Ok, here's an odd theory that I've been developing.

I have a 2003 E-150 Club Wagon 5.4, 4R70W, 3.55 Trac-Loc. We live in Northern Virginia in the close suburbs of Washington, DC. Most of the van's driving is done stop-and-go style, going from stoplight to stoplight on streets that have 25 or 35 MPH speed limits. The roads are basically flat with only the occasional hill.

I started thinking about all that shifting the tranny does. For example, from here to the grocery store is about a mile, and there are at least 7 stops just between here and there. I've already been locking out the OD, because it's just not necessary. Today I tried a 4 or 5 mile trip with the tranny locked in 2nd gear. It never really wound up much. After I got home, I calculated the following:

The way the van is equipped, it has a tire diameter of 28.87 Inches, a 2nd gear ratio of 1.56, and an axle ratio of 3.55. At 25 mph, the engine turns 1611 rpm; at 35 mph, the engine is turning 2256 RPM. Even at 45 mph, the engine is turning less than 3k, coming in at exactly 2900 rpm.

Lest you think that 2900 is high, it's almost exactly what the engine cranks when going 70mph in 3rd gear, the suggested way to tow a trailer. Besides, 45mph is about the max we ever go on any road around here. If I were going to go that speed for very long, of course I'd shift into 3rd.

Now, with all that in mind, wouldn't it be better just to put the selector in 2nd most of the time, or is there something I'm missing? With the stop and go, I doubt it would even affect the fuel economy.

 

why burn up the tranny by putting it in 2nd. the tranny will not shift but will stay in 2nd all the time. some gm trannies have a feature where it will shift 1st to 2nd when placed in 2nd. but ford does not so you will loose off the line power and place to much stress on 2nd gear.

 

If the tranny is locked in second gear, how can it burn it up?

 

Starting in second all the time will be too much stress. It was not designed for it. And if you forget to shift out it will get too hot.

 

I'm not at all trying to dispute you, but trying to understand the dynamics involved. Having said that:

How will it get too hot? My understanding is that heat is produced by excessive slippage and shifting. If the TC isn't slipping because it's on flat ground and rolling steadily, I don't understand how that can cause heat. Perhaps the take off could produce more TC slippage and thereby more heat if the throttle is overly used, but simply cracking the throttle is more than sufficient to get it rolling well on flat ground.

Also, it's obviously not producing heat from shifting, since it's not shifting.

 

Most of the heat in a transmission is generated in the torque converter. Taking off in 2nd gear means the converter must slip waaay more than designed in order to get the vehicle rolling. The more TC slip, the more heat. Heat is what kills transmissions and varnished the fluid. Also, the trans wasn't designed to take off in 2nd gear so you have too much load in too tall a gear. In a 4R70W the band is used in 2nd gear so you will be overloading the band and thus increasing the possibility of burning it up.

The way you drive its a good idea to cancel OD but leave the shifter in drive so the transmission can do its job. Lots of shifting is no bad for the transmission, lugging it is. If you don't go over 45 then letting the trans shift to OD is of no use so just cancel OD and let it do its job.

Steve
'95 Clubwagon XLT

 

Sure it was. If it wasn't designed to start in second the trans wouldn't be allowed to start in second. With the electronic controls that is really easy to do. Since the engineers allowed second gear starts it has to have been designed to start in second.

 

Yes and no. 2nd gear starts are a good thing in ice and snow. The taller gear ratio makes it harder to sping the tires. But then it doesn't snow in the heat of the summer and you typically are only forced to do that occasionally. The transmission was designed to make 1st gear starts in normal operation. It was not designed to make 2nd gear starts in normal operation. That it has the ability to do so doesn't mean that is what you _should_ do.

The point is: regular 2nd gear starts will cause the trans to run hotter than necessary. Heat is the enemy of automatic transmissions. So doing that is harder on the transmission and you gain nothing. So why do it?

Steve
'95 Clubwagon XLT

 

So you believe the slipping in 2nd is going to be sufficent enought to overheat the fluid? If so, then you're right about not starting in 2nd all the time.

What about the old 2 speed automatics though? I had a buddy who could wind his old Bel-Air 283 up to near 70 mph in L. Wouldn't that be geared very similarly to what we're talking about?

 

Again, its what it was designed to do. 2nd gear starts make the torque converter work much harder. If you drive around in 2nd all day your probably not "overheating" the fluid but it is being forced to operate at higher than normal temps. Over time the elevated temps will varnish the fluid and ruin the transmission.

That old PowerGlide in your buddies Bel-Air was designed to work that way. The converter had a higher stall rpm to accomodate it. I have seen "transmissions" that were really only foreward and reverse hung behind a torque converter. Therefore it had only one gear.

I guess I don't understand your wanting to make 2nd gear starts. Its harder on the motor (has to pull a taller gear), the transmission and is slower for a given load and throttle setting. I am curious what benefit you think you get? I undertstand not using OD around town, that makes sense. But 2nd gear starts don't.

Steve
'95 Clubwagon XLT

 

It's no big deal. Like I said, it's just a far out theory that I figured you guys could help me flesh out.

I'm sure you're right. Any increase in fluid temps is a bad thing.

Thanks to all of you!