Dana 60 Gear Ratio

[magik235]

I have a RV on a 1985 Chevy Van 30 chassis. It has a 350 / 350 with a Dana 60 in the rear on 27" dual wheels. It has a 4.11 gear ratio according to the tag. I tach 3500 rpms at 65 mph. Would the unit be drivable with 3.08 gearing to improve fuel economy?

The information below is from http://www.suspensionliftkit.net/superlift_tiresize.aspx

The chart is divided into three categories. The rpm highlighted in black are optimum for the tire size and ratio combination. These will most closely give you the best overall drivability. If you're looking for a ratio that will give better fuel economy for highway driving at the expense of some acceleration and overall performance, choose a ratio in the yellow shaded area. If you're looking for a ratio that will improve acceleration and towing power at the expense of some fuel economy, choose a ratio in the blue shaded area.

Note: This chart is based on engine rpm at 65 mph with the transmission in a 1:1 gear ratio (Third with a three-speed manual, Fourth with a four-speed manual, or Third with an Automatic). Remember, the actual rpm indicated in the chart will be slightly higher (between 100 and 300 rpm) on vehicles equipped with an automatic transmission. This is due to the slip present in an auto transmission's torque converter.

 

[nvrenuf]

Ratios that high don't come in a regular D60, they're used in D61's. I'm not sure if you can put a 3.07 in a standard D60 because the pinion head gets so big. I think the highest you can go is 3.54.

Btw, are you sure it's a D60 in the rear? I'm no expert on vans or RV type vehicles but I didn't think GM used a D60 in the rear of any 1 tons.

 

[magik235]

I am sure its a Dana 60. I would have preferred a 14 bolt but buying used and cheap doesn't have much flexibility when it comes to choosing axles. I haven't explored available ratios yet. I want to determine the best ratio then settle for what is actually available. Swapping rear axles is always a possibility.

 

[sweetk30]

you can get 3.21 for 14 bolt and member here has a set for sale .

also the lower you go the more a dog it will be on the road.

if you realy wana make it the best look in to a overdrive unit like gear vendors. that would make it a 6 speed auto and drop the rpms .

 

[magik235]

if you realy wana make it the best look in to a overdrive unit like gear vendors. that would make it a 6 speed auto and drop the rpms .

I just looked at their web site. Looks like a great product but its cost is more than I paid for the RV.

 

[sweetk30]

ebay and craigslist has them at times.

 

[alexsdad]

You would probably lose MPG if you geared it up. It would take more throttle to do the same work. Is it under 22'? Taller rear tires or something in the range of 3.73 ratio might get you better MPG on the flats with no wind if it wasn't too heavy.

 

[magik235]

It is 27 feet long and weighs 8000 pounds. The reason I created this thread is I am concerned that I might lose MPG if I gear it up. I also have a thread called Power Curve and Gear Ratio http://coloradok5.com/forums/showthread.php?t=290463 addressing the MPG issue. I am looking for opinions and input on how to optimize MPG.

 

[alexsdad]

My brother in law is a long time hot rodder. On their 1978 27' Motorhome, it had 4.88's with 30" tall tires. It was powered by a 440 Dodge.

This motorhome got 9.9 when we drove it right. He found a GearVendors overdrive and put it. On most of the flat roads, no wind, it dropped the RPMS's quite a bit. Best mpg was 9.5.

He would only use the overdrive when going downhill, or with a strong tailwind. But it drop the engine temps at 60mph by 5-8 degrees in the summer.

 

[runamok151]

seems the cheapest way to test it is to go up one size in tire and drive it around a little bit.