Speedo VSS differences in '96 & '99s

[section525]

Can anyone tell me for sure what the differences are in the two different methods of speed sensing? I know the '96s have the VSS at the output shaft... but does anyone know how and where the '99 ones work? It's on the rear axle, isn't it?

I'm going to need to make my '96 computer work on the '99 speed sensing system.

Thanks

 

[Jason_25]

What I would do is reuse your old transfer case in the swap, unless the "new" transfer case has a spot for the speedo gear.

 

[section525]

This is a pic of my '99 tranny and t-case. Can some point out where the speed sensor would be on the 96/97 version? Thanks!

 

[Robert]

Here are a couple of pictures from my '97 how it mounts. It basically mounts from the bottom, right next to the front speed sensor. Look for a plate or plug in the area that you can remove.

 

[Robert]

picture 2:

 

[section525]

Robert. Thanks for those pics! But I forgot to mention I need the AWD tcase. They're probably pretty different, right?

 

[section525]

Here is my dilema:

I am installing a 1999 All Wheel Drive transfercase on my 1999 4R70W. I previously had a 1996 2wd tailshaft housing attached to this tranny, that had the VSS built into the housing.

I don't appear to have a VSS port on my '99 T-case. Will the speed sensor in the rear axle satisfy my 1996 EEC-V's need for a VSS input??

Theres my prob!

 

[Okrazie1]

Making a quick guess, I'd say the RABS would not substitute for the VSS in supplying a signal for speed. From what I know about the systems, I believe that the VSS is a resolver, and the RABS is an encoder. They do similar functions, but work off of different principles, and their outputs would not be interchangable.

 

[Jason_25]

I'm sorry dude i'm REALLY confused now. Ok your 1996 is a all wheel drive right? And the new chassis you bought was a 2wd or AWD?

 

[section525]

Jason.. you got those backwards. My '99 is AWD and my '96 is 2WD.


Doug.. both sensors use the Hall Effect to output a digital reading, right? I was thinking that if the two units were not giving the exact same readings at the same speeds, I could get some sort of aftermarket speed calibrator like the Mustang guys use. (That is, if the function of the two different VSSs were remotely close even)

Thanks!

 

[Jason_25]

Ok I gotcha.

Well if all else fails, then you could find a used 4404 transfer case from a 96-97 V8 explorer and bolt it up.

 

[section525]

Yeah... I just might have to do that. But, damn, those things are pricey!

 

[Okrazie1]

I've done a little research of my '95 and '99 manuals, and the best I can figure out is my first guess was incorrect. It seems that that the VSS and the RABS may be quite similar. They both generate an AC signal which increases in frequency as the vehicle speed increases. It appears that the frequency is the same between them (65 Hz @ 30 MPH and 125 Hz @ 55 MPH). However, in the testing procedeure, it states that the VSS should generate a voltage between 1.0-5.0 V, while the RABS voltage should be between 100 mV-3.5V. Even though the RABS is producing the correct frequency, the lower voltage may not be strong enough to produce a trouble-free signal for your situation.


Edit: Something doesn't seem right, but I can't put my finger on it. The '99 lists the frequency given above as a "VSS" signal, but it doesn't have a VSS. The signal from the RABS is input to the 4WABS, then the 4WABS sends a speed signal to all the various components which require it. I don't know if the frequency given is the raw RABS signal, or the output from the 4WABS. My gut feeling is the frequency from the RABS is much higher (if I remember correctly, the toothed ring the RABS uses to generate a signal has 120 teeth) then the programming that is done to the computer correlates this raw signal to the frequencies required for the VSS signal. I do know that the more I look at it, the more confused I become.

 

[section525]

Wow Doug. Thanks a lot for that information! Know ing the info you gave me... what do you think I should do?

The EDIT in your last post was a little over my head! But if the frequency is the same, I think that is a step in the right direction, right? Thanks a lot for your help again!

 

[Okrazie1]

If the signal is different between the VSS and the RABS, something like this or Superlift's Truspeed might be able to convert the signal to what you need. You might want to contact one of these places and see if they can answer your questions. Good luck!

 

[section525]

Thanks Doug! Looks like I'm being doing the swap and fixing this afterwards then (probably, as of now. ha).

 

[oso_polar]

I think you guys could help me...

If I'm doing a SAS and want to change both axles, but my VSS is on the rear axle, WHAT T-CASE SHOULD I LOOK FOR?? I mean, if I don't wanna loose the VSS I will have to change it to the t-case, then I will need a t-case with a VSS recivier...
In wich truck I will find that??year??

 

[section525]

You'd basically be going to opposite of me. You'd have to get a 97- Explorer, and you'd have the exact same problems I am. Your VSS reads every axle turn, while 97 and lowers read output shaft turns. So they'd be around four times as few turns per mile.

I'll hopefully be doing my swap this weekend, and I'll let you know if the two different methods of VSS are compatable... and if they're not quite the same I should know how far off they'll be (if they even work). I'm going to try and use some sort of speedo calibration computer to fix my problem (if and when I have one) and if it works on mine, I'm sure it will work the other way for yours...

 

[section525]

Al, someone said something about hooking the VSS up to the OSS. Do you think that is a possibilty? It makes sense in theory. If my '99 tranny has an OSS sensor, that works exactly like the '96 VSS sensor, then all should be well, right??

 

[V8BoatBuilder]

Bump to the top... gotta love the search.

I'm installing a message center, and I'm having some weird issues getting the M/C to accept a VSS signal. My 97 has the VSS located in the t-case. I tapped into circuit 679, the tan/yellow wire coming out of the PCM. However, I am only getting speed data into the message center (as seen by the internal trip odometer) when the truck is above 40mph. The dash speedo/trip odometer reads fine.

Some questions:

1)Can I use a DVM to probe the VSS line?
2) What sort of signal does the dash speedo take? Did this signal change when ford elimiated the t-case VSS?
3) How sensititve is the signal in terms of ground - should the M/C ground be run to any special location?