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96+ OBS Chevy Speedo help

1K views 4 replies 3 participants last post by  SUBRUTUS 
#1 ·
Has anyone on here changed gear ratio in a 96+ OBS Chevy? I got a lead on a set of 3.42 gears for my truck and am looking into what it will take to change the speedometer. Not finding a concrete answer online and the computer button pushers at the dealer tell me that for a 96 the pcbc (don't ask me what it is, something brake controller he said) needs recalibrated but they can only do the factory ratio with tire size adjustment told me to go to someone aftermarket that specializes in gear changes. I don't believe him, I know ever inch of the trucks wiring and it doesn't have a (pcbc), the diesels and pre96 had a vssb, but on the 96+ gas the vss signal goes to the ecm which has outputs for cruise and seedo so the adjustment has to be in the ecm.
Anybody done it?

TIA, Glendon
 
#3 · (Edited)
VSSB "vehicle speed sensor buffer" is where you change ratio, search the web for GMT400 VSSB mods. Long ago I did one and soldered toggle switches to the VSSB so it is just a flip of the switches. One other setting is through a OBD2 device controller to change ABS cycling to match tire diameter change.

However; if you are not using a 40 tooth VSS for signal you will have to convert the Dodge VSS signal to GM signal Dakota Digital makes the converter.
 
#4 ·
Thanks, that abs setting may be what the dealer was talking about. Yes, I am using the original GM transfer case so I have the 40 tooth vss signal but I'm pretty sure the newer gas GMT400 (Vortec) trucks don't use the vssb.
 
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