Since the early '90's I've probably built more 8.8 rears for these cars than anyone else on the planet, both stock 4 link versions as well as my torque arm conversions. I no longer produce them and have since moved on, but still often get calls from people wanting to buy one. This thread is for is sharing info and build specs, maybe someone else might want to use the info to build their own. I generally used Crown Vic 8.8 housings, they were a good compromise between weight and strength. The F-150 and Explorer 8.8 housings were heavy with large 3-1/4" dia heavy wall axle tubes, while the FOX Mustang 8.8 housings used small 2-3/4" dia really thin wall tubes that were easily bent. The Crown Vic housings were in the middle with 3" dia tubes, and plenty long on both sides for even wide body conversions. Here's a pic of a raw Crown Vic rear fresh from the wrecking yard, before cutting all its original brackets off...



Most popular overall width was stock GSL-SE, 58-3/8" wheel flange to wheel flange. This width was popular because it worked with not only SE wheel offsets, but also for my V8 swap customers wanting to stuff the biggest wheel/tire possible in the stock SA/FB wheelwells. Here's a pic of a 275/60-15 drag radial on a 15x8 with 5" of backspace wheel with a 58" wide rear, no room to spare in the stock wheelwell and very little room for articulation. Note that the rear in the pic is 58" wide. The GSL-SE 58-3/8" width adds 3/16" more clearance between the inner wheel tubs and the tire sidewalls, making sure the inner sidewalls of a radial won't rub when the suspension articulates...




To achieve 58-3/8" overall width, housing width varies depending on choice of brakes. I made my own flat 1/4" thick brake adapter brackets that bolted onto the end of the axle tubes.
...Those wanting to use GSL-SE brakes needed 2.94" of brake offset, which meant the 8.8 housing needed to be 51.995" wide.
...Those wanting to use FC brakes needed to have 2.565" of brake offset, which meant the 8.8 housing needed to be 52.745" wide.
...Aftermarket brake kits use different brake offsets than the above, they will require a different housing width to properly center their calipers over their rotors.

Narrowing the 8.8 housing...
...The cast center that the axle tubes press into is pretty consistently 16.375" wide. If you cut both axle tubes to the same length, both axles will be the same length and the pinion will be offset 1/2" to the right.
...My builds usually had the pinion centered, which meant right and left axles/tubes were different lengths.

When narrowing the axle tubes, you need to allow for whatever width the housing ends will be. I usually used 2" wide housing ends, they were welded onto the ends of the tubes after cutting. Basically if you are using 2" wide housing ends, the axle tubes need to be cut 2" shorter to allow for welding on 2" wide ends.

For a centered pinion, using the GSL-SE brakes, and 2" wide tube ends...
...cut the right axle tube so that 16.31" extends from the cast center housing.
...cut the left axle tube so that 15.31" extends from the cast center housing.

For a centered pinion, using FC 4 or 5 lug brakes, and 2" wide tube ends...
...cut the right axle tube so that 16.685" extends from the cast center housing.
...cut the left axle tube so that 15.685" extends from the cast center housing.

Welding brackets onto the axle tubes causes the tubes to distort. If you wait to weld the ends on after all the other brackets are welded on, you will end up with alignment least affected by distortion.

I generally installed aftermarket billet 9" Torino style ends on the 8.8 axle tubes from Dutchman Machine in Idaho, they were 2" wide. Putting 9" ends on the 8.8 tubes allowed me to eliminate the 8.8's c-clip axle retention method, allowed me to use 9" style axles with pressed-on bearings. I ordered my custom 9" axles from Dutchman as well. Here's a pic of the billet tube ends from Dutchman, about $100/pr when I used to buy them...



Ordering Axles...
Here's the axle specs I sent Dutchman for a typical GSL-SE width hybrid 8.8 with 9" axle ends build, pinion centered, using GSL-SE brakes...
...57.875" axle flange / axle flange width (without brake rotors)
...51.995" housing width
...2.94" brake offset
...28.6875" right axle length
...27.6875" left axle length
...31 spline (31 spline most popular, although some wanted 28spl or more robust 33spl)
...5.85" axle flange O.D. (this diameter flange fits inside GSL-SE rotors)
...2.600" pilot O.D. (pilots GSL-SE rotors on the axles)
...4x4-1/2" lug pattern (stock GSL-SE pattern, although some were drilled dual pattern to also allow non-SE wheels to be bolted on)
...12mmx1.5 pitch stock length wheel studs
...no access holes

Here's the axle specs for a typical GSL-SE width hybrid 8.8 with 9" axle ends, pinion centered, using FC 5 lug brakes...
...57.875" axle flange / axle flange width (without brake rotors)
...52.745" housing width
...2.565" brake offset
...29.0" right axle length
...28.0" left axle length
...31 spline (31 spline most popular, although some wanted 28spl or more robust 33spl)
...5.85" axle flange O.D.
...2.600" pilot O.D.
...5x4-1/2" lug pattern (same as FC, also fits common 5 lug Ford pattern wheels)
...1/2"x3" long studs (long studs were to be legal with common drag wheels, some ordered short studs or 12mmx1.5 pitch stock length wheel studs)
...no access holes

More to come, I need to walk the dog...

Grant

 

Watts Pivot...
The watts pivot will end up farther forward and be a little more offset to the right, necessary for the bars to clear the 8.8's larger center section. The watts linkage pivot bracket that I used to make welded to the right side axle tube. The pivot itself was basically an allen head 3/4"x2" shoulder bolt that was pressed into a 1-1/2" long piece of 1-1/2"dia cold rolled stock, then welded. After welding, I turned the shoulder down to the same size as the SA/FB original watts pivot. This allowed the original watts bellcrank to be used. Here's a pic of that bracket installed on a housing...



Modifying the watts bars...
Few are aware that the typical stock '79-'85 RX-7 rear is offset in the car. You can walk up to a random car in a parking lot, slip your fingers between the tire and fender, and it will likely be much closer on the driver's side. It's almost as if Mazda designed their rear to be offset to the driver's side. We are not sure if they designed it that way or not, but for our purposes, we wanted the rear centered so that we could fit the largest tire possible with the maximum clearances for both sides. This allowed us to change the bar's configuration to better fit over the 8.8 rear's larger centersection. For those that used my fabricated watts linkage, we've already did that for you. For those that used stock watts bars, the bars themselves needed to be modified to make everything fit. The fix was to simply cut the ends from the oem bars and add custom "sleeves" to their center to correct their length and offset. We suppled "watts sleeves" that were bored out to a slip fit over the cut-off ends of the stock bars. After the correct lengths were determined, you simply removed the bars and took them to a shop for final welding. The kit used to include two 7/8" dia sleeves, one 8-1/2" long and one 13" long. Inside dia was 11/16", which allowed the original watts ends to slip inside. The following is a copy/paste from my original instruction page...
...STEP 1-...With the bellcrank's studs facing rearward and the longer arm extending downward, slide the watts bellcrank over the large stud that's welded to the right side axle tube. Install the large flatwasher and self-locking nut provided.
...STEP 2-...With the tires/wheels installed and the rear at ride height, center the rear so that you have equal tire/fenderwell clearances on both sides of the car.
...STEP 3-...Cut the ends from your stock watts rods. Leave a 2" long portion of the centersection attached to each end, which will slide into our watts sleeves to make your new rods. When finished w/ this step, you should have (2) rod ends that are straight, and (2) rod ends that are angled.
...STEP 4-...Install the angled rod ends into the long watts sleeve, then install the bar in position above the rear on the left side of the car.
...STEP 5-...Install the straight rod ends into the short watts sleeve, then install the bar in position below the rear on the right side of the car.
...STEP 6-...Adjust the rod lengths until the bellcrank arms are vertical.
...STEP 7-...mark or measure the required rod lengths, remove them, and have them finish welded.
...STEP 8-...Paint and re-install the modified watts rods.

Here's a pic of an original watts bar that has had its length changed by sleeving...



Here's a pic of the fabricated double shear watts bellcrank that I used to produce...



Grant

 

Here's a map of the stock '79 RX-7 rear axle bracket locations that I made back in the early 90's...



The very first narrowed rear I made for an RX-7 was a Chevy 8.5" 10 bolt for a '79 model. That rear used stock brackets that were cut off the '79 rear and then welded onto the 10 bolt. Even though these stock brackets are thinner than my fabricated 3/16" thick brackets, they never gave me a bit of trouble even when dead hooking 1000hp on drag radials. If you have a stock SA/FB rear and don't mind cutting it up, it's far easier to use those stock control arm brackets than it is to fab your own. That 10 bolt also used the original stamped spring pockets with no trouble.

Here's a pic of the notes I used as a baseline for side/side location of my hand made 3/16" thick link brackets, as well as the centerline locations of my fabricated spring pockets...



With the rear face of the 8.8 plumb, my spring pockets were rotated 5 degrees forward from level before welding.

Here's a pic of how I located the inner lower control arm brackets with the rear face "leveled", on the 3" dia axle tubes the plumb bob string passed directly across the center of the lower control arm hole...



After the inner lower control arm brackets were tacked in place, I used a set of machined aluminum spacers to set the distance between the inner/outer brackets...



Next would be the upper control arm brackets, the rotational angle of the these brackets varied depending on what pinion angle was needed. For a DIY guy, I would recommend just bolting the housing in the car and setting up the pinion angle before welding the upper brackets to the axle tubes.

More to come,

Grant
Granny's Speed Shop

 

Wow!

Thanks for sharing Grant!

 

There are a 2 "low-buck" narrowed 8.8 rears possible using stock Ford axles that are available in the wrecking yards. These are based on Ford Ranger and Explorer 8.8 housings that originally have both a long and short axle. When you shorten the long side axle tube to the same length as the short side axle tube, and then use short side axles on both sides, you end up with a narrowed rear with only 9/16" of pinion offset. Both combinations have 5 on 4-1/2" lug patterns, same as 5 lug 2nd gen RX-7.

......53-1/4" AF/AF WIDTH USING FORD RANGER HOUSING...4-5/8" narrower than the stock GSL-SE rear (2-5/16" narrower per side), made possible by shortening the long/left tube of a 4.0 Ranger 8.8 housing to the same length as the short/right tube and using 2 right side Ranger axles (26-1/4" long). These axles are 28 spline and use the smaller passenger car sized 1.40"id bearings. These are 28 spline c-clip style axles, which require a 28-spline differential with a .750" dia center pin.

......56-1/2" AF/AF WIDTH USING FORD EXPLORER HOUSING...1-3/8" narrower than the stock GSL-SE rear (3/16" narrower per side), made possible by shortening the long/left tube of a '91-'94 Ford Explorer rear housing to the same length as the short/right tube and using 2 right side Ford Explorer axles (27-13/16" long). These axles are 31 spline and use larger truck sized 1.625"id axle bearings. These are 31 spline c-clip style axles, which require a 31-spline differential with a .875" dia center pin.

Both the Ranger and Explorer 8.8 use the same cast center housing with the same ugly abs sensor and guard lugs...


I found the fastest way to remove the lugs was to use a thin 5" cutoff wheel on a 4-1/2" angle grinder. Here's what it looks like after I removed the abs boss/lugs and cleaned it up with a 36-grit flap wheel...


If you are sourcing the 8.8 rear from a pick-n-pull style yard, while you are in the yard you could take the long side axle out and stick another short side axle in before paying, saves the cost of buying an additional short side axle.

Grant

 

wish I found this a few years back when I built my own.. seems it all worked out similar... I used a 98 explorer rear with the 4:1 lsd I think... cut the long side etc... made my own brackets and was trying to figure out a watts setup but made my own panhard and welded on larger mounting points and longer so the panhar is almost parallel with the ground static...

 

This is incredible info. I know feel so stupid after reading this thread. Thanks guys! Lol!

 

How much shorter can you make 1 of these 8.8 rear? Would 20mm on each side be possible while keeping things in oem placement?

I would also like to go higher on the gear, maybe 410 to 430's

 

got a grinder and a welder make it as short as you want.. depending what rear end it is.. older mustang you can pretty much bolt it up I believe

explorer 8.8 its about 2 7/8 off the long side and a 2nd short acle either from the front diff or new.. you dont shorten both side evenly as the center section is already offset hence why you shorten the long side..

the. you need to figure out brackets, panhard or watts setup, brake setup etc etc..

 

The problem with the GSL-SE rear is the offset for wheels, at most a 15x8 et20 should be used with rolled fenders unless you're willing to run baby tires. Most 15x8 come in 0et. Which means I would need 22mm less on both sides but keep everything else oem. On a na 12a I think 410 gears isn't enough, I think something around 430's would really help without killing highway driving.

This pic here is 15x8 et20

 

its all about offsets.. if you want meaty rubber then yes 15s are the way for sidewalls

I wanted a street driven all around car

im running 17x8.25.. actually had to add some spacers think theyre like 3/8 thick.. just to bring tires out

245/40 rubber is wide but small sidewalls.. but handles corners well.. I was also putting around 450whp and maybe more with nee setup once tuned..

all depends on the goal.. key is measure and figure out offsets etc and build what ya want

 

These are of a rear that's 58" wide wms/wms. 15x8 Weld wheels with 5.5" backspace. 275/60-15 drag radials. I posted the pic of under the car earlier, thought it might be nice to show that pic along with a pic of the outer lip on the same post...






With this combo, i also added 1-1/2" dia aluminum spacers and longer bolts between my bump stops and the chassis to make sure the tire could not contact the outer lip, you can see them inside the spring in the upper pic.

I also had to notch my big Magneflow muffler to clear the tire...




Grant

 

Here's some pics of my '85 RX-7's current narrowed 8.8, with mini-tubs and radiused outer lips. 275/60-15 radials on Weld 15x12" wide-5 wheels...



I actually wanted the rear tires to stick out on this build, took me a couple months to decide just how much. In the end, it required moving the inner wheel wells inward 1-3/8" to get the look I wanted...



After welding a strip to the outer radius, the original wheelwells were re-installed...



The housing width on this 8.8 build is 46.6". With another 2.5" of brake offset on both sides, axle flange/flange width is 51.5" overall. Pinion is centered with big Ford 9" ends installed, each axle tube extends from the center housing 15.0625". The 9" axles are 25.3125" long, no c-clips. For this build I used Wilwood hats/rotors with weld-on caliper brackets. I wanted the widest possible spring base for this car, which required notching the stock sheetmetal frame rails for coilover clearance as well as new bump stops...



In the end, here's how it looks underneath...



Those rear springs are stock FC RX-7 rear springs, I machined some Delrin rings to adapt them to the 2-1/2" coilover spring seats.

Here's why I chose Weld wide 5 wheels, radiused lips and tires sticking out for this build- my hot rod back in the late 90's was a 4-rotor rotary powered outlaw dirt latemodel...



Grant

 

I used a 9" because besides having every gear ratio or diff under the sun available cheaply, the pinion length is so short that you can find a flanged pinion yoke from a large 70s Ford and machine it to take a Mazda driveshaft, and the length works out to be almost the same as stock. No custom length driveshaft needed if you are keeping the stock trans.

When I built a 9" for my car, for the Watts I used a harmonic damper bolt from an LS engine welded to the tube, then plated over it so it sat in a box of 1/8" wall steel. Then I put a brass bushing over the bolt to take up the difference in diameter for the bell crank.

I had to cut the ribbing off of of the top of the pumpkin (Yukon aluminum through bolt) and then lengthen the top of the bellcrank to clear as well. I also mounted the pivot on-center instead of 40mm above axle centerline, to lower the roll center.

I bought a pair of 5/8" Afco threaded tubes to make the links adjustable, because their ID in the middle is the same as the OD of the Watts links. Cut them in half, cut the tubes in half, weld together and use adjusters in between. In the end I realized that the upper link had to stay Mazda length to clear the exhaust so I only made the lower link adjustable, and due to lowering the Watts I extended the lover's body bracket down an inch and a half.

By some cosmic coincidence the lower link needed to be the same length as stock, after all that. Oh well, it's adjustable now

 

Because editing is a pain on a phone, I'll add a second post to say that my 9" uses Dutchman axles built with 4x4.5" bolt pattern and uses very non Mazda brakes. Volvo S40 rear rotors, VW New Beetle calipers, and the brackets were for small pattern Wilwoods that I cut to suit. I noted that the GSL-SE axle had the tires rubbing the wheelhouses at max articulation so I had the rearend made with axles for a 58" on-center axle on the left and a 60" on center on the right, this adds a half inch per side compared to GSL-SE and moves the pinion to the left to center it better. Mazda pinion are offset to the right and the pinion flange was hitting the right side of the tunnel.

With the solid disks, aluminum calipers, and aluminum centersection, the whole thing weighed 190lb with 5.43 gears, despite starting with an F-150 rear and having 31 spline axles and a backbrace. It has lightened 4.87s now. A GSL-SE rear weighs about 140 with brakes.

 

Awesome info in this thread, thanks for taking the time to post!

 

Here's some pics of the torque arm setup I used to make for the 1st gen. It allows removal of the SA/FB stock upper links, which eliminates 4 link binding problems and provides plenty of anti-squat for the drag strip. With 700hp and no roll bar or any other chassis stiffening at all, easy 1.30 60's with this setup...



The lower tubes of the arm are made from 36" long lengths of 1" od x .156" wall dom tubing. This allows direct threading of the tubes for 3/4" bolts to attach the tubes to the rear plate, also plenty strong to resist bending if you put a floor jack under them. The upper tubes are made from 1" od x .095" wall dom. Because the rear of the arm attached to the rear plate in back of the axle centerline, effective length of the completed torque arm from center of axle tube to center of front pivot eye was about 33". The plate that was fitted around the nose of the 8.8 was 3/16" thick, as was the rear plate.

I made a tube fixture that fit inside the 8.8's front pinion bearing bore and extended forward, that fixture made it easy to locate where the nose of the torque arm would be in relation to the pinion centerline. If the pinion of the 8.8 is centered and the drivetrain is also centered in the chassis, the nose of the torque arm needs to be centered as well. If the 8.8 has equal length axles as will be the case if narrowing the long side of an Explorer 8.8 and using two short side axles, the pinion will be offset 1/2" to the right. If the car is V8 swapped, the engine/trans will likely be centered. If the car is still rotary powered, the engine/trans will be offset to the left. Point is, you need to locate the nose of the torque arm where it will be directly below the driveshaft, as you want the driveshaft to pass between the nose anchor's shackle plates with equal room on both sides.

Here's a link to one of my webpages that's still up, it shows pics of how to install one of my torque arm kits in an 1st gen. I no longer produce these parts, feel free to use the info to fab your own...
Granny's '79-'85 RX-7 / Ford 8.8 and Torque Arm Installation Guide

Those big rubber grommets at the top of the tunnel? I used off-the-shelf hockey pucks, easy to find at a sporting goods store and easy to machine in a lathe!

Grant