Hi, I am basically new to the forum, and have learned a TON about these trucks via lurking here and doing a moderate restoration of a 2001 Scab. For those who want the short version and the quick question to answer, here it is:

I recently swapped the 3.08 diff (axle code 18) to a Trac-Lok 3.55 (axle code H9). The swap was fairly painless, but after spending well over 8 hours googling to no avail, I need to know how to recalibrate my speedometer (and by default also fix the odometer counting incorrectly going forward). I am completely lost. Everything I find on the net comes back to several things that I feel are incorrect - PSOM (which I believe is for pre-1999, possibly pre-1997), using ForScan (which I do have a paid license and correct hardware for, but the option to calibrate doesn't seem to exist), a physical tiny gear that you have to calculate the correct number of teeth for and physically replace (which also seems to be pre-1997), or a code change in the PCM (something about exciter rings and conversion constant... a whole lot of lingo I don't understand. Here is a link: https://www.f150forum.com/f6/re-cali...-ratio-372511/). Which of these (possibly multiple?) is actually correct for a 2001? Bonus question: not only is there a diff/gear swap in play, but also a tire size swap - 235/70R16 OEM now converted to 255/70R16. This is also affecting the speedo/odo. Do these both get fixed with the same process, or are these two separate fixes that need done?

If you need more specific info, the truck is a 03/2001 F-150 XLT 4.6L Scab PX, 4R70W, 2WD, 3.08 disc original but now 3.55 Trac-Lok disc, 139 wheelbase, 174K on the odometer.


For anyone still reading wanting to know what has been done or is in progress since I am new here, here is the long list. Starting with what has already been done - obviously I have upgraded the diff for towing purposes, done a proper Gotts mod, replaced the entire ignition system and EGR system while doing an intake gasket repair, all 8 passed a compression test with stellar results, knock sensor, temp sensor, full TB cleaning including the plugged EGR ports, replaced literally ALL fluids and filters, all vacuum and coolant hoses, replaced clutch fan, water pump, thermostat, belt, idler, tensioner, PCV system, purchased/programmed new OEM fobs and keys (thanks ForScan!), rear door cable repair kits, new headlight and tail light assemblies, saved the clogged heater core from being condemned (thank you Lisle 60800!), full front suspension (all tie rods, idler, pitman, links, control arms...everything), shocks on all 4, full A/C kit, and a full interior restoration including a full gutted detail job (removing all seats, full vac, shampoo, etc), lock actuators, window motors, replaced several of the dash panels due to paint peeling, replaced the missing dash cupholder, the center armrest around the cupholder... Basically I nitpicked the whole truck and made it nearly new again.
Still in progress is the rear cargo light/third brake light harness and window reinstall (found this one out by trying to replace a burnt cargo bulb and discovering the mushy connectors), adding a trans cooler (thank you @Krack499 for the write up! link: https://www.f150forum.com/f6/how-sup...nstall-270679/), adding a tuner (probably SCT so that I can see trans temp and other data real-time, not to mention the tune and trans shifting benefits), probably a bedliner (I'm guessing it previously had one but someone removed it along the way because there are little black textured pieces all over the bed, but it is now mostly scraped up paint), a full audio system which is partially started, some inevitable upgrades to make it more towing friendly (not sure exactly what yet), maybe a TB and some long tubes/exhaust since it will already have a tuner (although I am quite afraid of messing with the manifold bolts if they aren't currently problematic), and probably lots more. Basically this truck is going to be the most mechanically well-maintained 10th gen on the road when finished, she'll just never be the beauty queen on the exterior. The previous owner(s) abused the exterior paint and it is faded horribly on the hood and roof. My goal is to make it the ultra-reliable truck to replace the need for a tow truck - once I get a car hauler/winch anyway. I know, 4.6L... But I chose the 2V 4.6L engine because I know it like the back of my hand and I'll die on the hill of it being the most reliable Ford engine ever made. Plus, when I'm towing someone's Chevy with ease and they see it's just a measly 4.6L I wanna see them roll up their jaw off the ground. Once all is said and done, I may decide to do some body/paint work, but honestly it will be quite nice to have someone scratch it in a parking lot and for the first time ever...I won't care an ounce.

I bought this truck for $3800 several months ago with documentation of about $3K in suspension, brake, and A/C repairs already done less than 2,000 miles prior. I have spent the time since getting all of the previously listed items done. It drove like a new truck when I bought it, and has only improved since. Because I've done most of the work myself I'm currently only invested for almost exactly $7K including the $3800 purchase price, and that's including stuff I shouldn't count like the registration, battery, and wipers. No regrets. I'll be about $8-8500 at the finish line, but I'll have a rust-free truck I can count on to take me anywhere and to pull almost anything (with a W/D hitch anyway). I was the first to drop the trans pan due to finding the yellow cherry, but it has a pan with the plug in it now so it won't be the last. Even if the 4R70W fails, I just have to remove it, make a phone call, spend a flat $1K to have a pro pick it up, rebuild it, and re-deliver it back to me with a warranty, and then I reinstall it back into the truck - done. So I'm not worried. Besides, adding the cooler should be insurance also. All in all, I didn't think a basic Scab is what I would have ended up with due to initially looking at 03 HD editions (I'm a sucker for a supercharger), but I don't regret it an ounce after all the modifications and restoration. So I'll end the novel with saying I plan to spend a while here and hopefully I can contribute and get to know some of the other 10th gen folks around here. Thanks in advance for your help!

 

http://www.hypertech.com/SpeedometerCalibrator.aspx

 

I am aware of those, but I was hoping for a more direct method. As I said in my OP, I am already planning for a tuner that can also take care of this. I was just hoping for something more immediate I can do because the tuner is probably several months away. Surely there is another way, I just don't know what that is.

 

Bump - Does anyone know how to do this without a tuner or programmer? I'm hoping to have this done by Saturday. I'm replacing the rear window trim today (Thu), and obviously R&Ring the rear window, along with the cargo light assembly and gasket. I figure that will take 24 hours to cure properly. Then Saturday I'm having my truck realigned after all the suspension work and then Saturday evening or Sunday I have to go pick up a Ram for an engine replacement job, and I'm using this truck to pull it. I really don't want the shifting/odometer messed up while pulling that kind of load.

 

I had to be reminded of this
* Gear swaps do not change the speedo reading on a newer ford truck (with the VSS on the top of the rear end, sensing the speed / RPM of the ring gear)
The ring gear speed is the only thing the PSOM looks at
So,
The tire size is the only adjustable factor in the PSOM

 

Did you compare your speed to a GPS speed and see if they match?

I would think your tune is needed right away. I changed the gearing in my 2004 Town Car down to 3.73 and it would not drive right at all prior to the tune. It has a 4.6 with a 4R70W transmission and 8.8 rear. It is a very similar drivetrain. Heck, I have been told that it is an F100 frame, but I don't know for sure.

@manicmechanic007 my tuner allows for choice of gear ratio and tire rotations per mile. I assume this is for the shift pattern then? I really didnt pay attention to the speedometer. I notice is is about 3 mph different from GPS when cruising at 80.

 

3 mph is within design tolerance IIRR
If you change the tire size in the PSOM to correct for 3 mph it is liable to be off the other way by a few mph
Have fun with the tuner

 

That is another data point I've been seeing online, however, it was fine before (not sure if the prior-to-my-ownership tire size change was previously calibrated or not), and the ONLY change made was swapping the entire rear axle assembly from 18 to H9. Now there is a HUGE difference in the speedometer. It literally says I'm doing like 63 and I feel like it is going 47. I will obviously make it a point to test it against a GPS now to be sure and not trust the butt dyno, but it is a dramatic difference, and no, I'm not just talking about the expected perceived acceleration improvement. I'm even talking about just steady cruising at a set speed. That's why I'm skeptical that nothing needs done. I will definitely update this thread once I can confirm. If I am correct, could the VSS be faulty? Or is it just in need of recalibration? And what *exactly* needs calibrated? Does an 01 have a PSOM or that weird little gear thing that you have to do math and figure out how many teeth are needed? Or is it just the ECU itself? That's where I'm really lost and can't seem to get a clear answer even with a paid ForScan license.

 

Yes, the VSS could sure be faulty
When they fail, they sometimes get intermittent, the cruise will surge real bad or not work at all

 

Okay, I'll check for that also. I'm ripping out the rear window tonight to fix the cargo light issue, so it will be down until sometime Saturday when I can get back to it, but that is next on the list. Thanks for your help, I'll keep this thread updated.