rear end and ratio questions

[iluvmy72]

OK....I currently have a GMC LWB with leafs......I would like to put a 3/4 ton rear end underneith it to boost power.....but I was told if I change over to a 3/4 ton with 3.73, I would get horrible milage......but that's the ratio that I have now......wouldn't the milage be the same?....or would a 3/4 with a 3.11 ratio be a better fit?.....I am going to do some towing and put a camper on it....any suggestions would help.........thanks...

[COBALT]

I don't understand...you want a stronger differential? Obviously if you're going to a 3/4 ton axle. Does the one you want to swap to have a carrier that you really want, with maybe a posi unit or a locker? You shouldn't get worse gas mileage with the same ratio-you should just get better response with a different carrier, and have a stronger differential if you're moving from something less substantial, but you're not going to get a power boost. If you stepped up to 4.11 or 4.57 gears to get lots of low-end response then your gas mileage will seriously go to crap, but it would be a fun little drag truck. You could smoke tires, and haul serious loads (depending on your transmission and engine combo)...but forget about going high speeds on the freeway.

[Smooth68]

just changing to a 3/4 ton rear will not boost towing power. And yes if you have 3:73's now and the new 3/4 rear has 3:73's power and milage will be the same. To boost towing power you will want to go to a lower gear ratio - like 4:10's. This will indeed boost power but lower your MPG.

[GMC71k20]

Go with 4.57s, lousy gas mileage is worth neck snapping holeshots, and its fun to slow down traffic on the highway

[iluvmy72]

cobalt: what about load fromt the camper?....are you certain that I wouldn't need a 3/4 for that?

[adamls]

I got to agree with everyone else. What are you going to be pulling that needs a 3/4 ton rearend. And without switching the leafs in as well you wouldn't really get any benefit from it, especially if it is the same gear ratio.

[iluvmy72]

adamls:....I will be pulling a 5th wheel and a 24 foot travel trailer and sometimes a Camper on the bed with a boat being pulled.

[iluvmy72]

I guess I was under the impression that a 3/4 ton would increase power and maintain milage.....I've been wrong on lots of stuff before..this won't be the first.

[adamls]

Well then the 3/4 ton rear will help, but only if you include the springs as well. Otherwise I do not think there is going to be a whole lot of difference. Others may correct me though.

[dwaite72lnghrn]

I assume you have a 1/2 ton now. The 3/4 ton rear will give you a margin of safety with larger brakes heavier bearings. If you have 3.73 today and go to the new axle with 3.73 it won't change MPG at all.

[Longhorn Man]

Installing this rear mey mess up your braking too.

[adamls]

Longhornmail may be right, the 3/4 ton brakes are slightly larger I believe. Your current proportioning valve would not work. You may have to get an adjustable valve. Pulling those large loads you may want to think about some large discs up front and a power brake upgrade.

[mikep]

If you are hauling a 5th wheel it would be a good idea to step up to a 3/4 ton rear end because of the better braking for one but more because of the much stronger axles , beefier ring and pinion and stronger and more numerous spider gears. My dad hauls a HUGE abover camper around and Ive had to bail him out a few times when his rear end went out several hundred miles from home. Believe me that is no fun! That extra strain on the rear end from the 5th wheel will test the limits of your chassis and it WILL find the week link. Better to throw out a few hundred for a used Dana 60 now than wish you had later on when the tow and repair bill comes. 3.73 is a good gear for towing.