Speedometer confusion

[TagAllen]

1995 c1500
My speedometer was off by 7 mph consistently from slow speeds up to highway speeds. My fuel gauge bounced had many blown out bulbs.
I saw a 120 mph speedometer in the for sale section that was cleaner looking than mine. So I purchased it. My fuel gauge still bounces but in a different pattern but reads the same level overall. The confusing thing is that now the speedometer is off by a few mph at slow speeds but gets worse the faster I go. At 70mph by gps the speedometer reads 95mph. I have a adjustable vssb but have no Idea what to set it to with a different speedometer. The speedometer the previous owner thought it came from a 99 denali. The back of the speedometer says 97 c/k. Also When I put it in the dash it had no resistance it just fell into the plug where when I have changed them before it took a tiny bit of pressure.

 

[Erik the Awful]

Here's a link on converting your cluster with DIP switches to make calibrating it easier.

Recalibrating 1988-1991 speedometer / dash cluster - Chevy Message Forum - Restoration and Repair Help

Chevy Forums FREE technical assistance for your restoration and repair. Model specific subject matter experts, classified ads and more.

www.chevytalk.org

 

[someotherguy]

Here's a link on converting your cluster with DIP switches to make calibrating it easier.

Recalibrating 1988-1991 speedometer / dash cluster - Chevy Message Forum - Restoration and Repair Help

Chevy Forums FREE technical assistance for your restoration and repair. Model specific subject matter experts, classified ads and more.

www.chevytalk.org

That's for 1988-1991; he's got a 1995 which he says already has an adjustable VSSB, I'll assume he means he's got DIP switches in his DRAC module (last year you can do that, BTW.) Punch in the numbers and see if the results work.. https://harristuning.com/Tbi/vssb-drac-calibration/ - I'd write down your original settings before proceeding, though.

Richard

 

[TagAllen]

I think what I am going to do is add 24 percent to the gear in the calculation for the vssb. I took a closer look at the speedometer vs GPS and it appears to be off by 24 percent.

 

[TagAllen]

So that did not work. It did get much closer. i took the vssb to its highest setting. Its still about 7 percent off.

 

[TagAllen]

If /when I get new tires and gears it should be made up for.

 

[AuroraGirl]

if you have working ABS/RABS make sure to change your tire size calibration to match the new sizing (im assuming tires changed somewhere)

 

[TagAllen]

It does have ABS. But I don't believe on a obd1/tbi the ABS knows the tire size. I think it just detects the difference in speed tire to tire and sudden decel.

 

[AuroraGirl]

It does have ABS. But I don't believe on a obd1/tbi the ABS knows the tire size. I think it just detects the difference in speed tire to tire and sudden decel.

I know that on a gmc van, 1995, there was a tech 2 option to change tire size and its for ABS. if the systems are remotely similar i would say yes it does

 

[TagAllen]

Please elaborate. Is this plugged direct into the ABS or through the obd1 port?