Rear end gearing questions

wikdsvt

wikdsvt

Club Member
SO I'm swapping a AOD trans in the '66 this week (sitting behind a real mild 289)

(FMX trans will be for sale soon, along with B&M Shifter)

It has a factory 8" (not 8.8 or 9") rear end. I'm guessing gearing is factory 2:80 to a 3:00, since a vast majority of the '66 mustangs had this gearing and it definitely has a highway gear. Obviously, with a AOD trans, I do not need this gearing, unless I want to go 200 mph.

I really don't plan on racing this car, but the occasional stoplight race and burnout might be fun. I'd rather it be fast off the line, but still able to drive down the highway but not drive much over 110-110mph. It will be more a cruiser. Remember the '66 mustangs is very light weight, so I don't think I need a 4.11 gearing to help it off the line. I was thinking 3.55 or maybe 3.73.

THOUGHTS?
 
The factory 8" will not last doing occasional stoplight races and burnouts so start looking for a 9" now and do it right the first time.......
 
Make sure you purchase the correct flywheel for your application. They make one.
Installing a wide ratio planetary in the transmission will give you what you seek. Its the best of all worlds. Do the math 2.84 1.55 vs 2.40 1.47
Also, your going to have to correct the geometry of the TV linkage for proper up shifts. They sell the parts to do it. Use a gage.
 
Detroit Gearbox said:
Make sure you purchase the correct flywheel for your application. They make one.
Installing a wide ratio planetary in the transmission will give you what you seek. Its the best of all worlds. Do the math 2.84 1.55 vs 2.40 1.47
Also, your going to have to correct the geometry of the TV linkage for proper up shifts. They sell the parts to do it. Use a gage.
Click to expand...

English?

It is coming directly out of a '66 mustang and into mine. The guy switched over to a T56. It worded great in his car, plus he's a mechanic, so I assume it will work good in mine.
 
BIGCOWL-IMP said:
The factory 8" will not last doing occasional stoplight races and burnouts so start looking for a 9" now and do it right the first time.......
Click to expand...

Why? Is it just a weak rear end? It came with in the '66 289 Hipo cars.

I'd like to do a 9", but with a 5 week old baby, i have to limit this years spending on the car.
Any idea what rear ends could bolt up (and fit properly) to a '66 coupe?
 
wikdsvt said:
English?

It is coming directly out of a '66 mustang and into mine. The guy switched over to a T. It worded great in his car, plus he's a mechanic, so I assume it will work good in mine.
Click to expand...

Why body is your vehicle?
I'm assuming its a mustang. but you mentioned FMX. If he already has a flywheel, that fits the AOD "and" has the proper 28oz weight for a 1966 engine (assuming here yours is a 1966 engine) "and" its already the proper diameter then your good to go. They make a flywheel just for a swap into a mustang.
Ive seen people install the later flywheel on a early engine only to have a horrendous vibration.
Since you already have someone doing all of the work I would not sweat it. Im sure they know what they are doing.
You asked about rear axle ratios.
Installing a wide gear set into the AOD gives you a much lower first & second gear, and allows you to run a 3.00 or 3.55 gear but have the performance of a lower axle ratio.
Example: aod trans & a 3.0 axle = 2.40 x 3.00 (rear axle ratio) = 7.2 drive reduction aod w/wide ratio planet = 2.84 x 3.0 = 8.52 final drive reduction.
What this means is installing a wide ratio gear set into your existing aod transmission, would give you a much lower first & second gear final drive.
If your vehicle has a 3.0 ratio rear axle (which were common for 8" Assemblies), it would be like installing a 3.6 ring & pinion, but once the trans shift into 3rd, its back to a 3.0 ring & pinion. This gives you the added 0-60 performance and freeway crusing rpms your looking for with out changing ring & pinions
 
Detroit Gearbox said:
Why body is your vehicle?
I'm assuming its a mustang. but you mentioned FMX. If he already has a flywheel, that fits the AOD "and" has the proper 28oz weight for a 1966 engine (assuming here yours is a 1966 engine) "and" its already the proper diameter then your good to go. They make a flywheel just for a swap into a mustang.
Ive seen people install the later flywheel on a early engine only to have a horrendous vibration.
Since you already have someone doing all of the work I would not sweat it. Im sure they know what they are doing.
You asked about rear axle ratios.
Installing a wide gear set into the AOD gives you a much lower first & second gear, and allows you to run a 3.00 or 3.55 gear but have the performance of a lower axle ratio.
Example: aod trans & a 3.0 axle = 2.40 x 3.00 (rear axle ratio) = 7.2 drive reduction aod w/wide ratio planet = 2.84 x 3.0 = 8.52 final drive reduction.
What this means is installing a wide ratio gear set into your existing aod transmission, would give you a much lower first & second gear final drive.
If your vehicle has a 3.0 ratio rear axle (which were common for 8" Assemblies), it would be like installing a 3.6 ring & pinion, but once the trans shift into 3rd, its back to a 3.0 ring & pinion. This gives you the added 0-60 performance and freeway crusing rpms your looking for with out changing ring & pinions
Click to expand...

Trans swap is done.
I took it for a spin last night with the stock (likely 3.0 gearing) and that thing RIPS through first and second gear.
can't wait for him to finish it all up and I can start driving it.
 
You must log in or register to reply here.
Back
Top