Re: ar End vs. AOD?

Oh btw, it's a 66 coupe with stock 289 and Holley 2-barrel. I don't know the current rear end, but fairly sure it's a stock rear end, whatever ratio that would be.

Thanks.

 

Well....you will notice the difference.

Assuming you have a 2.80:1 ratio now you would end up with 1.88:1 to get the equivalent of a 33% overdrive.

That would be slower than a herd of turtles. By the time you got to where you were going you would need to turn around and come home.

By the time you got up to traffic speed granny with her walker would have beat you to the next red light.

By the time you got to the corner you would need snow tires.

 

An advantage of overdrive, is having a "performance" rear gear , in the car, and still have a low RPM cruise.
I use a 3.25, while sporty not really performance, because I like to do interstate driving and want to keep the MPG up. Will prolly up the ratio to 3.40-3.50, during a rear end up grade.
You can have real performance gears 3.75-4.11 and then with the OD not have to cruise @ 3700RPM

 

Have you thought about swapping the C-4 for a toploader and keeping your rear end stock, whatever that is ? Way more fun. Have you driven a vintage Mustang with a toploader ? If not, try to arrange a drive in one before you make any decision.

As pointed out, your current rear end ratio probably a 2.80, but it could be a 3.00:1 as well. If you're not doing a lot of Highway driving you won't miss the benefits (questionable in my view) of an AOD or a 5 speed transmission. Even if you do drive a lot on the highway, there are ways to keep a 4 speed, 3.00:1 gearing, and still have decent acceleration.

Z

both of these posts contain good information. the overdrive can be good choice if you are going to change the rear gear to something in the 3.50 and up range. that way if you do a lot fo freeway driving with the car, you wont be rolling down the road at above 3000rpm at 60mph.

however if you are only going to swap to the overdrive and keep the 2.80/3.00 rear gear, that will also be fine, once again if you are only doing freeway driving. otherwise when in od you will bog the engine down substantially, and you will hate it.

in the end, my advice would be to seal up the C4 properly and just go with that for day to day around town driving.

 

An advantage of overdrive, is having a "performance" rear gear , in the car, and still have a low RPM cruise.
I use a 3.25, while sporty not really performance, because I like to do interstate driving and want to keep the MPG up. Will prolly up the ratio to 3.40-3.50, during a rear end up grade.
You can have real performance gears 3.75-4.11 and then with the OD not have to cruise @ 3700RPM

Exactly..The overdrive lets you have your cake and eat it too!

 

An advantage of overdrive, is having a "performance" rear gear , in the car, and still have a low RPM cruise.
I use a 3.25, while sporty not really performance, because I like to do interstate driving and want to keep the MPG up. Will prolly up the ratio to 3.40-3.50, during a rear end up grade.
You can have real performance gears 3.75-4.11 and then with the OD not have to cruise @ 3700RPM

This is exactly why I changed to an AOD. I now have a 3.80 gear and that would be unacceptable with a non-lockup, non-overdrive C4 on the highway.

The 4R70W has a slightly wider gear ratio, and will work a little better with numerically lower rear gears.

 

Re: ar End vs. AOD?

I've been thinking about swapping my 3-speed automatic out for an AOD. I mentioned that to a friend (T-Bird and Corvette guy) and he said just swap out the rear end to one with a higher gear ratio and don't bother with the AOD. I said I thought that would lose too much on the low end, but he said unless I'm racing (I'm not), he was sure I wouldn't notice the difference.

Any advice?

Find a new friend. Hopefully one that knows something.

The addition of an overdriven transmission is one of the best improvements you can make to an old muscle car. A 4R70W with a 3.55 rear axle ratio is the berries.

Phil

 

I have also been thinking about doing this....is there a sticky or a thread on parts needed to do this, also what is a rough estimate of cost involved. Since I would probably have to have a shop do it.

thanks.

 

What is your objective with this? Performance or gas mileage?
If it's gas mileage, I doubt you'll justify the cost of doing the conversion. Really, you'll only notice a MPG difference if you do alot of highway driving.
If it's performance, you'll need to change the rear gear too anyway to see a difference. Why not just do that first and see if you can live with it.
My objective was to get a stick shift instead of the auto, the overdrive was a definate bonus but there's no way I'll get back the cost with the slight MPG gain (not enough hiway driving).

 

Re: ar End vs. AOD?

1971 Mach 1, exactly how much increase in your highway MPG did you acheive? What was your original MPG and what is it now with the OD? What rear end gearing? thanks!

 

You would have to drive the car a ton to justify paying a shop to do it. All shops have an hourly rate, but no shop will tell you how much time it will take them to customize your car. Even the bolt in stuff is more work than most parts-hangers are used to.

 

Re: ar End vs. AOD?

+1

What is your plan for the car? Do you commute or just drive on cruise night?

 

Re: ar End vs. AOD?

When I had my 68 GT Coupe I wanted more pep from the car, it had a C-4 trans & 2.80 rear. I left the C-4 in the car & replaed the rear gears & went up to a 3.50 & it made a very noticable difference. IMO was worth every penny.

 

Re: ar End vs. AOD?

Pretty much what everbody says when they go to a lower rear gear ratio. With an overdrive transmission you can have that fun and still cruise on the freeway without the engine screaming the whole time.
Vette/Tbird guy seems pretty clueless I'm afraid.

 

Re: ar End vs. AOD?

Depends what you'd pay for an AOD transmission.

Swapping gears is not necessarily cheap either.

It cost me $550 to change rear end gears. I still ended up changing to a 5 speed anyway.

Changing gears for me, was not a wise 1st expense

 

I view my Mustang as my hobby. I have no intention, after 18 years, of ever selling it.

With that in mind I continue to put more money into the car than is wise. I just do it because I love the car and want to keep working on it. I do everything myself.

I could have bought a new Currie 9 inch for what I will end up with in my 9 inch. Shrug, at least I can say I did it myself.

 

The deal with mine is that it's leaking, so I have to drop it out and replace the seal on it anyway. I have access to an AOD for cheap, so I thought "now's the time." I'd ultimately like to have it in a condition where I can take it on longish road trips (across the state) and have it run at lower RPM, and get somewhat better gas mileage.

But many of your comments are right on -- I'm not sure I'll ever drive it enough to justify it, financially. It's just something to do since I'm working on it anyway. BTW, I would plan to do the swap myself, hopefully with supervision from someone who's done it before or knows transmissions better than I do.

 

I have a 351c attached to a AOD and 4.11 traction loc unit. I also had a TCI valve body installed and it shifts hard, very pronounced from gear to gear and the drop off in OD significant (does that sound right?). I dont know about mileage as the car has been driven very little and the tach does not work (another issue with wiring the tach adapter) Also with the way the stock shifter is I cant keep it in 1st and I dont know the fix for that. The drive line was shortend an inch or two (72 Mach had FMX)

 

Re: ar End vs. AOD?

My 68 had a C-4 and 2.80 rear gears, since I drive my car a lot, long distance, I opted for an AOD and 3.25 gears. This was one of the most rewarding of mods on my car.
The core for the AOD came from a salvage yard, $50.00. A local tranny shop owned by a friend rebuilt it for $850.00. He used Baummans recomendations on upgrades to it with stronger components from an AODE and 470RW as well as premium clutch packs, Lightning OD band, super coupe servo, etc.
I ended up with freeway RPM's of 1900 @ 70 MPH. First gear is a real pleasure out of the hole yet highway gas mileage is 24+.

I did the diferential gear change myself with a kit from Motive Gear and I also got rid of the "peg leg" with a limited slip from Auburn.
I am sure you will be more than pleased with the performance of your car with the AOD swap, which is widely regarded as the best mod on a vintage Mustang.

 

I have a stock 302 C4 and 8 inch 3.0 rear gears I want to do AOD swap should I upgrade rear to a 8 inch 3.25 or 3.50 just want some performance but mostly want highway car

 

The 3.50 ratio isn't available for the 8" but 3.40 are. 3.55 is available as wel
I have a T-5 3.351st and .68 OD and an 8" with 3.40 :smile2:
Old thread BTW ,guess that means your searching though

 

Have you thought about swapping the C-4 for a toploader and keeping your rear end stock, whatever that is ? Way more fun. Have you driven a vintage Mustang with a toploader ? If not, try to arrange a drive in one before you make any decision.

As pointed out, your current rear end ratio probably a 2.80, but it could be a 3.00:1 as well. If you're not doing a lot of Highway driving you won't miss the benefits (questionable in my view) of an AOD or a 5 speed transmission. Even if you do drive a lot on the highway, there are ways to keep a 4 speed, 3.00:1 gearing, and still have decent acceleration.

Z

 

3.55 is just perfect with my AOD

 

what is your rpm at 70 with 3.55 and AOD

 

This chart will help for choosing gears with an aod at 65 mph.


Mustang Rear Gear Ratio to RPM Chart | AmericanMuscle

 

It's possible some none experts are confused/misled by nomenclature. High gear is low numeric. It may just be possible the the assumed stupid Vette and T-Bird friends meant you would get improved performance with lower gear (higher numeric). I.E. 3.25 numeric (lower gear)would give much improved performance and be tolerable overall!

Possible people?
Slim

I realize the OP rear vs AOD implies lower numeric rear. WOW maybe they just didn't understand at all!!!!!!!!!!!!!!

 

this chart has 3.50 for 8 inch
what gears can I change in the AOD instead of change the rear can I just change 1st and 4th gear in the AOD

 

I've seen the chart I believe it mostly refers to 9"and 8.8 .This is the text that goes with it
This is a list of some common ratios and their gear and pinion tooth combinations. The 8.8-inch factory and service ratios are highlighted in yellow. The 9-inch ratios from the factory are in blue. The ratio 4.56:1 (in green) is common for both axle sizes. You can see how the 2.86, 3.00, 3.25, 3.50:1, etc. are prone to gear whine issues, simply based on tooth combination. So, depending on the need for a specific ratio, I avoid the tooth combinations that are prone to make noise, which are the ratios with a common factor. This is not to say that all nonhunting ratios are noisy but if the vehicle is sensitive to this type of frequency, these ratios cause a problem. Ironically, many aftermarket gears with a 3.70:1 ratio tend to make noise. Note that the list only includes ratios up to 6.0:1. There are even higher values available in the aftermarket.
Not saying they don't exist but good luck finding a 3.50 gear set for an 8"

 

Soooo, rear gear vs. AOD = both needed for the win? #sad:crying:

If possible the easy choice would be an AOD with a different gear set, something with at least a 3.00 1st gear. Is that even possible?
Can you get an adapter for a 700R4?>
What the Corvette guys know is putting GMs version of AOD in gives 1st gear a 3.02, a yuuuge gain over early autos.