The Stovebolt Site Forums The Parking Lot Big Bolts 4 Speed Transmission Speedometer Drive

Doing some more cleaning and I noticed my speedometer cable was siezed up. I traced it down to the transmission and and it's no longer connected to the transmission and was filled full of solid gunk.
I tore it apart and cleaned everything out, now I have a few questions about it.
The first thing I'm wondering is if there are supposed to be any bushings or anything in there. Mine only has the two gears and nothing else.
My second question is how it connects to the transmission, I can't see any means of fixing them together.

If anyone has and diagrams or pictures that'd be awesome!

What year truck are you working on?

What transmission do you have?

Mike B

I believe its an SM420??
The truck is a 54 GMC 350

Usually there is a speedo drive assembly on the back of the trans, often covered with grease and dirt to protect it from rusting. Look carefully for a male threaded boss, usually at an angle under the bottom half of the trans, might have a 90* drive assembly attached.

Ed

I'll try and take a picture and get it uploaded tomorrow.
I can't find any pictures of what i've got anywhere. theres some sort of extension coming off of the transmission to get it past the parking brake drum. Then the 90 degree adapter (the part i disassembled) mounts on to that some how.
There is just more slop in the gears than i think there should be

We'll know more with a photo.

I think my 54 GMC 350 COE does not have an adapter at the transmission. There is a two-speed-rear range-selection adapter for the speedometer at/near the gauge.

Here is a link with a few pictures.
The one of under the truck is looking at the side of the transmission from the driver side. The red circle is around what i think the adapter goes into. the green line is on the PTO shaft that runs to the rear.

The exploded picture includes all of the pieces it had in it. just two gears, nothing else.

https://trello.com/c/5cvYFLkW/1-speedometer-pictures

Has anyone seen one like that?

Yup! I have one just like that on a spare trans and one trans without it. See my (3) pictures here

http://s160.photobucket.com/user/st...9d9a_zpsmaa0o5qs.jpg.html?sort=2&o=7

I haven't taken it apart but I'm betting there is a small 4-5" long square shaft (same size as the speedo cable end) that inserts into the transmission driven gear and extends out to the 90* adaptor

Mike B

That's it! How does the adapter attach to the transmission? There's no threads it clamps or anything that I can see.

Speedo parts usually have female threads on both ends of the cable, male threads on trans, male threads on output end of adapters, extensions. Make sure we are talking about same parts, dirt and grease disguise many parts.

Ed