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Length to cut Mustang II 8" rear?

AlpineII

AlpineII

Donation Time
After way too many delays finally getting shop time to start this project. Next weekend I am tearing 8" rear end out of a '78 Mustang II donor car that came with V6 and manual 4 speed. Off it goes to be shortened, but by how much? The real mechanic in this asked me what the distance of the mustang rear end should be shortened to, backing plate to backing plate. Any guidance on this would be appreciated as I get the feeling it's going to be a few dinaros and I only want to do it once and get it right at that. ;)

While I'm here, I plan to put the 8" rear under the Series 3 rear suspension. If I am out-to-lunch here could someone tell me?

Thanks,
Eddie
 
C

Chuck Ingram

Donation Time
While I'm here, I plan to put the 8" rear under the Series 3 rear suspension. If I am out-to-lunch here could someone tell me?

Thanks,
Eddie[/QUOTE]

Eddie
it mounts on top of the springs and not under.
 
V

V6 JOSE

Donation Time
Hi Eddie,

I recommend measuring your stock Alpine rear end and duplicate the length from axle flange to axle flange. The other important thing you want to do, is have the machinist put the pinion flange in the middle, between the spring pads, not in the stock offset position of the stock Alpine rear end. If you don´t do this, you may have trouble mounting the drive shaft, because it will be too close to the battery box. The spring perches should be the same distance apart as the stock Alpine rear end´s.

Sorry I can´t give you exact measurements, because I can´t remember them. If you use the measurements from your Alpine rear end, it will bold right in.

Jose
 
B

Bill Blue

Platinum Level Sponsor
Eddie, yes the driveshaft should be centered, but mine rubbed on the narrow tunnel. If you run a 2" driveshaft there is not much room available for offset.

Bill
 
Jim E

Jim E

Donation Time
I would just skip it, IMO going to the MII rear end is a mistake for almost all who are doing the V6 conversion. Unless you are drag racing or just have to have a locker.
 
D

donsVv6

Donation Time
Jim E said:
I would just skip it, IMO going to the MII rear end is a mistake for almost all who are doing the V6 conversion. Unless you are drag racing or just have to have a locker.
Click to expand...
After 5+ years with my 8" and 2 attempts to get it right, I absolutely agree! I really wish I had my wire wheels back!
 
AlpineII

AlpineII

Donation Time
Thanks for all the feedback. The Series 3 actually has the wire wheel set-up now with O/D and as part of this conversion I wanted to ditch the wires for steel wheels (minilites). I have wires and O/D on my Series II and really want the options that going to bolt-ons can provide on the Series 3.
 
bashby

bashby

Donation Time
The attached jpg shows what I had my Ford 8" cut to, note that initially I had the pinion angle set to 0 degrees but in reality mine ended up needing to be at +2 degrees (yoke pointing up); other than that it fitted perfectly on my Series 5 with a Nissan CA18DET and 5-speed. I bought the car with a Ford 8" but the PO had centered the pumpkin... it rubbed, therefore instead of just replacing the 3.31's I ended up starting from scratch. I am running 15x6 Minilites with a 4" backspace (coulda/shoulda gone with 4.25") and 195/55-15's.
 
S

Suta M

Donation Time
Hi there. Since my car needs rear floor repair I went in a very different
direction. I did cut down only the passenger side (long tube) by around 4"
and used a short axle. Now I have two short axles (stock) that give me some issues with the battery box being in my way and the drive shaft is 1 1/4'" to the right more than the original differential.

The battery box can be reduced by a couple of inches or eliminated. The floor
will need a modification on the passenger side to give the drive shaft a bit of room to move.

The differential now is 1 1/4" wider per side which is perfect in my case, because I'm using front wheel drive car aluminum wheels. It is too early for me to tell you how it is going to work, we'll see.:eek:
 

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V

V6 JOSE

Donation Time
I did cut down only the passenger side (long tube) by around 4"
and used a short axle. Now I have two short axles (stock) that give me some issues with the battery box being in my way and the drive shaft is 1 1/4'" to the right more than the original differential.

The battery box can be reduced by a couple of inches or eliminated. The floor
will need a modification on the passenger side to give the drive shaft a bit of room to move.

Hi Suta,

This is the reason I suggest putting the pinion in the middle of the car. If you don´t, you will have problems with rubbing and hitting, not to mention having a hard time mounting the drive shaft in the first place. You can save a few bucks on cutting just one side of the housing, but you pay for it trying to fix the problems generated by doing so.

Jose
 
S

Suta M

Donation Time
Hi Guys,

Robbie, I'm using 96" Mercury Mystique rear rotors, and 91' Mazda RX 7
Rear calipers, the custom caliper bracket is bolted to the differential flange
(No welding) I'll post a couple of pictures for you.

Jose, thank you. I totally agree with you, when I measured the original Dif.
I notice that the center of the pinion is located 0.750" off the center to
The passenger side of the car. As you point the best will be the center
But two custom axles etc. Are expensive at lest for me right now. I know
That is going to be a lot more work, floor, drive shaft tunnel, battery box, etc.

I'm also considering using a drive shaft with the diameter as close as I can to de original car. I'll post more pictures as I get things done :confused:
 

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AlpineII

AlpineII

Donation Time
In searching through the site I couldn't find any numbers on this so right or wrong here is what I have. Once the axle is cut down and I get it fitted and test run, I'll update this thread with hopefully positive results

* I will go with the +2 degree pinion angle as suggested.
* Backing plate to backing plate, my Series II and my Series 3 (which is the V6 donor) have a distance of 46 1/4".
* In Bashby's diagram below he shows a drum to drum distanse of 50 3/4" for the finished Mustang 8" rear.
* The Alpine rear drums measured 2 5/8" thick which gives a drum to drum distance of 51 1/2".


I have wire wheels on both my Alpines and wonder if there are differences because of this? I don't know the thickness of the Mustang drums which may also make the difference. I know wheel offset on the Mustang 2 is considerably different than the Alpines. Maybe I should just stick with backing plate to backing plate lengths which is effectively the flange to flange distance and should be the right length to have the 8" axle cut to.:eek:
 
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