I am trying to educate myself on our drivetrains... more specifically gears. I've heard terms such as 4.30, 4.88, 8", 9" nitro gears, etc. I was wondering if there was a place that i could read up on such info. There is so much info here on mud with respect to our trucks, but it all seems to be in many many little pieces. I'm looking for the newbie's guide to gears. I'd love to call slee or justdifferentials, but i really don't want to waste their time, although there is a distinct possibility i may be regearing.
Some may say, if you have to ask, it's probably not for you. This is normally true but this may be a case of "while you're in there..." I am exploring options.
Well, let's see if I can make my 3rd post here a helpful one. Don't particularly have a good FAQ available, but Google should be able to help you out on the generic terms. I'll give a quick rundown for the uninitiated.
Gear Ratio
This is the 4.30 or 4.88 you see. It's actually 4.30:1 which is where the ratio comes into play. This is saying that for every "1" rotation of the ring gear the pinion will rotate 4.30 times. Take that further, it also says that for each rotation of the tire the driveshaft will rotate 4.30 times. For 4.88s, the driveshaft will rotate 4.88 times to turn the wheels once. From a physics standpoint, the different ratios make it easier(or harder) for the motor to turn the wheels. Lot's of discussion can go on here about gear ratios, but the very basics are the numerically higher first number(lower ratio) make it easier for the motor to turn the wheels, leading to better acceleration and towing. But since it's all coupled together, it also means that at any given wheelspeed, the driveshaft is turning more times and thus your RPMs will be higher, possibly leading to less MPGs.
Gear Ratio Specific to 100 Series
From the '98 to '02 model years, the 100 Series was equipped with 4.30:1 gears to accommodate the gearing of the 4 speed automatic transmission.
'03+ got a 5 speed with a nice spread of ratios that allowed for 4.10:1 gears to be used. The low 1st gear in the transmission allowed for a better crawl ratio and the higher ratio allowed for ~1 more MPG in highway cruising...theoretically at least.
Differential sizing
Generally given in inches, it is the diameter of the ring gear. I believe the 100 Series has 9.5" rear diff and an 8" front. Front might be interchangeable with earlier models, but I believe the rear is specific with 32 spline axles whereas previous generations were 30 spline. Somebody can correct me if I'm wrong...
Third Members
Not mentioned in your list, but I thought I would throw it out there. The 100 Series used a style of differential with what is called a removable third member. Basically the ring and pinion are housed in this "third member" and can be removed from the axle as a unit. One thing this allows is for easy(relatively) removal of the third member to be taken to a pro to install/setup gears. This can save you some money if you're somewhat mechanically inclined, but don't have the tools or knowledge to correctly setup the gears. Also if you find yourself in need of a replacement after a breakage, you might be able to find a salvage yard to pull just a third member and replace it without any additional work.
Anyway, there are much more knowledgeable folks on here in regards to these technical bits, but I thought this might help answer some very basic questions in the meantime. Those of you who are more than just a keyboard mechanic like me, feel free to add to/correct anything I've posted here.
