Intro - Gearing Question

For the cost of the gear swap (unless you setup your own r&p) you have that transmission built. This your first diesel...gearing is not as important as a gasser rig and your going to kill any economy by over gearing it....

Build the transmission, get a good tune, open up the exhaust and gauges to monitor things.

I think you'll love the FWC Hawk. I had one for about 5 years and loved it. Only reason I sold it was our newborn filled the back of it with toys! Then we decided to have another kid. No way were we fitting all that stuff in. The flatbed Hawks look awesome, you'll have more room than I did.

Agreed with your statment of increasing the COG. These are relatively light campers with almost no weight above the cabover section. I offroaded in Moab with mine on the back, I didn't feel any more tippy but I wasn't doing extreme offroading either.

They sure do weight alot more than the factory states. I think they just use the shell weight of 795lbs. Mine was loaded and more about the 1200lbs. With gear, water and batteries, we were around 1600lbs (only 10gal water tank). Only 400lbs more but that's 50%, loaded for bear, I was 100% over initial dry weight.

How much twisting will happen at the camper will depend on how your tray is mounted to the truck. If you can have it mounted at three points, you will have little tray and camper twisting even if the truck frame does.

Thanks for all the responses guys. This a really active site, and I can see myself coming here a lot for opinions of people that have been doing this a lot longer than I have. I'll mention couple points to clear up confusion from some of the replies.

- The camper is relatively light weight compared to most, so I'm not really concerned w/ the increased CG associated with the larger wheels and tires. The bed height will only be increasing about 2" above stock (from the frame rail) Hopefully experience will prove me correct.
- The camper is designed to be bolted down. Being a flatbed model, there are no other places to attach to. Frame twist does bother me a bit, but the manufacturer assures that is is acceptable.
- I've heard from many people that the 4r100 is the relative week link in these trucks due to the power available from the engine. Gears will definitely mitagate that somewhat. Even if I can build more power to overcome the lower that factory gearing created by larger tires, I don't see that as the proper way to use that power. I'd rather have the gearing set up as it would have been stock, and any extra power is power that will improve towing/driving that much more.
- With the 35" tires, new 4.10 gearing will be the same as stock 3.73 gearing. 4.30 gearing will be similar to stock 4.10 gearing. Even with 4.30 gears and 35s, the RPM at 70MPH will only be ~2,085. Still very acceptable for the 7.3 in stock form.

Here is an example of the camper on a newer Dodge with a similar flat bed:



Don

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Vinsil wrote:
Had a 95 F350, 4x4, powerstroke, 5 speed, 3.55's and ran 35" tires.

Found that the powerstroke was most happy at 1800-1850 rpm fuel mileage wise. Once it started to turn over 2k, whether due to speed or downshift for hills, it sucked down the fuel.
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X2. My last 7.3 had 4.10s and even with 285s I felt it was geared too high. Anything over 2k sucks the fuel.

My current 7.3 is a 2001 SC LB with a 7.3 and 6 speed with 3.73s. Also around a 3 inch lift. WIth 35s it did great with a camper and trailer, loaded to 18.8k lbs. I recently put on 33s (305s) because there were no 35s with a high enough load rating, and lowered the front end an inch to compensate for the camper. It also rubs the inner well less with the 305s.

Make sure you keep a little rake in the truck, and also make sure you get tires with a rating of 3700 or more.

Keep the 3.73s, especially if you are getting a chip.




Here's with the 35s



And 33s with a little lower front.

Logically speaking, the stock effective gearing is set up to do everything the truck is rated to do with stock 3.73's and stock tires. If putting the 4.10's in with 35" tires maintains that same effective gear ratio, towing and hauling performance will be about the same.

Be aware that you will need a heck of a ladder to get up into that camper. Your flatbed is going to be pushing 4' above ground level, as it sits higher to begin with, plus the 4" lift and 2" more from the tires.

I feel the 4R100 is your weak link in your drive train and the 4.10's will stress it less. You may have CG issues with a lifted truck while carrying a truck camper and may have to spend money on front and rear stabilizer bars and heavier springs to counteract the leverage you create with a lift.

My 6.0 PSD with 5R110 and 3.73's did great with 33" tall tires while over 19K lbs GCW. I had more power than you and an extra gear, but I also live in the west where 3000-5000' mountain passes are within 100 miles of me.

Don't waste your $ on re-gearing. Especially if you plan on bumping up the power a bit. It's already a decent HD diesel. It has enough power to haul a camper especially a small one like you're quoting, with ease. Going to 35s isn't a huge jump in tire size. Yes the truck will seem anemic, stock, compared to all the newer diesels, but gearing isn't the answer unless you're really working the truck by towing heavy. There really isn't anything you can put in the bed that the truck will physically haul without severely overloading the suspension and or axles that will slow it to the point of needing to re gear to maintain speed.
By the way, nice find on a super low mile 7.3. They're getting rare
And the several thousand you'd spend on re gearing will go most of the ways towards a built trans when you need it.

Had a 95 F350, 4x4, powerstroke, 5 speed, 3.55's and ran 35" tires.

Found that the powerstroke was most happy at 1800-1850 rpm fuel mileage wise. Once it started to turn over 2k, whether due to speed or downshift for hills, it sucked down the fuel.

Carried a 9.5' Fleetwood for a few years and towed a toyhauler that hit 10k or so. Gearing wasn't too much of a problem. My truck was tuned, exhaust and intake. your truck already has more power than mine did....I wouldn't waste the money on gears for 35's....you won't see really any gains the tires won't put much more stress on the drivetrain.


Try it out, this being your first diesel....learn to drive it first...you will be surprised compared to gasser's.....also, look at tuners before injectors, I believe your injectors are good for 350 horses....injectors aren't cheap and 7.3's eat your wallet alive if your wanting to chase the horsepower.....

I can't really answer the diesel questions, since my truck has a V10 gas engine, but I do have 35" tires with a 4" lift and 4.30 gears. I don't feel like the lift makes my rig unstable, but my camper is probably under 3k pounds fully loaded. I also tow a trailer with it that I would guess is close to 8k pounds. I have plenty of power, even in the mountains. Yes, the transmission shifts out of overdrive on hills. Sometimes it downshifts even more than that. But that's what it's supposed to do. Doesn't bother me a bit.