Drive / driven gear problem?

[Peer81]

Hello everybody.

The problem is that me speedo isn't working anymore.
What happend is that I changed the diff ratio so I needed another driven gear to correct the speedo. Inside the 700R4 is a 17 tooth drive gear, I went from a 36 driven gear to a 43 driven gear (with other housing).
First my calculations were off because now the speedo was showing not enough (prevouis to much). But after around 60 miles the speedo stopped all together and stayed at zero.
When I got home I took out the driven gear to see that every teeth was eaten away. As I also had a 42 teeth driven gear I put that in so see how much correction it still needed but the speedo is staying at zero. When I took the driven gear out it still looked untoughed and like new (like it isn't toughing the drive gear). I tried it several times to see if the housing was far enough into the transmission but no problem there. Maybe the inner cable isn't far enough in the drive gear so I pulled it but is was already as far as it could. Tonight I returned the old 36 driven gear with the other housing but still no luck...

I checked the speedo cable all the way to the speedo and no problems. I connected the cable to a drill and slowly spung it around and the speedo was moving according to the speed of the drill. So I think there is no problem in the cables, cruise control module and speedo itself.
I also checked the drive gear inside the transmission. All the teeth are perfect and I cant move or turn the gear so it still seems to be locked into place.

So the question, what is it that I don't see?

Greetings Peter

 

[TimAT]

The drive gear is a pretty much press fit on the shaft with a clip so it won't slide forward or back. I use a 10" crescent wrench as a driver.

I'll bet the teeth on your drive gear are gone. At least where they don't mesh with the driven gear. If you twist the driven gear retainer in the housing a little you can change the depth of the gears.

With the cable off the trans, can you put a drill on the cable and make sure the speedo and cable are good?

 

[Peer81]

With the cable off the trans, can you put a drill on the cable and make sure the speedo and cable are good?

Yes, did that and that is working fine!

I was hoping the drive gear is from a harder plastic then the driven gear so it will survive longer then the drive gear. As I need to remove the axle and trans tailpiece, not my favorite hobby.
I'll look at it again this evening!

Greetings Peter

 

[TimAT]

I've seen a couple of drive gears that looked fine and didn't have enough left to turn the driven gear. I've seen a couple of them cracked and spinning on the shaft too. If the clip that locks it in place has broken it's also possible the gear could have move on the shaft. If it moves in either direction, the gears won't mesh.

 

[Peer81]

Hello Tim,

You're correct! The drive gear has moved to the back. Don't know if the clip is broken or not it looks alright to me. Also don't know if i can remove the axle (at the differenciel) to get acces to the rear of the trans? Thing is I see two dimples in the outgoing axle so the question is on which dimple should I lock the drive gear with the clip, the forward or rear dimple?

Greetings Peter

 

[TimAT]

My old memory says the clip fits into the forward hole of the two on the shaft. If you can drop the driveshaft all that's left is 4 bolts that hole the tail housing on the trans. (5 if it's a TH400). The open end of the clip goes to the rear. You'll need to get the gear up close, use a small screwdriver to hold the tabs on the clip down and then drive the gear forward until the tabs snap back up behind the gear. And a picture of the clip:http://compare.ebay.com/like/151037433239?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

 

[Peer81]

Hello Tim,

Thank you, I already found some good info on youtube.
It wasn't as easy as I hoped it would be. As I have a 700R4 with C4 yoke and alu axle. The axle can't be disconnected from the yoke on the car (joint is pressed in) so the yoke and axle have to move to the back so the yoke can come free from the tail housing. Well, not enough room so I had to lower the differential so the axle could slip over the front of the diff. Problem is with the diff loose but the spring still connected the diff goes up and not down. So also disconnected the rear spring. Now there was just enough room for the yoke to come free.
Took the tail housing off and now I could see clearly the clip was in two pieces!
The drive gear was i good shape (just some minor defects) but as I already had another one I changed it. Of course I forgot to order another clip, lucky for me I have my old 350 around that has the same clip. So used that one and put everything back together. Tomorrow I just need to reconnect the axle to the differential and then I'm set to go

Greetings Peter