Hi, I noticed some trans fluid on my garage floor. I jacked up my vette and crawled under for a look. The fluid was dripping a few drops from the speedometer cable unit, from under the coupler nut but I also noticed that the speedometer gear that the cable hooks to is loose. It can be moved up and down and back and forth on the side of the trans case. Is there a fix for this or will it be an expensive repair? The holder for the gear is in place to retain it but the gear is visibly loose where it goes into the trans. Does anyone have any help or assistance on this matter? I am afraid to run my car too far with this problem. Help. Thank you. 

This is not a bad fix.  If you have a stock transmission pan (without a drain plug), you'll have to remove the transmission pan to drain the fluid from the transmission.  The transmission gear housing comes out with one bolt.  There is a large o-ring around the housing, and a small (spring loaded) o-ring that surrounds the plastic gear itself.  Very cheap fix.

If you have to drop the pan, I would change the transmission filter while you've got it down.

Thank you for your input, I appreciate it but what about the gear moving when you wiggle the speedometer cable/ Is something worn there or will the new "O" rings tighten up the gear where it comes out on the side of the trans. Last year when the speedometer cable broke it was twisted apart at the end that goes into the trans gear. Again I appreciate you input. 

The gear is a bit sloppy, but it shouldn't wiggle too much.  The gear looks like this:



Your gear shaft may be snapped inside of the housing.  If the speedo cable siezed up, it's possible.  But it would usually just chew up the sqare drive on the gear shaft and not break the entire gear.  Either way, inspect the gear shaft and teeth when you get it out to make sure it's not chewed up.  The gear meshes with a gear inside the transmission; if one is messed up the other may be as well.  I'm not sure how hard it is to change the gear inside the tranny, but it would scare me...  Gear inside of the transmission looks like this:



The gears are colored based on the number of teeth (makes your speedo correct for your rear end ratio).  So if you need a new one, they are about 10 bucks on eBay.  Just buy the same color.  But because transmission fluid can stain a white gear, count the teeth just to make sure.

The housing and o-rings look like this: 



The small o-ring isn't visible in this picture. 

One thing to be careful of... It is VERY possible to drop the gear in the transmission during reinstallation!  Be careful.

Let me know how you make out...

Since we are on speedo gears, I need to change mine. Doing it is no problem but what I need to know is WHAT gear do i need to put in it.

Speedo Chart

This will get you in the ball park

You only need this one gear (Brown 18 teeth)

(modified large image to link, and added live link-aapple)
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|UPDATED|8/12/2013 10:00:46 AM (AZT)|/UPDATED|

Cool !!!

The housing with the cable end in it, that bots to the trans is loose because it moves to allow for different size gears, swing the housing so the gear is in mesh with the gear in the trans and tighten down the bolt.

I been kinda watching this thread, and so far, I haven't seen anyone ask what trans the car has...
A '77 L48 should have a 350 trans. The l82 had the 400 trans. Both take different speedo housings & gears.
The 400 uses the large housing posted above, and if that thing is loose, there's a problem...
The 350 uses the small, "bullet" housing, and those can normally be wiggled around some. Here is the bullet, speedo gear, retainer, and bolt that holds it all in.








We really need to know exactly WHAT it is that is moving around, since you can't actually grab the speedo gear on either one.

also, do I need to drain the 4 speed tranny to change this?
or do I just take it out, let it drain by itself and refill when done.
Thanks again and in advance!!
Joe