I have a 73 Runabout with Ranger 94 2.3 with 5 speed. 3.40 - 3.55 works good for me.   Fred   

Unless your going to go for aftermarket gears your basic (Ford) choices are 3.00, 3.40 or 3.55.  I was told that Ford did use a 3.25 in very limited 8" application but is difficult to find.  Tire size is also a factor to choosing rear ratios.  This leaves 3.40 or 3.55.  If your using 13" tires (or low profile 14" tires) I'd go with the 3.40.  If you move up to 15" or 16" I'd go with 3.55.

I had a 3.00 rear with my T-5 (and Turbo 2.3).  It just seemed like every gear was not right for the speed limit.  I went to 3.40 (currently 215-60-14" tires) and for everyday driving it is far more applicable. Interestingly, I did not find a substantial difference between the 3.00 and the 3.40 during flat out acceleration. But then the boost does come on strongly.

If you hunt the Pick N Pull type yards you will probably find the 8" ratios in this order of availability: 3.00 (about 60%), 3.55 ( about 30%) then 3.40 (less than 10%).  So, if your looking for a 3.40 don't pass opportunities to do so.  There are door sticker codes available on the internet to simplify locating the desired ratio (without having to crawl under every car).  That said, I'd still do a rotation check before going to the trouble to pull the third member.  Lastly make sure you take the ID tag.  I see they are going for about $20 on Ebay.

A few trips ago to the self serve yards I found a 3.40 tag lying on the ground.  I picked it up and tossed it in my tool bag. Wouldn't you know the next trip I found a 3.40 - less the tag. The door sticker  I.D-ed as a 3.40 and the rotation confirmed it.

Tom

To my knowledge (somewhat limited) I believe any Ford 8" third member will fit any Ford 8" axle housing.  When you get into the performance products there may be different spline counts on the axles. But, as far as I know, stock they are the same. My housing was out of a Mustang II and the third member from a Bobcat.

I'm not sure if you have ever done this before, but the brake backing plates need to be removed and the axles slid out of the third member. Often the third member doesn't want to slide right out, but when it eventually does you realize how heavy it is. Be safe and have the help and tools needed.

When I checked the Internet most people did not use a gasket on the re-install.  If I ever did it again (and I'm hoping not to) I would get the third member situated on the studs (not always easy - remember the difficulty in getting it out). I would keep it from falling with a few loose nuts and THEN apply the RTV sealant.  With the pointed tip it should get between the housing and the third member.  I put my RTV on first and then struggled (by myself - thus, the reason I recommended help) to get the third member on the studs.  By the time I finally got everything aligned the RTV was rather (as in too) tacky.

Lastly don't forget to refill the housing with gear oil.  It likely dripped all over you during the process and the smell that doesn't go away for a day or so should help to remind you.  I have a friend with a Cobra replica that made that error. When the rear locked up it cause the car to spin and crash.  It also broke teeth in the transmission. In the end it was a $2,000 repair.

Yea, I guess I should have said, " backing plates UNBOLTED and the axles slid out." In my mind I was "removing" (as in "releasing") the plates from the housing (but not removing them so as to disassociated them from the other involved parts).  So, I see how it could be considered otherwise.

Why..., your just like my wife, you don't understand me at all. LOL 

Tom

The 3:40 is ideal with the 4 speed. I'm running 235/60R15's on an 8" axle with 4:11 posi through a T5. Final drive in 5th overdrive computes back to 3:40. If you start with a 3:40 in overdrive 5th you'll effectively be running 2:80's making 5th gear useless.


Billderbeast

If you don't want to use RTV, where is a good place to find the 8" gasket? I've looked all over for some with no luck. Thanks for any help.

For what it's worth: Since I recently swapped out my 3.00 for a 3.40 I did a search regarding just using RTV or using it with a gasket.  The overwhelming consensus was that the gasket eventually wicks the gear oil and leaks.  Thus the advice I took away was to use RTV without the gasket.

  There was an argument  about wheel bearing alignment without the gasket thickness.  It was stated that the offset was virtually unmeasurable over the axle length and not to worry about it.