Solid rear axle options
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Author:  GatoEnFuego [ October 11, 2006, 8:09 pm ]
Post subject:  Solid rear axle options

Looks like I'm going to be ditching the RX7 rear end for a few reasons. The big issue is the offset shaft and being how i don't want to cut down the passanger side to less than 18" i need some other alternatives. it needs to be wide enough to clear the +4 chassis, needs centered diff, rear disk and much prefered LSD and would be topping on the cake if it had the 5x4.5 Ford or popular 5 lug Chevy pattern to match my Mustang II front pattern. I know that is alot to ask for, but any suggestions? Only thing that comes to mind is possibly S10 or fox body Mustang but i'm not sure of the diff spacing or bolt patterns on those. Much help needed.

Author:  calvin [ October 11, 2006, 10:45 pm ]
Post subject: 

The rear in the fox body mustangs (82-93 technically) are the same rears as in the 94-2004 cars with different axles with 5 bolt flanges and different brakes. The 4 cylinder and pre-86 V8 cars had a 7.5" rear and the later V8's had the heavier 8.8. For the Locost weight I can't imagine the 7.5" rear would not be more than adequate and there are lots of Mustang people who will give away a 7.5" rear. I think I have one if you are anywhere near SE Virginia, I'll let you have it. I think this one has a limited slip also.

The axles from any of the above mentioned rear ends will interchange with any of the above mentioned rear end housings. So you have a couple of different choices of bolt pattern (5x4.5" or 4x4.25") and several different widths varying about 3" from the narrowest to the widest which should give you something to work with. If you do a google search there are several places on the web that list widths of the various Mustang rear ends.

Basically relative to each other

Drum brake 82-93 Mustangs 4 bolt 7.5" or 8.8" ring gear
The above can be converted to 5 bolt using Ford Ranger axles same width
Disc brake 93 Cobras, T-birdt Turbo Coupe 87-88 4 bolt +1.5" in width 8.8"
94-04 Mustang +1.5" width and 5 bolt 8.8" for V8 7.5" for 4 cylinder
84-86 SVO Mustang +3" width 5 bolt 7.5"
Lincon MkVII +3" width 5 bolt 8.8"

There are a few others in there, but those are most common.

Author:  locostv8 [ October 12, 2006, 12:54 am ]
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Or look for one from an Explorer which is just less than 58" WMS to
WMS and you won't have to cut off the UCA mounts. Look for one out of a 96 or later V8 which should have 3.75s, LSD, and disks as well as be 5 on 4.5.

Author:  GatoEnFuego [ October 14, 2006, 1:24 pm ]
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wow, great info from both of you. now i guess the most important question to ask is, is the shaft centered on the axle? and what should one expect to pay for a 8.8 rear? if i can find a 7.5 with LSD and rear disk then that would be a score, but i might need to step it up to get the options i want. thanks again.

Author:  locostv8 [ October 14, 2006, 2:52 pm ]
Post subject: 

I don't have one out to measure. To convert to 5 bolt you use two axles, r/h I believe, from a Ranger so the pumpkin would have to be centered that would put the flange at about 1 to 1.5 off center toward the passenger. This would not ba all bad just offset the engine an equal amount which would help with balance with just the driver on board as well as help with pedal space.

Another axle to consider would be the Dana out of about a 95 to 98 Grand cherokee. They have an aluminum center section and Explorer style disks and I believe they are a D44 variant, between the strength of a 7.5 and 8.8. Both of my V8 ZJs had over 150k when I got rid of them and the rear axle was a non problem area. Watch for gouges on the bottom of the housing and pass if present. With a bit of thought you could probably bolt the axle in since it is a 4 bar coil suspension.

My Jeep friend is coming over so I'll check whether it is a D44 or D35. In either case they stand up in a 4k+ vehicle with a 250 hp eng pulling a 6k trailer or big tires off road.

Author:  GatoEnFuego [ October 14, 2006, 4:41 pm ]
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i'm trying to keep the passenger side usable with the seats that i already have an i need a good 19-20 inches each. with some creative tunnel design and a centered driveshaft it should be perfect. so from my measurements of the +4 chassis, the rear end needs to be between 58-60" from WMS. 57" will work (1st gen RX7) but may require some spacers to clear the frame but the shaft is seriously offset not to mention would require having the rear hubs redrilled to a normal pattern.

Author:  calvin [ October 14, 2006, 8:39 pm ]
Post subject: 

I don't know if the 7.5 LSD's are easy to find or not. I know the 85 and earlier V8 Mustangs had them. If you find an 85 Mustang GT that is very near an ideal donor from that prespective. That is the last of the carburated Mustangs, and it had the 7.5 LSD, as did the 82-85 V8's I think. Earlier than 82 had a different style rearend that is basically junk.

Both Mustang axles (left to right) are the same length. Without measuring, I am about 90% sure the diff flange is centered on them. The axles are the same length and the cross pin is the center. The ring gear is to the side from that, and it seems to me the pinion centerline is centered with the crosspin. So the ring gear is offset, but the driveshaft is centered I am pretty sure.

I would be very surprised if you can't find a 7.5" rear that someone will give you locally. You should be able to get an old 8.8 fairly cheaply too....

In this picture you can see it is pretty much centered


The engine and trans in a mustang IS cenered in the chassis, and you can see the driveshaft goes straight back... so.... I would assume the flange is centered.

Author:  GatoEnFuego [ October 22, 2006, 12:23 am ]
Post subject: 

per this technical drawing it appears the flange is offset to the passenger side by about 1-2". That won't fly, I need this tunnel to be dead centered. back the drawing board. maybe the Ranger is centered...


Author:  zetec7 [ October 23, 2006, 3:55 pm ]
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I used Pinto, and the diff flange is offset to the DRIVER's side by 3/4". My buddy used what was supposed to be the same rear axle (from possibly a Mustang II, though) and, although the pumpkin is offset, the diff flange is exactly centered. You might have to look at a few, but they're out there. By the way, his is (if I recall correctly) a 3.9 ratio, and mine is a 3.40 I think. His will be a real stump-puller!

Author:  calvin [ October 23, 2006, 4:31 pm ]
Post subject: 

The Pinto/M II diff is a different animal. That is the 6-3/4" (I think that is the right number) rear. It is a different design, anything may or may not be the same as the 8.8/7.5 family.

Author:  locostv8 [ October 23, 2006, 8:20 pm ]
Post subject: 

calvin wrote:
The Pinto/M II diff is a different animal. That is the 6-3/4" (I think that is the right number) rear. It is a different design, anything may or may not be the same as the 8.8/7.5 family.

I believe at least the V6 & V8 MII were 8", my 78 MII V8 was.

Author:  Tbird7 [ October 24, 2006, 12:04 pm ]
Post subject: 

I just measured the Thunderbird 8.8" that is sitting in my garage.
It is 61" flange to flange and the drive falnge seems to be offset 1/2" to the passenger side.

Author:  calvin [ October 24, 2006, 2:56 pm ]
Post subject: 

I knew the 8.8 would be close if it was not centered.

Author:  GatoEnFuego [ October 24, 2006, 8:25 pm ]
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1/2" is doable. now i'm having a problem finding anyone locally that doesn't think their 8.8 is made out of platinum...

Author:  Locost_Johnh [ October 25, 2006, 10:00 am ]
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As far as Pinto/Mustang II axles, I have two from different cars, one an 8" and the other a 6-3/4". The 8" came in the 1976 Pinto I used as a donor for the Locost. That car had a 2.3L with 4-speed FOG tranny. The axle ratio is 3.0 on that one, but there are other rations available in other cars. There is aftermarket support for 8" ring and pinon sets, and I'm pretty sure there are limited slip diffs available, but don't quote me on that. The 8" is 140 pounds on the bathroom scale with the axles installed. I didn't have the presence of mind to weigh the 6-3/4" but I would guess it is on the order of 40 or 50 pounds lighter.

The 6-3/4" came in my 1971 Pinto Wagon, 2.0L and a 3.55 ratio behind a C4 automatic. It seemed a lot lighter weight than the 8", so I swapped them. The 6-3/4 went in the Locost and the 8" went into the wagon. Perfect fit, everything the same including the distance between the axle centerline and U-joint centerline, so no changes to drive shaft on the wagon. Even the spring perches were the same. I was so thrilled when I got done. Then I found the ONLY DIFFERENCE. the hub is about 1/16" larger on the 8" axle, so the hub-centric original steel wheels for the 6-3/4" won't fit the 8" axle. Oh well. The wagon now has slightly different wheels front and back, but the Locost has old Ansen Sprint mags that aren't hub centric..

As near as I can tell, the pinion is centered on both axles, and both are 56-3/4" from axle face to axle face.

Although the 6-3/4" is a nice lightweight axle, there is no aftermarket support at all that I can find and no limited slip diff. There are a number of ratios out there, but good luck finding what you need in the junk yards. I explored the 7.5" used in many early Fox Mustangs and other cars. There is some aftermarket support and there are limited slip diffs too. The closest I found measuring axles in a junkyard was a Ranger at about 56-1/4" wide. Most cars including the Mustang were wider than that. The 7.5 looks lighter than the 8" and heavier than the 6-3/4. There are a lot of 7.5 axles out there - I must have seen a dozen in that one trip. Only saw one limited slip though.


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