Speedo reading about 30 to high. stock tires.

[cybrfire]

I got a question for yall.

Made a trip with the crew cab today and my speedo is reading 85 (pegged) and I'm backing up traffic. I know I wasn't going more than 55-60 MPH my wife was following and didn't rag me about going too fast (got a speeding ticket last week and had I been speeding tonight I would of heard about it). RPM's are right on and I'm sure I would have noticed that kinda slippage from the 465 clutch. Stock size tires and factory gearing, so anybody know why it would read so high??? I personally never had one read this far off no matter what was wrong or had been altered.

 

[dyeager535]

Has the speedo been doing this forever, or something new?

Mine once in awhile decided it wanted to go crazy and peg out, even if I was doing like 35MPH. Typically it would start making a buzzing noise though as it decided to do this.

Never actually fixed the problem, it just kind of went away, but the only culprit possible is the speedometer itself, since nothing can "overdrive" the speedometer except different speedometer gears, and if the cable binds, it will only result in a bouncy reading.

Has done it a couple of times after the initial incident, but that first time it did it all day that I drove, the other couple of times since, its read high for a bit, then went back to "normal".

 

[diesel4me]

Speed kills..

It could be the speedometer itself--did it work ok,then just start doing this??--Some GM trucks have a little "gearbox" ,a ratio adapter,that screws onto the transfer case,and the speedo cable screws onto it--if someone removed it and screwed the cable in without it,it would read very high----

I have a "squeaky" speedometer in my 79 C10--sometimes in the cold it chirps like a bird,or makes an unnerving knocking sound--more than once I though my motor was losing a bearing!--I did try to take the dash out,and lube it with some WD-40,but it didnt stay quiet for long--I guess I will have to wear earplugs,and keep my eyes open for another speedometer with 113.000 miles on the clock(or close to it..).

 

[cybrfire]

I bought the truck a month or so ago and it worked properly on the 2 plus hour drive home. since then I've bee bopped around town with it a couple times but I don't remember the speedo operating funny at that time. It did bounce a bit on the way home initially.

Today I drove it round trip 30 miles and it read high the whole time. Wife tells me now I was going about 50. I had a load so I was taking it easy. Thing kinda baffles me. I understand how the speedo works and it almost seems like there isn't enough resistance to the cable turning.

I guess its just another quirk with this old bomber.

I did play with the 4 wheel drive a bit but that shouldn't effect anything as far as I know.