formula350sd

iTrader: (2)

Ok I swapped from my T-5 to an LT-1 T-56 everything is in the car working flawlessly wish exception of the speedometer..

I've searched all the threads and couldn't find a definitive answer for my question so here goes..

How do I get my speedomoeter to work properly? I wired in the vss from the trans but it appears to send a different signal than the factory unit seeing as how my speedo pegs as soon as I start rolling..

I imagine I need some sort of conversion box like that dakota digital one or something correct? or is there a VSS I can get that will fit the transmission and run my speedo like normal?

Any help is appreciated...

Thanks
AL

sofakingdom

iTrader: (1)

Yes the Dakota box should work in your case.... right now I'm guessing your speedo pegs the instant the car starts moving.... that would be because the T-56 VSS puts out about 17 pulses per rev or some such, but your car is expecting 4. So it thinks you're going at warp speed. The Dakota box acts as a divider.

Here's what you've got.



You need to electronically divide the # of pulses down quite a bit to get to 4 per rev, as you can see.

Jaxom

I wonder how well it'd work to just cut all but 4 of the teeth off the reluctor.....

I know the spacing would be slightly uneven, but AFAIK the $8D code doesn't check the speed or timing of the pulses, it just counts them as they come I'd think $6E (what your '89 runs) would work the same way. Trimming 13 teeth off with a die grinder might be the cheapest and easiest way to make this work. If my IROC still had a factory cluster I'd try it and see for myself.

And yes, the 4th gen T56 reluctor has 17 teeth. So 17 pulses per driveshaft rev.

jmd

iTrader: (4)

You'll notice there's no aftermarket 4 tooth reluctor ring. That is because it's not 4 pulses per revolution in anything.

Early Third-gen VSS was driven by speedo gears or within the speedo and is 2 pulse per speedo cable revolution (2002 square-wave pulses / mile.)

Then, the 90-92 cars all had VSS driven by speedo gearrs at the trans. and were 4 pulses per "speedo cable revolution" (4004 sine-wave pulses / mile.)

Some early 1993 F-body T56s had an 11 tooth reluctor. Later ones were 17 tooth. 1994-up Automatics got a 40 tooth reluctor.

Those are 11 / 17 / 40 pulse per driveshaft / output revolution. Number of tire rotations per mile * gear ratio * 11 (or 17 or 40) = the pulse per mile for comparison purposes.

formula350sd

iTrader: (2)

Thats what I thought thanks guys

Jaxom

Yar. 4 pulses per driven gear revolution, not per driveshaft revolution. My mistake. It's been a LONG time since I worked with the factory speedo setup.