3.73 AOD

Lower gears reduce the amount of torque that the tranny has to digest before the rear wheels turn. This makes your AODs life easier and it should live longer. An oil cooler would be another plus too.

C8oe

No.

True. However, lower rear-end gears will also cause the gears in the transmission to turn faster thus causing more wear.

Agreed. A trans oil cooler will better cool the faster spinning transmission gears.

Patrick '93 Cobra '83 LTD

Uhhh . . . . . . I smell bullshit.

Do either of you experts want to clarify your "true" statements? Or should the rest of us just drive in first gear all the time?

Or fifth?

I doubt this is a real issue.

C8oe

Actually, what they said was pretty much irrefutable. But it's not really all that important to the discussion at hand.

"Joe" wrote in news: snipped-for-privacy@corp.supernews.com:

Irrefutable? Nonsense. Conjecture at best.

Joe (the original one) Calypso Green '93 5.0 LX AOD hatch with a few goodies Black '03 Dakota 5.9 R/T CC

Or hocus-pocus. Putting lower (higher numerical) gears in a car is akin to adding a granny gear for 1st, 1st for 2nd, 2nd for 3rd, etc. You go to a higher rpm than you did before. You multiply torque. How does multiplying torque make it easier on your transmission? Or your engine?

Joe, I agree with you. It's nonsense. That's why I smelled bullshit.

BTW, I think every Mustang can do with a rear-gear change, but to say it's better on the tranny is just pushing the envelope a little. You're going to trade longer engine-tranny life for better performance. If Ford thought that lower gears would improve performance and also extend drivetrain life, they'd have gone with the steepest gears they could manufacture. Instead, they went the other way. I wonder what wactoe thinks about that.

doc

I'd also like to recommend adding a transmission shift kit. Mine is Baumann but I think B&M also makes a good one. It can be set for street or strip, and reduces the time spent between gears. Less time spent in the "between" mode means less friction, which in turn means less heat. However, I should warn you that the much quicker, crisper shifts take some getting used to. At times you may feel it is clunking into gear, if you accelerate slowly. However, when you stomp it, you can have quick, tire-barking shifts. Mine is a 90 with 3.73s, shift kit, and trans cooler. In well-tuned condition I can get a pretty good squeal in all 3 gears. Anyway, just my two cents.

Randy

We're living in a world that's been pulled over our eyes to blind us from the truth. Where are you, white rabbit?

Huh?

The torquiest situation for any engine is from a dead stop. That torque has to be applied through the transmission. Making the rear end spin by putting

3.73's or 4.10's doesn't do an engine or tranny any favors, much less lengthen their life.

Irrefutable?

By your reasoning, a wimpy 3-cylinder AOD Suzuki should whip a 5-speed, V-8 Mustang off the line, and win the quarter-mile, too, by a wide margin.

Pretty irrefutable, by your reasoning. And get better mileage, too!

Shit . . .

doc

Changing the rear gears does not affect the torque at the transmission, the torque an engine puts out at a specific rpm remains the same no matter what the rear gear is. Changing the rear gears allows use of the available power quicker but does not change the power levels through the drivetrain. Here's an example similar to a 5.0L V8;

300 lb.ft. X 4000 rpm / 5252 = 228.5 hp at the crank. Put this rpm and torque through a trans in 4th gear which is a 1:1 ratio (for simplicity) and the same 300 lb.ft. of torque is now being applied through the driveshaft into the rear end. A 3.55 gear would change that to 1126.8 rpm at 1065 lb.ft. of torque through the axel to the ground. A 3.73 gear would change that to 1072.4 rpm at 1119 lb.ft. of torque through the axel to the ground. A 4.10 gear would change that to 975.6 rpm at 1230 lb.ft. of torque through the axel to the ground. Each of these examples, when ran through the conversion equation still add up to the same 228.5 hp. Higher gear ratios multiply torque at the expense of higher rpm but the total horsepower remains the same. The input side of the trans sees whatever torque at rpm the engine is putting out, that torque is multiplied on the output side of the trans depending on gear selection which lowers the rpm (an overdrive lowers the torque and raises the rpm) and the rear gears multiply that torque which lowers rpm again for the final torque and rpm being applied to the ground. Also remember that 300 lb.ft. of torque applied to a stationary object is the same as 300 lb.ft. of torque applied to an object already turning, torque is torque.

Cool! Money for nothing and your chicks for free! So, why do you figure Ford didn't see that?

Actually, they did; you don't. Changing the rear gears has a HUGE effect on the torque at the transmission. More engine/trans rpms required to turn the rear wheels, more torque.

You DO understand torque, don't you?

Maybe you don't. Let's put it in bycicle-boy terms, so you'll understand. Put your Lance Armstrong-mobile in first gear and start pedalling. Lot of leg power, lot of lifting-off, lot of muscle. Shift to 2nd. Little less leg power required, right? And gaining speed. Now to third. Cool! Legs are feeling better and speed is increasing. By the time you're in tenth, you're practically coasting! No stress (torque) on the legs at all.

No, I don't think you understand torque at all. I think you're just another side-of-the-road cemetary-wanna-be; a cross with your name and two other kids on it, with a few semi-fresh flowers. Everyone else just drives by; your Mom and Dad slow down to remember you. Hopefully, they don't get rear-ended and more names don't get added to your pitiful little shrine.

Yeah! That's way cool!

Oh yeah, tell us again about torque and gears!

You need to understand physics, your bicycle explanation is wrong. A bicycle's low gear is about 1:1, the higher gears are overdriven. You need to apply more torque to do the same work in the higher gear because the tire is being turned faster than the pedals. In low gear (1:1), if you turn the pedals at 100 rpm with 100 lb.ft of torque the rear tire will turn 100 rpm and apply 100 lb.ft of torque to the ground. In high gear (say 1:4), pedaling at the same rpm with the same torque will turn the wheel at 400 rpm and apply only 25 lb.ft. of torque to the ground. It feels harder to pedal because you have to add more torque to maintain the 100 lb.ft. to the ground, which in our high gear would be 400 lb.ft. If you didn't pedal harder than 100 lb.ft. the pedals would only have 100 lb.ft. applied to them. In a car the engine can only apply the torque it has, say from 100 lb.ft. at 1000 rpm to 300 lb.ft. at 4000 rpm, to the input shaft of the trans. The input shaft can't have more torque than the engine provides applied to it. It's like pulling a rope through one pulley fixed to the ceiling and tied to a 100 lb weight. There's no mechanical advantage with one pulley, you will need to pull with 100 lbs of force to lift the 100 lb weight, pulling one foot will lift it one foot. If you attach a second pulley to the weight, attach one end of the rope to the ceiling, thread it through the pulley on the weight, then through the pulley on the ceiling and pull the other end things change. Now you have a 2:1 mechanical advantage, but there's a trade off. You will only need 50 lbs of force to lift that 100 lb weight, but pulling the rope one foot only lifts the weight 1/2 a foot. If you still use 100 lbs of force and lift the weight one foot you will do the work twice as fast but pull two foot of rope to do it. That's what gears do, they allow the engines available torque to be multiplied but the rpm will be used faster.

You need to understand physics, your bicycle explanation is wrong. A bicycle's low gear is about 1:1, the higher gears are overdriven. You need to apply more torque to do the same work in the higher gear because the tire is being turned faster than the pedals. In low gear (1:1), if you turn the pedals at 100 rpm with 100 lb.ft of torque the rear tire will turn 100 rpm and apply 100 lb.ft of torque to the ground. In high gear (say 1:4), pedaling at the same rpm with the same torque will turn the wheel at 400 rpm and apply only 25 lb.ft. of torque to the ground. It feels harder to pedal because you have to add more torque to maintain the 100 lb.ft. to the ground, which in our high gear would be 400 lb.ft. If you didn't pedal harder than 100 lb.ft. the pedals would only have 100 lb.ft. applied to them. In a car the engine can only apply the torque it has, say from 100 lb.ft. at 1000 rpm to 300 lb.ft. at 4000 rpm, to the input shaft of the trans. The input shaft can't have more torque than the engine provides applied to it. It's like pulling a rope through one pulley fixed to the ceiling and tied to a 100 lb weight. There's no mechanical advantage with one pulley, you will need to pull with 100 lbs of force to lift the 100 lb weight, pulling one foot will lift it one foot. If you attach a second pulley to the weight, attach one end of the rope to the ceiling, thread it through the pulley on the weight, then through the pulley on the ceiling and pull the other end things change. Now you have a 2:1 mechanical advantage, but there's a trade off. You will only need 50 lbs of force to lift that 100 lb weight, but pulling the rope one foot only lifts the weight 1/2 a foot. If you still use 100 lbs of force and lift the weight one foot you will do the work twice as fast but pull two foot of rope to do it. That's what gears do, they allow the engines available torque to be multiplied but the rpm will be used faster.

By putting lower gears in the rear you are multiplying torque at the rear wheels, not the output shaft of the transmission. This reduces the load on the transmission. The rear wheels will spin easier, reducing clutch slipage and converter heating.

As far as the bicycle analogy goes, the other writer is clueless. Using 1st gear on a bike puts less strain on the chain than trying to climb a hill in 10th gear. Sure you will pedel faster but it's easier on the chain/transmission. Trust me.

C8oe

You were doing good up till then. Bicycle, motorcycle, or automobile, you need more torque to get it going then you need to keep it going. That's why manual transmissions have a low gear ratio in first and get progessively higher. Stick a 3.73 or 4.10 on the ass end and you wind your engine--and tranny--much faster than you did with stock gears. You end up with better acceleration but lower top end. If you want to cruise at high mph, you'll do it at higher revs. Running at higher rpm means shorter lifetime, mostly due to frictional losses.

I can always use a physics review, so I thank you for that. My major was in nuclear physics, but that was thirty years ago. I can still do diffy-q's, though, if that's any help.

Obviously, you do not. Lower gears reduce the work load on the engine/transmission. As work load decreases, so does torque. RPM has nothing to do with it.

If anyone doubts this, all you have to do is go put a torque wrench on your pinion yoke and rotate the wheels, then change to a lower gear and repeat the test. There will a lesser torque reading with the lower gears.

And you no doubt have never ridden a bicycle before.

C8oe

By your reasoning, the bigger the rear ratio, the better. Ford could certainly use a little help, don't you think? Maybe 5.32's or even 9.64's in the 4.6 L Mustang could whup the Corvette, and get better gas mileage, too. Not to mention making the engine last longer.

Am I missing something?

We all have our prefered ratios for our particular driving styles. Sure Ford should offer more optional gear ratios for the buyers, don't know about 9.64s though. I don't believe bigger is always better. Just hate to have to explain drivetrain torque loads to some of these guys. Their minds are set in their ways. Negetive torque may be too much for them to handle.

C8oe

Are you sure about this? I thought torque was proportional to power/RPM.