Hi guys (and gals),
Been lurking here for a while and decided to get some advice from you folks. I have an '04 Dodge Ram 4x4 with the 4.7 liter engine. Maximum torque output is around 300 lb.ft. The differential gears are 3.55:1. I am considering a gear change, but since this vehicle is four wheel drive, the expense is quite high - around $1300+ for the change. If this were a two wheel drive vehicle, I would probably just go ahead and do the swap. However, 1300 bucks is a lot of dough to spend for an experiment. I should mention that the Dodge, when in Tow/Haul mode, locks out 5th gear, but is still allowed to hit 4th (the first overdrive gear).
I tow an X189-FBR Shadow Cruiser Fun Finder that has a GVWR of 4200#. Fully loaded and wet, we are tipping the scales at ~3400#. We just took an 1800 mile round trip from California through Arizona and New Mexico. On flat land, we did very well, cruising at 60-65 MPH. However, the transmission shifts constantly from 4th to 3rd and back again. When we hit any substantial rise in the road (especially with any head wind), the truck shifts down to second. In second gear, we are winding up around 4000 RPM @ 60 MPH. This doesn't bother me terribly, as long as it doesn't happen often. However, it was happening more than I would like.
Now for the questions. I would like to know from those of you with experience, how a gear change to either 4.10's or 4.56's will affect my towing, especially at highway speeds. I ran some calculations and came up with the following:
Assuming a constant torque of 300 lb.ft. (I know torque is not constant, but I had to use some baseline for calculation), I would gain about 22% torque by going to 4.56 gears (instead of my current 3.55). That sounds great, but I'm worried about whether I would have enough torque available to keep the transmission from shifting into second gear under normal driving conditions. Does this calculation sound correct? Will the transmission run cooler? (I do have a trans temp gauge with the sender in the line going to the trans coolers). Will the transmission shift back and forth less?
I know that some of this may be a bit subjective, but I'm hoping for a voice of exerience to chime in here. Sorry for the long post.
RP

 

Bigger gears will help, but solving how often you shift, I don't know. You're putting a good load on that size motor. That is a big effect. You are peaking with that size load for what it can handle and stay at a constant area of those RPMs (mid60s)

 

LOL Yes, very long post. I started reading it earlier today and said screw it!

 

Thanks for the response. I have been thinking a bit about it. I used to have a different trailer that weighed in about 1500# heavier and with a considerably larger frontal area. I pulled that unit with a 94 Chevy with a 350. That engine had roughly the same torque figures as my current Dodge. It pulled my trailer pretty well, considering. BUT, it had 3.73 gears in it. I'm thinking that going to 4.56's may be pretty good. Hmmm . . .

 

1300 dollars makes a good down payment on a Cummins powered 2500 that will tow with ease lol. Gears will help but I dunno how much. wth why not try it and see.

 

I have a 1500 RC 4X4 4.7 auto with 3:55 gears. When I bought it the prior owner had replaced the tires with 265s. Stock was 245s. This took the final drive ratio even lower/higher. Not a good combination. Actaully the replacement tires were a little larger than the normal spec for 265s.

You can check your door jamb sticker to see what size tire your truck was born with.

I know everybody wants big *** tires! But that was not in my budget. To change out front and rear differentials and then recalibrate the speedo and buy a new spare was way out of my price.

I found Pirelli Scorpion ATR 245s Light truck with E load ratings. These are actually 265 in cross section measurement on the stock dodge 8� rims. The height is less of course. I have a load rating exceeding most all 265s and the tires look good on the truck. I did not have all of the expense and my stock spare is now compatible.

I tow more than you have referred to with no problems. We have a lot of hills and mountains where I’m at.

With the oversize tires the truck was never happy even when not towing.

If you can afford the diff changes – go for it. I’m sure that it would work well. I just couldn’t afford that procedure.

Yeah, next time 2500 diesel.

 

Thanks for your replies guys. I'll try to answer some of your thoughts here:

The tires on the truck now are stock size, although I would like to go a little bit larger when these wear out, probably 265s. I'll have to wait and see after these tires are worn out.

This is the 04 model, so it does have the 5 speed tranny. That gives me an advantage and a disadvantage. Since it is an 04, I don't have the tri-mode switch for the transmission. I only have a 'tow/haul' mode which when engaged, does not lock out 4th. If it would run in third only, I probably would be less inclined to change diff. gears. But from what I have found in my research, there's no way to lock the truck in 3rd. However, since it has the 5th gear, if I do install 4.56 gears, when I run empty with tow/haul turned off, I will still only be running ~2300 RPM @ 70 MPH.

When towing, with the tow/haul mode on, 4th gear will be at 2200 @ 60 MPH and 2400 @ 65. At those speeds, if it kicks down to third, it will run 2950 & 3200 respectively. That seems a lot closer to the sweet spot for torque.

As far as purchasing the Cummins, I had to make that decision back in 2000, when I bought my '01. That $5000 upcharge hit for the diesel just didn't make sense to me. So, I bought the V-10. I wish I still had that truck, but I got rid of it because of the empty gas mileage. I take at least one long trip per year running about 2200 miles round trip with nothing in the truck except hunting gear. That V-10 wouldn't get better than 10 MPG unloaded. I just didn't see the sense in that. Long story short, I'm keeping this truck until the half ton Dodge diesels have been out for a couple of years (just to make sure that they don't have problems). Then we'll probably upgrade, depending on how many gazzillion dollars they want for that new animal.

Long story short, I'm going to go for the gear change. I have two estimates so far and am going to get a third later in the week. The first was for $1500. The second was for $1350. If I can get it down to around $11-1200, I'll be happy.

Thanks for your responses.

Oh and as a P.S. - I realize that torque is not a constant and that HP and TQ change with engine RPM. However, the gears should do two things - #1 put the engine in a better part of the torque curve and #2 multiply that torque by something over 20%. Is my math funky here?

 

Your Chevy towed a similar weight in an easier fashion because the TBI 350 makes its torque basically right off idle. Your highway cruising speed just happened to take place at the peak torque, making it easier for it to maintain speed. My 92 GMC (extd cab 4x4) had only the 3.43 gears but towed a 6500lb load (Grand Marquis on U-Haul trailer) well -- not easily, but not badly either. That was certainly the most I'd feel safe attempting in that truck.

 

I have a 4.7 as well, rpounder, and the fact comes down to it, that even with a lower geared rear, although the truck will pull the trailer easier, you'll use more fuel to do it.

So this begs to be answered: When does a vehicle NOT become the right choice for your needs?

In this case, I think the 4.7 may not be sufficient for your needs, rather a vehicle that's built more for towing, like a larger gas V8 or a diesel. The 4.7 engine is an overhead cam motor, and they're not noted for good low-end torque, like an overhead valve engine that makes torque sooner, and at lower rpms.

I don't know about the rest of you, but I see guys that have a tow-specific vehicle for their trailers, and a daily driver as well, however,I can't afford both. When I bought my truck, I knew that I was only pulling 3000 lbs max for my trailer, so I wasn't concerned with getting something more then what I have/need.

A 5Klbs trailer isn;t the end of the world, but if you're doing LONG DISTANCE hauling, that's a different story. I tow a trailer with a racing motorcycle. Towing it to Pocono Speedway, 45 minutes from my house, is a completely different story then towing it to Summit Point Raceway in WV, or even Barber Motorsports Park in Alabama, this last May.

Same trailer, same truck, same gear and the Alabama trip (18 hours and the hills of VA) was almost unbearable. Summit WV, (4 hours) is bearable, but less hills.(Not the 4.7, rather, a completely different vehicle) This is exactly why I bought my Dodge 1500 with the 4.7 to use now...

I'm wondering if a 4.7 is too small for your needs with a trailer of your weight, and the distances you want to haul it.

Food for thought....

 

Have you tried any power adders as well, intake, exhaust programme, that might help manipulate the tranny by provideding more torque.