As you can see in some of the pictures, this truck came with some moderately silly "play tires" (33 x 12.50 x 16.5 M&S). Since it is destined to be a work truck for me, it's going to need some work boots. Luckily I have a set of nice mud & snow tires (9.50 x 16.5 LT) on 8 lug rims I bought many years ago as spares for my decrepit Ford. However, these work tires will be quite a bit shorter than the donuts currently on the truck (improving torque...), and the speedometer right now is fairly accurate. So I will have to change the speedometer gear. I called my local friendly Chevy/Audi parts counter, and was told I needed to tell them the final drive ratio (and tire size) before I could order the correct part. I had him tell me my choices so I'd know what to look for. So, I figure I will have to jack up a rear wheel, put a mark on the driveshaft and the raised tire, and start turning and counting until both marks hit whole numbers at the same time. Somewhere in what those two numbers are will be the final drive gear ratio. (They have to be whole numbers, since you can't have a fraction of a gear tooth...) But one of the techs next door told me that the gear ratio is stamped on the ring gear, all I'd have to do is pull the differential cover and dump the stink oil - which would insure that the truck would get at least one actual gear oil change in its lifetime. Here is the closest thing to interesting I have found :
I am tempted to think that where is says "11 41 10 77" signifies an 11 tooth pinion and a 41 tooth ring gear, which would be 3.73, one of the ratios the parts guy told me it might be. And the 10 and the 77? Well, it occurs to me that it could be the date of manufacture, since this is a 1978 truck. Not sealing things up until I know these answers, though. Luckily it is unseasonably warm for November! Well, since I have photos and relative confirmation that "those" numbers are the ones that matter, I painted up the differential cover, stuck a new gasket on it, bolted it up and refilled the differential with stink oil.Today I removed the play tires and bolted on the work boots, using some nice new lug nuts I had to buy a new 1 1/16" impact socket for. I measured the hub height before and after to get a rough idea of the effect on y speedometer. Before was about 15 1/2", and after was an inch less, 14 1/2". This is a ratio of 1.069 or 0.935, meaning my speedometer will read about 7% high (and the odometer will accrue that many more pretend miles) until I get a new speedometer gear. My pretty painted pumpkin cover (note where the brake line bracket was taken off it and left free when the lift kit was installed):    |
