ezstang

I have a 1966 Mustang with a 89' 5.0HO Motor and a 84' Police AOD transmission. I purchased a 66' 8" rear end out of a mustang fastback with a 3.00 gear. I am planning on driving this in the summer 40 miles on the highway to work each day. Need some input on if this will be the right gear. Also I plan on putting a Detroit Locker Tru Trac in it.

GT350R Klone

I don't have time to check right now and would need to compare the final drive ration of your auto vs. a T5 5 speed. I had a 3.50 ratio which was great street gear, but could have gone 3.73 for more spirited driving. I wouldn't have gone above that for street use.

stephen.osborne1

That 3.00:1 ratio will work well for your daily commuting, though it may be a little sluggish off the line. If there are a lot of stops and starts in your normal commute, then a lower (higher numerically) will likely net you better mileage as your motor won't be working as hard to get going off the line. I believe your OD is about a .64:1 ratio, pretty close to the T-5, so rear gear comparisons in relation to performance is pretty much apples to apples. Personally, I'd go with about a 3.27 - 3.55 ratio for a lot better acceleration but still decent mileage in OD. It's a compromise. Mileage I could live with but with decent acceleration.

Gun Jam

If the AOD OD is really .64:1 then thats equal to the t5 cobra / z spec trans.

I run a 3.80 which is available for 8" and I initially had 3.00 gears when i Did the t5 swap..it sucked you had to go 85mph to get a good run in 5th and off the line sucked.

with a 25" tall rear tire and a .64 OD and a 3.80 you'll turn 2100 RPM at 65mph or 2500 at 75mph OR 3000 Rpm at 91mph. I dont know your 1st gear ratio but the 3.80s have worked great for me. I never find my self saying damn I wish I went 3.50 BUT I do find once in a while saying Damn! a 4.11 would be nice right now. (but not often) so like 99% of the time Im happy

-Gun

tx65coupe

I'm going to also say 3.55 or 3.73 gears.

boogerschnot

I run a 93 aod behind my 351. And with a 255-55-17grinder rear wheel im turning about 1900you rpm at 65mph with a 3.70 trac lock. The final drive is lower with the aod than with the t-5 so I would say stick in the 3.50- 3.90 range and youll be fine. 3.70 would probably be all around the best for mileage and acceleration off the line. But if you do more than 70that mph for that 40the miles a day the engine would probably like yhe 3.50's a little better.

stephen.osborne1

Another point to consider when looking for gear sets is how a certain gear and pinion wears... For example, a traditional 3.50 gear set's teeth rotate so that the same pinion tooth hits the same ring tooth every time. With 3.55s the odd number of teeth ensures each tooth eventually wears on every other tooth of the complimentary part. Many people claim this allows a gear set to run cooler, quieter and last longer than the first example... I see the logic in this theory. I believe, but don't quote me on it, that any odd numbered gear set runs like this.

musnicki

I run 3.89 gears with 25" tires and a tko500, I think the 5th gear is .68. 3k rpms going about 80 on the highway.

3.89 is nice and perky and has good drivability.

Use this link for gear, tire and tranny ratio:

http://www.5speedtransmissions.com/gear_calculator.html

James

rmodel65

most 5.0 mustang guys run 4.10s with an AOD tranny along with a stall converter.....

PaulS

If you are running a carb then you will need something between 3.75 and 4.25 :1
If you are running EFI you can use the 3.0 gears or any other ratio you want.

Paul