Strahley

iTrader: (4)

(obligatory "i already searched this for hours with no luck" line)

I'm going to be using this method to get my (what would be if I didn't remove it at least) factory speedometer working correctly (yeah I'll lose ABS, but I'll be losing it from other mods anyway). Basically splicing my speed sensor into a front wheel sensor for a free speedometer with my th350

Anyhow, I've decided to just redo the dash gauges completely. I know how to get most all of the other gauges to work right, but the speedometer has stumped me. I'll ask the questions I have, but I'm sure there are other things I need to do also

1. Will a mechanical speedometer work, or do I need to use an electric speedometer to work with the front wheel splice method?

2. Can an aftermarket speedometer even work without using the speedo drive gear (is that what it's called? the spot near the tailshaft) for readings? I want to use the speed sensor/front wheel method

3. In the event that it would need an electrical gauge (since it is an electric speed/front wheel sensor signal afterall), is there a way to convert the electric signal to be used on a mechanical gauge? Or would it not even be worth the hassle to convert? Is that even possible anyway?

I'll probably need a bit of guidance on this project, as this is an area I have little knowledge on right now

9000th01ss

iTrader: (10)

Think for a second............You're asking if a mechanical speedo will work with the electric signal from the wheel speed sensor. No, it won't.

You have a mechanical speedo output on your trans.

Why on earth would you not just run a mechanical cable from the mechanical trans output to the mechanical speedo?

Why would you even think of adapting an electric signal to mechanical?

What you're saying makes no sense.

The answer is this: electric signal needs to go to an electric gauge.
If you have a choice between a mech speedo and electric, get a mech speedo and mech cable to run to your th350.

Or get an electric speedo and run an electric speedo signal to it.

Strahley

iTrader: (4)

In my searches I read something about adapter kits, which is why I had asked. It didn't make much sense to me either, so I figured I would get some clear answers

And as far as the mechanical trans output goes, I want to use the front wheel method so that if I change the trans out for something else later, I won't have to bother with doing this again, since I'm going to lose ABS anyway. Also, the output area was damaged from the previous trans owner (bought it from a guy who used it on his race car before he sold the car), so I don't really trust using it

So I'll get an electric gauge. Once I do my front wheel/speed sensor splice, does that wire go directly to whichever input plug is on the new speedometer? I'm going to assume that there will not be any cables to mess around with since this will not be a mechanical output/input setup. Again, please excuse my ignorance on this topic, I've never had to mess with or research speedometers! I don't want to buy an aftermarket speedo only to find out they won't work with the method I'm using

9000th01ss

iTrader: (10)

Sounds like you know what you need to do, get an electric speedo, and run it off the wheel sensor.
Most people who've done this run it through the cars pcm so they can fine tune it.
I'm not sure if there is a speedo capable of being connected directly to the wheel sensor.
But all you need to do to find out is count the reluctor wheel teeth, then make sure the new speedo can be calibrated to run at the pulse per minute it will put out.

Strahley

iTrader: (4)

Where would that wire be found? At the dash where the factory gauges are housed, or at the double silver box under the hood, passenger side?

All Black SS

You'd use the wire that went to the speed sensor in the original transmission.

Strahley

iTrader: (4)

I belive that's the wire I have to use to hook into the front wheel sensor though. I would imagine that wire would go from the old M6 trans to the pcm then to the factory gauge, right?

All Black SS

Well you either run a signal wire from the wheel sensor to the gauge, or from the wheel sensor to the old speedo wire.
I would highly recommend connecting it to the old speedo wire, this way your engine computer also knows how fast the vehicle is going, you can fine tune it through the ecm, etc.

Strahley

iTrader: (4)

I guess I always figured it went from the plug in the tranny to the pcm then to the factory gauge

Right now the factory VSS plug isn't connected to anything at all on the trans side. I plan on hooking it into the front wheel sensor. From what I understand, when I get the car tuned for what I'm doing (the info is in the link in my original post in this thread) the pcm will adjust itself to figure out what mph I'm going, so it has to be running to the pcm at some point, right? I just need to find out what wire(s) supply that information, after the pcm calibration, to the factory speedo

I'm probably going to start taking the dash apart tomorrow, maybe it'll make more sense once I see what's behind the factory gauges

All Black SS

The pcm won't adjust itself, that needs to be put into the tune. The tuning stuff I use allows you to change the VSS pulses per revolution. You just find out how many teeth are on the wheel speed sensor and program that number (as pulses per revolution) into the ecm.

Strahley

iTrader: (4)

Right, that's what I meant (but not what I typed )

But doesn't the (retuned) pcm act as the middleman for this though? I can't see hooking an aftermarket speedo up directly to the VSS wire, as there would be no way of tuning it that way

Am I correct in expecting to see a specific wire hook into the factory speedo, which leads to the pcm, and then to where the adapter was hooked into the factory trans (in which that adapter will be what I splice into the front wheel sensor)?

If so, then this seems like a pretty simple modification. Reprogram the pcm how I need it, then just plug the aftermarket speedo up to the same connection that the factory one has (which means no need to calibrate or program the aftermarket speedo)

Strahley

iTrader: (4)

Got the car all ripped apart, and I see there aren't really any wires I can tap into behind the factory gauges

I found a thread on here that says that an aftermarket speedo cannot accept the signal coming out of the pcm (the info that the VSS wire sends to the pcm). Is there another wire that gives both the correct signal (from the VSS) and the correct calibration from the pcm? If there is, that's the wire I'm looking for

All Black SS

I don't know.
I've never run anything without a speed signal going to the pcm, I just think that will be a problem, maybe I'm wrong. I know from tuning, some things reference the mph, so I would think you'd need it.

Either way you look at it, if your speedo can be calibrated to work with the number of teeth on the wheel sensor, then just wire it direct.

I'm not sure if I'm much help here, but I know you can connect an aftermarket speedo to an electric speedo sensor at the trans. The wheel sensor and the trans speed sensor are the same type of sensor.

Strahley

iTrader: (4)

Turns out the speedo I was looking at does accept the square wave signal, so I can tap into the pcm afterall! It seems the pinout I need to tap into will be B8. Somebody please correct me if this is wrong

LS6 Silverado

iTrader: (27)

Can you adjust(change) the VSS pulses per revolution on the pcm? Will HP Tuners do that?? Wouldnt that be alot more accurate than the method of changing your gear ratio mentioned in the link above?? This is good stuff! Been losin sleep over how to get my factory speedo to work with my TH350.

All Black SS

Yes, thats a factory tuning difference between the factory installed A4 and M6. They have a different number of teeth on the VSS reluctor wheel.
I've done a trans swap and used HP Tuners to change the VSS number in the ecm.

LS6 Silverado

iTrader: (27)

Awesome- Thanks for the info.