bigdooly

How can I determine gear ratio of my rear. I did the spin the drive shaft count the revolutions of the rim routine, and came up with 373. Was available in 74 in a delta 88. I ask because I swapped rears, & forgot to take speedo drive gear from donor car. Rear removed from 74' 88 & installed in 75' 88. 75 had highway gears, I think 273 not sure. Are there any #'s on rear to help me determine what I have, & what speedo gear I need. Both cars 350 cid/ th375. Thanks.

monzaz

aGAIN THIS WILL DEPEND ON THE REAR END YOU HAVE UNDER THE CAR from 10 bolt 8.5 (low powered base) to 8.875 pontiac (350 -400 ci) to 12 bolt full size olds (455 cars)

It is not 3.73 :0 we all wish. pretty sure 3.42 was the highest full size cars had in the Corporate era (1971 -1976)

You can not do a spin test with A OPEN NONE POSI REAR AS THE PLANTERY SPIDERS WILL THROW THE SPIN OFF WHEN YOU HAVE BRAKE DRUM DRAG etc. YOU might get it to work if you remove all the wheels and drums. BUT the bearing drag STILL could make a mesh of it.

Easiest way is to remove the rear cover and read the ring gear outer diameter edge as you wipe the oil off it.
The numbers will be tooth count NOT ratio
IE 17 41 = 2.41

ratios were 2.29 2.41 2.56 2.73 2.93 3.08 3.23 3.42

Jim
J D