T350 Box and FC Speedo

[jwm]

My FE is running a T350 box and the original FE Speedo. The speedo is everywhere, speed wise, and I am currently using the speed reading on an old GPS to keep me on track and out of the clutches of the law.This is a pretty common conversion, so my question is, is there a replacement drive gear for the speedo drive in the box to get the FE speedo back within some reasonable proximity of being correct.

Thanks guys, any help much appreciated.
jwm

[Harv]

G'day JWM,

It's a good question, and one that I need to sort out for my own EK wagon project. I currently have the TH350 connected to an FB/EK speedo head, and I get the same problem (speedo is all over the place). The info below is my current thinking, but I still need to try it out.

The original grey motor crashbox has the following ratio:
Speedometer drive gear: 6
Speedometer driven gear fitting assembly: 23

So you need to find a TH350 drive/driven gear ratio that is similar to this by swapping out one gear or the other. You can then fine-tune the ratio to suit the tyre size that you have. Speedo gears for TH350s are still readily available from places like American Autos.

There are a huge number of speedo drive and driven gears available for the TH350 box:

Driven gears
# of teeth Gear color   GM part #
18            Brown         3987918
19            Natural        3987919
20            Blue            3987920
21            Red             3987921
22            Grey            3987922
23            Black           3980346
34            Green          9774413 
35            Orange         9780387
36            Natural         1359270
37            Red             1359271
38            Blue             1359272
39            Brown          1359273
40            Black           1362048/25513047
41            Yellow          1362195
42            Green          1362049/25513049
43            Purple          1362196/25513050
44            Grey             9780470
45            Lt. Blue         9775187

Drive Gears
# of teeth Gear color GM part #   Shaft size Clip size
8             Black         6261783     1.19"       5/16
10           Purple        6261785     1.19"       5/16
18           Green        6260037      1.19"       7/16
19           Natural       8640188      1.19"      7/16
15           Grey          8642620      1.19"      5/16
17            Red           8640517      1.19"      5/16

Hope this helps.

Cheers,
Harv