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  Mustangsandmore Forum Archive
  '64 1/2 to '68 1/2 -- The Classic Mustang
  rear end questions and help please

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Author Topic:   rear end questions and help please

Posts: 1459
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 08-12-2001 08:59 PM     Click Here to See the Profile for rockafellz        Reply w/Quote
Hello All,

Thanks again for all the prompt responses regarding the 289 mods thread that I posted.

I had another question. When you guys talk about changing your gears to 3.50 gears or 3.55 or 3.73 etc etc., what exactly are you referring to? Is it the ring and pinion gears? Also, in reference to that question, what are the exact specs for a stock rear end on a 1965 Mustang 289? In my last thread someone recommended that I upgrade to 3.50-55 gears. What exactly will that do and if I plan on getting some newer gears, what is the recommended brand/part number?

Everyone, thanks again so much in advance. You guys are great!



Posts: 48752
From: Saco, Maine
Registered: May 99

posted 08-12-2001 09:06 PM     Click Here to See the Profile for SteveLaRiviere        Reply w/Quote

Yes, it's the ring and pinion ratio people are talking about when they advise you to switch to a 3.50 or 3.55 gears.

By doing this, you will apply more of your engine torque to the rear wheels and get the engine in it's power band quicker.

Car get many different rear end gears. To find out what yours are you need to check the rear end tag if it still has it, or jack your car up, and count the ratio of driveshaft revolution to wheel revolution.

For example, if you have 2.80 gears, your driveshaft will turn 2.8 times for every revolution of the rear wheel.

'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
Ford. The closer you look, the better WE look!


Posts: 11
From: Stockton, CA US A
Registered: Aug 2001

posted 08-14-2001 12:43 PM     Click Here to See the Profile for Ronster        Reply w/Quote
rockafellz - Ah, gears! Gears will make you Superman, for the rirst 50 feet or so! When I talk about gears, I'm usually refering to the "pumpkin". On the 8" and 9" ford units, the center section (pumpkin) houses the ring and pinion gears, as well as the Trac-Loc unit, if it is so equipped. The pumpkin is an easy swap, usually taking no more than a couple of hours, laying on your back in the driveway. To change the ring and pinion gears, you first have to remove the pumpkin, then take it to a shop to have the gears changed as most people don't have the tools to do the job. That's why most times it is eaiser, and more ecomanical to find a new unit or a used unit, and install it. That way, you always have the stock unit to put back in.

Now, on to what they will, and will not, do for you. You mentioned 3:50 to 3:55 ratios. If your Mustang is now equipped with a 2:80, (automatic) that's a drastic increase. If your Mustang turns 2,500 RPM at 60 MPH with the 2:80's, it will now be turning around 3,500 with the 3:50's. But the car will be quicker off the line. It will also use a lot more gas, have a slower top speed, etc.

What came in the cars? Usually, automatic cars came with 2:80's to 3:00's. Manual transmission cars with 3:50 to 4:11's. This is because C-4 torque converters don't convert all the engine RPMs to direct engery. Somewhere around 80%, not 100% as a clutch does. Also, tire size figures into ths. If poor gas milage and high RPM's on the freeway don't bother you, gears are great!

My advice is to figure out what it is you want to accomplish and then you'll be beter prepaired to do the job right the first time. A T-5, with a .69 overdrive 5th gear, and a set of 4:11's. Good street combo. An set of 3:00's to 3:25's is about all I would recommend, if you are concerned with freeway driving. Good Luck!

BTW - The Mustangs Plus Newsletter went over Rear Gears in great detail a few issues back. Call and have a salesperson find a spare copy and send it to you.


Posts: 11
From: Stockton, CA US A
Registered: Aug 2001

posted 08-14-2001 12:52 PM     Click Here to See the Profile for Ronster        Reply w/Quote
I made one misleading statement in my last post. When I said "3:00's to 3:25's is all I'd go", that was if your car is equipped with an automatic transmission. Sorry for the confusion. Ron


Posts: 1724
From: Athens,GA
Registered: Jul 2001

posted 08-14-2001 02:32 PM     Click Here to See the Profile for bluestreek        Reply w/Quote

'66 Stang with traction problem!!
289 320hp 4 spd 3.50 trac-loc


Posts: 27681
From: Hampton Va MCA#39406 M&M #12 Member Mustang Club of Tidewater
Registered: May 99

posted 08-14-2001 08:21 PM     Click Here to See the Profile for mustangs68        Reply w/Quote
most of the time around here when gears are mention usually it my lack of gears.



Posts: 682
From: San Bernardino, Ca
Registered: Jul 2001

posted 08-15-2001 12:17 AM     Click Here to See the Profile for unklshu        Reply w/Quote
Rockafellz, when I first got my car I made the mistake of going to 411 gears. man this was hard on the car and myself, and i ended up going back down to 350's. this wasn't too bad but I like to drive a little more on the right sidde of my speedometer so I swapped to a tremmec 5 speed and now highway cruising and stop light runs are more enjoyable. I cruise the highway at about 2000rpm at about 70 to 75. make sure you now what kind of driving you want to do before swapping the gears.



Posts: 1163
From: St. Louis, MO
Registered: Jul 2001

posted 08-15-2001 01:31 AM     Click Here to See the Profile for Toronado3800        Reply w/Quote
Like they say, the right gears are a beautiful thing.

I downloaded the program at the link to Car Test 4.5 about 9/10ths of the way down on this site.

The program requires the type of information on your car mangazines like Motortrend (yuck!) lists in it's road tests. After you enter information on your car it will fairly accurately predict how changes in gears will affect acceleration and the speed in gears screen will show how your RPMs at 60mph will change.

Gernerally I'd say go with the lowest (numerically) gears which give you the performance you desire for drivability, and boy is it a good feeling to put your foot to the floor and have a relatively tame motor snap your head back.

P.S. I know Ford Auto -Trans listed at are


C-4 C-6 AOD
Lo 2.46 2.46 2.40
2 1.46 1.46 1.47
3 1.00 1.00 1.00
4 0.67


Posts: 1459
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 08-15-2001 01:45 AM     Click Here to See the Profile for rockafellz        Reply w/Quote
Hey Guys,

Thanks a million for all the posts. Everything is getting jotted down on my notebook. All comments and suggestions are priceless. Thanks a million. This place has become a great meeting spot and I hope to be eventually meet some of you and check out each others cars.

Thanks again.


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