Ok here is the scoop, truck runs good lots of power but I want to put the rpm in the sweat spot when I'm on the highway I think I have d-70. I know I'm running 4:10 gears tire size is 37" my goal is 4th gear (ZF5spd) 3400 rpm 60 mph (currently running 2500 @ 60 mph in 4th) so what happens is I have to shift down to 3rd on the big hills loaded, (4000 @ 60 mph) pulls real nice but maxed out in the rpm range on the long climbs.
So my first question is how do you tell the difference between the d-70 and the sterling ( I was told it could be either d-70 or sterling) and the second question is has someone run the same combination and / or upgraded to other gear ratio. (p.s power plant is a 460 thus my rpm concern)
regards Domenico....

 

sorry about the typo guy's, the truck is running in the sweat spot I'm looking for the sweet spot, ha ha ......
regards Domenico....

 

i can almost garrentee you that you have a sterling. if i where you id check the Randys Offroad website and use there Gear ratio/rpm chart to find which ever RPM you want with 4.10s, then id put that smaller tire on it just to make shure that finall gearing is what you want. id do that just becasue it costs quite alot to regear to somthing that youl just want to change again, but if it where me, id go 4.88s or 5.13s since you want that added kick.

 

the d70 has the filler plug on the inspection cover, the sterling has it up by the pinion on the front if the axle......unless something has changed

 

Thanks for the info guy's, I will try that web site to confirm the proper required ratio.
Are there a good selection of gear ratios in both types of diff.s?, and or mojor advantages of either type. I havn't looked yet but it sounds like I have a sterling from what I can remember, would this be a good time to upgrade to d-7o or d-80 for that matter?.
regards, Domenico....

 

your stuck with the sterling acually, its a very sturdy axle though. you need it for the VSS sensor ontop the axle to run your speedometer (if you had an auto, it would also control the shift points) along with the ABS. any Fords dont acually rely on that VSS before 92 where ford got rid of the setup being ran off the T-case. but youll find that both front and rear axles will go as low as 5.38s (pleanty deep enough, overkill if you ask me). but the sterling has the same strength that you would get out of a D70 and 14B.

 

Sterling- 12 bolts around the cover. Dana 70- 10 bolts around the cover. Your '97 should have the Sterling 10.25" full-float.

Wow, someone who wants to gear even lower than me! I run 4.56's with 33's in my F350 with Sterling axle and 351W/C6 auto. My rpms at 60 in direct gear are about 3000. The truck tows pretty good with that gear/tire size combo. If I had an overdrive gear, my gearing would be perfect for all uses- fast highway cruising unloaded and mountain roads towing.

Your 460 revs a little slower than my 351 and the torque peak is at a lower rpm too. Torque peak for my engine is 2800 rpm. I think the 460 is 2400 rpm. I can see where you are bogging with 4.10's and 37's towing. The big tires are killing your towing power.

A change to 4.88 gears will correct for the 37" tires and bring you back to the effective stock ratio of about 4.10, which is a good gear for these trucks to pull with. My effective gear ratio is about 4.30 with the 33's and I feel that provided just the extra oomph I needed without over revving the engine at cruise, since I have no overdrive. Of course I don't cruise at 75mph either. 55-60 is where I like to cruise for better mileage.

According to the formula,

GearRatio = (RPM x TireDiameter) / (MPH x 336),

You would need 6.24 gears to spin 3400 rpm at 60 mph in direct gear (4th) with 37" tires.

Personally, I think that's too low a gear ratio (numerically high) for a 460 with 37's. I would gear it 4.88 or 5.13. 5.13's would put you at about 2800 rpm at 60 in direct gear. That's still about 400 rpm above peak torque rpm for your motor and should be plenty of power for towing. 4.88's will put it at about 2660 rpm at 60 in direct.

How much weight are you towing?

[EDIT]: By the way, your speedometer is probably quite a bit off because of the taller tires. You said you're spinning 2550 rpm at 60 mph in direct with 4.10's and 37's, but the hieght difference between 37's and stock tires is about 17%, so when your speedo says 60 mph, assuming it was accurate to begin with, you're actually going about 70 mph. Plugging the numbers into the formula,

MPH = (RPM x TireDiameter) / (GearRatio x 336),

2550 rpm with 4.10 gears and 37's equals about 68.5 mph. Your 37's are probably just a little under 37" actual diameter, accounting for the difference between 117% of 60 (70) and 68.5.

Your actual rpm's at 60 mph with 4.10's and 37's in direct gear should be about 2230. That's basically a good rpm to be spinning in Overdrive, not direct, which is probably the reason you are having to downshift to 3rd to pull the hills, since 2200 rpm is comming in below the peak torque rpm of your engine.

If you want to make some rpm calculations with your truck in different transmission gears, the ratios in your ZF 5-speed gas engine trans should be:

5.72, 2.94, 1.61, 1.00, 0.76, rev- 5.24.

Here's the formula for RPM:

RPM = (MPH x AxleRatio x TransRatio x 336) / TireDiameter.

If you know your tire's revs per mile, usually available on the manufacturer's website, you can use this more accurate formula:

RPM = (MPH x AxleRatio x TransRatio x RevsPerMile) / 60.

 

theres all the info i was too lazy to type, good job SoCal! i still think 4.88s would be a good choice for your tire size and demands. im probably going to go to 5.13s with my D60/sterling becasue its gonna be running 38s and i want my 351w to be able to move em

 

thank's for the info I must of spent 4 hours on the internet last night looking for that fomula (never did find it).
I was leaning towards the 4:88 but now I can crunch the numbers and see what happens, I did re-calibrate the the speedo but I over shot the the math and ended up 10 k over @ a 100kph (8mph over @ 62mph I think that translates) never did re-calibrate. From what I found out the instrument cluster can only be programed 5 times then it freezes and has to be replaced to re-program, so I thought I would do all of the gear changes first then try it again.
I did make some phone calls today and found 4:88 and 5:13 ratios available, my parts guys told me I had a 10.5 sterling (10.5/10.25 ?)
"Quality Gears" was the brand, never heard of them any input on the brand would be appreciated.
My plan is to replace the rear set run a couple of trips confirm I'm happy and then do the d-60 up front.
As for towing weight hunting trips: 8.5foot camper towing a suzuki samurai and full gear for 3 weeks est. 12500 lbs, camping trips:same camper 9' trailer and 3 dirt bikes and all the gear needed for me the wife and 3 kids ( some times if feels like we are moving every long weekend) est weight 11000lbs.
I know it dosn't sound like a lot of weight but it's those dang rocky mountains that get in the way.
Please feel free to do the math and give me your opinnion on the gear ratio of your choice, ( ps most of the time it's used for hauling my hunting / camping gear around,
with the mods I have done it pulls hard from 2800 to 4000 rpm)
Regards Domenico....

 

Domenico,

Your '97 truck has the 10.25" axle. The 10.50" axle came on the '99-up Superduty F250/350SRW truck and has rear disc brakes. The gearsets can interchange on the 10.25 and 10.50 though, from what I hear.

Your speedometer will not be effected by the gear change. It is electronic and takes a reading from the rear axle vehicle speed sensor, which reads from a 'tone ring' attatched to the ring gear. Only tire size will effect the speedo, not gears.

I have not heard of 'Qualit Gears'. I know there are a few good brands: Precision, Motive, Superior, Richmond, Dana/Spicer, and Yukon. I have heard Genuine Gear is a brand to stay away from, something about Chinese steel used in them. I used Dana/Spicer gears in my front Dana 60 and Precision Gears in my rear 10.25". They were about $275 per axle for 4.56's. I could have gone with cheaper gears, but I only wanted to do it one time and do it right. I have no regrets about going with the expensive gears .

If that's 12,500 lbs + the weight of the truck (about another 6500 lbs), I would go with the 5.13's, since you are over the 16,500 lb GCWR for the truck and trailer together.

How does your truck handle with the camper on with the 37" tires and lift kit? Mine does alright with stock suspension hieght and 33's with my 8' slide-in camper in the bed. I put on Rancho 9000 rear shocks and polyurethane sway bar bushings and with the tires aired up to max pressure in the rear it feels fairly stable on the road. I plan to raise up my overload springs to get them to contact the stops sooner for more stability in the future and may add a leaf or 2 more in the main packs too so it rides a little above level instead of a little below level when loaded. It actually feels more stable with the camper on and trailer hooked up than just with the camper because the trailer tongue weight pushes the truck down more onto the overload springs. That's why I think raising the overload spring (or lowering the bump stops) will help stabilize it better. I haul dirtbikes and atc's on my trailer too and sometimes haul the Bronco on a flatbed trailer. I understand about the mountains, we have some mountains between here (the coast) and the desert to go over too. I'm real happy with the lower ratio gears in this truck .

-Glen.

 

the 10.5 is an axle that only came in the new Superduty trucks and never had drum brakes on them anything 97 and older will have a 10.25 till 86-87 ish where they go back to using D60s and D70s.
For quality, id go with Spicer R&P sets along with bearings, that in my opinon is the best way to go, if not id go with Yukon gears, im not too shure about them though. anyways goodluck!

 

huh...too funny, we both responded in a simular way at practicly the same time.

 

Thank's Stokes and SoCalDesertRider for the quick response. (great minds think alike?)
I should of been more specific on the weight, I was talking total rolling wieght.
As for the truck and the way it handles not a problem, when I did the mono beam coversion I added all the extra leaf springs and over load springs from the doner truck a 90 f-350. I do have a 2" body lift to boot, (lerned from my last truck that if you install a body lift, fabricate and install the missing spacers between the box and the frame if your going to use it as a truck) as for tires I'm running the milatary isssue michelin 9.00 16 xr, rated @3970lbs per tire ( total over kill in the tire department) but @ 60psi those tire are solid on the highway (max psi is 80) I also run the rancho 9000 on all 4 corners (awsome shocks), I also installed those polyurathane bushigs.(it's amasing how all these little things add up to good handling. As for the speed sensor I must of had a brain fart when I came to that conclusion, I should of known better
I will make some calls and confirm the interchangeability of the 10.25 and 10.5 ( and still the question 4:88 or 5:13?)
Regards Domenico

 

Domenico, since you're only talking about 12,500 lbs total combined wieght, I think you'll be fine with the 4.88's. You can still go with the 5.13's if you want a little more goose on the hills and gettin up from a stop. My Reider Racing catalog lists the same part number for 10.25" and 10.50" gear sets. Check out www.reiderracing.com or www.precisiongear.com. You need to know if your rear axle is a '92-down or '93-up to get the right gearset for it.

Stokes, looks like we're both on the same page!

 

OK guy's I bit the bullet today went out and ordered new gears (for the rear diff.) did the math and came up with 5:13 as the optimum ratio (you can always get bigger tires, that's my theory) got a fair price on yukon gears, from what I found out the quality is not bad either.
So now we sit and wait........
Regards Domenico