1990 chevy truck No speedo

[Memphis]

1990 K2500 Chevy turbo 400 5.7L. Anyone know where to look to figure out my damn speedometer? It isnt the cluster and not the speed sensor, according to the wiring diagram I have power where I need to have it at the cluster but still NO speedometer. Any suggestions?

[PB86MCSS]

The speedo itself as part of the cluster went bad maybe? Doubtful but who knows...if the wire that gives signal to the speedo was tested ok that would be my next guess.

[Memphis]

I tried 5 different clusters. doubt they are all no good.

[wrath]

Is the ABS light on?

[PonyKiller87]

There is a weather pack connector that goes into the trans, I think it has 4 wires on it, check that. On my 90 k5 it had that connector and it would pop off every once and while and the speedo would go out.

[Memphis]

Is the ABS light on?

If it worked, I believe it is on, yes.

[wrath]

Unplug and then plug back in the ABS module. The speedo will probably work for a while then spaz out again, rinse, repeat.

The ABS module will cause the speedo to go out which on a 700R4 will cause the torque converter to never lock which eventually caused entirely too many 700R4s to burn up.

Thousands of these trucks had bad circuit boards in the IP. I don't remember where it's at on the IP but you can put a solder bridge in to fix it. I'll ask my Dad about it, I never had any of these trucks. I know he's battled with a great many with this problem including his own 89 with 260,000 miles.

[PB86MCSS]

I tried 5 different cl;usters. doubt they are all no good.

Could of added that to the original post ;) .

[Memphis]

Could of added that to the original post ;) .

lol, sorry. in my defense, I DID say it wasnt the cluster though.

[Memphis]

Unplug and then plug back in the ABS module. The speedo will probably work for a while then spaz out again, rinse, repeat.

The ABS module will cause the speedo to go out which on a 700R4 will cause the torque converter to never lock which eventually caused entirely too many 700R4s to burn up.

Thousands of these trucks had bad circuit boards in the IP. I don't remember where it's at on the IP but you can put a solder bridge in to fix it. I'll ask my Dad about it, I never had any of these trucks. I know he's battled with a great many with this problem including his own 89 with 260,000 miles.

Will try that, lemme know if you find any secret fixs...

[Windsors 03 Cobra]

Sounds like bad speedo buffer.

[Memphis]

abs unplug no go, any other suggestions? Diagram shows a DRAC module (maybe a speedo buffer?) but damned if I can find it anywhere.

[Windsors 03 Cobra]

A guy I worked with that has a 454SS said his was behind the glove box on a truck of that vintage, I think the buffer feeds the ECM and the ECM then feeds the IP. And being that the ECM is over near there it kinda makes sense.

I think I read on the later models with needle type gauges the buffer was built onto the IP printed circuit.

[Dr.Buick]

If you have a scanner you can go into the data screen and see what your vss speed is than you will know up to the ecm is ok.

[Coops Brother]

A guy I worked with that has a 454SS said his was behind the glove box on a truck of that vintage, I think the buffer feeds the ECM and the ECM then feeds the IP. And being that the ECM is over near there it kinda makes sense.

I think I read on the later models with needle type gauges the buffer was built onto the IP printed circuit.

There should be a DRAC digital ratio adaptor calibrator somewhere above the brake pedal it is a small white plastic box, smaller than a cassette tape. this will knock out the speedo, you will need to know the gear ratio and a bunch of other info to get the right one, call GM dealer they will know the questions.