'97 F250 HD differential gear ratio - Diesel Forum - TheDieselStop.com
Power Strokes 1994-1997 General Technical discussion of topics related to vehicles powered by the Power Stroke engine in 1994 through 1997 models.

 
LinkBack Thread Tools Display Modes
post #1 of 13 (permalink) Old 08-11-2005, 12:50 AM Thread Starter
Member
 
Brianedwardss's Avatar
 
Join Date: Mar 2005
Location: Oregon City, OR
Posts: 78
My Photos: (2)
Feedback Score: 0 reviews
'97 F250 HD differential gear ratio

Hi, I just bought a 1997 f250 4x4, ex-cab, HEAVY DUTY, 5-speed.

Ok, this is the issue. My axle code is C5. the C5 code always has been the 4.1 rear end ratio. But, my truck is turning 2500 rpm at 70 mph.

the truck has 255/85-16 tires. doing the math, (5280/8.65 x 4.56 x.76 /60 x 70 = 2472) indicates that I have a 4.56 rear end. I had a buddy drive beside me on the phone and my speedometer was accurate!

does the C5 code on a 97 HD indicate 4.56???? I'd like to know cause for just being my daily driver, 2500 at 70 is way to low, especially with diesel prices the way they are!!!

1988 F-350 srw, Crew Cab, 2WD, 7.3L, Rebuilt C6, 4.10 Rear, Manual GP Switch, No Soup Bowl. Getting a 3.08 Rear Soon.

ASE Master med/hvy Truck Technician
Brianedwardss is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old 08-11-2005, 01:10 AM
Senior Member
 
Join Date: Dec 2003
Location: Tucson,Arizona
Posts: 671
My Photos: (0)
Feedback Score: 0 reviews
re: '97 F250 HD differential gear ratio

Not sure about your code or your math (no disrespect, I make mistakes all the time), my truck has 4.10 gearing and spins just below 2500 @ 70mph every morning. On the math part, I could not follow the "/8.65". Where does that come from? I assume the overdrive is .76.

BTW, I get better mileage running 65 or under, but I can't stand to go that slow. Getting right at 18.7mpg running 70mph.

Bill

Bone stock 94 1/2 DI turbo 4x2 F250, Rancho steering stabilizer to eliminate front end shake, sensor safe clamp mod, filler neck mod

Gun Control: The ability to consistently hit what you are aiming at.
Graduate, UA, Mech. Eng.
arizonian is offline  
post #3 of 13 (permalink) Old 08-11-2005, 09:14 AM
Senior Member
 
Join Date: Jan 2003
Location: Florida
Posts: 206
My Photos: (0)
Feedback Score: 0 reviews
re: '97 F250 HD differential gear ratio

My 97 Owners Guide has C5 as a 4.10.

2002 F250 Stock PSD Crew Cab SRW
1998 HR Endeavor MH w/275 Cummins Diesel and MD3060 Allison 6 speed

PREVIOUS TRUCK 97 F250 PSD 3.55 Draw-Tite Slider, pulling 2850RK Keystone Montana DIY Exhaust brake with TC Lockup
redtopman is offline  
post #4 of 13 (permalink) Old 08-11-2005, 11:36 AM
Senior Member
 
Join Date: Jun 2005
Location: New Jersey
Posts: 304
My Photos: (0)
Feedback Score: 0 reviews
re: '97 F250 HD differential gear ratio

I have a 1984 Chevy M1008 Pick-up running 4.56's and 235 85 16 tires. I can not even hit 70! The governor kicks in at about 3600 and I hit that at about 69 MPH. Your RPM sounds about right for 4.10's. I have 3.55's in my 96 and 265 75 16 tires and I run about 1800 at 70.
Rick

1996 F250 S/C, Auto, BD convertor, transgo kit, 3.55's, 285-75-16's, Switched 10k, 220K Miles
rickf is offline  
post #5 of 13 (permalink) Old 08-11-2005, 12:02 PM
Senior Member
 
Join Date: Sep 2003
Location: Washington State
Posts: 1,601
My Photos: (32)
Feedback Score: 0 reviews
re: '97 F250 HD differential gear ratio

Hey Brian!

I have been considering tires sizes and gear options so I happen to have thrown together a little spreadsheet...

Based on 4:10 gear, the ZF-5 OD ratio of .77, and 255/85-16 turning 629 revs per mile, the theoretic rpm at 70 mph is 2,316 rpm.

Reality when compared to the figures my spreadsheet generates has shown that if I add about 3% to the claculated rpm, I come real close to what the tach shows. Your calculated 2,316 ends up at 2,385. So if you are on the low side of 2,500 on your tach, you are probably calibrated about right.

For reference, if I plug in 4.56's with your OD and add the 3% factor I come up with 2,653 rpm...?

Last thoughts, the PSOM is supposed to be adjusted when you change tire size, though you say you have confirmed your speedo's accuracy.
Finally, you could jack up the rear end and (since the "C" in C% represents a locking dif you shouldn't need to block the opposite wheel) rotate the tire one revolution and see whether the driveshaft rotates 4 time (for a 4.1) or closer to 4.5 times (for a 4.56).

Good luck!

God Bless,

TC

97 F350 XLT, 4x4, Toreador Red, CC, PSD, MLE0, ZF5, 3.55 l/s, LUK clutch,Velvet Rides, ISSPRO gauges, v/cover vented to tailpipe, DPPI downpipe - modded to 4" right below firewall seam, open element intake using Duralite filter, coolant filter mounted between washer fluid bottle and jack, gutted EBPV, 99+ I/C installed using early 99 Y-pipe and custom pipes, 4-pos chip, BigBopper Seat Mod, Bilsteins, 130cc injectors, homegrown 4" exhaust, uses 36" Magnaflow muffler (Model #12773 body is a full 30" long - nice and quiet!) Custom Fuel System using Carter electric pump, Aeromotive regulator and frame-mounted filters...
2003 Tahoe MS27TT (27' Lite travel trailer), Prodigy Brake Controller.
1991 5.0 LX, runs 12.57 @ 109 mph
My Intercooler/Fuel System Install Webpage (section on CCV Mod too): http://members.localnet.com/~boys3/
TimC63 is offline  
post #6 of 13 (permalink) Old 10-26-2015, 12:19 AM
Junior Member
 
Join Date: Oct 2015
Posts: 8
My Photos: (0)
Feedback Score: 0 reviews
I have a 96 with the same problem. Can you tell me what RPM I would turn at 70 with 3.73 gears?
robervl is offline  
post #7 of 13 (permalink) Old 10-26-2015, 09:09 AM
Member
 
Join Date: Feb 2015
Location: Ky
Posts: 50
My Photos: (0)
Feedback Score: 0 reviews
It would take a long time just to breakeven on the cost to switch gears to save on mileage, especially on a 4x4. Of course it will tow and handle heavy loads much worse as well if you were to switch. If you are looking for mileage at the expense of tow/load ability not sure why you would buy a heavy duty diesel truck.

Take the number of miles you drive per year at 70mph, divide by your current mileage at that speed. That will give you the number of gallons you burn per year currently. Do the same calculation with your expected mileage with 3.55s. You can compare the gallons and decide based on the savings per year, i think you will find it will take 5-6 years just to break even. Remember not all your miles per year are at 70mph, and at lower speeds and stop and go etc you may actually have an advantage with the gearing you currently have.

I also have found that when i do the math for my 4.10s that it came out to something like 4.30. I figured out that if you measure the distance from the ground to the center of your hub with the weight if the truck on it, multiply by 2 to get the diameter of the tire, multiply that by 3.14159 to get the circumference of the tire, the divide 5280 by the cicumference you just found you will get the actual revolutions per mile rather than the optimistic manufacturer number.

Ths calculation involves mulitplying and dividing by big numbers, which means that very small measurement errors get multiplied and throw off your results, so the easiest way is to count the teeth on the ring or count axle rotations as was mentioned.

96 F350 CCLB SRW. 3 in lift. 3 in downpipe, 4 in exhaust, Tymar 6637 intake. Beans chip. Banks intercooler. 37gal bronco rear tank.
KYpatriot is offline  
post #8 of 13 (permalink) Old 10-26-2015, 03:59 PM
Junior Member
 
Join Date: Oct 2015
Posts: 8
My Photos: (0)
Feedback Score: 0 reviews
Quote:
Originally Posted by rickf View Post
I have a 1984 Chevy M1008 Pick-up running 4.56's and 235 85 16 tires. I can not even hit 70! The governor kicks in at about 3600 and I hit that at about 69 MPH. Your RPM sounds about right for 4.10's. I have 3.55's in my 96 and 265 75 16 tires and I run about 1800 at 70.
Rick
I have a 96 powerstroke with a 5 speed and it is turning about 2,350 @ 70 mph. I know it probably doesn't make much sense to spend the money on gears, but I used to have a 5.9 dodge that would turn 1,900 @70 mph. I know these are two completely different engines that make different torque at different RPM's. I don't think I would want to go to 3.55's but might be interested in going to 3.73's if it makes the RPM's around 2,000 @70 MPH. I'm just looking at a ballpark #. I currently have 285/R75/16's.
robervl is offline  
post #9 of 13 (permalink) Old 10-26-2015, 04:37 PM
Lifetime Supporting Member
Lifetime Supporting Member
 
bugman's Avatar
 
Join Date: May 2002
Location: Gypsum, Co
Posts: 7,078
My Photos: (12)
Feedback Score: 1 reviews
It wouldn't be worth going to 3:73's unless you needed to do that because of bigger tires. Trucks that have the 7.3 in them with 3:55 gears have very little problems until they try to get larger loads moving but owners compensate for the gears by going with more fuel from a custom burnt chip.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
bugman is offline  
post #10 of 13 (permalink) Old 10-26-2015, 05:20 PM
Junior Member
 
Join Date: Oct 2015
Posts: 8
My Photos: (0)
Feedback Score: 0 reviews
Quote:
Originally Posted by bugman View Post
It wouldn't be worth going to 3:73's unless you needed to do that because of bigger tires. Trucks that have the 7.3 in them with 3:55 gears have very little problems until they try to get larger loads moving but owners compensate for the gears by going with more fuel from a custom burnt chip.
Probably ok the way I am. Was there any noticeable fuel mileage gains with 3.55 gears?
robervl is offline  
post #11 of 13 (permalink) Old 10-26-2015, 08:16 PM
Lifetime Supporting Member
Lifetime Supporting Member
 
bugman's Avatar
 
Join Date: May 2002
Location: Gypsum, Co
Posts: 7,078
My Photos: (12)
Feedback Score: 1 reviews
3:55's would give you around 2 more mpg over 4:10's

These trucks like to run at 2000 rpm's or below for the best fuel mileage.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
bugman is offline  
post #12 of 13 (permalink) Old 10-27-2015, 09:04 AM
Senior Member
 
Patrick Feeley's Avatar
 
Join Date: Feb 2000
Location: Tehachapi, CA, USA
Posts: 10,288
My Photos: (19)
Feedback Score: 0 reviews
Just another data point: My 94 with 235/85-16E, 4.10 rear, and 5-speed ran about 2550 at 70 mph. Cheers!

97 F250 SC 4x4 (CA model), E4OD, 4.10 LS, Relocated Block Heater Plug, Ext Trans Filter, Tru-Cool Max, I/C Mounted but not Plumbed

SOLD: 94 F350 CC DRW, 5 Speed, SBC Con-O, Baldwin Filter, Tymar HPX Hose, 3 DP, Bilsteins, $12 AIC, Coolant Filter, Explorer O/H Console, Trans Temp, Boost, and Pyro, Pedestal Mod, Gutted EBPV
Patrick Feeley is offline  
post #13 of 13 (permalink) Old 10-27-2015, 10:08 AM
Senior Member
 
Join Date: Nov 2008
Location: Madison, WI
Posts: 1,863
My Photos: (0)
Feedback Score: 1 reviews
Quote:
Originally Posted by bugman View Post
These trucks like to run at 2000 rpm's or below for the best fuel mileage.
This has been my experience. Mileage seems to fall off a cliff at 2000 RPM. So the fuel economy gain really depends on your driving. If you drive at 55 MPH most of the time, the gain between 3.55 and 4.10 will be minimal, because in both cases, you're going under 2000 RPM. Same if you drive 75 MPH or more, because you're over 2000 RPM in both cases.

Now if you drive mostly between 60 and 70 MPH, that's where you'll see the most gain. The 3.55s will keep you below 2000 most of the time, whereas the 4.10s will have you at 2000 or above.

I like the 3.55s in our trucks simply because at 2000 RPM, it feels a lot less "busy" than it would at 2400-2500.
madpogue is offline  
Sponsored Links
Advertisement
 
Reply

  Diesel Forum - TheDieselStop.com > Ford Diesels > Power Strokes 1994-1997 General
Gear in this thread - Powered by O'Reilly Auto Parts

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Diesel Forum - TheDieselStop.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome