Speedo Problems - Gear/Cable?

[Ludigdrums]

So, I've been trying to get my speedometer ('81) to read correctly with the new rims and tires, and calculated that I needed a 17 tooth driven gear and everything would be great. So I went to my local chevy dealer and got one ordered, although it wasn't listed.

So, I put it in, and it read exactly the same as the 20 tooth gear I replaced it with. It further deteriorated until it didn't work at all except for a slight little bump every once in a while.

So, yesterday, I removed the gear to see what was going on, and nothing looked wrong. I was able to spin the cable and see the speedo working. So, I know that the cables are fine, plus the transducer is a little over a year old. So, I reseated everything, and still nothing?

Can a 17 tooth gear not work with a 350 tranny?! The drive gear is blue.
But what I don't get is that it worked originally, although not reading correctly, and then died. I'm going to switch the 20 back in and see if it starts working again.

I want to get the speedo right, cause with the 20 tooth, it reads 10 MPH slow.

Thanks for any thoughts!

- Jeremy

 

[arctic fox]

Jeremy I have a 76 4 speed that that was reading about 20 mph slow at 60. I checked the driven gear and cable like you did and it should have worked. after futher research I found that the drive gear in the transmision would turn by hand I have not got into yet but I think it is probably stripped internal but has draging enough to give me a reading. Yours might be stripped and quit reading. Can you reach in the automatic with the driven gear out to see if the drive gear can be turned. Good luck jag

 

[Ludigdrums]

Thanks Jag...I actually did this a bunch of times and it doesn't move.

I actually put in the old 20 tooth and it started working fine again. I don't understand why the 17 won't work...the teeth slant the same way, everything's the same size an all!

Thanks and keep 'em comming!

- Jeremy

 

[john1977]

Had same problem on my 77, the drive gear clip came out,or was never put on right after trans, rebuild. I would remove driven gear and reinstall and it might work for a little while.Pulled tail shaft,clip was gone and if it just happened to be in the right place it would work until it moved again put knew clip in,works fine now.

 

[Ludigdrums]

Sounds interesting. So, what is the drive gear clip supposed to hold? The drive gear itself? Also, is there any way to tell if the clip is there or not by looking?

When I put my finger straight in the hole, I can feel some sort of ridge, which I assumed the center of the driven gear rides on...however, it's barely a ridge at all. Is this correct?

Thanks again!

- Jeremy

 

[john1977]

Its really hard to feel the drive gear thru the hole that the driven gear comes out of. The dirve gear is what drives the driven gear,it is around the output shaft and there is a small spring clip that holds it in place (just bought one from GM garage as well as a new drive gear,less than 10 bucks) To get to the drive gear,unbolt driveshaft at trans. slide output yoke out,remove the 4 bolts that hold the tailshaft housing ( will be a little fluid) then you will see the drive gear.I could stick my finger in the hole that the driven gear goes and feel the drive gear and it felt tight only because it had slid up on the output shaft and wasn't really engaging the driven gear. This can be done with trans crossmember in ,but is a little harder. About a 1 hr job the first time. Good luck