Of course I'm talking about the differential in my '78 Mach1, so heads out of the gutter! 
Operation Why? is complete, I have put a bunch of money into this differential because why not. I did things that sane people reserve for 9 inch diffs...lol!
Strange/US Gear 3.55:1 (9x32) ring & pinion, QP aluminum pinion support, solid pinion spacer, Speedmaster 1350 pinion yoke, a Detroit Truetrac with Strange 28 spline axles, all held together with ARP bolts/studs. Breaking it in now, 35 miles on it so far and everything is going smoothly. Heat cycling it for the first 100 miles, easy for another 400 miles then change the oil before letting it rip. No racing, just coastal highway and twisties that I like to rip through in the car. I have a Z spec T5 I built in it (2.95 first/.63 OD, all new Tremec gears) that replaced the C4 that was in it, thus the gear change from 3.00:1 and an open differential (code WDY-AA axle). A mildly built 351W provides the power for the fun. I have hammered on this rear end for almost 40 years now and it's earned some love. It's light, it fits and it hasn't broke (yet!), so it's good enough for me.
I figured that I would build something that would be a bit tougher than stock and fun to run on the twisties. I changed out the yoke as the OEM 1310 had side to side play in the saddles. Getting a Speedmaster yoke that was machined right was a bit of a trick but I did it with a little extra work. The axles were changed out as one flange had .014" runout and the other was .010". Needless to say the guy at Strange was a bit confused by my request as they had never dealt with a MII 8 inch diff, but they came through with the goods that work. I had been having vibration problems and those are now a thing of the past, thank goodness. I'm looking at upgrading the driveshaft to one in the 3"-3.5" diameter range. The current shaft is 2.75" and I'm using a combo U joint to tie it together. Overall goal is smooth cruising at higher speeds so my wife and I can do some regional travel in the car when we want.
Just thought I would post this here so someone can trip across it and wonder at my sanity. I may be crazy but I'm having fun!!
A footnote: I used the Ford/Rotunda Pinion Setup Tool kit (T79P-4020-A) to set the gears up and it made it a snap to do. Pattern was right on target on the first attempt. I tried thinner and thicker shims to check the pattern movement and I got the reversed half moon 'too high/too low' drive side patterns. I have seen it posted that the Ford tool set only works on Ford gears and I can confidently tell you that this is not true, it also works with aftermarket gears. All you have to do is measure the distance between the rear pinion bearing seat and the tip of the stub, then add that to the measurement on the end of the pinion gear (painted on). For example, mine was seat to stub end of 2.819" and the painted number was 1.184, making my total pinion depth 4.003".
The Ford 8 inch master housing dimension (MHD) is 4.006", so using Ford's terminology my aftermarket gear set is -3 at 4.003". The Ford tool set calls for fitting it in place, measuring the gap and adding shim to that number to equal .040". Installing the tool in my housing and measuring it gave me a gap of .019". Since I am -3" with the gear set then I need to shim to .037" to put my gear set at 4.003". Subtracting .019" from .037" gives me .018" as a shim size. I installed that shim with the backlash at .010" and the pattern looked great! After that all I had to do is adjust the backlash to position the pattern slightly favoring the toe direction. At .008" it was too much towards the toe. At .012" it looked good so I dialed it back to .010" as it will move when it opens up a hair after break in. Done! I have done this in the past by eye only and this was the easiest setup I have ever done. It's running quiet under load, coasting and decel.
It was fun doing this, especially learning that the Rotunda tool works with aftermarket gears. Nothing like proving the internet experts wrong...lol! I can say that even with the little time I have on this break in I like the way the Truetrac corners, real tight feel to it. I can't wait to take it up Highway 101 for some fun after break in!
Operation Why? is complete, I have put a bunch of money into this differential because why not. I did things that sane people reserve for 9 inch diffs...lol!
Strange/US Gear 3.55:1 (9x32) ring & pinion, QP aluminum pinion support, solid pinion spacer, Speedmaster 1350 pinion yoke, a Detroit Truetrac with Strange 28 spline axles, all held together with ARP bolts/studs. Breaking it in now, 35 miles on it so far and everything is going smoothly. Heat cycling it for the first 100 miles, easy for another 400 miles then change the oil before letting it rip. No racing, just coastal highway and twisties that I like to rip through in the car. I have a Z spec T5 I built in it (2.95 first/.63 OD, all new Tremec gears) that replaced the C4 that was in it, thus the gear change from 3.00:1 and an open differential (code WDY-AA axle). A mildly built 351W provides the power for the fun. I have hammered on this rear end for almost 40 years now and it's earned some love. It's light, it fits and it hasn't broke (yet!), so it's good enough for me.
I figured that I would build something that would be a bit tougher than stock and fun to run on the twisties. I changed out the yoke as the OEM 1310 had side to side play in the saddles. Getting a Speedmaster yoke that was machined right was a bit of a trick but I did it with a little extra work. The axles were changed out as one flange had .014" runout and the other was .010". Needless to say the guy at Strange was a bit confused by my request as they had never dealt with a MII 8 inch diff, but they came through with the goods that work. I had been having vibration problems and those are now a thing of the past, thank goodness. I'm looking at upgrading the driveshaft to one in the 3"-3.5" diameter range. The current shaft is 2.75" and I'm using a combo U joint to tie it together. Overall goal is smooth cruising at higher speeds so my wife and I can do some regional travel in the car when we want.
Just thought I would post this here so someone can trip across it and wonder at my sanity. I may be crazy but I'm having fun!!
A footnote: I used the Ford/Rotunda Pinion Setup Tool kit (T79P-4020-A) to set the gears up and it made it a snap to do. Pattern was right on target on the first attempt. I tried thinner and thicker shims to check the pattern movement and I got the reversed half moon 'too high/too low' drive side patterns. I have seen it posted that the Ford tool set only works on Ford gears and I can confidently tell you that this is not true, it also works with aftermarket gears. All you have to do is measure the distance between the rear pinion bearing seat and the tip of the stub, then add that to the measurement on the end of the pinion gear (painted on). For example, mine was seat to stub end of 2.819" and the painted number was 1.184, making my total pinion depth 4.003".
The Ford 8 inch master housing dimension (MHD) is 4.006", so using Ford's terminology my aftermarket gear set is -3 at 4.003". The Ford tool set calls for fitting it in place, measuring the gap and adding shim to that number to equal .040". Installing the tool in my housing and measuring it gave me a gap of .019". Since I am -3" with the gear set then I need to shim to .037" to put my gear set at 4.003". Subtracting .019" from .037" gives me .018" as a shim size. I installed that shim with the backlash at .010" and the pattern looked great! After that all I had to do is adjust the backlash to position the pattern slightly favoring the toe direction. At .008" it was too much towards the toe. At .012" it looked good so I dialed it back to .010" as it will move when it opens up a hair after break in. Done! I have done this in the past by eye only and this was the easiest setup I have ever done. It's running quiet under load, coasting and decel.
It was fun doing this, especially learning that the Rotunda tool works with aftermarket gears. Nothing like proving the internet experts wrong...lol! I can say that even with the little time I have on this break in I like the way the Truetrac corners, real tight feel to it. I can't wait to take it up Highway 101 for some fun after break in!
