what is the difference in gears in the rear end of the trucks?  I had a F350 with the 4/10 rear end.  Now I have a F250 with 3/55 rear end.  What exactly is the difference? 

I know that the 3/55 is more of a highway gear.  But what is the difference in pulling capabilities?  The F250 has the 7.3 engine in it, so I know it can pull anything with that engine, but what can the truck actually handle?

It is a 97 Ford F250 HD 4x4 with the 7.3 powerstroke and the 3/55 gears.  Will include a photo.

I am selling my Exiss in my signature, and getting a 3 horse, but the same type of trailer.  Will be adding a LQ to the trailer eventually, but will have no more then a six foot short wall.  I am assuming that this truck will pull it fine.

Just wasn't really sure what the difference in the gears was.  So it should pull it fine, just might not take off as fast or as easily as one with a 4/10 rear end, while pulling?  Is that correct?

Here is a photo of it.  I am also upgrading the rear leaf springs to 1 ton springs, since it had some broken springs.

We have a Ford 7.3 with 3.73 gears. At 70 mph, the engine turns ~1800 RPM, a very easy cruising speed. We live in SW PA which has numerous hills, and often travel in NY, OH and WV which has the same.

Our largest trailer weighs ~9800 # empty. It has a 13' LQ, mid tack and is a 3H SL. When it was loaded, our transmission would kick out of OD on the steeper hills into 3rd gear. The engine rpm would jump to 2450 RPM at 70 mph, and the cruise would hold the same road speed while we crested the top of the hill.

I installed a Bully Dog 6 way chip, a free flowing exhaust and added a tranmission shift kit. Now, with the chip in the lowest setting, (towing)  the same hills are pulled in OD, the transmission does not down shift, and my engine maintains a constant 1800 RPM.

Because of the exhaust system mods, I can top the same hills pulling our smaller trailer (~5500# empty) at the same speeds in OD with the chip OFF.

My wife and I vacationed in MI last year and noted that it was relatively flat with few mountains. If that is where most of your pulling miles will accumulate, pulling 7-8k# shouldn't be a problem with your diesel and a 3.55 rear axle ratio. Whenever you do come to a steep hill, the tranny will automatically kick out of OD or you can manually downshift. Your diesel produces quite a bit of torque at lower RPMs, and it doesn't have to rev at a higher speed to make its torque like a gas engine. The flat terrain will not tax your drive train. You only have to use common sense on hills, and not unnecessarily lug the motor.

I would make sure your cooling system is up to snuff, and change your transmission fluid to one with a synthetic base. If you are breaking rear leaf springs, you might want to consider installing Timbren overload devices.

If you reread some of the common earlier postings about "what can I pull with this truck?", you will find that several truck owners were told, it would be proper to pull similar loads to yours, while using smaller gas motors.

You have a good truck, and it should do the job.

Thanks Gard, that makes sense to me.

I bought it with broken leaf springs....well I found out after...stupid girl mistake! LOL!  So now we are fixing it and instead of just fixing the three that are broke, we are replacing both sides, so it will basicly have a whole new rear end as far as springs go.  And they got the 1 ton springs, to beef it up a little more.

I usually only put about 3000 miles on the truck in a year, and most all of that is pulling....and that is the HIGH side of the miles.  Most is local and you are right, we are not that hilly in MI.... even though I have seen some hillbillies! LOL!

I figured my truck would be fine for what I wanted it for and I just love that 7.3 engine.  Will check into the tranny fluid though as you suggested.

Thanks!

Towing heavy loads in OD can cause excessive engine heat, which raises the transmission oil temps if it shares a common radiator for cooling. If your transmission doesn't have a locking gear other than OD, the slipping torque converter can also cause the transmission fluid to heat up.

A gas engine doesn't deliver its torque at low RPMs like a diesel. If it is constantly lugged at a low RPM, it will result in a higher operating temperature which can be detrimental to its life span. To properly cool a gas engine and transmission under load, you increase its operating speed and decrease its load. This is accomplished by running it in a lower gear.

The common problem with these scenarios is overheating. When the transmission fluid cannot be adequately cooled, it will break down, cook and stop lubricating. When this happens, your transmission has just been completely ruined.

Fortunately this can be prevented in several ways from happening. The first is having an engine cooling system large enough tp prevent overheating, no matter how hard the engine is working. The second is having a large volume, independent transmission oil cooler, that too, has enough capacity to prevent fluid from overheating when the transmission is being used hard. The third is having a transmission fluid that has a high boilng temperature, one that will not break down under high temperatures and will continue to lubricate at temperatures far exceeding petroleum based fluids.

You have a diesel motor and with it, heavy duty components. You already have large volume cooling systems for your engine and transmission. The only thing you may not have is synthetic transmission fluid. This can safetly protect your transmission at temperatures almost three times higher than a petroleum based product.

Yes, whever possible, I always run my diesel in OD while towing. I have a transmission fluid temp guage, that shows its operating temperatures have never come close to reaching dangerous temperatures. My diesel doesn't often work hard pulling my rig at highway speeds, but when it does, the computer automatically kicks the transmission out of OD. This happens before my oil temperature changes at all. I know my truck well enough by feel and experience, to understand when it is pulling hard and when its loafing.

I have never encountered a situation when I have endangered my truck's drive train by overheating its components. Every fluid has been replaced by synthetics, even the power steering fluid. It has never had to work hard enough or long enough to reach dangerous temperatures. We have one hill that we frequently travel that has a 11% grade. The computer kicks the tranny down, the engine pulls smoothly to the top, there is no overheating or damage to any of the mechanical components.

If you have some "stick" time, you should be able to feel how well your rig is pulling. If it isn't lugging, you're not running a high throttle and the temps are normal, the transmission isn't being damaged. Run the highest gear your engine is comfortable pulling. It can change with the terrain, your speeds and your loads.

With our lighter trailer and fairly level roads, an 80 degree day, no chip, cruise on at highway speeds, about 175-180 degrees. Last year we went from Morgantown WV thru Deep Creek MD to Cumberland Md. There are many long, fairly steep hills. I turned the chip on and let the motor torque its way over them all in OD, on cruise at 65 MPH with the AC on. It was about a 90 degree day. My temps on the steepest hills were about 210 degrees going up, 175 near the bottom going down.

Our larger trailer increases the tranny temps about 10 -15 degrees when pulling hard, the same 175 degrees running easy.

Yes, I'm talking about the main engine computer that controls the engine and transmission functions. Whenever cruise control is selected, the computer through many sensors, will attempt to maintain the same selected road speed, regardless of changing inputs. If the engine starts to slow on a hill, the speed sensor will input a signal, more fuel will be automatically added to increase the torque, and the speed will be maintained.

If the engine has insufficient torque to maintain the speed with all the fuel it can burn, the computer will select a transmission downshift to a lower gear. At the same time it will monentarily lower the amount of fuel during the shift so as not to over rev the motor, and just before the shift is completed and before the clutch pack fully engages, it will add more fuel to increase the engine speed, needed to exactly to match the higher RPM of the lower gear ratio. It pretty amazing stuff, when you consider all that the computer takes in, and determines exactly how much fuel to squirt into the cylinders, and what gear should be used depending on the load and throttle setting.

I have read where Dodge trucks have auto trans problems, even to the point where they had to derate the power of the diesel when an auto is optioned, because it couldn't handle the additional torque. I have never owned a Dodge truck, so when I say to use the highest gear possible, I do so for the very reasons you mentioned; lower RPMs, more relaxed cruise, better fuel economy, less engine wear.

With my experiences with GM and Ford products, this has never been a detrimental driving method, and I have enjoyed excellent drive train reliability while doing so. If this somehow is damaging to the Dodge transmission, I can't say, other than it is atypical to normal driving habits. HGB is our Dodge drive train expert. Perhaps he can shed more light, on the reliability of these transmissions being dependent on driving habits.

We had always run 4:10 rear ends in our duallys since we were always pulling alot of mountains in our travels. In 08, I got talked into a F450 with a 4:88. HATED IT! The engine, tranny, rear end and 4WD could not work together. We had nothing but problems. Gave up on that truck and got the  new Dodge this year with a 3:42, I think.  And so far, it sure can walk the dog! It's getting between 15 -18 mpg without a trailer and about 12.5mpg  with the 4H weekender. All without sacrificing power!  It was hard for me to except that the days of needing the 4:10 were over........

Bought this truck in Apr and it has not been in the shop once!  It has already pulled the same trailer alot more miles than the Ford F450 did in 2 years. Yeah! She gets her first oil change this week!