What's the best way to upgrade my rear end.

Right now I am running the stock 8" with 2.8 or so gears.

I've been thinking it wouldn't hurt my feeling to go to a 3.25. If you haven't guessed I do about zero freeway driving in the Mustang but want it with more snap off the line.

Can I swap out the gears in my existing rear or would it be better to change out the rear as a whole?

 

As long as your running a warmed over 289 with <350-400hp and an auto the 8" should be fine. Cheapest way would be to find a local shop and get a price quote on you or them pulling your 3rd member installing and setting up new gears and reinstall. I'd have your axle bearings pressed off/on for new ones while you're at it, 40yr. old bearings dry up and lock up eventually (I've had 2 do this). The axles have to be pulled to get the rear out, new bearings and seals are cheap insurance for long life as well as ujoints.

I looked into just buying a setup 3rd member to swap into my 8" but fleabay was the cheapest I could find @$500-$600 so I just built a 9" for <$500, however I hope to see 400+hp.

If you don't go over 60mph you might want to look at 3.50/3.55:1 gears for good jump. From what I'ver read you'll see a marginal diff. going 3.25 but not climb RPM's as bad when running 60mph, most who go 3.25 seem to want to be able to cruise at 60-65 still w/o overrevving the engine.
Jon

 

yeah if it never sees the freeway 2,800 rpms will get you 60 mph with a c4 trans and a 3.50 rear end gear with a 25' tall tire

Thats pretty doable.

-Gun

 

I've heard the 8" is about 100 lbs less than a 9"... dunno if this is true, but that also most of the internals of an 8 and 9 are for the most part the same. I have an 8, with 4:10 rear gears and a mini-spool, (which I need to take out and go trak-Lok/ posi). When I had a 4 speed I was I think 35- 3700 rpms at 65 mph, with my 5 speed I think I am around 2-2200 at 70mph. I've seen 8" posi's newly built for around 700-800 with the x rib and that particular person will knock 80 or 100 bucks off if you send him your x rib cross member back in the box that he sends your new one in. 2 of my friends bought from that particular vendor on ebay with no problems and drag race all the time.

 

I have 3.80 gears with my c4 and the most I ever drive on the freeway is 10 miles at a time. If I could do it again I would probably go for the 3.55 but the 3.80 gears are pretty fun on the street.

 

A lot will depend upon what transmission you're running. We run a T-5 with an Auburn LS 3.55 3rd member and the car is great on the highway and off the line.

 

i do mostly country roads/ windy stuff with occaisional highway.
3.55's work fine for me.

Imo the biggest issue with 8" is the axles are weak

 

I am running a C4 w/ B&M shift kit and slightly higher than stock stall.

I am leaning towards the 3.25.

I don't do a lot of "freeway" driving but have been known to get it up to 65 or 70 on some of the main drags around here that basically are a four lane divided road that might as well be a freeway. But then again, I am only on those roads for maybe a few miles here and there.

My old college room mate has a '65 w/ 3.25 and he said it makes his car pretty snappy even though he is only running a slightly better than bone stock 289.

I am certain that I don't want to go any higher than 3.55

My only decision is do I try to pull my rear end and have the work done or do I find someone that sells the rear end already worked over and ready to install. I'd almost prefer to go the route of having it already worked over where all I have to do is trade out the rears.

 

I'd really recommend the 3.55's. We started with 2.x somethings, went to 3.27's and then went to 3.55's. Much happier with the 3.55's.

Also, if your car has an open rear, I'd highly suggest buying a limited slip 3rd member with the gears already installed. It will make a night and day difference in your traction off the line.

This is the one we have: http://www.cjponyparts.com/currie-3r...-1973/p/CE325/

 

+1

The idea is to get max performance boost without making the car unreasonable to drive. The 3.50s @ 3300 RPM will get you 70 MPH.

If you are going to go through the PITA to mess with this thing you might as well get the most out of it. My 302 purrs along very nice at 3300 there is nothing wrong with running this kind of RPM unless you drive it a lot on the freeway which you dont. With the amount of freeway driving you do there is no reason to not get the 3.50s

In you situation I think it would be a waste of time and money to go 3.25s because the end result does not fully accomplish the goal nor does the end result provide benefits that justify the work that was input.

Thats just my feelings on this situation.

-Gun