Your braking math is backwards if the 120 mph example you gave holds true, which I believe it does: for the same ground speed, pinion speed will be 1/2 the original speed if one rear wheel locks up and the other remains at ground speed.

That's all I'm going to say so I'm not the one dragging this thread off topic.

Personally, I have not seen a 92-up truck with a tailshaft mounted VSS, but I haven't seen them all, so I can't say that is the case across the board, but everything I have read indicates that none use it (even ZF's website has a dash for speedo gear in 92-up transmissions). I've also read several people here have trouble with the parts guy selling them a VSS as listed in all the parts lookups and then have no place to install it on their trucks.

 

So based on that when one tire spins and one sits still, the spinning wheel spins at twice the given gear ratio??????

Ok.....

 

Yes, I agree with your strategy cuz apparently I and 'All these ford techs at dealerships' are unable to read our step guides, TSBs or service manuals.

[sarcastically]
I shoulda stayed a hobbyist, it apparently makes one more knowledgable
[/sarcastically]

and FTE wonders why I stop posting for large chunks of time at a time

 

Open diff: axle blocked up truck in gear both wheels spinning walk over and slow one with your foot on the side wall and the other side speeds up at the same ratio that you're slowing this one down. If 100% stopped the other is 100% ________

 

I know I said I would not post again but I have to make this one comment.

I have all the Ford Truck Shop Manuals, wiring diagrams and TSB's from 1986 to 2004 and I have not found one to agree with you.
Can you name the section and page in one Ford F-series Truck Shop Manual or Ford F-series Wiring Diagram form 1992-1996 that backs you up.

I only use Ford Manuals, I do not use or own any off brand manuals.

 

That is not what he said, he said:

Quote
"** = the exciter ring will actually SPEED UP if one rear wheel locks and the other does not, but the tranny VSS will continue giving true vehicle speed (I leave the 'why this occurs' as a homework exercise)"

And this is not true, the exciter ring will not speed up.
True the other tire will but not the exciter ring on the ring gear.
And since the exciter ring is on the ring gear for the VSS (speedometer) and the axles are not hooked to the ring gear if one turns faster then the other the ring gear will never know it.

 

See this is what I am talking about, in the last 5 or so hours while I was on the road did no one availed themselves of the time to TTFE.

In the first instance, 1 tire on ground and therefore locked, other on ice, open diff.

It has been known for oh I dunno, a hundred or some years that in this type of differential (side gears linked to spiders whose shaft is attached to the carrier) the spinning tire will spin at a rate TWICE that indicated on the speedo. not 1.1. not 1.5 but twice. This was known before they invented damn brakes for crying out loud.

The reason? the spiders are on the shaft turned by the carrier. If the carrier makes exactly one rotation in a minute then the locked (on dry land) wheel transcribes essentially 1 revolution in the OPPOSITE direction - in plain english if the carrier went clockwise, 1 revolution later the same starting points met.

since the side gears are linked by the spiders, then this 'apparent' opposite motion must have an EXACT equal counter motion in the same clockwise motion.

However as I pointed out 2 paragraphs above, the shaft the spiders are on is ALREADY turning 1 revolution clockwise. Therefore the effective revolution of the icy side gear is *2* and exactly 2.

Being that I just so happen to have a couple axles hanging around the shop, I filmed doing just that. I locked down one wheel of a 2.50 axle (in reality 2.47 but who is counting). I marked one wheel stud. In almost EXACTLY 1.25 revolutions of the pinion yoke, the wheel stud made a complete revolution. How can that be? You assured us it could not!

Read this over and over and visualize until you understand it. Or dont, I dont give a damn.

Since this ratio must exist, the inverse must also exist. if braking in the wet causes one wheel to lock and the other has a perfect contact, at 60mph, the carrier will spin half as fast as it should. (therefore so will the driveshaft - earlier in my hast I think I wrote *2 for the braking case AND the acceleration case - my bad, 5 pts to the person who caught it while I was offline)

In a 2.50 rear, one revolution of the axle should produce exactly 2.50 laps of the pinion yoke. In my locked wheel example, it did 1.25.

quelle surprise!

if I can figure out how to capture and upload a hi8 camcorder tape to youtube, I will and post the link. But trust me, the narration is going to be extremely unflattering.

I did however err, the speedometer reading will also jump, regardless of where its pulse source is located. IT will read half true vehicle speed, but the single channel ABS will never trigger.

 

You're right on about the axle speeds. The RABS works by limiting the rate of change in the measured speed of the differential carrier. Even if only one wheel locks up, the speed of the carrier should drop fast enough to trigger the ABS system. It may not work flawlessly, but it should pick up on a quick change to 1/2 original speed.

 

Why do you keep relating this, I do think anybody has said anything different and everybody agrees with you on this.
This also does not have anything to do with what we are talking about.

That said, what I said in post #21 above is also true.

I did not want to start posting images and diagrams but you seem to have a little problem understanding the ring gear and VSS on the rear end.
The Poster on this Thread is talking about a 1995 F250 so I will use this truck.

These Images will only be up for a very short time as they may be copyrighted. They are both from the 1995 Ford Manuals.

I am done with all of this now.

The 1995 F250 VSS System.


And the 1995 Speed Sensor Ring.

/

 

eh wrong. read the g-damn NOTES. that is not the only wiring diagram for the 95 F250 (the poster said he had a f150 - nice to move the target)[retracted - I re-read and the f250 was mentioned] and you know it.

you just cant bring yourself to admit that what I and 'all those ford techs at dealerships' said just might be right.

The actual ford wiring blueprints will have quite clearly a string like 'MS-FOTB'/'MS-F1TB' (or very similar - for this year you want MSF5TB) followed by the sequence number and the version number. This is why I knew you did not have the actual wiring diagrams as you said. Only those who are AT a dealership or pay a very expensive subscription fee can get them. they are nice and big and foldoutable and best of all - professional.

I have already posted not only the part number, but the PICTURE of the part you said that does not exist. Talk about chutzpah.

(meets the requirements of what I said: you can order it, you can buy it, you can install it) and should the truck meet the requirement I listed you can also plug it in - as I said.

the mystery plug which you insist does not exist is 12a581. or 9c887 depending.

and guess what, taking speed pulses from the rear axle predates 92 and was done on SOME 4x4 models. one size does not fit all.

gee. I wonder how I knew that? Or are you now going to assert that does not exist as well?

this is too retarded for words.

 

What notes?? This is the only diagram for the 1995 F250.

I think you have this backwards. Do not forget we are talking F-150 to F350 1992-1996 Trucks and not the larger trucks or some cars that do use the older sensor at the transmission.
I have those too but not easy to post online, I have in my hand right now one for the 1994 F150-F350 and the number is for your information is: FPS-12135-94S FORD Technical Publications Department.
The Axle sensor is at A-147 on diagram MS-F4TB-3458-AA.
Too many locations to list for all of the items in this system in the big fold out but the diagrams match the diagram I posted above.
I did not say it did not exist. It is used on some cars and very large truck though the 90's but it is not used on the 1992-1996 F-150/250/350 trucks that we are talking about.

I am sorry but you can not.
By the way if you did not notice I own one of these 1995 trucks and there is no place to install that Item.
I can go out and take photos of any place on it and post them here but I do not think you would take them as evendence even then.

As I said above we are only talking about the trucks covered in this Forums and zeroing in on the 1992-1996.

The Poster of this Thread dose not have the part you keep talking about and you are not helping him fix his problem.
As I told him his PSOM, Speedometer head or wiring and plugs may be bad.
Why did you post in this Thread when you do not know how this system works?

The PSOM:

/

 

Variable ratio differential's huh? I see....

 

I posted in there because the only parameters were 1995, f250 and 5.8 of which there is more than one answer, and my reply was pretty much worded exactly that way. AS I said from post 1 and expand year range now, heaving read more wiring diagrams, there are more than one VSS method from 1989-1995 used. and it appears, that large F350 4x4s without E4OD use the tranny mount one still - like the 93 my customer has. (his is specifically a 93 133wb, dana axled, HD susp with ford overloads and snowplow prep, 460 zf with the psom.)

I didnt say I didnt know how the system worked, I said I never paid attention to every truck that comes in here to see what it uses. why would I?

 

Wow; some thread drift here! And - lots of useful info!

Anyway, I picked up a speedometer module at a local scrapyard for $10. Got it home, wired it up on the bench with a function generator and a power supply - looks like it works good! Smooth speed readings across the whole spectrum.

For what it's worth, the odometer seems to keep tracking right up to 14k hertz speed input - equivalent to 225MPH!

The odometer reads about 100,000 miles low. I've figured out that I can make up that difference by leaving it plugged in on the bench for 18.5 days at the max speed. Being the ethical type, I'd like to have it reading correctly, but who knows how accurate the current odometer is? (due to speedometer problems...)

Anyway, I'll probably install it tomorrow. If anyone is interested in how to rack up odometer mileage on the workbench, let me know. It's pretty simple.

 

Sounds like you have under control, any extra information is always welcome on the Forums.