Speedo gear question
 

My shop manual is pretty beat and as a result I've lost the cover as well as the first few pages including the pages showing which drive and driven gears go with which rears. The car is a 66 Bonneville with a TH400 and I've gone from a 2.56 (red driven gear) to a 2.73. I have a yellow driven gear from the 2.73. Can someone tell me (a) whether yellow is the correct driven gear color for the 2.73 and (b) whether I need to change the drive gear?

Thanks much for your help.

FWIW I managed to find the stray page of the shop manual in a pile of receipts. It looks like for big cars in '66 there is only one drive gear (20 teeth for the a 389 4 bbl car) for all ratios, and that the yellow gear (41 teeth) is for a 2.73 rear with small tires (14 x 8.25). That answers the original questions.

Now what I don't understand is how all these different size driven gears can mesh with the same drive gear. Are there different housings to hold the driven gear to keep it the proper distance from the drive gear? The original red gear (37 teeth) is quite a bit smaller than the yellow gear in diameter.

The housing for the gear has numbers on it to tell what driven will work with it. Going from memory but the numbers are something like 37 38 39 40. The housing has the bore in a slightly different place to accommodate different series gears.

Thanks. After some searching, it appears that going from a 37 tooth driven gear to a 41 tooth driven gear will require changing housings. One housing is for 40-45 and one for 34-39 (at least for the TH400). I ordered one of these:

http://www.summitracing.com/parts/NAL-1362293/

Hopefully that will take care of it.