Cascade Crew

Magman · Posted: Sat Feb 17, 2007 1:14 am Post subject: 700R4 Speedo Gears

I'm working on an 86 IROC-Z, LG4 that I just installed a 3.45 9-bolt, disk brake, posi rear (previous rear was 2.73 10 bolt, peg leg). I bought new gears for a cable driven speedo to match the 3.45's but, when I went to install them in the trans tonight, the gears in the 88 trans were not the same style as the ones I got from GM (ordered for cable driven speedo).

The trans is a rebuilt unit from an 88 IROC I plan to install tomorrow, but now the speedo gears have me confused. I'm guessing the 86 has a cable driven speedo and the 88 had VSS, hence, the difference in styles.

The drive gear that sits on the output shaft of the rebuilt trans (1988) was the same, no problem there. But, the driven gear that the cable is supposed to plug into has a conical end with a steel shaft and is much shorter than the new gear I just bought from GM (which is all plastic).

I think I can still do the swap tomorrow if I replace the complete tailshaft on the 88 trans with the one from the 86 then, use the new cable driven speedo gears. Just need to confirm with someone with a little more experience with 700R4's than me. Is this my fix or am I missing something?

Sorry this sounds confusing, it's just hard to describe!

Magman

Magman · Posted: Sat Feb 17, 2007 2:04 am Post subject:

Maybe some pics will help.
The speedo gears I'm installing on the 88 trans, in the 86 IROC are: 15-tooth grey drive gear (#8642620) and 41-tooth yellow driven gear (#25513048)

PIC#1: Gears from the rebuilt trans I'm installing
http://i89.photobucket.com/albums/k206/IROC-magman/88Gears.jpg

Pic#2: New gears purchased from GM, for a cable driven speedo
http://i89.photobucket.com/albums/k206/IROC-magman/newgears.jpg

Pic#3: The difference of the two "driven" gears
http://i89.photobucket.com/albums/k206/IROC-magman/DiffGears.jpg

Pic#4: The trans I'm installing
http://i89.photobucket.com/albums/k206/IROC-magman/transtailshaft.jpg

Magman · Posted: Sat Feb 17, 2007 11:55 am Post subject:

Well I droppped the 86 trans today and it has the exact same speedo gears in it as the 88 (steel shaft) so, I simply ordered the wrong driven gear.

Guess I'll make another trip to the stealership.

chevymad · Posted: Sat Feb 17, 2007 12:02 pm Post subject:

I'm not sure that the gear is actually wrong. But you may need another bullet to hold it, due the diameter difference. I think they made 3 different ones. At least they did for the electronic ones.

Magman · Posted: Sat Feb 17, 2007 7:17 pm Post subject:

I think your'e right. I found my old VSS driven gear from my 90 today and it is half the size, not even close. Guess I'll take a trip to my favorite tranny shop and see if he can help me out.

Anyway, I got the trans in and left the old driven gear. Until I can get the correct bullet. Thanks!

Magman

Magman · Posted: Mon Feb 19, 2007 9:48 pm Post subject:

Got it figured out. I've learned that GM makes two different sizes of the Speedo Gear Housings for a cable driven 700R4; one that works for a 40-45 tooth driven gear and the other covers all the lower gears. Found what I needed at the link below for $25.00. Should be GTG when it arrives in a few days.

http://www.eatmyshift.com/

Magman

Schultzy89GTA · Posted: Mon Feb 19, 2007 9:56 pm Post subject:

Good info

Glad you got it figured out.

-Schultzy