-Changing Gear Ratios-

[BryanCregger]

okay i have a 98 GMC 1500 ext. cab with 6 inch lift and 35" tires. I'm changing my gear ratios from 3.73 to 4.56.

at jegs there are ring and pinion kits i was told i would need the 8.5 ones but my question is do i just buy to sets of those because i would have to change the front and rear differential or are they different items?

here is wat the product says

GM Ring and Pinion with Install Kit 10-Bolt
1.626'' Diameter
30 Spline Pinion
8.5'' Diameter Ring Gear
4.56 Ratio
41-9 Teeth
555-60033K Fits 1970-Up (New-Style 10-Bolt Housing) Cars and Light Trucks. Will not work with pinion mount ABS sensor.

[junior3382]

The final ratio will be the same, yes, but from I have found, since that truck has an IFS front and a solid axle rear, there are some differences. If you look at the description for the kit, it will tell you wether or not you can use them on both. Sometimes yes, sometimes no. I have a S10 and I looked into it, they were different, however due to some advice from a few guys here, I am going with a live axle conversion anyways. but I would double check with the manufactuer. And yes you do need to change both ends, or else you will confuse the **** out of your transfer case, and that will just lead to more problems.

[BryanCregger]

well there is also a 4.1:1 ratio gear but would the 4.56:1 be the better route? and wat about a master kit? would i need to buy 2 or just one....or none?

here is wat the product says

GM Ring and Pinion with Install Kit 10-Bolt
1.626'' Diameter
30 Spline Pinion
8.5'' Diameter Ring Gear
4.56 Ratio
41-9 Teeth
555-60033K Fits 1970-Up (New-Style 10-Bolt Housing) Cars and Light Trucks. Will not work with pinion mount ABS sensor.

[junior3382]

I wasn't suggesting you didn't know that, just answering a future question from another reader... anyways, that description doesn't say if it is end specific. I would hate to see you buy it and have it be misssing a peice for the front end. Thats all....lol.

[bradrhale]

yes, you will have to buy kits. i would not suggest going into a carrier and replace gears without shims and bearings and other junk. if you tend to do alot of hauling or towing with it, the 4.56 should work out well. if you are making a show off toy with better gas mileage and no hard work, i would step it back down to the 4.11 they should have a gear somewhere between there. 4.33 4.25 something like that, i cant remember. as for if the same thing will fit the front diff, dont know. i dont think it will but there ar others here on this forum that will know exactly what you need and possibly even the part numbers.

[BryanCregger]

alright thanx everyone lots of good info here

[junior3382]

when you complete this, since it seems we are all a little curious, you should post whether or not the kit was interchangable. I am sure there are some of us that will need that info in the future. And since the truck has as much as a lift as you say, I would go with the 4:56 gears, and save the trouble of being under geared in the future.... Good luck.

[BryanCregger]

my dad is set on the fact that my fuel economy will plumit....can anyone shed light on this?

[75K30]

Your dad is right,,,,almost. Mpg is based on an average. He is correct about the mileage if the truck could magically start off at highway speed, and never have to slow down, and speed up again. Since that is impossible, the truck still has to accellerate from a dead stop, it takes that much more power, and gas to get the truck moving, and has a poor affect on mileage as an average. The addition of lower gears helps the truck get going, and the compromise is a slightly higher rpm at highway speeds. But this type of trade off is worth it, because the truck will accelerate much better at any speed, with the better ratio. If your truck could stay at 60 mph forever without going uphill, you would be better off without the gear change, and dad would be right. But in the real world, we have to stop, and go again, and this requires a better gear ratio. My money says, depending on how much street use you get, you will achieve better mileage with the 4.56's, over the gears you are running now. I am assuming that you currently have 3.42's or maybe 3.73's.

[nate3436]

The front ring gear should be like an 8.2" It's not the same size as a 10 bolt ring gear which is 8.5". And I too would stick around a 4.10 gear.