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Fox Body 5-lug Conversion Process

Written By: Connor MC

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You could be looking for performance parts to upgrade your 20+ year old Fox or simply restoring it back to factory original. Either way, AmericanMuscle carries all of your Fox Body drivetrain needs.

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Converting your Fox Body Mustang from a 4 lug wheel pattern to 5 lug is essential for a number of reasons. Besides being able to fit a larger selection of wheels, you'll also increase performance capabilities and be able to launch your Mustang harder off the line.

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Perks of the 5-Lug Conversion

All Fox Body Mustangs came from the factory with a 4-lug wheel pattern. That is what Ford decided, and subsequently that is what was used for the Fox Mustang platform. At the time, it was certainly not a problem, as millions of cars came standard with 4-lug. Even today, the 4-lug pattern has no real questionable issues, as vehicle manufacturers continue to use them. Why is it then that a 5-lug conversion is so popular amongst Mustang enthusiasts? If it were a question of reliability or strength, surely the 4-lug pattern would’ve disappeared many years ago.

  • A proper 5-lug conversion kit will have front rotors, rear axles, and 5 lug drums with the necessary axle bearings
  • To change the front, you must simply swap the old rotors with 5-lug new ones
  • To convert the rear, first you must pull off the drums and the axles out of their housing
  • Once completed, slide the new axles in with the proper bearings and put on the matching 5-lug drums
Fox Body Rear with 5-Lug Rotors

So, why convert a Fox Body Mustang to a 5-lug wheel pattern?

First and foremost, we have to understand a 5-lug conversion is not a performance upgrade that can be measured in horsepower or torque. Rather, the choice to go 5-lug is based upon something entirely different. At first glance strength probably springs to mind; 5-lug is stronger than 4-lug. Yes, this is most definitely correct. Having 5 lugs as opposed to 4 lugs does offer an increase in strength as now there are 5-lugs to bear the load instead of 4. However, a stock 28-spline Mustang axle will usually break long before a wheel lug does even on a 4-lug setup. So, no, strength is not the main reason that people choose to convert their Foxbody to 5-lug. The choice is based more or less on style and adaptability.

The Mustangs of today come with a 5-lug wheel pattern direct from Dearborn, Michigan. Subsequently, the aftermarket wheel companies have followed suit and switched their focus from 4-lug to 5-lug designs. Thus, the majority of bling-bling, flashy wheels are now 5 lug, and the only way to get them on a Fox is, of course, to convert the Fox to 5 lug so that the new wheels can be accommodated.

Furthermore (we'll get a little technical here), when switching the front over using parts from an SN95 donor, steering geometry is improved and thus is turn in, and the SN95 setup uses a sealed wheel bearing that is separated from the rotor. No more packing and repacking bearings if you need to take the rotor off. It also lays the foundation if you wish to go with an aftermarket or Cobra big brake upgrade kit (SSBC, Brembo, Baer, Wilwood etc.).

Switching the rear to 5 lug is all about upgrading the drums to discs. You can retain the drum brakes AND use 5 lug wheels, but as previously mentioned, the rear brakes aren't so great, so if you're gonna swap to 5 lug, it is advisable to spend a few extra dollars and convert the drums to discs, which you can read about a bit further down.

1987 Foxbody Msutang on 4-Lug Rims
87 GT on Stock, 4-lug Turbines

A 5 Lug Swap & Wheel Selections

Converting to 5-lug really isn’t all that hard, especially with aftermarket offerings that include all the parts necessary in one kit. You'll recall two reasons were mentioned for the 5-lug push – style and adaptability. Before continuing on in detail about the conversion process, let us address the second reason, adaptability.

What is meant precisely by the term "adaptability?" Well, let's begin by saying wheel manufacturers aren’t the only ones to have moved on. It's well known that the Fox Body braking system leaves a lot to be desired. Furthermore upgrading the brakes in 4-lug form is very limited.

Certain manufacturers offer big brake kits for Fox Mustangs. However with factory the 4-lug setup, these brake kits will not fit due to clearance issues with the 4-lug wheels. If you wish for a big brake kit, you must convert to a 5 lug pattern first, so you can get wheels with the appropriate spacing to fit the larger brake components.

All of this to say, the term ‘adaptability’ simply means you have more room to grow and more options to choose from in terms of brake upgrades with a 5-lug wheel setup. With that explained, let’s move on to the conversion process.

Mustang 5-lug Conversion Process

As already stated, converting from 4-lug to 5-lug is not a daunting task. A good handyman could have it done in time to catch the evening game. Aftermarket 5-lug conversion kits are sold with all the parts you need to get the job done properly. A proper kit will have the front rotors, rear axles (most kits come with stock 28-spline axles), accompanying 5 lug drums, and the necessary axle bearings to do the swap.

Converting the front to 5 lug is pretty simple. You can use the rotors from any of the following:

  • Mid-80's Lincoln Continental
  • 1985-91 Lincoln Mark VII
  • 1984-86 Ford Mustang SVO
  • Aftermarket 5 lug discs

Not all wheels fit, however, with these rotors. Most noticeably, the following wheels will NOT fit on these rotors: 2000 Cobra R, 1998-99 Cobra and 1997 Mustang GT wheels (17"). To use any of these wheels on the front, you will need to convert the front Foxbody disc brake setup to a SN95 setup (spindles, hubs, calipers & rotors). A brief note, 94-95 SN95 spindles retain the stock width. 1996 add 8mm to each side (marginal, but fair warning). It depends on the width of the wheel you want to run. For a larger 9" wheel you want to keep stock width (i.e: use 94-95 gear). For an 8" wheel, you can use either. The extra width from 96 spindles will not hurt.

Converting the Rear to 5-Lug

For the back, it’ll take a bit more work, but again, not too hard at all. First thing you will need are some new axles:

Whichever donor car you scrounge the axles from, they must measure 29-5/32" in length if you wish to keep the stock wheel track. If you wish to retain the drum setup, grab the accompanying 9" drums from either vehicle.

Axles from 1994-98 Mustangs can work too, but they will increase the wheel track by 3/4" per side. Be careful when you choose what axles you want to go with, because although stock track and SN95 track axles both work to swap the Foxbody to 5-lug, you have to watch wheel spacing and fitment dependent on which track you've chosen to go with.

To summarize, you’ll need to pull the drums off and the axles out of their housing. Once done, slide the new axles in with the proper bearings, throw on the matching 5-lug drums and you’re set. Of course, these instructions are just a shadow and don’t quite encapsulate all the detail necessary to do the job, so don’t follow them to a T! Fair warning!​

5-lug Drum on a Fox Body Mustang

On a side note, if you plan on building a horsepower monster, a 5-lug conversion is a good time to upgrade the stock 28-spline axles to something more durable like 31-spline, since you will be pulling them for the 5-lug conversion anyway.

Do not forget, with a 5-lug conversion you’ll need new 5-lug wheels for your Mustang! The neighbors would have a good laugh if they witness you doing all this work and then trying to put the 4-lug wheels back on! Anyways, this ought not to be a problem, because the main purpose of a 5-lug conversion is to expand the pool of potential rims. Finding a unique set of wheels to match your ride definitely shouldn’t pose a problem.

What Can I Do To Improve The Stock Foxbody Brake System?

  • Proper maintenance! This is perhaps the most important and cheapest aspect. Make sure to use a quality brake fluid, verify there is no air in the system, no contaminants, the pads and rotors are not worn out etc. An often overlooked measure is to flush the brake system entirely with new fluid (I'll admit, guilty as charged), not just topping it up when necessary.
  • Get some performance rotors from a reputable manufacturer. There are slotted and cross-drilled rotors on eBay that list for $50 each, but I am not too confident of their quality. Mind you, I am always open to a bargain, so if you have run eBay rotors, please share your experience with me. Anyways, performance rotors tend to be slotted, dimpled or cross-drilled (or any combination of the 3) with the whole theory behind them is to better dispel heat, thus reducing brake fade. Some may argue that a cross-drilled and or vented rotor really doesn't do much and that a solid rotor is actually better, because it provides a larger rotating mass to heat. That is quite true, regarding the larger mass - however, it is my opinion that a solid rotor may take longer to heat up, but once heated, dissipating the heat is much harder and say hello to brake fade.
  • Add some performance brake pads. Hawk is a highly touted name and have, I believe, 3 different selections depending on use (street, street/track, track only). Again, some good pads will reduce brake fade and increase overall bite.
  • Install stainless steel brake lines. The potential issue with stock rubber lines arises within the composition - i.e: the rubber. Rubber is flexible material, and during hard braking it is possible for the brake fluid running through them to expand the lines, wasting pedal effort and travel. Stainless steel lines should prevent any major expansion and help firm up the brake pedal.
  • Upgrade the stock caliper pin bushings (made of rubber) to steel. Just like the brake lines, because rubber is compressible, some of the braking force will go into compressing the bushings which in turn can marginally slide the caliper such that pad to rotor contact is not perfectly square.
  • Regarding the drums, there isn't much you can do. Just verify they are in good (as good as they can get, which I believe isn't very good) working order and are properly adjusted. Check that the wheel cylinder is not locked up or leaking, the springs are not damaged or otherwise broken. If so, replace them. You can adjust the drums manually by taking the drum off and adjusting the adjuster nut, or by reversing your car, slamming on the brakes, going forward, slam on the brakes. Repeat this cycle a few times (I'm talking at speeds of 15 mph).

Upgrading The Stock Foxbody Front Calipers

Another common and somewhat budget friendly option is to upgrade the caliper to a bigger one. The stock single-piston unit has a diameter of 60 mm. A direct bolt in replacement can be found from a 1991 Lincoln Mark VII. The Lincoln caliper has a bore diameter of 72.9 mm, so it should be able to provide some more clamping force. The larger caliper can also be found on these cars; 1986-91 Lincoln Mark VII 1986-91 Crown Victoria, 1984-86 SVO Mustang (4 cylinder turbo). You'll also need to upgrade the stock master cylinder (stock bore size: 21 mm) in order to run the larger calipers. A master cylinder from a 1993 Cobra or from 1994-98 Mustang V6 (all have bore size of 1-1/8") will work. All of these parts can be found in a scrap yard for dirt cheap.

Summary:

73 mm calipers found on:

  • 1986-91 Lincoln Mark VII
  • 1986-91 Ford Crown Victoria
  • 1984-86 Ford Mustang SVO (4-cylinder turbo)

1-1/8" Master cylinder upgrade:

  • 1993 Ford Mustang Cobra
  • 1994-1998 Ford Mustang V6 models

Converting The Rear Drum Brakes to Disc Brakes

Please note, it is not necessary to convert your Fox to 5-lug in order to perform a rear disc brake conversion. You can keep the car 4-lug (as it is from the factory) and still have disc brakes. This next section denotes this (staying 4-lug, but converting the rear drum brakes to disc). However, as mentioned, many owners swap to 5-lug at the same time as it gives them a larger choice of wheels.

4-lug: converting the rear disc brakes

Converting the OE 4-lug rear drum into a 4-lug disc brake setup using the stock Mustang axles necessitates the use of rear calipers from any of the following cars:

  • 1987-88 Ford Thunderbird
  • 1993 Mustang Cobra
  • 1987-88 Mercury Cougar
  • 1989-92 Ford Taurus
  • 1988-92 Lincoln Continental, 1991-92 Lincoln Mark VII
  • 1990-92 Mercury Sable

Be sure to grab all accompanying hardware with the calipers as well (bolts, brackets). Factory 4-lug rotors can be sourced from 1993 Cobras or 1987-88 Thunderbirds. Now that all brakes are a disc, you will need a larger master cylinder as well. A 1-1/8" bore master cylinder from 1984-86 Mustang, 1974-89 Lincoln Continental or 1984-89 Lincoln Mark VII will work.

Regarding caliper brackets, I do not believe any of the stock Ford sourced brackets will fit. Perhaps with some modification they can be made to work, but I am unsure. Alternatively, there is a ready-made version, by North Race Cars, that you can purchase and will bolt right up, no modification to any component necessary. (I think they are $150 for a set).

5-lug: converting the rear to disc

If you want to go with a 5-lug disc brake setup, of course you first have to convert to 5-lug! After that, you can source nearly all of the parts from any 1994-98 Mustang (be it a GT, V6 or Cobra... any will do).

What you need from any 1994-98 Mustang: left & right calipers, caliper brackets and 10.5" solid rear rotors (5-lug, booyah baby!). I have heard that the stock SN95 (94-98) caliper brackets will work, with a little modification, simply by swapping right to left and left to right. The previously mentioned 'little modification' comes in the form of grinding down the inside of the bracket so that it doesn't grate against the bracket mount. Again, North Race Cars also sells a pre-made, direct fit bracket kit if you prefer a guaranteed fit. Alternatively, just grab the entire rear-end (8.8") and drop it in.

Aftermarket Kits

Up until now we focused solely on a budget build, sourcing nearly all parts from other vehicles. The aftermarket does provide pre-packaged kits for both 5-lug conversion and disc brake conversion. If you would prefer to go this route, check online with your favorite vendors. Most offer their own conversion package featuring new parts. For example, Alloy USA has a complete 4-lug to 5-lug conversion kit with all new parts for $400. If you don't feel like scrounging around your local scrap yard, it's a great option.

If you want to go seriously aftermarket (and spend a pretty penny or two), check the offerings from known brake vendors such as Wilwood and Brembo. Wilwood has a lot of really nice options for Mustangs of all years. They offer full conversion kits (drum to disc with everything included), big brake upgrades etc. They have nice stuff, and it is reasonably priced in my opinion.

Some other useful information for BOTH 4-lug and 5-lug disc conversions

Some other parts you will need; adjustable proportioning valve and solid end cap, a new master cylinder (2 port, bore size dependent on caliper size) and some adapters to connect the caliper soft brake lines to the rigid lines. Generally speaking, a 1-1/8" master cylinder from a 93 Cobra or SN95 Mustang will be more than fine for the job.

Soft lines can be sourced from 1994-98 Mustangs, or be a handy-man and come up with your own adaptive solution. A note about the master cylinder, it is possible to convert a 3-port MC to a 2-port, so there is always that option too. As far as I know, it isn't too difficult, you just need some special adapters.

Furthermore, you may need to swap the stock brake booster out for another one if you change master cylinders. A booster from any SN95 V6 will work great.

The dreaded parking brake (FIX)

Perhaps the biggest area of confusion regarding a disc brake swap (regardless of 4 or 5-lug) is how to get the parking brake to work. For this, you will need new e-brake cables. Specifically: (2) FMS M-2809-A cables, (1) FMS M-2810-A center e-brake cable. There is also a special modification that must be done at the parking brake handle for it to work correctly. In a nutshell, it requires eliminating the self-adjusting mechanism on the handle by cutting the tensioning spring and permanently attaching (via welding) the pawl onto the ratchet gear.

Fitment includes: 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, GT, Cobra, LX, SVO