Changing Rear Ends

[69volunteer 84]

I am considering changing rear-ends in the Mustang as it doesn't have the get up and go I would have thought after building it. I am NOT looking to set record ETs at the local traffic light but I would like to smoke the tires every once in a while. The car is a neighborhood cruiser--I am trying to think of the last time the car has been on the highway greater than 60 mph.....I can only think of once and that was to avoid a service road that was backed up.

 

The car has a 302 with a 351 cam and GT40 heads (another discussion on the heads later). C4 auto with (if I remember correctly) an 8 inch 2.79 open diff.

 

I know asking what gears I should go with is like asking what is your favorite flavor of ice cream but, if I wanted to start sourcing parts, where should I start? My first inclination is a LSD somewhere in the 3.50-3.80 range. Can I keep my 8 inch and just swap out the gear set or will i need new axles as well? 

 

Open to all thoughts.

[shaun071 62]

3.50 is a good starting point and not too low for the occasional highway run. Unless the axles are damaged they should be fine. You'll have good pick up compared to the 2.79.

[Grenadier116 24]

My '70 Mach 1 is running 3.50 gears and it gets pretty busy at interstate speeds but it's a real hoot around town. If you're looking for strong take-offs from stops you'll probably like them.

My '69 Coupe has 3.25 gears and I actually enjoy that combination more. It has a strong take-off yet is a good bit more comfortable at interstate speeds. This would my personal choice for a regular driver.

[MN69Grande 203]

I ordered a complete 3rd gear and swapped it out this fall.  I didn't get much driving on it yet (3.55 gears) so I won't say if I like the ratio or not.  But I got the 3rd member without sending a core from Terry Todd ttodd21@hotmail.com, 812-749-4308. I got a True Track setup under a grand which I thought was a good price for a complete LSD third member.  Terry was really easy to work with.  You can search on VMF and see there are other people who have used him as well.

[newstang 388]

3:50 are a great compromise. 

[cavboy78 28]

I bought my 8" third member with tru track from tj1141 on ebay several years ago for about $900. Zero complaints and a nice guy to work with. Gears were one of the biggest performance changes I made! Easy enough to do. No relationship with TJ1141, just wanted to pass on a positive experience.

[mustangmike6996 34]

My 69 has a 2.79 open 8".  I bought a foxbody Mustang 8.8 3.08 TrackLoc. 

 

I need to chop the 4 link brackets and weld spring perches to it once I set pinion angle. 

 

So I bought a complete 4 lug axle for $100.  I picked up disc brake conversion kit and 5 lug axles for another $250, brackets are $20.  For less than $400 I have a very strong axle with easy access to parts. 

[Mike65 475]

My last Mustang (68 GT Coupe) I put 3.50 gears in it & I liked it a lot, I will be using the same ratio in my 69 Coupe.

[69volunteer 84]

I have not done much research on this but I assume new gear sets are not available to fit my 3rd member and I would need to do something similar to MustangMike or MN69?

 

I've read some posts about using an 8.8 out of an Explorer but some issues with 3rd member being offset? I can weld new spring perches but I dont think I want to get into solving a bunch of issues. I can live with what I got.

 

Any issues with the foxbody axle? Same width? Those only had 4 lugs on the rear? That is surprising.

[uncledoodoo 31]

8.8 from an Explorer is 31 spline and stronger than the late model Mustangs.  the offset doesn't hurt anything and the width is perfect for a 67 through 70.  You also get disc brakes as a bonus.  You can pick them up in junkyards for around $125.  we bought 3 of them in 3.55, 3.78 and 4.10 traction-lock.  You can google for the process or if you're near Dallas I have a guy that can do it very reasonably and probably has a rearend or two ready to go.

[shaun071 62]

I have not done much research on this but I assume new gear sets are not available to fit my 3rd member and I would need to do something similar to MustangMike or MN69?

 

I've read some posts about using an 8.8 out of an Explorer but some issues with 3rd member being offset? I can weld new spring perches but I dont think I want to get into solving a bunch of issues. I can live with what I got.

 

Any issues with the foxbody axle? Same width? Those only had 4 lugs on the rear? That is surprising.

New gears are available for 8" rear

[mustangmike6996 34]

I just bought a set of 3.55 gears for $52 shipped to my door from an Ebay seller.  You have to price shop but they are not a desirable gear for many late model mustang guys because of the amount of hassle swapping gears, they move to 3.73s usually.

 

I also picked up 2 spring perches for $25 shipped as well.

 

I swapped an explorer 8.8 into my 1951 Ford F1.  The center section is offset a few inches so it will be a very tight fit in an older Mustang.  The Fox Body housings are close to correct width and SN95 axles (up to 1998 ABS or non) get you within about 5/8 inch if I remember correctly.  Yes you only get 28 spline internals but you can pic up an Explorer carrier (31 spline) for less than $100 then you can get 2 aftermarket axles.  Unless you are going to get crazy with power, you don't need 31 spline.  The 28 splines are very good axles up to 800 hp or more in many applications.

 

The downfall of the Explorer rear end is the disc brake setup.  They have the drum in the rotor tophat instead of utilizing the calipers like the mustangs. 

 

 

As for staying with the 8" rear end, you can buy a set of gears for $150-200, plus replacement parts (shims, bearings,lube) and labor.  At the end of the day, you will have an 8 inch rear with whatever ratio you choose and it will still only spin 1 tire for $500-700 parts and labor.  You can buy the Mustang 8.8 and spring perches, do a bit of welding and you are all set.

[danno 128]

It sounds like the 3.50 gears are the solution.  Then also add a AOD tranny, and you will be good on the highway also.  I already have the AOD, I have thought about the 3.50 option for mine. 

[69volunteer 84]

I've done a little bit of looking and found 3.50 gears for an 8inch. Can I not get a complete posi for an 8 inch as well?

[cavboy78 28]

I've done a little bit of looking and found 3.50 gears for an 8inch. Can I not get a complete posi for an 8 inch as well?

 

reference post #6. complete 3rd member with posi for ~900. All you have to do is put it in...

[RPM 1,190]

I just bought a set of 3.55 gears for $52 shipped to my door from an Ebay seller.  You have to price shop but they are not a desirable gear for many late model mustang guys because of the amount of hassle swapping gears, they move to 3.73s usually.

 

I also picked up 2 spring perches for $25 shipped as well.

 

 

Do you have a seller name or link?

[69volunteer 84]

reference post #6. complete 3rd member with posi for ~900. All you have to do is put it in...

I found him on ebay and some other forums. Seems to have good reviews. He is out of PA somewhere.

 

You have been happy with yours?

 

RPM you can search ford 8inch on ebay or it may be cheaper to call him direct

http://www.ford8and9inchrears.com/contact-us/

[MN69Grande 203]

I found him on ebay and some other forums. Seems to have good reviews. He is out of PA somewhere.

 

You have been happy with yours?

 

RPM you can search ford 8inch on ebay or it may be cheaper to call him direct

http://www.ford8and9inchrears.com/contact-us/

 

 

Do you have a seller name or link?

 

Here is an eBay link for one tj1141 current auctions.  It has his phone # 610-485-4858

http://www.ebay.ca/itm/8-INCH-FORD-THIRD-MEMBER-MAVERICK-STREET-ROD-MUSTANG-POSI-550hp-9-/222393734034

 

I would still suggest you call  Terry Todd ttodd21@hotmail.com, 812-749-4308.  He came in more then $100 cheaper and has great reviews on a bunch of other forums like VMF and I saw him show up on a Camero or Chevelle site too when I googled him.  See my post #4.

[cavboy78 28]

I think wires got crossed here as RPM was asking for the link to the guy who sells just gears, not the built 3rd member. Either way, yes have been happy with mine. Shipped in a milk crate with the posi fluid and was returned with my old 3rd member for a core refund. Answered the phone when I called and spent the time with me to figure exactly what I needed.

[bryonbush 85]

i kept my 8" and went from 2.79 to a 3.80 for my 4r70w swap. I bought the parts from ebay, then had a shop put the 3rd member together for $50. put it back in myself. 

i ordered a kit like this and logged about 4k miles with some racing and burnouts. so far so good. 

http://www.ebay.com/itm/RING-AND-PINION-BEARING-INSTALL-KIT-NEW-POSI-FORD-8-3-55-RATIO-/281811563845?vxp=mtr&hash=item419d473545

[69volunteer 84]

that looks like a good option as well.  Thanks everyone.

[Vicfreg 771]

I vote for the 8.8" if you want the best bang for the buck. You will spend a wad of money taking your 8" rear apart, replacing bearings and axle seals (should do this while its apart), then dropping $800 on a 8" posi center section. Plus you still have original 28 spline axles.

 

I have a 8.8 in my '68, and have about $700 total invested and it has a 3.73 traction lock with disc brakes...

 

With a stock C4 I would use a 3:25 or 3:50 gear set.

 

Keep us posted on what you do. Good luck!

[gsxrken 21]

3.50 if you don't have overdrive but if you do, you want AT LEAST 3.70 or 3.90s. Real men drove many of these with 4.11s back in the day... without overdrive. :-)

My 3.73s turn around 2k at 70mph with a 25.5" tire and .68 overdrive. It lugs at much below that.