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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: HeavyK20 on March 18, 2011, 03:47:15 pm

Title: Speedometer inop grrrrrr
Post by: HeavyK20 on March 18, 2011, 03:47:15 pm

Recently bought my 78 k20 money pit. Trucks speedo was inop when I bought it. So I went to auto zone and bought a new one hooked it up jumped in it and took it down the road Still inop  Anyone have any ideas? Turbo 400 with 4x4.

Title: Re: Speedometer inop grrrrrr
Post by: beastie_3 on March 18, 2011, 03:54:59 pm

what did you buy, a gauge or the cable?

Title: Re: Speedometer inop grrrrrr
Post by: HeavyK20 on March 18, 2011, 04:01:47 pm

I purchased a new cable because the previous owner didn't have on on it.

Title: Re: Speedometer inop grrrrrr
Post by: beastie_3 on March 18, 2011, 04:54:04 pm

Check to see if your cable is spinning when the truck is moving.

Title: Re: Speedometer inop grrrrrr
Post by: HeavyK20 on March 18, 2011, 04:57:18 pm

I did that I pulled the guage out aNd drove up my driveway and it wAsnt spinning. So does that mean it's my transfer case or where it screws on?

Title: Re: Speedometer inop grrrrrr
Post by: Lt.Del on March 18, 2011, 07:21:30 pm

your trans has a gear on the tail shaft. That gear may be stripped or missing.  You have to remove the 4 bolts holding the tail shaft cover on the transmission.  Of course, you have to drop the drive shaft to remove the tail.  

from my picture archives from my 79 th350 trans

(http://www.delbridge.net/transgear3.jpg)

(http://www.delbridge.net/transgear2.jpg)

Title: Re: Speedometer inop grrrrrr
Post by: HeavyK20 on March 18, 2011, 09:39:25 pm

With the the turbo 400 the speedo screws on the back passenger side of the transfer case.

Title: Re: Speedometer inop grrrrrr
Post by: beastie_3 on March 18, 2011, 10:34:49 pm

he was just showing you an example

Title: Re: Speedometer inop grrrrrr
Post by: Lt.Del on March 18, 2011, 10:46:25 pm

Thanks beastie.  I guess i should've read the original post a little better, but, perhaps the pics will help someone else w/ a similar problem--to understand the mechanics of a speedo. 

Title: Re: Speedometer inop grrrrrr
Post by: beastie_3 on March 18, 2011, 11:37:40 pm

well how much different is the tailshaft of a 350 and 400? What about the transfer case?


HeavyK20, what transfer case do you have?

Title: Re: Speedometer inop grrrrrr
Post by: Grim 82 on March 19, 2011, 02:03:39 pm

On the side of the tail housing for the t-case there will be a bolt and a steel retainer that hold the speedometer housing in place. This is where the cable threads on. Remove the speedo housing and the driven gear will slide out. It's plastic, and it's pretty common for all the teeth to be melted and ground off, and if this is the case there will be a groove in the drive gear where the teeth are also missing. To replace the drive gear you will need to remove the tailshaft housing just like in SgtDel's example, but it will be the t-case rather than the trans. The driven gear just slides in from the side and is held by the round speedo housing where the cable threads on. This should be true of a 208, 205, or 203 case.