Does anyone know how to recalibrate the speedo for smaller tires?

[Caman96]

its a 96 sierra 1500

Need pcm reprogrammed.

 

[PlayingWithTBI]

its a 96 sierra

Need pcm reprogrammed.

Beat me to it, LOL.

 

[df2x4]

its a 96 sierra 1500

A '96 will have to be done in the PCM (computer) tune. Unfortunately that's probably going to cost you a couple hundred bucks no matter which way you go about it. I can think of three options which I'll describe below, number one being my personal recommendation.

1. Buy a copy of JET DST tuning software for $500. This is the only software on the market that's compatible with the '96 and '97 black box PCMs in these trucks. As long as you have a Windows laptop with a USB port, you can use this software to change just about anything you can think of in the PCM programming. Here's a screenshot I took of the speedometer calibration options for one of my '97s, it's very simple to edit these parameters.

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2.) Get a mail order tune from Black Bear Performance, for $350ish. They can make the required speedometer changes and at the same time optimize the rest of the tune, which will gain you some power. They're the only company I'm aware of that offers mail order tunes for the '96 and '97 trucks.

3.) Buy a handheld programmer from Hypertech or JET for around $450. These can do speedometer calibration, but the other options are very limited compared to actual tuning software like JET DST and will not gain you as much as a mail order tune would.

 

[Caman96]

…or just ignore it.

 

[Drunkcanuk]

Huh, FWIU all GMT400 trucks came with the VSS and a reluctor on the tail shaft giving you ~2,000 PPM (40/revolution), then you set your speedo with the jumpers on your VSSB (88-91) or DRAC (92-95). On my 88, with the EBL I wound up setting the VSS to 2417.11 (rounded off for Hexadecimal data tables) and my Dakota Digital based on mile markers to get it within 1 MPH using the radar speed traps around the neighborhood YMMV

Not sure what to say, lol.
All I remember was the different color gears on a chart in the instructions. And I know I've seen the same charts online, maybe can be done both ways???
I would like think there is another easier way to adjust the speedo without ripping the transmission apart. Lol.
And doing jumpers sounds a LOT easier!

 

[PlayingWithTBI]

I would like think there is another easier way to adjust the speedo without ripping the transmission apart. Lol.
And doing jumpers sounds a LOT easier!

The reluctor isn't too hard to install, you just have to drop the tail shaft housing, pull the seal housing, heat the reluctor, and slide it on the shaft A lot of 700R4s don't even come with them anymore, you have to install the cable gear or VSS reluctor on them, depending on how your speedo is set up/

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[Sean Buick 76]

Like @1998_K1500_Sub said, it depends on the year for sure.
On my 91 with a 4l60 there is a little gear in the tail shaft that can get switched out.
On other years there are DIP switches, others it's in the computer.

Yes the 91 has the 4L60 that’s basically the most refined version of the 700R4 which uses a TV cable still and no computer control except the lockup converter wiring.