Best gear ratio for towing and MPG

My 91 OCC is not a tow pack car but I want to change it to one by adding the correct oil coolers, limited slip and gearing. For you guys that have done the same type thing, what ratio is the best compromise for tow power and mileage when not towing?

What gears to you have now?

How far/how much do you typically tow?

Fix Until Broke wrote:

What gears to you have now?

How far/how much do you typically tow?

Somebody probably knows better than I, but I think the ratio is the standard 2.56 with an open diff. I checked the data plate a long while back and I'm pretty sure thats what it showed. As far as towing, max weight would be 5000 lbs maybe twice a year. Otherwise we are looking to get a hybrid camper in the 3500 lbs range to use, hopefully, many times a year. Distance probably would max at 600 miles round trip, mostly flat land around here, but occasionally in the Smoky mountains.

Start by confirming your rear end ratio, but the simplest solution is to tow in Drive and when you're not towing run in overdrive.

2.56's in drive are = 3.42's in overdrive so if you're thinking 3.42's you can get the same effect on the highway just by pulling the shifter down a notch. You won't have limited slip, but that's not really any benefit towing on the highway.

You can go 2.73, 2.93 (there's a carrier split between these somewhere), 3.08, 3.23, 3.42

2.93 or 3.08's are likely the best compromise, but the cost/time/effort of gears/limited slip/install/speedo correction, etc can buy a LOT of gasoline and running the engine at a higher RPM is easier on all the driveline, transmission, cooling system, etc

Not the only solution, just something to consider...

The SPID on the passenger's side D pillar has a G code. GU5 is 3.42. If you have another number, it is a 2.73. Those are the only ratios that the TBI wagons came with. If you are going to change gears, you need a set that will accept the tone ring for the ABS, and a correct tone ring for the gear ratio. The cheapest GOOD LSD is the Yukon clutch model. While you have the rear apart, you may need new axles. If you need new axles, Moser is the place. Similar price to the Chinese/Indian ones. That would also require new wheel bearings, and seals. You are going to spend about $100-150 on tools to reassemble the rear. You can put any gears in the rear of the 91-93 rears, because they never came with the 2.56 gears, and since you are putting an LSD in it anyway, there are no conflicts. If you decide to do it yourself, use a 0.038 shim on the pinion shaft, and you will only have to put it on once.

3.23 gears are known as 200 mph gears. A 3.42 would be considered a 190 mph gear. You are running a 305/5L engine. The 3.42 gears would pull a bit better from the start, and go up hills better. Your gas mileage would be slightly reduced, but the car will feel a lot stronger. You are working with 170 hp in a 4400 lb car, so anything will help with the pulling of a trailer. You can easily put $700-1000 in a rear if you rebuild it yourself. Gears wil be about $150, LSD $350, axles $200-350, tools $100-150, and misc $70-100.

Thanks for the input guys. I checked and the code is GU2 so it seems I have the 2.73 rear gear. I don't really want to spend the money but the times I have driven the wagon, I've noticed a slight whine on deceleration, so I know the rear is going to need to have some love thrown at it in the future. I figured while I was in there I'd upgrade it a bit.

Meh, a lot of GM rears have a slight whine to them. Heck, two of my Chrysler minivans had differential whine in the front including a very low mileage Jasper unit. I wouldn't worry about it one bit.

If your car has a 2.73 rear, just tow in D and don't worry about it. Unless you need traction on a boat ramp or drag-race from stop-lights, don't bother with the a limited slip differential. As Fix Until Broke said above, rear axle parts and labor can get pricey fast. If you do most of your driving NOT towing, and/or only tow short distances, I wouldn't change anything.

Cool. I'll go with what I have and upgrade if need be. Thanks!