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I have a 1968 Mustang Convertible with 289 automatic with C4 and 2.79 rear end. I upgraded the wheels to 15" Magnum 500's with BF T/A 's and the front are 205/60/15 and the rear are 245/60/15 giving it nice appearance. It is a driver and drive to cruises and day trips. I will not use it for racing.

I am looking to change the rear end to 3.25 or 3.50 or 3.55 to give it a little more tire burning power. I am willing to give up some MPG for the tire peeling. The current 2.79 won't burn a tire even if you were on wet pavement.

Again, I am not looking to race and go to 4.11, so I am asking opinions from the experts or those that have made the switch. I have pictures of my car, and feel free to email me at [email protected].

I have a 66 Fairlane Convertible 289, 68 Cougar XR-7 302-4V, and the 68 Mustang Convertible

Greg in Pittsburgh, PA
 

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Have a 3:25 9" in my 68. It is a "one liner" which is what it will leave across an intersection "If I find it necessary" which seldom do. Guess it's fun to know it's there. Engine is a mild HO with ported E-7 heads,very mild cam,Pertronix and hipo exhaust manifolds, C-4. Good "old man's" car!! lol!
Several years ago, had a yellow 68 cv that had a stock 289 with a 3:00 rear, C-4 and that car would burn it!! In S. Fl., all "black top" streets, which is conducive to leaving a "mark" on the hot blacktop!
 

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since you mention that day trips are a major part of the cars function, I wouldn't go any lower than a 3.25 rear end gear ratio. Going from the 2.79 to a 3.25 will be a healthy jump & you will notice the difference.

Anyway you look at it, it's going to be a compromise.

Z. Ray
 

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I started a similar thread a few days back, and had quite a few opinions.....I was looking at 3.80 or 3.55......kind of settled on 3.55 but now might be thinking 3.25.....since I will be using an 8" the center sections are quite a bit more expensive (I want a locker, and have a 3.0 open diff now)......I'm running the same back tires as you and turn about 2500 at 70........decisions, decisions....
Tom
 

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Greg, I agree with the others. Just swapped out my 2.79s for a 3.25 Trac-Loc in my 68 vert with the same set-up as yours. It was like adding 50-60 hp........the difference is considerable. At 70, on the highway, behind the C4, I'm turning 3K rpm.
After doing my usual due diligence, I bought mine from TJ Rebert, in Penn. (on eBay). He's terriffic to deal with, and I had my new chuck in two days.
I had never done any rear end work, and the swap was very straightforward. My old bearings were just about ready to leave me stuck somewhere. Be sure and do your bearings and shaft seals.
 

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I recommend going with the 3.25. IMO a 3.50 or 3.55 will get annoying on a cruise with significant highway driving.

Keep in mind the 289 C code is a low revving engine. With a big numeric (low gear) rear it'll quickly be past it's high torque range.

The 3.25 will be a good compromise off the line without making the C code gasp!

By the way I'd love to have a 3.25 in my C code 68 vert. Other higher priorities!
 
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My 68 with a 289, 2V, C4 and 2.79 rear could leave a good scratch even with fairly wide tires. The only mods were headers, a decent air cleaner, and a pop-open gas cap. Don't underestimate those gas caps!!! :)
 

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Negative on the TJ REBERT rear end builder. I just got beat by him. EBay has him at 100% but I called and dealt direct so I can't leave feedback.. like probably many others. Will not honor his mistakes or correct problems. I even offered to pay shipping for the return. I have the E-Mails to verify his unwillingness to right a wrong. Go to a larger name shop where you can talk to someone other than an owner/operator out of a garage.
 

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Depends on what types of roads you drive on and how fast you plan on driving. If you plan on doing a substantial amount of highway driving at high speeds (70mph and over) I would go with the 3.25's.

3.25's @ 2500 rpms = 60.87 mph
3.25's @ 3000 rpms = 73.05 mph

3.50's @ 2500 rpms = 56.53 mph
3.50's @ 3000 rpms = 67.83 mph
 

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I recently made the switch from an open 2.79 to a posi 3.55. I like it but it does cruise at higher RPM with the 4-spd. A 5-spd or AOD would be prefect. I used Phil Cook at Nine Inch Nodular. He was close enough that I was able to drive to his shop, which was very clean and well equipped. He works for a Nextel race team. Here's his ebay listing:

FORD 8 EIGHT INCH GEAR TRAC LOC POSI 500HP STRONG 9: eBay Motors (item 150411166658 end time Nov-30-10 13:41:24 PST)

Use this calculator to figure your combination:

Engine RPM Calculator

My old 2.79 was a dog, wouldn't hardly leave rubber. The 3:55 will leave 2 very long strips and catch hell outta 2nd gear too.
 

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Another vote for 3.25. I tried both in my '66 when it still had the C4 in it. The 3.55 was too low for comfortable highway cruising. The 3.25 was a great compromise, and I ran it for several years that way.

I also bought a TJ Rebert 3rd member off Ebay. It worked great, put it leaked around the pinion flange. I pulled it out to change the seal, and discovered that the entire thing had been bead blasted, including the chromed surface where the seal rides. I thought that was pretty strange, but I just put in the flange from my original chunk and it worked fine. I didn't bother complaining, he's a long way from me and I doubted it was worth the hassle. Hopefully blasting that part was a one time brain freeze and not a policy. Otherwise the rear worked great (3.55 trac lock).

Good luck,
MrFreeze
 

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Have a 3:25 9" in my 68. It is a "one liner" which is what it will leave across an intersection "If I find it necessary" which seldom do. Guess it's fun to know it's there. Engine is a mild HO with ported E-7 heads,very mild cam,Pertronix and hipo exhaust manifolds, C-4. Good "old man's" car!! lol!
Several years ago, had a yellow 68 cv that had a stock 289 with a 3:00 rear, C-4 and that car would burn it!! In S. Fl., all "black top" streets, which is conducive to leaving a "mark" on the hot blacktop!
 

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So I’m looking to change my rear end in my 68 Ford mustang with a 302. 3 speed manual transmission It has a 2.79 and it now I found a 3.00. Online pretty close to me do you think it would make much of a difference or should I hold out for a 3.25 Any info or suggestions would be great thanks
 

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So I’m looking to change my rear end in my 68 Ford mustang with a 302. 3 speed manual transmission It has a 2.79 and it now I found a 3.00. Online pretty close to me do you think it would make much of a difference or should I hold out for a 3.25 Any info or suggestions would be great thanks
Unless it is a trac loc unit I would not bother changing it. Not enough of a difference from 2.79 to 3.00 to make it worth while but with that said it is a better ratio
 

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The current 2.79 won't burn a tire even if you were on wet pavement.
I hope that this statement is an exaggeration. I have owned my 67 coupe (302 w/ 2.79 gears) for ~33 years. If you can‘t make a burnout (on dry or wet pavement) then there are probably other issues that need to be addressed.

Dcubedus
 

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Negative on the TJ REBERT rear end builder. I just got beat by him. EBay has him at 100% but I called and dealt direct so I can't leave feedback.. like probably many others. Will not honor his mistakes or correct problems. I even offered to pay shipping for the return. I have the E-Mails to verify his unwillingness to right a wrong. Go to a larger name shop where you can talk to someone other than an owner/operator out of a garage.
What happened?
 
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