2nd Gen Non-Engine/Transmission Gears and the highway-anyone?

[Lightfoot]

My '96 2500 has an AT with 354 gears. I recently pulled an empty 5120 lb. , 21' Desert Fox toy hauler up from Oregon. The 354 gears are great when the truck is on it's own, but seemed a little tall for pulling even the empty Desert Fox. Think I only got 11 mpg. I am reluctant to go to 410's, prefer a higher crusing range. Is there a 372 or 373 series gearing that will work for my '96 ? Will it help the pulling situation enough to make the switch worth while,or do I really need to go all the way to 410 gearing? Any help is much appreciated.



'96 2500, AT,4x4,quad cab,4"exhaust,high flo muffler,PowerLock reardiff. ,PacBrake,OffRoadTech bumpers,12000 lb. Warn winch

 

[jandtjil]

I am pretty sure you can get a gear set in 3. 73.

Not knowing what tire size you run, I think it depends on how often/far you pull whether the cost of making two swaps is going to be beneficial. Having pulled heavy from N CA to Colo once, I can sympathize. Lots of 2nd gear under 60 gets old, quickly. The alternative is toasted AT. If I pulled more I would defintiely consider it.



JJ

 

[BElting]

Is the motor stock? I recently pulled a 7,000 pd trailer up the Grapevine on I5 @ 65 mph and never came out of 5th. Same rear gears as mentioned but the ratio on the auto is . 69 I believe, vs. . 74 on the 5 speed. I run stock wheels with a 235/85/16 tire. Still it should handle the trailer in direct. What kind of boost readings are you getting on hard pulls? I agree with jandtjil, on the gear swap, a whole lot of money for the slight gear improvement. Fuel mileage with the 3. 5 is hard to beat as mine routinely runs 20. Barry.

 

[Lightfoot]

Yes , except for a 4" exhaust system the engine is stock. Tires are 265 75 R16s, stock wheels. The truck will make two, possibly three runs into Mexico from Wash. with the toy hauler loaded to around 8000 lb. GVW. When it makes the runs it will have a fuel plate and injectors to boost the power, plus gauges, none of which it has now. With the power increase can the truck make it with 354 gears ? Seems like the egts will still be a problem. That is why I think 373 gears could be an egt, milage and transmission saver. Also, my question is still will the 373 gears be enough of a gear drop to get the job done? We're going to put a Tork Loc and pressure boost on the converter and transmission, which has been rebuilt and is very strong. Jars your body when it shifts. Any help will be much appreciated.

 

[jandtjil]

this is a tough choice!

I am a bit shocked by the numbers, I though it would be more dramatic between 3. 54 and 3. 73.

Using the link http://www.4lo.com/calc/gearratio.htm and using 65 mph. It appears that 4. 10 will add about 270 RPMs over 3. 54 if I added the right numbers, while the 3:73 will add about 100 RPM. Hopefully someone can comment on the EGT reduction 100 RPM can make, I am guessing it is minimal.

I too love the top end the 3. 54 supplies when running light, but the 4. 10 does appear to put the power right in the sweet spot. Putting in 3. 73 and still having to drop down to 2nd or to start causing premature AT failure by driving through OD would not be good.

When I bought my last set of tires I briefly considered going to 245 to gain some RPM, couldn't do it, too much wheel opening for my ego.

 

[LandShark]

Prior to spending tons of cash, put in a low level fuel plate and crank the star wheel about 15 to 20 turns. Made a huge difference for my truck when hauling a 3600 pound camper. No more down shifting on big hills!



11mpg seems a bit low for your truck with a 5100# trailer, but it mostly depends on how fast you're driving.

 

[Lightfoot]

Land Shark,thanks for the input. Yes,you are pulling the hills without the speed drop due to downshifting with the fuel plate and 354s but whats the egt story, how does the AT like it? If youre not using gauges, are you seeing a water temp rise toward the top of those grades ? I was. But still, I definately will run a modest fuel plate and possibly injectors. Maybe not on the injectors, this stuff is starating to add up.

 

[Lightfoot]

jandtjil, your comment:" Going with 373s and still having to drop down to 2nd or to start causing premature AT falure by driving through OD would not be good. " My AT is 3 speeds with OD. What I was having to do was drop out of OD into third to keep the egt,trans temp down. Was this what you meant? Thanks for your gear/rpm formula. Randy's Ring and Pinion came up with the same numbers that you did. A friend of mine has an '01 with 410s and insists that this is the ratio for my truck. But his is a 24 valve, and they run 500 rpm higher at the sweet spot. Both of our trucks are ATs. My 12 valve likes 1775 to 1800 RPM. If 373 gears will give me 1800 to 1900 RPMs @ 65 mph whats the problem ? The load factor ? I'm still thinking on this, maybe 410's are in the trucks future. I just keep thinking back to my '85 Ford 7. 3, (we dumped the 6. 9) and it's 410 gears. 2900 RPM at 60mph, what a nightmare. They tell me that 410 gears in a ctd is quite a bit different because of the TC . and OD. , so I'm still mulling it over.

 

[MPalachuk]

My dad has a 97 3. 54 manual trans, engine has a 10 plate. Had egt issues then we put a 4 inch exhaust on and no more egt problems. With this he pulls a 27 foot 5th wheel with no probles. His fuel mileage is around 13 give or take on average, Does go lower or higher depending on how he runs. How fast were you going, Speed kills mileage. sounds like there is some sort of a problem.

 

[klaybus]

Gears

High Miles,

I too am considering a gear swap. I'm running 3. 5s & they kinda suck for towing. On my truck (24 valve) I pull in 3rd direct (no OD) & get by, but on large curving roads I can still run into problems if I have to slow down or stop. Keeping the EGT's in check & or boost up to keep the EGT's in check can really be one heck of a balancing act. Add to that, keeping the water temp in check.

Gets frustratiing sometimes. With my 24 valve I routinly pull in the 2250 rpm range to maintain 60 mph. 4. 10s IMO would be the way to go.



Good Luck,

Clay

 

[Lightfoot]

MPalachuk,

Does your dad drive much in hill country at say 65 mph? That is where the overtemp seems to happen with my 354s, auto trans, and trailer. I run 4" pipe also. The issue I encounter is not a problem with going a steady 65 on hilly freeway country, its a phenomina called other vehicles, which seem to somehow inhibit that steady 65. Suddenly you're boxed into a long grade in overdrive at 60. That doesn't cut it with 354 gears and an AT. And, with my 12 valve, neither does prolonged driving at 60 in third at 2300 RPM. , which is the alternative. Both drink the diesel but the second is the lesser of two evils for my truck. The 11 mpg. probably came from a combination of long grades at 2300 and eating up the flats at 70 to 75 with a tall trailer. Though it is only 21' the Desert Fox tops out at 11'6". I was in a hurry on that run. On it's own the truck gets 19- 20 mpg on the freeway 14-15 in town. We just pressure tested the trans at 90 lbs in gear at idle so it will handle a hefty fuel plate. Still hate the idea of 410 gears. I may just run east of the mountains on desert highways with 354s to avoid that freewaylock up driving, and the change to 410s. Thanks for the input.

 

[jandtjil]

Q ) My AT is 3 speeds with OD. What I was having to do was drop out of OD into third to keep the egt,trans temp down. Was this what you meant?

A ) Trans yes. I read a thread a couple years back that suggested keeping RPMs up to keep pressure up and increase the life of the stock trans when pulling heavy. I have followed that advice religiously, when pulling moderate to heavy I do not let it get below about 1600-1700RPM in OD. Until last week my truck was completely stock so EGT was never an issue.



Undoubtedly, installing 3. 73 and still having a heat issue would not be good, you would never hear the end of that from the financial advisor :-laf



Not to throw another log onto the fire, but can the 3. 73 change be adjusted for in the electronics, or does it require an aftermarket box? obviously the 4. 10 can be.

 

[bkroupa]

I just bought a 3. 54 rear end to replace my 4. 10's, but I'm running a 5 speed.

My truck is mild but tweeked a bit (see sig). My trailer is simular weight & If I towed all the time I would've kept the 4. 10's with the 285 tires, but I drive empty 98% of the time & I'm always looking for 6th gear on my 5 speed.

3. 73 gears are available but expensive, you should be able to buy a complete 4. 10 rear axle for $500 (mine's in the classifieds I think with your steeper overdrive you might like them, but for me I just could'nt stand the engine screaming along at 2300-2400 rpm on the hwy running empty even with the b-quiet sound deadener.

 

[GAmes]

My '96 2500 has an AT with 354 gears. I recently pulled an empty 5120 lb. , 21' Desert Fox toy hauler up from Oregon. The 354 gears are great when the truck is on it's own, but seemed a little tall for pulling even the empty Desert Fox. Think I only got 11 mpg.

Weight has little to do with mileage when pulling an RV, wind resistance is the fuel sucker. Toy haulers are the worst of all the RVs for aerodynamics, that big back door creates a powerful suction when going down the road. If I got 11 mpg pulling one at 65 or 70 I'd be one happy transporter. I pull everything at 60 which is about 1900 rpm with my 5 speed and 215/85R16 tires and on a good day see 11 mpg with a 21 ft Desert Fox. I honestly get better mileage with a 10,000 lb triple slide Alpenlite 5er. An easier alternative to 4:10s could be 215s instead of your 265s. At any rate the best you will probably see is 12 mpg, maybe 13 but I doubt it. A 2 mile per gallon increase would net you 3 cents per mile in savings at $2. 20 a gallon. So if a gear set change was $500 you would only need to tow the trailer 16,667 miles to pay for it.

 

[LandShark]

high miles: No gauges in my truck, so no idea of egt's. I had my truck in Texas for 7 years and would run (with camper) between Dripping Springs and El Paso (and north) several times a year, often in temps over 100 degrees. Never had any over heating problems. After installing a 230/605 plate I could do the trip without any down shifting. Prior to the plate, the auto would down shift perhaps a dozen times going up the hills of west Texas. I've never seen the temps go out of the normal range in all the years I've had the truck. I usually run at 60 to 65 on the interstate and get about 15. 5 mpg. Running empty, either in town or highway, I get about 20 mpg. I also pulled a ranch trailer a few times (Austin area) loaded with 5000 pounds of rock, with another 3000 pounds in the truck bed, in 110 degrees with no hint of overheating.



I don't recall many overheating problems on the TDR over the years. EGT's are often a problem, but not water temps.

 

[pwknapp]

I ran hot shot for over 420k with 4. 10's. I wished every hour for some 3. 55's. 2450 rpms @ 70 for a few years. Sure would have been nice to cruise home at 1950 rpms. I've left the business and have increased tire size for a better highway rpm. Adding hp and associated "cooling parts" has made pulling anything a nicer venture. With all the added hp and an increase in tire size from 215's to 255's my mileage has gone up from 13. 4 to 16. 5 at 70-75 mph. JM. 02

 

[MPalachuk]

High Miles, We like by Yakima Washington It is pretty close to the center of the state. We cant get out of the area with out some pretty good pulls, Long and steep. He has said that if he runs 65 to 70 he notices a drop in mpg. He has talked about some heat still but not as bad, If he down shifts and gets his rpm up his pyro temp drops down to something like 750. We dont now where the timing is but that can make a difference. Also have you cleaned between the aftercooler and the radiator? We have seen many with alot of junk in there slowing down airflow. good luck and let us now

 

[RustyJC]

On the 2nd gen dually with LT235/85R-16Es and the NV5600, 70 MPH with 4. 10s = 2350 RPM. 70 MPH with 3. 54s = 2000 RPM.



The 4. 10s are excellent for towing heavy as we do (and, in my truck, are worth an extra 1500 lbs of GCWR). The 4. 10s, however, leave me always wanting a 7th gear when running empty on the freeway. If I ran empty more often, I'd probably spring for a U. S. Gear auxiliary OD.



Rusty

 

[Balzac]

I have 3:55 rear, 250 RWHP, and pull 16,000#'s. It is awesome at 75mph or faster. I am now switching to 03 -3:73 complete rear end with disc brakes.

Have looked at all options and this is the one that gives the two changes I need. Much better stopping power, and the ability to tow my fifth a little slower and remain in OD.

You would have to do the trans. upgrades, my DTT is awesome. My towing mileage is 16mpg Imperial or around 12 in US mpg. EGT never over 1200 F

Did add an air scoop on the hood feeding into the AFE filter.

 

[Bart]

If it'll help anyone, I found a vehicle speed vs Enginge speed (rpm) chart at

http://dodgeram.org/tech/specs/axle/47auto.htm