So I have a nasty speedometer jitter in my 95 F250 5.8L. I replaced the speed sensor on the differential - from my searching here, I believe that is the only speed sensor on this truck. No change in the speedometer.

What is the next most likely candidate? The speedometer it's self? Is the gauge cluster interchangeable with any of the ford cars or SUV's from that era?

Thanks!

 

Is this true? the speedo cable output on the tranny/xfer case includes a pickup for VSS. I have seen others allude that the exciter ring is used as a VSS signal but i dont know how true that is, its resolution is far higher (the typical drive/driven gear is set up 18/8-ish with 2 pulses per rev. if yo uare running say 3.55, the exiter does a rev at a slower rate, BUT has 50-60 pulses per rev.

 

1992-1996 (and a few newer) F-series use only the VSS (or DSS) sensor on the differential.

Before 1992 they used a sensor at the rear of the transmission or X-Fer case for 4x4's.This VSS sensor was used by the EEC Computer and the speed control. But it was not used for the speedometer, the cable under it was.

 

The PSOM (and this may be your problem) can be used from 1992-1996 from F-series and Broncos (and others) but they improved it for the 94-96 years.
The speedometer head I think is the same from also 1992-1996.
The whole cluster would only be from 1994 & 1995.
Other years will fit but you have swap a few wires around and the some of the lights are labeled different.
Also some have a tachometer and some do not.

 

Far be it from me to disagree with anyone, but my catalogs list the EXACT same part for a 90 or 96 VSS that is tranny (2wd) or xfer (4wd) mounted that provides speedo cable output and VSS. Even rock auto does. Hence my skepticism....if'n ya know what I mean

 

True same part was used on the 90-91. It had one on the tranny (2wd) or xfer (4wd) mounted but it had nothing to do with the speedometer. It was called the VSS sensor. The 90-91 and before the speedometer was cable driven and not electrical.

 

I think some wires are crossed - this 'appliance' lets the speedo cable come out of the tranny/xfer, but adds a VSS (its a rotating aluminum or plastic drum with a small magnet imbedded. and a simple pickup with 2 wires attached

this is the part here and the speedo cable pins into the back end of it.

which looks like this

looking further, it appears there are no cables for the 1996 speedo, BUT the VSS is used.

based on that, Id say its highly likely the speedo gets the PPM count from the VSS and not the exciter ring for the aforementioned reasons.**Interesting. Ill have to pay attn to the next 'later' model F series that visits.


** = 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)

 

This part was used on the 1991 and older, as stated above on the 1991 and before the electrical part of this part was used by the speed control and the EEC Computer.
The part on the rear end was call the DSS sensor 1991 and before (for the ABS) but it is the same part that was used in the 1992-96 trucks for the VSS (called DSS in 92-93 trucks) sensor and was also mounted on the rear end. They no longer used any signal from the tranny/xfer for the speed control or speedometer. However they did use another sensor on the transmission call the output shaft sensor and its signal only when to the PCM Computer.
There are no speedometer cables used on the 1992-1996 trucks
I do not buy this, the exciter ring is mounted on the ring gear and ring gear is locked to the drive shaft through the pinion gear.

Do you work at a Ford dealer as their Techs. seem to have a problem understanding this.

 

Quaddriver, this post of Bill's is 100% correct. This is exactly how it works.

 

Im not sure what you are getting at. That part I posted a picture of, IS available on all F series trucks 87-96.

It has zero material changes in any part of its construction. (although I can show a picture of one where the cable output is blocked off)

Meaning the ability to drive a speedo cable *is* present, even if the cable is not orderable as I pointed out. However, I am not talking about cables.

**IF** this appliance is present then another scenario exists:

The DSS is wired into the ABS module.

the VSS (tranny mount) is wired into exactly 2 modules. The ECM (PCM once e-type trannys became used) and the cruise module. Druing this time period there were trucks built 'OBD1.5' where crossover parts were used. From the problem description, I cannot tell what PCM/ECM or PSOM he has - or even the tranny. not having an E4OD makes this different.

The VSS, as illustrated in the part I showed, *IS* exactly a transmission output shaft sensor. And it *IS* driven by the same drive gear mechanism, therefore it will have the correct, easily settable ratio to give the speedo head (electronic or cable driven, I dont care which) the required 1000PPM input.

so for the 1995 model year F-truck, more homework is required to determine if this appliance is present or not. Or even better, unplug one at a time and see when Mr Jumpy speedo stops working. the moral: in 1995 one size DOES NOT fit all. (some may argue that the 'no-one size fits all' date range is corerctly stated 92-95, but the fact it is a 95 with a 5.8 are two red flags that DIYers wont pick up on.)

From alldata:

(and the alldata 'data' is only correct to c2001-ish as the tranny mounted VSS is once again used)


when you are trying to move with an open diff, and one wheel does not move and the other spins...the speedo says 60mph as you gun the engine. how fast is the tire turning?

answer: 120mph. you have these things called spider gears which must dissipate the rotational movement against a non-moving shaft. This is why tires explode.

well guess what, when you brake in the wet, if one rear wheel locks, but the other maintains full contact, the reverse must happen and the engine rpms will actually climb as the carrier wil be driven at a greater rate. The RABS or 4WABS will not activate and it makes a hell of a racket.

no, I do not work at a dealership, but your misunderstanding of their position is likely based on what I have listed above.

 

It's only used on '87 to '91 trucks. '92 & up trucks ONLY have the VSS on the rear diff.

Now I think you're making this up. Can you explain that statement?

What difference does it make which PCM he has???

I'll save you some time - it's not there.

Um, no. There's so much wrong with that statement I'm not sure where to begin.

 

I do not have a misunderstanding of this system and it seems you do.
Not true, it is not used after 1991.


Wrong again, the OSS is and entirely different sensor.

In 1995 he only has the one on the rear end for the VSS and he may also have the OSS sensor on the transmission but it has nothing to do with his problem.

Please quit putting out bad information on this as you need to do a lot of reading on this subject.

this is the 1987-1996 Forum and this information does not apply.

 

this is just flat out incorrect. this appliance is available on nearly EVERY year of the F series since EFI, with the exception of 96-00.

you can order it. you can pay for it. You can install it. and depending on the model/year/drivetrain/states sold in, there will be wires to plug into it.


In 1994 (technically 1993) Ford and GM started installing OBD2 capable systems in OBD1 equipped vehicles. Unofficially they are called 'OBD1.5'.. Some versions send OBD1 data out the OBD2 connector. Some versions send OBD2 data truncated because only the OBD1 hardware is under the hood. Particularly troublesome are versions the use a true ECM (the phrase PCM did not technically come about until the advent of the electronic transmission as it controls the Powertrain, not just the Engine as in ECM) such as manual transmission models.

In this truck particularly with or without an E4OD makes a difference. in fact, all pre-96 years of 5.8/E4OD are scary 'cuz if there is one combo that will have a different ECM/PCM box or jumpered wiring harness - this is it. Hence my answer that one size does NOT fit all.


consult the schematics available as to find out how the PCM gets VSS. As I pointed out, VSS and DSS have different resolutions and various 'divide by' counters must be used. One size does not fit all!


If you say so. One of my best customers has a 93 F350 4x4 with RABS and a 460 and a ZF and a PSOM. His speedo works juuuuuuuuuuuuuuuuust fine with every single wire from the midship tank back ripped in two. How can that be? (splicing wires or replacing harnesses for 1/;10 dealer cost is part of the reason he is one of my best customers)


figures.

This is so easy to actually see its not even funny. Take ANY axle you have laying around not connected. spin BOTH axles and by counting the pinion rotations, you can guess pretty good at the axle ratio. We all do this right? there are procedures on this website listing this, RIGHT? RIGHT?

have a buddy hold one side and spin one axle. now what happened? did the axle ratio magically double? DO NOT comment further on this sub-topic until you have performed the experiment (and the results of this experiment are one reason why they (ford) went BACK to a tranny mounted VSS circa 2001)

One size, one methodology does NOT fit all. I cannot repeat this enuf apparently.

 

100% you're wrong. Go ahead and install it on a 92 to 96 truck. Let me know how it works.

This *sounds* like BS but I can't say for sure it's wrong. Since you've managed to get everything else wrong, this is probably suspect too.

I know how this works. I've looked at the schematics - I think you need to do the same.

Rubbish. If his truck is a 93, it gets its speedo reading from the VSS on the diff just like on any other 93 F350. Next time you're under there take a closer look.

LMAO and now you have the stones to tell me what to do? I'll comment all I want on this topic, if nothing more than to correct the BAD information coming from you.

If you think that having one wheel lock up while the other maintains traction makes the carrier spin faster then you don't know how a differential works. Again, given everything else that you've gotten wrong this doesn't surprise me.

But it still doesn't make any sense.

OK, I'm done here. No more from me in this thread.

I think most folks who read this know that I do know what I'm talking about even if it *weren't* for the fact that subford, one of the most knowledgeable and respected members of the forum, and I are both agreeing with each other and you are the one who is out in left field.

 

I will not be posting anymore in this thread unless it is to answer a post by Nick1911.