I just bought a T56 conversion today... i have an 89 iroc and i'm not sure exactly what i need... i'm pretty sure i need JTR's tailshaft that is converted for my cable driven speedo, but do i also need the dakota digital box as well? when ordering the tailshaft they ask for tire size, gear ratio, etc. so your speedo will be calibrated. and isn't that what the dakota box is for too? not real sure what i do and don't need...

 

What year is your car? Camaro or Firebird?

 

The Dak box converts an electrical signal to a different elec. signal. For simplicity, you could get a cable driver to run your speedo cable (Abbott)

The JTR tailhousing had some availability issues. If you're able to get it, that's cool. There's also a a mention or two of how to do it yourself on this forum. (search & read; it's a good bit of work)

Personally, I'm going to gut a spare cluster for my car (non third gen) and build a new gauge setup w/ elec. speedo so I can bypass the use of a cable. You could do that if the later elec. speed cluster swaps in, and use the Dak box to convert the T56 signal to one that's usable by the ECM, and you might need a DRAC (as used in later 80's `birds.

 

 

Glossed over that didn't I. Then you have a mechanical speedo.

Another option is to just use an Autometer speedo. You don't need a buffer box, because it works right offf the T56 VSS. It isn't cheap, but neither is the buffer box. This is what I did.

 

If he has an ECM, he needs to retain a proper VSS signal to the ECM.

 

But if the car has a mechanical speedo how does the ECM get a VSS signal if there is no VSS? It should be mechanical if it's pre '90. Seriously, I'm wondering, because I'm driving my car around like this now! I don't want bad things to happed because something isn't connected properly.

BTW, the Autometer speedo does have a signal out prong on the back, just for this reason, but I don't know if it's the same waveform as the T56 VSS or the stock VSS. If it's like the T56 you'd need a buffer box between it and the ECM.

 

The VSS is in the back of the speedo.


You keep doubting me. It has the same setup as 4 of my cars. It has a VSS.


Mileage will be down a bit, and drivability is lessened. I drove my 86 SS (w/ 86 IROC TPI) without it just for fun. And drove it with park/neutral switch in park, etc.


I am not familiar with the Autometer line and what the output from the speedo is. This is a good reason for using the Dak box - it can feed the speedo, and the ECM correct signals. In your case with the Otto Metre speedo, it will accept any signal and you just "calibrate it," right? In which case, you'd just T56 to Dak box, and feed that signal to the ECM.

Unless your park/neutral switch is stuck in P or N, you should be getting an SES light....

 

I'll have to check into the factory VSS deal. I don't doubt you. I just can't believe that no one mentioned this on the five sites about the T56 swap that I checked before I spun the first wrench.

The Autometer speedo is self calibrating in that it doesn't matter what gears or tire size you run. It is only designed to read one of two waveform outputs from a VSS (so many turns/sec). One of these just happens to be the same as the factory 4th gen VSS signal. This allows it to work without the need of a buffer box.

Basically to calibrate it you hold a button in and start the car. Then once the car is running you let go of the button and press it again. Now drive a know 2 mile distance. Stop, press the button again. You're done it works perfectly. I even tested mine against mile markers on the highway.

I'll go over the instructions and my wiring diagrams and see if I can get to the bottom of the VSS signal to the ECM thing. I'll post back with more info.

 

thanks for the info... to sum things up i could get away with just an autometer speedo? no buffer box or aftermarket tailshaft?

 

If you have no ECM, yes. If you've an ECM, there's a lot more to it than that.

 

All right, I've got an update.

I can't find the VSS on any of my wiring diagrams, but I know that the ones in my Haynes manual are not perfect. I do have confirmation from several people that even with a mechanical speedo there is a VSS signal going to the ECM from the speedometer assembly.

I double checked my autometer speedo instructions, and there isn't a designated VSS signal output terminal as I though. This means that to get a VSS signal you'd have to tap the VSS sender wire directly.

This is where things start to get interesting. To give the ECM a VSS signal it would understand you would need to run the wire from the T56 sender through a buffer box like the SGI-5 from Dakota Digital.

The Autometer speedometer is self calibrating, and I believe that it will work directly off of a 3rd gen VSS, from what the instructions say. You would still need the factory buffer box for the ECM though.

The funny thing is that even without a VSS signal at all I do not have a VSS related trouble code. The car runs and drives fine, and even gets decent mileage (nearly 20MPG). I've also heard that even on cars that use an electronic speedo that if the VSS isn't connected they don't get a code. This to me means that the ECM doesn't need to "see" a signal from the VSS to operate properly, or at least without throwing a code (like what happens if the knock sensor is disconnected). It seems to me that all the VSS may give you is a bit better mileage, which at this point isn't worth it to me to buy the buffer box and rewire the setup. Eventually I'll probably do it, just because that's the way I am, but strictly speaking I don't think it's necessary.