[bobzdar]

My speedometer stopped working a little while ago suddenly while driving. I pulled the speedo cable out of the trans to see if it was broken but spun it by hand and the speedo moved, so pulled the speedo gear out of the trans and it appears the drive gear has broken and disintegrated - it's no longer there. Driven gear (red) looks fine, so I need a new drive gear but have no idea which it is. Car is stone stock 403 auto with 2.73posi. anybody know which gear I need and how to install it? Looks like I have to drop the driveshaft, anything else?

[burd]

That gear is called out on your build sheet.
What color was the old one? Any trans shop has them. I went to one for my 78: he had a box of them.

[bobzdar]

I don't know, it's gone, likely in the trans pan now. The driven gear is red.

[Trevor78]

1979 Firebird 2.73 auto trans 403 w/225-70 R15.

Red Driven-gear 37-tooth #1359271.

Blue Drive-gear 18-tooth #1246222.

[burd]

Look in box 28

[Trevor78]

And when the car doesn't have a build sheet, you look in the manual and supply info.

Plus, Box 28 tells him exactly the info he already has. Red 37-tooth Driven gear.

[bobzdar]

Originally Posted by Trevor78

And when the car doesn't have a build sheet, you look in the manual and supply info.

Plus, Box 28 tells him exactly the info he already has. Red 37-tooth Driven gear.

I don't think I have found the build sheet, unfortunately, but I haven't pulled the rear seat to see if it's there.

I ordered the blue gear, now install - is it remove driveshaft, slide gear on and then done? Or is there some retention mechanism? Or do I have to drop the trans (sure hope not)?

I found a video on it, essentially drop driveshaft, remove tail housing, slide new gear on with metal retention clip, then re-install tail housing and driveshaft.

[Trevor78]

You have to drop the tail shaft and remove the tail snout of the transmission as it slides over the inside shaft and has a small retainer clip to release. Not hard, just messy as with anything trans fluid. A good excuse to clean it all out and see why old gear shredded and remove the pieces. Be aware that these are the BOP TH350 which is the same as TH-700 speedo gears and not the chev TH-350. Handy to check the retainer clip also matches the slot, there's different sizes.

https://www.gtsparkplugs.com/images/...SpeedoGear.jpg

[bobzdar]

Originally Posted by Trevor78

You have to drop the tail shaft and remove the tail snout of the transmission as it slides over the inside shaft and has a small retainer clip to release. Not hard, just messy as with anything trans fluid. A good excuse to clean it all out and see why old gear shredded and remove the pieces. Be aware that these are the BOP TH350 which is the same as TH-700 speedo gears and not the chev TH-350. Handy to check the retainer clip also matches the slot, there's different sizes.

https://www.gtsparkplugs.com/images/...SpeedoGear.jpg

This is what I ordered (shown in combo with retention clip under 'frequently bought together' if you scroll down a bit). Says 700r4 and BOP th350 with 'GM manual transmission' retention clip.

https://www.amazon.com/Speedometer-G...s%2C327&sr=8-3

[bobzdar]

Just to close the book on this, the speedo gear was still on the shaft but had slid forward, clip was lying in the tail shaft housing. As far as I could tell, both were in perfect shape so I put the clip back on pulled the gear back into place with a gear puller (it's a really tight fit) and made sure the clip was properly seated and all is working well. If it happens again I'll replace with the parts I purchased.

[Trevor78]

Was it the same gear as the one you had ordered? From memory I used a sleeve of PVC pipe to tap mine on, can't recall taking it off, strangely enough.

[bobzdar]

Yup, color was a little faded but otherwise identical.