Speedometer issue

[The-Pagemaster]

While i'm driving my speedometer is not accurate.  Its does work but the first thing I notice is this 5mph jump. As im speeding up it will bounce in 5mph increments the second issue is it says im going way faster then I actually am going. I just bought this truck. I am not sure what the factory tire size is. The tire/wheels that are on it now are 225/55r17. Also I unclipped the speedometer cable from the back of the gauge and dropped some wd40 down in it but it seems to spin just fine. I think the issue is my tire/wheel size.

I went to the discount tire site and it says the original tire size is 235/75r15. Is that correct?

If it is correct and my math is right then my tire wheel combination should still be close to the same as the factory right? The guy before me added wheel diameter and took away some tire diameter?

I hope that makes sense.

[zieg85]

The jumping around is the speedometer cable. 

[zieg85]

The speedometer is probably off due to the previous owner having a used transmission put in it.  It can be calibrated with the plastic driven or drive gear.

[The-Pagemaster]

How do you know that? The used transmission part.

[The-Pagemaster]

Guess i will replace the speedometer cable. how difficult is it to calibrate or change those gears? Do you know which ones I need? I should get them from here right?
http://www.transmissioncenter.org/GM_Speedometer_Gears.htm

T

[zieg85]

Great place to get what you need.  Be sure to find out what gear ratio you have in back.

[blazing816]

I had the same problem with my spedo jumping (mine was not off) and once I went above 55mph it was fine. However this was a brand new cable from the local auto parts store that was supposed to work in my truck. After much headache and buying a universal kit to make it longer, I found out the the the stock cables have a plastic end on spedo side that hold the inner part from moving back in forth so the gauge can read it properly.

So I got a AcDelco spedo cable from Amazon (not my first place to look but best price) it was like $24 and it fixed my problem instantly. However you will still have to play with the gears to get the spedo dialed in correctly like 'zieg85' said.

[SchneidR]

I did this too, replaced the cable and it still jumps all over the place!  Really effected by cold weather too.


E-mail:
Killerconceptz@gmail.com

[bd]

Some of the most common causes of "bouncy" mechanical speedometers, in order of occurrence, are:

* dry cable (remove cable from housing, clean, then lubricate with light grease)
* kinked cable housing or cable (replacement is the only solution)
* worn plastic driven gear shaft (replace the driven gear, gear seal, and support bushing o-ring)
* worn driven gear support bushing (replace the bushing, bushing o-ring, driven gear, and gear seal)
* worn out cable housing (replace complete cable assembly)
* worn out plastic driven and/or drive gear teeth (replace both gears, the driven gear seal, and the bushing o-ring)
* worn out speedometer head bushing (speedometer shop overhaul or complete head replacement)
* worn out or dry ratio adapter at transmission (rebuild & lubricate, or replace, the ratio adapter and drive key)

[The-Pagemaster]

So I got a AcDelco spedo cable from Amazon (not my first place to look but best price)

What is a good name to look for? I see speedometer cables ranging from 10 bucks to 100

[blazing816]

This is the cable I bought...that fixed all my problems after 3 different cables, this was the champ.

http://www.amazon.com/ACDelco-88959481-Speedometer-Cable/dp/B000C9QRCY/ref=sr_1_1?s=automotive&ie=UTF8&qid=1352406025&sr=1-1&keywords=ACDelco+88959481