Gear question

jban126_f350 · Feb 6, 2015

I have a 6.0 running stock gearing now and I'm adding power to it but I'm also running on 37" tires what gearing would I need to swap to to get better performance with 37's? I have 3.73 right now. Don't really know about the gearing and stuff. Also where is a good place to buy a kit when it comes time? Also if I were to re-gear will it make my speedometer more accurate? New to gear ratios.
Thanks Jacob

cbf9703 · Feb 6, 2015

Yes, re-gearing can make speedo more accurate if you make it closer to the stock ratio with your 37s. What are you looking for by "better performance"? Are you looking for more responsive down low? Lower cruising rpms on the hwy?

Go with name brand gears (like Yukon, G2, etc), the cheaper ones can be noisier, IMO not worth the money you save for an on-road vehicle. I don't know your local area, but while you can find kits online it might be worth your while to have an offroad shop take care of the install if you're not that comfortable with setting up a rear end.

I order my gears and rebuild kits from Randy's Ring and Pinion. Save yourself the aggravation and make sure you get the master rebuild kit.

jban126_f350 · Feb 7, 2015

I can rebuild it. My problem was just finding what ratio is best for me. It's a daily driver with some competition and higher performance mods with 37's. I will be driving hwy a good bit. I just don't know what my options are but I will look into those brands thank you

jban126_f350 · Feb 19, 2015

Looking at 4.10's or 4.30's I currently have 3.73. Might sound stupid but is it a d60 or d80 in the rear. Also is the front a ford 10.5? Will this work? Anyone know any pricing? Looking to install it myself.

RedRice589 · Feb 19, 2015

You have it backwards. Rear axle is a sterling 10.5 and the front should be a Dana 60 I believe lol Dana 80 is a dually

swinky · Feb 19, 2015

4.30 if it was me.

Powerstroke Man 6.4 · Feb 20, 2015

jban126_f350 said:
Looking at 4.10's or 4.30's I currently have 3.73. Might sound stupid but is it a d60 or d80 in the rear. Also is the front a ford 10.5? Will this work? Anyone know any pricing? Looking to install it myself.

Sterling 10.5 in the rear for F-250/F-350's SRWs. Dana 80 in the rear for F-350 DRW's. Dana 60's front axle for all trucks except for F-350 wide track drw and f-450's drw's which have Dana super 60's.

timj · Feb 20, 2015

Re-gearing it will obviously help get your performance back, as well as helping your trans live longer with bigger tires. It won't however change anything with the speedo on any truck that gets its speedo reading from the ring gear such as your truck.

tbsimmons · Feb 20, 2015

Gearing will have no effect on your speedometer, the sensor is on the ring gear. Tires is only thing that will change the speedometer.
If you tow, 4.56's, if you dont 4.30's.
I had 4.56's wtih 35's in my 04 and loved it, but I towed a lot. Unloaded the RPM's were a little high but I didnt mind it.
My dually had 4.88's with 34's. So its even higher, but like above tow a lot.

jban126_f350 · Feb 20, 2015

Yeah I'm not to concerned about the speedo anymore because my new tunes give me the option the change that. But 4.30 would run to hi on the highway? Will it fit ok in my rears? I've heard it won't fit in there if it had 3.73

RedRice589 · Feb 20, 2015

jban126_f350 said:
Yeah I'm not to concerned about the speedo anymore because my new tunes give me the option the change that. But 4.30 would run to hi on the highway? Will it fit ok in my rears? I've heard it won't fit in there if it had 3.73

I cant believe the crap other people will tell you. If you buy a gearset for the correct axle it will fit. Had 4.10s in my 6.4 with 35s and loved it. If i had 37s itd have gotten 4.30s. Theyll fit just fine if installed properly. Just dont be surprised when they quote you for front and rear gear swaps. I had no other option but to use the dealer because the two good shops in town couldnt lift my truck up on their lifts lol hit me with 2300 for just a rear end and an oil change.

TyCorr · Feb 20, 2015

Wow, you guys run super tall gears...

Id maybe run a 4.10 with 37s...4.30 is too much....you'll be running 2500rpms on the interstate or higher...

I dont agree with gearings accepted rules for tire size increases. I find stock gearing to be sometimes high for cruising at 75...which is fine if you dont do it for long periods.

I run 3.73 and 35s....it was fine with stock tuned power and with 450 hp worth of fuel it was perfect even towing. With 550ish its not even a thought lol.

One place id say its ok to "overgear" a truck to 4.30s running a 37 is if you run two lane higways and just jump from one town to the next. The extra pull down low would be welcomed.

cbf9703 · Feb 20, 2015

timj said:
Re-gearing it will obviously help get your performance back, as well as helping your trans live longer with bigger tires. It won't however change anything with the speedo on any truck that gets its speedo reading from the ring gear such as your truck.

tbsimmons said:
Gearing will have no effect on your speedometer, the sensor is on the ring gear. Tires is only thing that will change the speedometer.

Thanks for saving me from myself! Correct on the gearing having no effect on the speedo for this truck. I've been so focused on my older projects I didn't think before I posted. :doh:

Guys help me out if I go wrong here: the variable speed sensor (VSS) counts the teeth on the tone ring as the axle (& tire) turns, and sends that count to the ABS module. Each time the VSS counts to 120 (number of teeth on the ring), the ABS module knows the tire has turned one revolution. The ABS module has a stored parameter for the number of tire revolutions needed to go one mile (tire revs/mile) based on the stock tire. ABS counts the number of tire revs, and every time it counts the number in the parameter, it knows you have traveled one mile. The problem here is that stored parameter. IIRC, my '03 stock parameter is like 655, while 37s are like 570.

BBottoms · Feb 20, 2015

4.30s would increase your RPMs by 15% so 250-300 rpms at highway speeds.

4.10s increase by ~10% so 150-200 rpms at highway speeds

BBottoms · Feb 20, 2015

You might check around local salvage yards for axles from a gas truck. They'll bolt right in and came in 4.10s and 4.30s. The 4.30s are harder to come by but are out there. You might be able to pick up a set for cheaper than you could buy gears and install kits then pay for the labor. Then you could turn around and sell your old axles or keep them in case you ever wanted to swap back.

suprhlr · Feb 20, 2015

jban126_f350 said:
Looking at 4.10's or 4.30's I currently have 3.73. Might sound stupid but is it a d60 or d80 in the rear. Also is the front a ford 10.5? Will this work? Anyone know any pricing? Looking to install it myself.

If you don't even know what the axles in your truck are, I would recommend having someone else do the gear swap.

scparrish · Feb 20, 2015

rpm = (speed x (axle gear x od gear) x 336) / tire diameter

OD Gear - .71 (trans over drive)
Speed - Average highway speed, I usually plug in 70

4.30s will put you back into the factory rpm band with a 37.

jban126_f350 · Feb 20, 2015

suprhlr said:
If you don't even know what the axles in your truck are, I would recommend having someone else do the gear swap.

I've swapped gears in a rear multiple times someone told me 4.30 wouldnt work in my rears. So I was just checking to make sure I don't have to buy another rear(s)

jban126_f350 · Feb 20, 2015

scparrish said:
rpm = (speed x (axle gear x od gear) x 336) / tire diameter

OD Gear - .71 (trans over drive)
Speed - Average highway speed, I usually plug in 70

4.30s will put you back into the factory rpm band with a 37.

So you think 4.30 will work good with 37's get some of my horsepower back. I wanna re gear so I don't have terrible turbo lag off the line