75SHARK

Hi,

On my '67 4-speed vette, the speedometer lately has been working off and on and now it doesn't work at all. So I unscrew the cable at the transmission, remove the plastic gear and it feels like the speedomter gear inside the transmission is much too far forward to contact the plastic gear. I thought this gear was pressed onto a shaft in there. Is it possible that it could have moved? Or perhaps the entire shaft has moved? After all, when the speedometer first started acting strange it would work in 1st, 2nd and 3rd gears and then go to zero as soon as I shifted into 4th. Then when I would downshift it would start working again. Either way, I'm bummed out that the transmission will probably have to come out again. Thanks for any suggestions.

Rob

r67427/435

Rob, you are correct, the speedometer gear is pressed on to the output shaft and as interference fit should not move. I rebuilt my Muncie this winter and the only critical dimension for the speedo drive gear is the distance from the center bearing. If this were incorrect it would not work in any gear. I would look at the plastic gear or the speedometer cable as the source of the problem. Rick

75SHARK

Well, I looked at the gears inside the transmissions on both my '67 and '75 (the speedometer works fine in the '75). Sure enough, the gear inside the transmission that the plastic gear comes into contact with is much farther forward on the '67. The gear must have slid forward on the shaft. I'm not sure how because I thought these gears were welded to the shaft.

5speeds

Don't go crazy with exact positions of speed drive gears on mainshafts.

The drive gear when positioned properly on the mainshaft has to have the center of the gear centered in the speedo fitting hole of the tail when the tail is bolted on. That simple.

So if you don't know where the gear should be simply take a Sharpie Marker, stick it in the tailhousing speedo fitting hole and mark the mainshaft. It doen't have to be exact. You can easily be off .100" each way and it still will work.

Paul

75SHARK

On my '75 (in which the speedo works), the mainshaft gear is centered in relation to the hole when I look inside. On the '67 though, only about one thread is showing. Therefore I don't see how the plastic gear is contacting the mainshaft gear at all. That is a good idea about marking it with a marker. I'll try that to see where they are contacting. Thanks for the suggestion!

Allcoupedup

Try connecting the transmission end of your speedo cable to a power drill to make sure your speedometer works properly. Make sure you have the drill spinning the in the right direction.
Brian

buns

Click on the link below....lots of good info.

http://forums.corvetteforum.com/show...edo+drive+gear

75SHARK

Thanks for the link to the post. The picture was especially good. My cable works fine and the metal gear is certainly there. The only thing I can think is that is slid forward. Boy I wish there was some way I could hook it and pull it back with the tranny still in the car! I guess it will have to come out eventually.

5speeds

The plastic drive speedo gears ( NOT driven ) appear to be in 1969 and 1970 model Muncies only. They are held in place ( lossely I might add ) with a spring clip that will break and kick the gear off with the slightest speedo cable bind.

If a metal gear has moved, get a new one. More than likely its been pressed on and off too many times and the ID is stretched. I never press them on, I heat them up and shrink them into place. If you feel compelled to reuse it coat the ID and mainshaft with Locktite red

Paul

75SHARK

If I take down the transmission and discover that the gear has indeed moved on the shaft, should I just replace the entire shaft (with the gear already pressed on)...or do they not come this way?

Plasticman

No, too costly and unnecessary. Just get a new drive gear, or Loctite the existing gear (if it is a metal version). Follow Paul's (5Speeds) advise.

Plasticman

edfrye

As all of you know, to replace the plastic gear (the driven gear) in the transmission on my 1969 Corvette it is necessary to remove the rear transmission housing. To do this it is necessary to remove the rear transmission housing. I see 5 bolts holding the rear housing to the main trans main assy. I also see that the drive shaft must be detached. Can the housing then be removed? Is there anything else..
Thanks Ed

edfrye

As all of you know, to replace the plastic gear (the driven gear) in the transmission on my 1969 Corvette it is necessary to remove the rear transmission housing. To do this it is necessary to remove the rear transmission housing. I see 5 bolts holding the rear housing to the main trans main assy. I also see that the drive shaft must be detached. Can the housing then be removed? Is there anything else..
Thanks Ed

DZAUTO

jimmies63

on my 63, the plastic gear was easy to replace on jack stands, but the gear in the tailpiece slipped forward so no contact. the trans had to come out completely and a new gear sweated on. waiting this week for the return. last thing to do after almost 18 mos in the shop.