Speedometer issues

[Maggro]

I have a 69 c20 Suburban with a th400. The speedometer is good and accurate for about 10 miles on the highway then starts to jump around. It then slowly starts to read slower and slower until it dies completely. I have replaced the cable and still the same issue. Anyone know what might be causing this.
Thanks, Mondo.

[LockDoc]

Originally Posted by Maggro

I have a 69 c20 Suburban with a th400. The speedometer is good and accurate for about 10 miles on the highway then starts to jump around. It then slowly starts to read slower and slower until it dies completely. I have replaced the cable and still the same issue. Anyone know what might be causing this.
Thanks, Mondo.

That's a new one on me.... Seems like if it died it would stay dead. If you stop and take off again does it come back to life or do you have to leave it set for a while?

I will have T-Bone take a look at this thread and see if he has any ideas.

LockDoc

[Maggro]

Thanks for the reply, yeah kind of a strange speedometer issue. When I stop I have to let it sit for a while before the speedometer starts working. It’s almost like it only works when the transmission and motor aren’t up to full operating temperature. My next step was gonna be to change out the gear drive but I don’t know what color to get yet.
Mondo

[LockDoc]

Originally Posted by Maggro

Thanks for the reply, yeah kind of a strange speedometer issue. When I stop I have to let it sit for a while before the speedometer starts working. It’s almost like it only works when the transmission and motor aren’t up to full operating temperature. My next step was gonna be to change out the gear drive but I don’t know what color to get yet.
Mondo

I wonder if the gear on the trans output shaft could be slipping when it gets hot.... I can't remember what locks it onto the shaft off the top of my head.

LockDoc

[LockDoc]

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Here is the clip that holds it on the shaft.

https://www.ebay.com/itm/Speedometer...-/222540623107

LockDoc

[Franks 72]

Doc,where does this clip go? I dont remember seeing it in my frame off resto.

[LockDoc]

Originally Posted by Franks 72

Doc,where does this clip go? I dont remember seeing it in my frame off resto.

It secures speedometer gear onto the transmission output shaft inside the transmission.

LockDoc

[franken]

Maybe spin the drive w/ a drill to see if the trouble is on the speedo end?