for lowered cars.

Hubs: This is a sealed unit that contains both inner and outer bearings, and all seals. Any 1994-2004 Mustang can provide the hubs; they're all the same. New they are about $70 US each. Ford sells remanufactured units (check dealership for pricing).

Brackets: These hold the caliper to the spindle. The system is designed for easier brake size upgrades; for example, if you were to ever go from 11" to 13" Cobra rotors, the appropriate bracket change is also needed. Make sure your brackets match the calipers and rotors (see below). Bracket bolts (2 per side) are metric!

Pads: Again, these must match the caliper (see below).

Rotors: BE CAREFUL. With the "New Edge" styling of the Mustang in 1999, Ford also made suspension and braking changes with the Mustang across the board. The front rotors increased in size then, and the calipers went to a dual-piston design. Therefore, if you are using 1994-98 calipers then you must use 1994-98 rotors, pads and brackets. And if you're going with 1999-2004 calipers then obviously you'll need 1999-2004 rotors, pads and brackets. It is really your choice as to which years' system to use, so long as you understand that everything must match. A lot of people are opting for the 1999-2004 braking system just to get the better calipers.

Mustang Cobra Upgrade (13")
Mustang Cobra Upgrade (13")

If want to upgrade to a killer braking system, the Cobra 13" disc brake conversion is a very popular choice and probably one of the most affordable in comparison. It's basically the same brake setup as the 1995-2004 Cobras (and the Bullitt/Mach I). You will need at least 17" rims to clear these brakes (5.75" backspacing). Essentially the upgrade is just like the 11" SN95 upgrade outlined above, with these exceptions:

Calipers: You actually have several choices. Ford opted to use the braking system designed by Australian manufacturer PBR on the Cobra and Bullitt. Therefore you can use the 1995-2004 Cobra caliper (black with white COBRA letters on the front) or the 2001 Bullitt caliper (red with a silver Pony on the front). Or, if you want to be different, you can use a 1988-96 C4 Corvette PBR caliper (silver and finned) made for 13" rotors.

Brake Lines: It is highly recommended that you use Russell street-legal stainless steel brake lines. Factory Cobra lines were notorious for bad pedal feel.

Banjo Bolts: The PBR caliper uses a metric banjo bolt. If you cannot obtain these bolts from Ford then take a trip to the GM dealer and get them for a C4 Corvette (1988-96 vintage).

Brackets: 1995-2004 Cobra. Bracket bolts (2 per side) are metric!

Pads: All of the PBR 13" calipers use the same pad so a Corvette pad fits the Cobra, and vice versa. Bad news is, they aren't cheap. The ultimate in pads are NAPA Ceramix, which are very quiet and produce much less brake dust than any other pad out there, but cost around $150 US. Shop around for pads if price is a factor.

Ford M-2300-K Cobra Brake Kit

Rotors: DO NOT use pre-1999 factory Cobra rotors as they are notorious for warping prematurely. These faulty rotors were replaced in 1999 with much stronger Brembo 13" units. You can get them new at the Ford dealer for roughly $100 each. You also have choices in the aftermarket, such as slotted or cross-drilled, from a variety of manufacturers.

Ford Racing used to sell a complete upgrade kit (M-2300-K) which made life easier for this conversion (well, save for the price tag). Since the kit is now obsolete, you'll have much better luck gathering the individual parts for the conversion.

Misc. Aftermarket Front Brake Upgrade

If none of the above appeals to you, you'll probably want to check out manufacturers like Brembo, SSBC and Baer in this case. The good news is, anything that fits a 1979-2004 Mustang will work on your car. So that means multi-piston, exotic rotor systems can definitely be adapted to a Fox Cougar/T-Bird.


In back, things do get a bit trickier. What is true is that you must change the axle shafts to those with a 5-lug pattern. Then you must get the appropriate 5-lug brake drum (stock) or disc brake rotor (upgraded). Really, that's it in a nutshell, although that's really simplified. The reality is that there's still quite a bit of work involved.

Axle Shafts

Now you can have your stock shafts machined for the 5-lug pattern, but as affordable and plentiful as new or used 5-lug axle shafts are these days, it makes more sense to search those out. Regardless of your model year 1983-88 and your rear end width, these axle shafts will directly swap into your Cougar's rear axle:

  • 1994-98 Mustang-width axle shafts (29 15/16", 7.5" or 8.8", non-ABS)
  • 1983-92 Ford Ranger pickup axle shafts (2 driver's side, 29 1/8")
  • 1986-97 Ford Aerostar minivan (2 passenger side, 29 1/8").

All stock Ford passenger car rear ends of our era had 28-spline axle shafts. If you need to see more specific information concerning rear end widths, axle shafts, and brake configurations, or simply need photographic references, please see the thread posted here. You can also visit this site for a chart with measurements.

It's also been brought to our attention that while the bearing location on the 1994-98 V6 Mustang axle shafts is basically correct, the location where the axle seal rides is .190" larger in diameter, necessitating an alternative axle seal (Timken 3459S).


9" Drum Brakes

Most Cougars from 1983-88 had the standard 9" rear drum brakes, as denoted by the finned side profile. Now there were two types of drums: those used on 1983 through Nov. 1984 (mid-85), and those used from Nov. 1985 (mid-85) through 1988. The earlier drums had a large hat section bump out. We haven't found any stock 5-lug drums with that larger hat section; if you have this type then you'll probably have to get your drums machined with the 5-lug bolt pattern.

For mid-85 through 1988 owners, all you will need is new 9" 5-lug drums from either a Ranger or Aerostar. You can leave your stock backing plate and old hardware on the rear end. All there is to it—no other mods necessary.

10" Drum Brakes

The 10" drum came standard on all 1988 Cougar XR7's (8.8" axle), and other 1988 Cougars (7.5" axle). The side profile of a 10" drum is totally smooth. Unfortunately we don't know of a direct-swap 10" 5-lug drum although it may be possible that Rangers had them as well. You can simply get your drums machined for the 5-lug pattern to solve the problem.

Bob found some 10" drums that are very close, with minimal machining needed: "I found 10" drums that fit the 29-1/8" Ranger axles. The only modification is to machine 100/1000 out of the hub center hole. They are sold at NAPA, part # 440-1099. They are made for 1964-72 Mustang."

It's possible that there is a 10" 5-lug drum out there waiting to be swapped in. If you do find that information, please contact us so that we can share that info with everyone here.


1987-88 Turbo Coupe 10" Rear Discs

If you've already swapped in a Turbo Coupe rear with its stock 10" disc brakes, it's a little tricky to try to keep the stock vented rotors and just redrill them with the 5-lug pattern. Eric writes, "I had my stock TC vented rotors machined to accept the 5-lug pattern, and used 1994-98 Mustang axle shafts. But I found out that the center hole in the rotors were too small for the hub on the they had to be machined out. Then the flange on the axle would not allow the hub of the stock rotor to seat properly. So the shafts came back out and the flanges had to be machined down to a 45 degree bevel. Only then could I bolt everything back up. Yes, it was a royal pain and yes, it was expensive. The job got done, but it was a real trial to keep the stock TC rotors with 5-lug."

While you could use a 1994-2004 Mustang rear braking system (see below) and install that, the rotors would be solid. That requires removal of the TC mounting plate for the caliper bracket. Since it's tack-welded on, you'll need to grind/hammer it off. All of the more modern Ford rear ends with disc brakes use a clamp-style hold down for the brackets, similar to a muffler clamp. Then you can install the rest of the SN95 components without a hitch. Again remember that you would be downgrading to solid discs.

If you want to keep vented discs, the ones found on the 1991-92 Mark VII (see below) should work just fine.

Or, you could do the ol' Mustang conversion trick: use 1990 Mazda MPV (V6, 3.0) front rotors, and 1/8" spacers. Place the spacers between the rotor hat and axle flange to put the rotor back into alignment with the stock Turbo Coupe caliper location.

1984-92 Mark VII Rear Discs

The Lincoln Mark VII usually had 4-wheel disc brakes but some had drums, so be careful when checking them out. The Mark VII, as with a lot of Lincoln components, had their own unique vented 10.5" rear discs through 1990. This means you would need to use Mark VII rotors, calipers, pads, brackets and bolts. From what we understand it's not simple to do the 1984-90 Mark VII rear disc swap. From 1991-92 the Mark VII had 10" vented rear discs in 5-lug and those would be the ones to get. You could then reuse the other stock Turbo Coupe components.

1994-Up SN95 Mustang Rear Discs

If you don't want to go through the hassle of machining the rotors for the 5-lug pattern, or if you just want to make everything match with your current rear end, then SN95 Mustangs can provide a very nice rear disc braking system for your car. The beauty of the system is that it uses Turbo Coupe-style parking brake cables, making installation easy on your car. The stock 1994-98 Mustangs had a ~10" solid rear rotor with a small Varga caliper. In 1999 Ford bumped up the size to almost 11". To get either system to work on your car you will need the calipers, rotors, brackets, bolts, backing plates and pads. Make sure that you get all the parts from the same year car—do not mix parts from a 1996 with a 2000, in other words. See above for the appropriate axle shafts needed.

1995-Up 11.65" Mustang Cobra Rear Discs

The Cobras, Bullitts and Mach I's are the only SN95 cars to use vented rear discs. You cannot use a Turbo Coupe/Varga style caliper with the Cobra rear disc; you must use an SN95 rear caliper at least, possibly Cobra-only. Also, you must use Cobra mounting brackets available at MPS. Everything else is similar to the Turbo Coupe/SN95 solid disc info as outlined above.


What happens if you want to directly swap in a 5-lug rear end? See here for more information.