HomeResources > 5-Lug Conversion

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By: Sean FitzPatrick
May 17, 2000


This article will detail the conversion of my 1990 Mustang GT from 4-lug to 5-lug for the purpose of mounting 17x8 wheels from a 1999 Cobra (this also applies to 1998 Cobra wheels and the 17" 'Split 5-Spoke' style wheel). This conversion was done with cost kept to a minimum. It would have been easy to simply order an M2300-K Cobra Brake Kit from FRPP but I wasn't ready to drop the $1,600 for the kit. This article details the conversion that retains the front discs and rear drums for budget issues.

1987 to 1993 Fox body 5.0 liter Mustangs can be easily upgraded to 5-lugs by simply installing 5-lug axles and drums from a Ranger or Bronco II in the rear and 5-lug brake rotors from a late 80's Lincoln Mark VII in the front. This conversion will work for most types of wheels. But, if you are planning on installing a Ford OEM wheel such as the 1998 or 1999 Cobra wheel or the 17" 'Split 5-Spoke' wheel then this conversion will not work for you. This is due to the fact that the Mark VII rotor hat is too tall and the dust cap on the rotor extends too far out. This prohibits the center cap of the wheel from being installed. 

There are two solutions to this problem. The first is to install " wheel spacers behind the front wheels to allow more clearance for the dust cap. This also requires that longer wheel studs be installed on the front rotors for safety. The other solution is to replace the front spindle, rotor and caliper assemblies from the Fox Mustang with complete spindle, hub, rotor and caliper assemblies from an SN95 Mustang. Wheel spacers are simply a Band-Aid for this fitment problem, though, and that is why I chose the latter option. The SN95 assemblies are also designed with improved geometry for better steering feel and the caliper assemblies provide improved braking as well. All in all, it is a better setup and is also the basis for any big brake upgrades in the future (i.e. - Baer or Cobra brakes). It is a project of low to moderate difficulty that can be performed in a garage or driveway with basic tools by anyone with the ability to perform a complete brake job.

Parts List

To convert the rear end to 5-lugs you need to replace the 4-lug axles and drums with 5-lug units. The axles that are needed will be either off of a Ranger, Bronco II or Aerostar van. 
From an '83 to '92 4 cylinder or 3.0L V6 Ranger/Bronco II with a 7.5" rear end you will need two driver's side axles. Only the driver's side will work as the pumpkin on these rear ends is offset and the axles are different lengths (you need the longer of the two axles). It should measure 29-5/32". 
From an Aerostar you will need two of the passenger side axles from an 86 to 97 model.
The axles are all the same so they can be mix-matched (i.e. - one driver's side axle from a Ranger and one passenger side axle from an Aerostar).
You can use the brake drums from either side of the above listed vehicles but make sure that they are 9" drums. The 4.0L Rangers came with an 8.8" rear end with 10" drums - these will not work.
Prices will vary, of course, but I was able to get the axles and drums from a local "Pull It Yourself" type yard. The axles run about $20 each and the drums will run about $15 each.
Be sure to check the axles to make sure they are not bent or worn on the bearing surface and check the drums to ensure that they are smooth or can be turned to no more than the maximum diameter.
Miscellaneous items for the rear include new brake shoes, fresh gear oil, RTV gasket maker to seal the differential cover and one additional lug nut for each side.

For the front you will need one each left and right side spindles, hubs, rotors and calipers from either a '94 or '95 V6 or V8 Mustang. The assemblies are the same for the V6 and V8 so either will work but it must be from a '94 or '95. This is because the spindle was moved out about " - " on the '96 and later Mustangs. This will cause the wheel to stick out too far and possibly cause interference problems with the wheel well lip on the fender. 

If you are getting the parts from a wrecker in a complete assembly (as I did) then make sure that they include the Banjo Bolt that attaches the flexible brake line to the caliper. This will allow you to connect your existing brake lines to the SN95 caliper since the threads are different and the Fox Banjo Bolt will not thread into the SN95 caliper. Using the SN95 Banjo Bolt is the easiest way to do it rather than connecting the SN95 flexible lines to the Fox hard lines because they are different sizes and will require adapters (and the SN95 uses two different size connectors left and right side). Just use the SN95 Banjo Bolt on your flexible line for ease of installation (they even worked with my stainless steel braided lines). I was able to get the complete assemblies for $125 per side from the wrecker.

Miscellaneous parts needed for the front include new brake pads, one additional lug nut for each side, new cotter pins (4), new copper washers for the Banjo Bolts (4) and a 0.330" tall spacer (or washers totaling 0.330"). The last item is necessary to properly fasten the crown nut on the lower control arm ball joint/spindle connection. I will explain this in more detail in the reassembly section.


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