The first thing I have discovered…
There is no such thing as “a bolt in” other than another AMC
rear differential.
Tried to do a bunch of research before I picked out the
differential that I was going to put into my 73’. Many, many thanks to “Mopar_guy” for giving me some
direction on this forum.
I read a great forum item that was several years old about
narrowing a Ford Explorer rear end to put in a Rambler, and using two of the
passenger side axles to create a narrowed rear end. The issue for me at that point was that the
narrowed rear end was “too” narrow and the pinion was still offset by 2 inches.
I read all of the information that I could find about rear
differential specs for the 73-74 Javelins. Everything I read stated that the factory
rear end was 60.0 inches (+/- 1/2") wide with spring perches at 43.5 inches. My particular rear end in the car (an AMC 10) measured
in at exactly 61.0 WMS to WMS. I am not exactly sure why this would be
different…maybe thicker flange on after-market drums? The measurement for the 8.8 from WMS to WMS is 61.25 inches. I can live with it having a 1/8th inch wider track on each side. (No narrowing required).
I was looking for a rear end that would give me a few
things…low price, easy parts availability, posi traction and disc brakes. As I searched around, I landed on a 1994
Mustang GT 8.8 28-spline trac-loc with 3:08 gears in it for $150.00. H.P. for my set up should be somewhere in the 350-375 area, which is well within the capabilities of this rear end. A nice feature for the 8.8 is that should the 28 spline ever fail, I could purchase a (stronger) 31 spline carrier and axles for this differential and it fits right in to this rear end.
After cutting and grinding all of the brackets off this rear
end, I ordered the 2.5 width by 2.75 perches from Chassis Unlimited for $42.00
bucks. I also found a set of 3:55 gears
on Craigslist for $25.00! I opted to
have a shop install the gears & weld on the perches. All tolled with all new axle, pinion and
carrier bearings, welding and setting up the gear set, I have about $390.00
into it. I did have to purchase a new axle.
When the shop installed the new axle bearings, they noticed some pitting
on the shaft. Add another $80.00 for a
new axle. I also bought a cast aluminum
cover with a built in stud girdle for another $99.00. New brake pads and turn the rotors, new
(fabricated) hard lines, new 2-3/4” U-bolts and nuts and new rubber lines and I
am in it $649.00 complete.
So…a few tips I can offer if you opt to go this route. After you have the perches welded on and reassemble the
brakes, you will find that the support bracket for the caliper mount is too
close to the perch to allow the U-bolts to fit in. You have to cut the weld on
the bracket and trim it back about ½” and re-weld to give yourself the
clearance to get the U-bolts that hold the differential to the leaf springs.
I also welded a plate and stud inside the perch to hold the
factory Ford rubber brake lines and brackets in place. I inserted a steel spacer over the stud to
keep it at just the right height where it didn’t tip to one side or the
other. I also ground a small indentation
into the perch to accept the stabilizing tab on the brake bracket. (Pardon my crappy welding) This made for a strong and I think very clean
installation. Next was turning the bracket under the axle vent, so it
faced in the opposite direction. I used
this bracket to hold the e-brake cable coming off the passenger side. I also took the bracket that held the (Mustang)
center rubber brake line, removed the rubber line from it, and bolted another
loop (from the Mustang e-brake) in order to hold the e-brake line. (see last pic on this posting)
I managed to use the factory AMC e-brake lines on this rear
end! With just a tiny bit of
modification. I turned both lines around
so the end that originally went into the bracket that is welded to the frame
rail of the car, now fit into the bracket of the caliper on the new rear
end. The cable end fit into the bracket
on the caliper perfectly, I just had to take a Dremel tool and cut a small
groove into the housing to accept a “C” clip to hold it in place.
The other end of the cables go into the bracket welded on
the car. I had to open the holes just
slightly to get the end that used to go into the brake backing plates, through
the holes. Kept the flat pinion flange on the new differential and ordered the
Spicer mounting flange from Denny's Driveshafts and a set of new u-joints. After taking a ton of measurements, this set
up will not require any modification to the driveshaft other than the new flange! Both the original driveshaft and the new flange use a
1310 u-joint that bolts right in. The
measurement of the flange to the transmission output shaft is less than a ¼’ (shorter)
than the factory set up with the AMC 10 differential in place. This was truly the only “bolt in” part of
this mod.
Here is what it looks like with the wheels on...and a pic of the completed rear end.
So far, it is working
out well, but we will see once I have all of this back on the car… The factory mounting plates for the U-bolts will work, I just need to open the holes up 1/16" for the bolts to fit through. (more than enough material remains around the hole). Just a side note. I sent this last pic to Mopar_guy and he suggested I check the rear cover dimensions to make sure it wouldn't hit the gas tank when installed! Never even thought about that until he mentioned it. Good news, after measuring the clearance it has about an inch of clearance behind the differential.
Will keep updating as I go. Thanks again to this Forum. A ton of really helpful information in here.
UPDATES!!! Hey everyone just have some updates that I wanted to share with anyone who wants to try this rear differential swap. A few things I have discovered now that I am reassembling. 1. The factory AMC e-brake cables will not work. The cables are just about right, but the housings are too long. I ended up figuring out the housing and cable lengths and then went to the "Dorman" web site and typed in "emergency brake cable 64" housing, 68" cable" I'm sorry I didn't make note of the exact part number. Everything else has worked out well. 2. The other exception is the drive line. If you have the 727 in your Javelin and you replace the rear mountinf flange on your drive shaft to match up with the Ford "flat flange"... your drive shaft will come up just about 1" short (not a 1/4" short as I stated earlier). The front yoke will make contact for almost 3-1/4" inches, but it could go 4-1/4" with the correct drive shaft length. After some discussion with Mopar_guy, I think i'll run it and see how it does. I do not have a big horsepower/big torque monster motor in this and i think this will be more than enough spline contact. Other than those two points, so far the install has gone as planned. Once the car is up and running i'll update gain as to the drive ability and performance. Pic below is of the differential in the car before the gas tank went in.
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