Speedo acting up

[Graystone]

I have a 89 Jimmy and when it is colder out or when I first start driving it the speedo will work fine then shoot up to 15 to 20 faster then I am traveling. It is worse when its cold out. Whrn this is happening it makes quite the noise behind the dash. What would cause this to happen?

 

[RetroC10Sport]

More than likely your cable needs lubed up.

 

[Graystone]

More than likely your cable needs lubed up.

Why would that cause a constant 15 to 20 mph over for an extended periods of time

 

[Boone83K10]

Why would that cause a constant 15 to 20 mph over for an extended periods of time

the noise is because the lack of lube. mine does it too, I just shoot some graphite spray in every few months. the jumping says to me that you have a missing tooth or even the wrong gear.

 

[Graystone]

I understand however it normally is 5 mph over when it suddenly jumps and will stay 15 to 20 mph for miles on end not just surging like the cable is binding. It is not a momentary thing.

 

[bucket]

This happens with probably 50% of the cable speedo vehicles I've ever owned or driven. I chalk it up to "it's just the way it is". Really though, I've never thought much of it, it's just what happens with some age and cold temps.

 

[Graystone]

This happens with probably 50% of the cable speedo vehicles I've ever owned or driven. I chalk it up to "it's just the way it is". Really though, I've never thought much of it, it's just what happens with some age and cold temps.

I just find it odd how I could drive it 40 miles with it happening and then stop and it begins working correctly again. I was wondering if it was something other then a sticky cable

 

[bucket]

I just find it odd how I could drive it 40 miles with it happening and then stop and it begins working correctly again. I was wondering if it was something other then a sticky cable

My theory is this. The cold temps cause the cable not to rotate freely which makes it vibe and cause a whacky speedo. The vibrating cable causes the cable temp to warm up a bit, so when you drive a little while and then stop, the cable will then spin freely once you start driving again.

I always just tolerate it. It's not a constant problem and IMHO, the other gauges are more important anyway. Speedo is just an added bonus if it works.

 

[MrMarty51]

UUUMMmmmmm, correct Me if I am wrong but, is`nt a 89 an electronic speedo, it should be a TBI unit I think, which would have an ECM and a vehicle speed sensor with wires to the speedo instead of a cable.
Not really familiar with the Jimmys though.

 

[bucket]

UUUMMmmmmm, correct Me if I am wrong but, is`nt a 89 an electronic speedo, it should be a TBI unit I think, which would have an ECM and a vehicle speed sensor with wires to the speedo instead of a cable.
Not really familiar with the Jimmys though.

'89 was the last year for cable speedo. There was a VSS, it mounted to the back of the cluster and read off the speedo. In those years, the VSS was used only for ECM (cruise too I guess), then later they got smart and used the VSS (now mounted to trans/t-case) to signal ECM and power the speedo.

 

[MrMarty51]

'89 was the last year for cable speedo. There was a VSS, it mounted to the back of the cluster and read off the speedo. In those years, the VSS was used only for ECM (cruise too I guess), then later they got smart and used the VSS (now mounted to trans/t-case) to signal ECM and power the speedo.

Hey Bucket, thanks fur the infurmashun, musch appreciated, You see, evenus "OLD" dogs is`nt beyond learning.

 

[jt1200r]

mine did that till the plastic piece the cable goes into on the tranny broke

 

[Graystone]

I have been dealing with it this long so its no big deal but it made no sense on how it was happening

 

[87ChevyR10]

I have a 89 Jimmy and when it is colder out or when I first start driving it the speedo will work fine then shoot up to 15 to 20 faster then I am traveling. It is worse when its cold out. Whrn this is happening it makes quite the noise behind the dash. What would cause this to happen?

Mine started doing the same thing this morning on my way home from work. Albeit, slightly different outcome. Once I hit 40 MPH, the speedo doubles my speed and makes a buzzing/whirring sound behind it. Once I slow down below 40, it returns to normal.

I'm thinking something is up with the speedo or in the transmission. A binding cable wont cause this. If anything, a binding cable would drop the speedo needle temporarily and then shoot needle passed current speed or cause a severe, constant needle bounce or the speedo would quit registering speed altogether.

 

[Graystone]

Mine started doing the same thing this morning on my way home from work. Albeit, slightly different outcome. Once I hit 40 MPH, the speedo doubles my speed and makes a buzzing/whirring sound behind it. Once I slow down below 40, it returns to normal.

I'm thinking something is up with the speedo or in the transmission. A binding cable wont cause this. If anything, a binding cable would drop the speedo needle temporarily and then shoot needle passed current speed or cause a severe, constant needle bounce or the speedo would quit registering speed altogether.

Yes this is what mine is doing. Very similar