Speedometer Cable Leaking

[78projectchevy]

Hey everyone, first post here.

My aftermarket speedometer cable is leaking at the connection where it meets the transmission. Here's a pic of the leak:



 Any ideas how to fix? It leaks pretty bad overnight, maybe a grapefruit sized puddle.

[bd]

Welcome to the Forum!

You probably need to replace the driven gear and seals, at minimum...

Remove the 6 mm bolt that retains the driven gear and its support bushing in the tailshaft housing, and remove the support bushing with the gear.  Grab the toothed end of the gear and wiggle it side-to-side while it's still inside its support bushing.  There should be no more than about 0.006" of sideplay.  Next, remove the gear from its bushing and inspect the bore of the bushing.  If there is more than 0.006" of sideplay in the gear, or the bushing hole appears to be worn non-concentric (oblong), replace the gear, the bushing, the bushing external o-ring and the soft seal at the outer end of the gear shaft (image). 

If the bushing passed inspection, with the gear removed from the bushing, inspect the outer end of the gear shaft.  If there is a concentric groove worn in the shaft where it contacts the seal, replace the gear, the gear seal and the bushing external o-ring. 

Lubricate the gear shaft with ATF or petroleum jelly (Vaseline) and reassemble.

[78projectchevy]

Thanks for the very well written response BD. I'll need to order the replacement gear and seals (or maybe just get the whole assembly).  I'll get under there and thoroughly inspect as you mentioned. I'm assuming transmission fluid will flow out when this is removed, so I'll have to be ready. Maybe I should buy a new speedometer cable too. Can always return it if unused.

[bd]

You will lose a small quantity of fluid.  When looking for a new bushing, count the number of teeth on the driven gear.  Bushings are offset to compensate for various gear diameters, which directly relate to the number of gear teeth.  The bushing has to match the gear for proper fitment.

While you're there, check the condition of the transmission mount.  Petroleum based fluids will make the rubber spongy after a time, resulting in separation of the mount.

[Stewart G Griffin]

Out of curiosity, which way does the driven gear, the one that drives the cable, turn?

[78projectchevy]

Counterclockwise.

I say this because to test the speedometer, you can attach your drill to the cable, set drill to reverse, and watch your speedo needle move up.

[Stewart G Griffin]

Counterclockwise.

I say this because to test the speedometer, you can attach your drill to the cable, set drill to reverse, and watch your speedo needle move up.

Ok, that makes sense as i may be having problems with my speed sensor for my aftermarket digital speedo.  It seems to be loose.