FIXED -- Big Red 02 ST SAS -- Weird speedo issue

[Fire]

I've got a weird problem with my recently completed SAS and rear SOA. The speedo (which on 02's reads the ABS speed sensor instead of transm), now displays my speed about 10% higher than GPS actual. Yeah, higher. It had always read about 20% low since I went from 29-30" tires to 35s, but when I did the SAS/SOA and regeared from 3.73 to 4.88, now it's 10% high. A Big shift.

The ABS sensor on the rear is the on the diff housing and reads the big toothed disk next to the ring gear. I didn't change the disk, so it sends the same number of pulses per axle rev as before.

Just wondering if anyone has any experience with the phenom. Thanks for any ideas. --I did replace the sensor and make sure it hadn't been hitting the disk, but no change. grrr


Background -- Well to make a long story short, I've had the ST since new, starting wheeling it maybe 10 yrs ago, got tired of no front suspension travel and CV's binding up/breaking and did a Dana 30 SAS on Wagoneer leafs, and just put the 8.8 SOA. Just copied all the great work done by 410 and also all the other SAS's in the Registry. Here are a couple pics of my pig.

 

[410Fortune]

Sweet rig!!!
The change in tire size changes the number of rotations per mile.
True the 108 tooth ring gear still spins the same amount per axle shaft rotation, but the axle shaft rotations per Mile are effected by tire size

A Dakota digital speedometer interface can be used to adjust the speedometer signal. You can get gps enabled speedometer interface as well

I would love to see your steering box and trac bar setup!!!

 

[Fire]

The riddle is that I didnt change the tires. They are unchnaged from several years ago, well before the SAS/SOA/regearing.

For steering box, I just copied the SAS traiblazers that came before: std Ford gearbox, mounted inside frame with the frame plated. I positioned the box so that I could use the std ranger steering shaft. I'll grab some photos to share.

Man, the track bar didnt go well. I tried to use a 3" lift adapter to raise the axle mounting location, and then welded a mount to the inside of the frame. The track bar was pretty short tho, and deformed the leafs pretty good on suspension cycling. Ended up giving up. My steering is a bit boatish, lol.

 

[Fire]

Oh, and I had tried a speedo calibrator, but it won't work with the signal coming thru the ABS. (I think because the ABS would see the rear sensor at a different speed than the front wheel sensors?). I also tried Forscan, but it couldn't change ABS speed/tire settings, at least not on my 02.

 

[410Fortune]

I use the Dakota as an interface between the rear axle speed sensor and the 02
Cluster

You see when I convert these trucks to v8 the v6 pcm goes away and the v6 pcm is what does the smoothing of the speedometer signal.
The abs pump is designed to operate the abs system directly from the 8.8 vss

The dash cluster and pcm and cruise control all want to see 8000 pulses per mile,
Just like the old fords with a trans mounted vss and driven gear

The Dakota digital can use ANY speed sensor in your drivelines and convert the signal down to 8000ppm using parameters you control

Or you can get the gps version and it will just use gps to calculate your speed and send the 8000ppm to your
Cluster

It is very odd that your speed sig al changed without a tire or rear axle or abs module change and no changes to the cluster

You may scan the pcm and see if it is happy, no vss codes. Also watch live data and make sure the pcm is seeing proper speed and compare it to what your dash is reading

Here is a detailed Dakota digital install thread I did for a 5.0 ranger

Ford Ranger forum

The Premiere Site For Ford Ranger Enthusiasts

ford-rangers.com

 

[Fire]

Thanks bro. I don't have any lights or codes set, but I'll check it realtime with my OBD2 scanner for any flakiness. That Dakota looks great, I'll plan to get it after I verify my system is behaving. One question, you are splicing the output side, not cutting it, but doesn't the original signal then conflict with the new signal you are injecting?

Just to detail what I'm seeing:
1) For the last several years with the 35" tires: speedo ~60 and GPS ~72mph. Makes sense with 35" tires having 20% larger circumference than 29" stock tires.
2) Now with the same tires: speedo ~60 and GPS ~54mph. Senseless, lol.

--PS -- I did have the truck battery discon for about a year, so maybe the ABS lost it's programmed tire size setting from teh factory and defaulted to some minimum value? Not that I can change it back (and a dealer I talked to years ago said they got rid of their programming equipment for that year long ago). But maybe it's an explanation for the behavior.

 

[410Fortune]

Is the drivetrain and instrument cluster all stock?

I’m not injecting any signals on that side by splicing into the one speed sensor signal wire. I am simply getting an input for the Dakota

The output gets wired to the vss circuit in the truck for me because I am doing a drivetrain conversion and I need to replace the now Mia v6 pcm

For you can directly output from the Dakota just to the speedometer / cluster only.
Basically taking control of your speedo so you can fine tune the speed it reads at the needle for your tire size with Bluetooth as you drive and hopefully that speed matches more
Closely what live data says (what the pcm, cruise , speed they are getting)

It Could be your speedometer is just getting weak for age and reading slow? How many miles? Moving parts do wear out!

 

[Fire]

Ok, I got ya. I'll track down the speedo's input wire and tie the Dakota into that.

Speedo showing 10% high, not low.

Here are the pics I promised of the steering. Had to replace the torn rag joint, so got a Lares 207 replacement coupler and had to add a bnuch of washers and to get it to pivot correctly. Had to get a custom pressure-side hose made to fit with the A/C compressor so close.

EDIT -- Yes the instrument cluster is all stock.

 

[410Fortune]

Thanks for the pics!

I have wiring diagrams for you when needed

 

[Fire]

Got it fixed:
1) Checked OBD2 scanner to verify speedo signal was consistent. It was.

2) Ordered Dakota Digital SGI-100BT around $100. Got it in a few days ago.

3) Wired in in like 410 said: See pics.

a) Splice into the rear diff speed sensor wire where it runs into the ABS module under the hood. Leave the connection, just add the new wire and run it into the cabin.
b) Add 3 wires from speedo connector in instrument panel. Note Ign and gnd need to stay intact, just splice in your added wire. The speedo vss signal wire is cut and only the new wire is tied to the speedo. Just put a cap on the unused OEM vss source wire.
c) Managed to get the calibrator to fit in the ashtray with wires running out the back. Had to cut the mounting tabs off. Out of the way but accessible.

Fiddled with the calibrator settings but final got them right. I used the Dakota android bluetooth app. If you have different tires you can use the bluetoth app screenshot, and just click on the calibration value and adjust to whatever works. See pic.

To clarify, this work was to fix the speedo reading with 35" tires, and after leaving the pcm/abs unpowered for a year when I did a SAS/SOA so it apparently went into some kind of default setting. This fixed it and my speedo is correct!!!

Thanks @410Fortune

edited -- to improve pic quality

 

[410Fortune]

Yeah buddy!!! You control your speedo now