rear end questions

Erik · 08-12-2001, 08:24 PM

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!

Erik

Gearhead999 · 08-12-2001, 10:11 PM

The numbers 3.50, 3.70, 3.89, 4.10, etc. are the numerical ratio of the rear. Yes, the ring and pinion. As in 3.50, the drive shaft makes 3.5 revolutions to one of the rear axle. The higher the number, the lower the rear. High number rears give more out of the hole acceleration. But, at the sacrafice of high RPM cruising down the highway. This is why O/D is so popular. It reduces the highway RPM.

Good rear for driving around and just plain all around use is a 3.50. As far what make, well there are alot of them out there. I'm pretty sure that a shop near you that does differential work can recomend one to you.

thunderbolt · 08-12-2001, 10:17 PM

As to your stock rear, you should have a ford 8inch differential. To check on the gears, you will need to look at the door tag and get the rear code. Someone here or a manual can decode the ratio you have from that.

66fastback · 08-13-2001, 01:07 PM

2.80 gears with a 2 barrell carb, 3.00 gears if the car came with a 4 barrell. Chances are good it's 2.80's. Swap from 2.80 to 3.55's and you'll be wondering why every car didn't come equipped that way.

------------------
66 GT Fastback,fuel injected 5.0, 5-speed, cable clutch, JBA's and duals, 3.40 gears and handling mods...just call me "Doc"

diablopony · 08-13-2001, 06:59 PM

Depending on how much highway driving you do, you might think about 3.25s. My 289 tachs about 3,000 RPM going 70 MPH. That is plenty high for me. 3.55s would put you up another 500 or so RPM.

3.25s are a definite step up from the 2.80s, but still very nice on the freeway. I got the complete 3rd member from Currie. About $800 + shipping.

Rev · 08-13-2001, 07:26 PM

My '66 with a C-4 and 235/60/15's also runs 3000 at 70 with a 3.25. That's why I didn't go any more than a 3.25. Diablo is exactly right about that. I got mine from Currie as well.

Rev

------------------
'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

08-12-2001, 08:24 PM	#1
Erik Registered Member Join Date: Aug 2001 Location: San Lorenzo, CA, USA Posts: 2	rear end questions 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! Erik

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08-12-2001, 10:11 PM	#2
Gearhead999 Registered Member Join Date: Sep 1998 Location: Oviedo, FL Posts: 992	The numbers 3.50, 3.70, 3.89, 4.10, etc. are the numerical ratio of the rear. Yes, the ring and pinion. As in 3.50, the drive shaft makes 3.5 revolutions to one of the rear axle. The higher the number, the lower the rear. High number rears give more out of the hole acceleration. But, at the sacrafice of high RPM cruising down the highway. This is why O/D is so popular. It reduces the highway RPM. Good rear for driving around and just plain all around use is a 3.50. As far what make, well there are alot of them out there. I'm pretty sure that a shop near you that does differential work can recomend one to you.

08-12-2001, 10:17 PM	#3
thunderbolt Registered Member Join Date: Oct 1998 Location: Houston, TX, USA Posts: 380	As to your stock rear, you should have a ford 8inch differential. To check on the gears, you will need to look at the door tag and get the rear code. Someone here or a manual can decode the ratio you have from that.

08-13-2001, 01:07 PM	#4
66fastback Registered Member Join Date: Mar 1999 Location: Dallas, TX Posts: 208	2.80 gears with a 2 barrell carb, 3.00 gears if the car came with a 4 barrell. Chances are good it's 2.80's. Swap from 2.80 to 3.55's and you'll be wondering why every car didn't come equipped that way. ------------------ 66 GT Fastback,fuel injected 5.0, 5-speed, cable clutch, JBA's and duals, 3.40 gears and handling mods...just call me "Doc"

08-13-2001, 06:59 PM	#5
diablopony Registered Member Join Date: Jan 2001 Location: Clayton, CA USA Posts: 116	Depending on how much highway driving you do, you might think about 3.25s. My 289 tachs about 3,000 RPM going 70 MPH. That is plenty high for me. 3.55s would put you up another 500 or so RPM. 3.25s are a definite step up from the 2.80s, but still very nice on the freeway. I got the complete 3rd member from Currie. About $800 + shipping.

08-13-2001, 07:26 PM	#6
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	My '66 with a C-4 and 235/60/15's also runs 3000 at 70 with a 3.25. That's why I didn't go any more than a 3.25. Diablo is exactly right about that. I got mine from Currie as well. Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi.