Axle code 85

[hat_man]

Hello all.

I haven't posted here in quite some time. I still come in and look around from time to time though.

My old '97 Ranger finally died and I bought a "new" '03. From the reading I have done here I am wanting to swap out the rear end to one with the 3.55 gears. I'm sure this comes as a surprise to most here, but let me explain. My daily drive to work is anywhere from 90-120 miles round trip on almost all two lane blacktops at 55 mph. Occasionally I'll end up on the interstate at 65 but only for 5-10 miles at most. My current Ranger is a 2003 XL with the 2.3L and a 5 speed manual and a 7.5" rear with 3.73 gears. At 55mph I'm cruising at about 2k rpm and currently getting 30 mpg in the winter and 33 mpg in the summer. Most would say "Don't mess with it." or more often than not "There's no way you're getting that. You can't do math." I've been tracking my mileage for years and have figured out how to drive the truck for mileage.

The one thing I have noticed is that when I am going from a 45 zone to a 55 zone the engine really settles down and is almost un-noticeable at around 1800 rpm. It's smooth as glass. I can only guess that it is at it's most efficient point in that range. The center of the BSFC "island" if you will. The problem is, at that rpm range I'm at about 48-50 mph and I'm not going to be the one holding up traffic. After doing the math I find a 3.55 puts me in the 1850 rpm range at 55 mph. Seems perfect for my situation. The 3.55 was offered in a few configurations so that is what I'm looking for. I know there was a 3.45 in the 7.5" but I believe it was only offered in the older models that got it's speedometer signal from the cable on the transmission and a specific speedometer cable gear on it's end. I believe mine gets it's signal from the rear end so a 3.45 is probably a "no go" situation.

The questions I have are this......

1) From the reading I see the 3.55 offered in 7.5 open (axle code 85). Does this rear end send the speedometer signal or is it like the old ones that don't do that? If it does send the signal, this is what I am going to look for. Seems like the easiest to swap in. (Same question for the 3.45 open 7.5" but I'm pretty sure it doesn't.)

2) If the answer above is NO then my next option is a 3.55 in an 8.8" rear (axle code 95). This one I'm pretty sure uses the rear end to signal the speedometer and from what I can see should bolt right in. I keep seeing conflicting information on the flange being compatible. Can anyone confirm or deny this?

3) I see a limited slip 3.55 option available in both 7.5" and 8.8" (axle codes F5 and R5 respectively) and a 3.45 limited slip option (axle code F4) in the 7.5". Would these be basically "plug and play" or are there lots of modifications that need to be made? Would they work at all? Are they rare and hard to find?

4) It would be a bonus if any of these options came with disc brakes but if not, I'm not all that worried about it. Any insight on this?

I want this to be as simple as possible without tons of mods and cutting and welding, so the Explorer swap is probably out. Not that I can't do it, I just don't have the time. I work 58 hours a week over 6 days. Down time is at a premium. I would prefer the 3.55 to the 3.45 but would be willing to go with the taller option of it's all I can find. The 3.45 is about 50 rpm lower so I guess I could go just shy of 60 on the blacktops to get back into that 1800 rpm range. Maybe not all that bad an option? 3rd gear in town might be a bit low on the rpms. I don't want to lug the engine.

Any information you all have on this would be greatly appreciated.

Thank you

 

[sheep herder]

For an '03, I thought they went back to picking up the speed info from the transmission.

You could also go to a taller tire and get the same thing as higher axle gears.

 

[pjtoledo]

it would be interesting to see what the intake vacuum and percent throttle are at the 2 speeds.
that's something that would indicate how hard the engine is working.
tuners could probably elaborate more on that, all I know is lower vacuum usually means I'm using my right foot too much.

the engine smoothing out may just be where the vibrations & harmonics cancel each other out.

and that's my 2 cent opinion for the night. (it's a slow night )

 

[hat_man]

Thanks for the replies.

It could be the vibrations cancelling each other out, but taller gearing is going to help with mileage anyhow and the smoother ride feel would be a bonus for my just over an hour commute. A bit of a win-win.

I may have been given bad information and ran with it rather than just checking myself. I read a few more threads on here and took a pic to help figure this out. Is the sensor I see in the pic an Output Shaft Sensor that may be sending the signal to the computer? If so, then I am assuming the computer makes the adjustment and does the math and controls the speedometer. If this is true then if I change rear ends all I would need to do to correct the speedometer is change a setting in the computer to tell it the new gearing?

 

[scotts90ranger]

With a 4 cylinder I don't think I would go through the work of doing that. My '97 has 4.10 gears in it and when I got it had 27" tires and was around 3000rpm at 60mph in 4th or 2250rpm in 5th, so I went with 29" tires to try to drop the engine speed a little (250rpm at cruise is what I got) and the result was zero change in fuel mileage (including adding the 10% the odometer is now off) and more shifting when I get to a hill or any incline... I think the giant wheel openings on the third gen and up Rangers look silly with tiny tires so I like the 235 75 15's on there but will probably plop an Explorer 8.8 in it eventually and swap to 4.30 gears...

That said, if you found an axle with the gears you wanted in a '93-09 Ranger you can swap that right over... everything '88 and newer has the sensor on the rear diff, the disc brake axles in '10 and '11 are apparently different...

 

[hat_man]

pjtoledo.....One of the things I'm hoping for is the added load from the taller gear will offset the pumping losses from the throttle being so closed at cruise. Sounds counter intuitive to push harder on the "go pedal" to save fuel, but it works.

I would love to mount a vacuum gauge on the dash somewhere. It's probably the simplest tool to learning to drive for efficiency.

 

[hat_man]

Scotts90Ranger....

I'm running the same tire now. 235/75/15. About 5% larger than stock on the '03. So with the 29" tires and a 4.10 rear you were running about 2k rpm at 60 mph? My rear end tag says I have the 3.73 and I'm running the same rpm at 55. After doing some quick math I should be at 1900 rpm at 55 with the 3.73 and the tach says I'm just a hair over 2k. Makes me wonder if the previous owner would have paid to have the gears changed and left the tag on the stock diff cover.

 

[RonD]

2001 and up Rangers use the OSS(output shaft speed) sensor on rear of transmission for speedometer/odometer
The computer does the conversion of OSS 30,000ppm to the 8,000ppm the speedo needs for correct speed(5% deviation allowed)
PPM = pulse per mile, Ford has used 8,000ppm since early 1980's when VSS(vehicle speed sensors) were first used

Rear axle ratio and stock tire size is used by the computer for this PPM calculation, so a change in either would cause speed conversion to be inaccurate
Computer can be updated with new ratio and tire size

If you have a flat straight stretch of road you can use a GPS app to see how close speedo is to GPS speed, best results are at higher speeds, 55+ MPH, high speed gets higher deviations, of course, so best to do the higher speeds

 

[hat_man]

Thanks RonD.

I just confirmed I have a 3.73 rear end. Little piece of colored tape on a rear U-joint bolt and roll it in neutral. Works like a charm. Get a bolt to stop at 6 o'clock and put on a piece of tape. Mark the tire at 12 o'clock and roll it forward one revolution. If the tape is back at 6 o'clock it's a 4.10. If it's at 3 o'clock it's a 3.73. 12 o'clock could be either a 3.45 or 3.55 and 9 o'clock is a 3.27.

I have checked the speedometer against my Garmin and my Google Maps app on the phone. Both confirm speedometer reads 3 mph fast at 60 mph. 5% larger tires than stock so all the math seems correct.

Scotts90ranger has the sensor on the differential and RonD has it on the transmission.

I'm actually happy that the changes can be made in the computer for BOTH tire size and rear gear. It makes the decisions easier. Now it's more of a mechanical thing. Obviously a 7.5" rear end would be the easiest to swap in. It should be all plug and play including the flanges.

So I guess I'm now looking for an axle code 85 (3.55 gear 7.5" open) or an axle code F5 (3.55 gear 7.5" Limited Slip)

I have never seen the F5 option. Is it a rare piece? Maybe only offered on certain trucks? The limited slip might be nice in the winter when things can get a little squirrely. Then I'll have to find someone to get into the computer and make the changes.

 

[hat_man]

Sorry sheep herder. I must have missed your post somehow.

I've already gone to a 235/75/15. I'm not sure I can fit anything larger in there.

 

[RonD]

1998-2000 Rangers used rear axle ABS sensor for speed, the GEM Module did the 8,000ppm conversion in those years

2001 and up is when Rangers were switched to use the OSS sensor for speed, and PCM(computer) did the conversion

 

[hat_man]

Thanks RonD.

I just thought of another question you might be able to answer.

In the PCM when I have to change the gear and tire size, are there only options for what the Ranger may have come with or just a "blank" spot to put whatever ratio I switch to?

 

[RonD]

No, you can change parameters to what works, its just an on the fly calculator, I am not sure what Ford used in 2003, as far as parameters, it won't be "axle ratio" and "tire size" more like "revs/mile" which is tire revolutions per mile

 

[scotts90ranger]

What I was saying is the sensor has been in the axle since '88, listen to Ron on what was used for the speedo input, I'm behind on that...

3.55:1 is an 8.8 axle ratio, not that it makes any difference as it'll bolt in from Ranger to Ranger, 3.45:1 is what was used in the 7.5" axle...

I don't have a tachometer, so I'm just going off of calculations (and my OBD II dongle with Torque). My 10% odometer calculation is from the odometer check section on the local freeway from multiple tests.

Completely different 2.3L between yours and mine, but mine is gutless around 2000rpm apparently, much more pleasant driving around in 4th on the highway than 5th...

 

[hat_man]

I used to have a '97 Ranger. That little Lima was a bit "gut-less" but got me great mileage. Never needed the big HP. I was sorry to see it die. I still have it and hope to resurrect it someday just to pass it on to one of the kids. It's a stick and none of them want to learn. I wish I could find a "top load" transmission to go behind the 2.3 so I wouldn't have to mess with linkage and such. Just use a new hole in the tunnel and have the shifter near the same location.

I was using the chart in this thread to find the 7.5" rear with the 3.55 gears. I'm hoping it wasn't a misprint.

Ford 7.5 & 8.8 Inch Axle Tag & Door Codes - The Ranger Station

Identifying Your Axle From The Axle Tag: You can identify which axle you have by the tag attached to the inspection cover. Here is an example of an axle tag: Looking at that tag, you can see the gear ratio … Continued

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