Speedometer quit working

[ChesterChop]

I unhooked the speedometer cable from the back of the gauge and down below from the rear of the transmission.  The cable turns in the cab when I spin it from underneath.  When I hook up the end to the transmission and leave the gauge end unhooked, the cable doesn't spin when going down the road.  Is there something I can replace were the cable screws into the transmission? When I took that end off a little bit of oil ran out. 

[Hayseed]

Is the Transmission end of the Cable rounded off or still has the Drive pin On It..

Also is there a Ratio Adapter something Like this on the Transmission?? they can & will fail..

 

[ChesterChop]

lIt still has the pin.  Another guy suggested chucking up a cordless drill to the cable.  The end in the cab rotates whether chucked to the pin or the cable itself.  When its hooked to the speedometer and turned with the drill I get nothing.  Not sure if the drill isn't turning fast enough to register or if two things went out at the same time. On the transmission mine screws into something like what you have pictured.  I have a 1987 Super liner.  Is it just as simple as unbolting and replacing that? Does oil pressure spin that pin? Thanks for the input. 

[Joey Mack]

it is a mechanical gear driven cable.  if you pull too much cable out at the end, you stand the chance of pulling the square drive end of the cable out of the speedo..  push the cable in as much as you can and chuck only a little bit in the drill and try it.   the gear drive unit is easy to repair/replace. remove it at the  seal housing and look inside for a spiral cut gear. that drives the spedo drive unit. also clean the unit really good and check the operation of it, right in youre hand...

[ChesterChop]

I had my girlfriend in the cab watching the speedometer.  She said she could hear something moving in there.  I thought the same thing and pushed it in as far as I could.  The speedometer end of the cable and where it plugs into the speedo look a little worn but hard to tell because I don't know what a new one looks like. I would think the first thing I need to do is get the end in the cab spinning going down the road.  I'll see if I can get a ratio adapter from mack on Monday and go from there.  Thank you.  

[Vladislav]

1 hour ago, ChesterChop said:

lIt still has the pin.  Another guy suggested chucking up a cordless drill to the cable.  The end in the cab rotates whether chucked to the pin or the cable itself.  When its hooked to the speedometer and turned with the drill I get nothing.  Not sure if the drill isn't turning fast enough to register or if two things went out at the same time. On the transmission mine screws into something like what you have pictured.  I have a 1987 Super liner.  Is it just as simple as unbolting and replacing that? Does oil pressure spin that pin? Thanks for the input. 

You can put a cordless drill right into the speedometer head input. It must show speed. Try slow at first since you need to figure the direction. Speaking the drill revs required I had luck just putting a wooden stick a bit thicker than a match and spin it fast between two my fingers. The needle popped up to nearly 10-15 mph for half a second with that.

No no oil pressure involved. Just all mechanical. Worm drive off the tranny output shaft.

Edited October 24, 2021 by Vladislav

[ChesterChop]

There's kinda of a collar on the back of the speedo that I can spin with my fingers and it reads on the gauge. If the cable in the cab spins with the drill on the transmission end but not going down the road hooked up,  I probably should start there, shouldn't I? I can't think of a way to see if the pin on the transmission drive is turning driving down the road.  My luck the speedometer head went bad along with the drive. Its not really making sense to me. 

[D-Day]

The end of the cable that goes into the collar on the back of the speedo can become slightly rounded off as well as the inside of the collar letting it slip internally if the cable is not connected it can float in the housing losing contact at the transmission end also best to pull the speedo and check the fit we always did this check with a new cable  but not having access to another cable with a fresh end you might pull your inner cable up out of the housing a few inches and check the fit that way

[Vladislav]

Also you can drive the truck for a few meters or a bit longer with the cable off the speedo gauge but connected to the tranny. Actually holding its end in hand. It must show spinning when the truck moves.

[ChesterChop]

I've only had the truck for a year so I don't know how old the components all are.  I can get a cable from mack.  $62. I'll start there and see what available as far as the drive/ratio adapter is available.  Thanks for all the info guys.