Can gears hurt?
 

I just had my AOD rebuilt on my 91 GT. I have a set of 3.55's and a set of 3.73's. They mechanic at the shop said gears could actually hurt my car including my motor and tranny if not used properly. Is this true? One other thing... Which gear should I install first if I won't be running my car at the track, but driving it a lot of the highway?

If your going to do highway driving a lot, go with 3.55's. the only way that gears can hurt your motor or trans is the harder the hit off the line, and the higher the rpm that your car will run at on the highway. basically i think that your mechanic doesnt know what he is talking about.

I agree, your mechanic doesn't know what he's talking about.

Gears won't hurt your tranny or motor at all. The only think it's going to hurt if your gas budget :D

The ONLY way gears are going to hurt your car is by reving it more therefore causing more wear. It will actually put less stress on the rear differential gear teeth. You are still putting out the same Horsepower with gears.

Go 3.55's if you spend all your time on the highway and this is your daily driver. Otherwise go 3.73's.

Gears and gas mileage
 

Use the 3.73 gearset. It's only a slightly higher RPM difference from the 3.55's and with your AOD you need all the torque multiplication you can get.

The 3.73's will add around 400 RPM at highway speeds which is negligible and probably will make a 1 or 2 mpg difference in your gas use.

In my opinion, the words 'gas mileage' and 'Mustang' should not be used on the same line.

Better performance and good gas mileage are not compatible goals. If gas mileage is that important to you you've bought the wrong car. A Mustang V-8 gets somewhere in the low 20's for mpg on highway driving, maybe 18 or so overall, which isn't bad. You're feeding eight cylinders and pulling over 3,000 pounds. Be reasonable when it comes to gas mileage expectations and you won't be disappointed.

On other thing: Find a different mechanic.

This gentleman above knows best....

3.73 with AOD, period. Mileage can actually increase in around-town driving, and will only suffer slightly on the highway. Engine wear is really a non-issue, as the 5.0 plant is very tight.

Also, as I work at a dealership I can tell you....mechanics are not enthusiats. They think that removing any perfectly functioning part from a car is a bad thing! Take their advice for what it's worth...

I do want to put the 3.73's in more than the 3.55's, but you see, my car is my daily driver. I don't have another car. I drive it through the rain and snow. I live in New England and the winters tend to get pretty bad from time to time, but I have a seperate set of studded snow tires... And with those on, my car flies through the snow. I just want to know what will be better for a daily driver. If you guys think the 3.73's will be good for me, then great.

The majority of those here will say

AOD 3.73 for street 4.10 for racing

T-5 3.55 for street 3.73 or 4.10 for racing

Going too steep in the rear gears can hurt your performance if the motor does not have a high enough RPM power peak, like a stock 5.0. The engine will run out of steam too soon, and you loose some of your top speed too!
If you install the gears wrong, that can hurt the car too!


I'm not certian here, but I suspect the AOD has a deeper OD gear.

Of course I have 2.73's and I'm in bummerville

There is only a is only a small difference between the 3.55's and the 3.73's. I went with the 3.73's and definately have no regrets at all. I get better mileage around town and suffer only slightly on the highway.

I do notice the car running out of breath at the upper RPM's, but there is still plenty of time to keep shifting, even on the "stock" 5.0.

I though 3.73's would be too steep, but now I now why people like 4.10's. If I did it again I would even condsider 4.10's (but my car is not a daily driver anymore)

3.73
 

I have had 3.73's in my 5speed 5.0 LX for 8 years,have driven cross country about 30 times since 1989,and have had no problems.

First up find another mechanic like everyone else has said,with an AOD get the 3.73's you will not be disappointed.

Gas mileage and Mustang V8 do not go hand in hand as Mr 5.0 said but a little sanity helps also when you are driving.On those cross country jaunts I went on,I averaged 22-24 mpg with the cruise control on,that is why it is there,use it and you will be surprised at how well your gas mileage really is.

Get the 3.73.

3.73's no doubt about it! Don't waste your time going with 3.55's in an auto! I'm running 3.73's and its just fine for a daily driver (which my car is). I almost wish I went with 4.10's, but oh well. Where abouts in MA do you live TwiLighTBluEGT? If you really want to see what 3.73's are like in an auto I'll take you for a ride, thats if your not too far away.

Hey HiFlow5 0,
I wish I heard that offer when I was out at amherst. I wouldn't have minded you taking me for a rip to see what the 3.73s feel like. Oh well.
I agree with these guys. Not to repeat others here but don't waste your money on the 3.55s, its pointless.

Scott

3.73's as a minimun in an AOD. I had them and went up to 4.10's.

3.55s are a waste in AOD car.

HiFlo50, I live in East Longmeadow, MA. I sure would like to see what 3.73's are like in an AOD. If your not too far away, let me know.

I got 4.10's with an AOD and its not really an issue as far as im concerned. I cruise at 90 mph=2200rpm on the clock thats NOT adjusted for the 4.10's. Tires are 65R 215 w/ 15" rims. I Figure the speedo is about 30% off with the 4.10 gears.

Drop a pinion gear on your foot when your wearing your Vans, and then ask me if they can hurt. :eek:

Don't ask, I'm not in the mood.

The only decision you should be considering is whether or not you want to install a new torque convertor to go with your 3.73's.

:)

Take care,
~Chris

Exactly. Throw a Stallion converter in there while your at it, and you will really be happy with the combination, and you will be beating 5 speeds with lousy drivers.

If 4.10's may cause a stock car to run out of steam in the top end, would I have that problem? My combo makes peak power from 4500 - 6000 rpms.

Also, what is the bottom line as far as ET improvements that gears offer? Will I actually pick up anything or will the car just feel faster?

Another question. WIth the 4.10's, I wont hit OD before I finish the quarter will I?

93 GT, it looks like your motor combo should have plenty of higher RPM power. I would imagine only a real stock motor, meaning stock everything or just a catback and filter etc would actually slow down with 4.10's

Sounds like 4.10s are perfect for your car. You should see a couple tenths E/T improvement with gears. You wont hit OD because you will have your shifter in the D position, thus holding third gear. This will vary depending on tranny modifications.

If your trap RPM is to high that you run out of motor with the 4.10s by the end of the quarter in third gear, adjust the rear tire size to fine tune.