1998 silverado speedometer issue

[j66442]

My new to me 1998 Silverado C1500 5.0 auto has a speedometer that is reading fast. it operates smoothly but is off at all speeds. 45 mph ground speed reads at 61 mph on the cluster. I checked with a scan tool and the reading put out by the computer seems accurate as verified by GPS.

The previous owner had put on larger tires, 31X10.50X15, but I am back to a similar to original size 275X60X15, which is almost identical overall height to the 235X75X15 original tires. The rear axle is stock 3.73 verified by counting the teeth and against glovebox codes.


i used a hypertech to change tire height and gear ratio. It did not give me an option to see what previous entries were.

Is is possible that when PO changed tire size the shop found a different way (besides programming) to change the speedometer reading to account for the tire size? If so what am I looking for? Since OBD output is correct I would think behind cluster?

Cruise control doesn't work. I haven't tried to troubleshoot yet. Oil pressure sometimes reads correctly other times pegs. I have a 1999 suburban donor that I can try the cluster from if needed.

 

[east302]

Oil pressure sometimes reads correctly other times pegs. I have a 1999 suburban donor that I can try the cluster from if needed.

I’d try that. The odometer can be swapped over if needed.




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[98chevy2500SS]

I usually get a junk yard cluster if something ain't working right. When my 98 was a half ton, it used to read like 70 going 55 before I swapped in a new cluster, then it read 60 going 55 (since the PO put 265/70r16s on it).

My 97 is kind of doing the same thing yours is doing, I have to be at 65 to go 60, which is odd because I have the factory tire height and factory gear ratio. Odd... Planned on putting 285's to help to issue some.