Differential Swap from Dana 60 to 70?

[Clyde9]

From: ZR91 (Original Message)
Sent: 3/21/2008 11:04 PM

My 79 Minnie Winnie has a Dana 60 differential with 4.10 gears.
I just bought a Dana 70 from a 1998 GMC dually. -It also has 4.10 gears, but Randy's ring & Pinion carries a 3.54 gear set for this differential.
According to my math this would drop my rpm's from 3,000 at 60 mph to 2,550-exactly at the torque peak of the 440.

Has anyone tried this?

Thank-you,
Jay



From: captrowdy1
Sent: 3/21/2008 11:55 PM

Well if its the change in RPMs you want to know from the Dana 60 to the 70 go to the Dana web site and they a chart that should give you all the info you need to figure RPMs. Or if they don't most off road gear head site have the charts. They tell you both RPMs and also what MPH to expect. I don't know why the swap wouldn't work.

Rowdy



From: denisondc
Sent: 3/22/2008 9:20 AM

I would be glad to know your results. But will the 3.54 let the RV go up the slopes in the mountains okay? I would think at the least you would lose some of your towing capability.



From: cupcake
Sent: 3/22/2008 11:10 AM

Before you try this you may want to do more research into what effect a higher gear ratio will have on your transmission & engine. Manufacturers of motor home chassis use those gear ratios for a reason, like your transmissions ability to get the vehicle rolling and the engines power to keep it rolling. Usually the bigger the motor home the lower the gear ratio.

Mine is a 70 22' class A , I have a Dana 70 with 4.56 gears. The bigger 30' motor homes will have gear ratios in the 5.00 range, but they also have overdrive transmissions to make up for those lower gears once they get rolling. I guess all I am trying to say is, the higher the gear ratio the more stress on your automatic transmission to get it rolling, especially if you are towing, and the more power it takes to keep it rolling once you are up to speed. Usually lower rpm's for fuel economy are gained by OD transmissions not higher rear end ratios, for those reasons.

Like I said - more research. The actual physical swap should be easy, maybe relocating leaf spring perches, Is axle width and lug pattern the same? When relocating leaf spring perches make sure axle is rotated to correct position for correct universal joint angle.



From: bluebird5750
Sent: 3/22/2008 5:23 PM


I agree. That ratio is probably way too high for a mh. Even if you're not towing. An overdrive tranny would be the way to go if you're wanting fuel mileage. It will take off much easier too, as the overdrive trannys have a deeper low gear. I bought a 95 model last summer, and it has a 4l80e trans. It has a much lower 1 st gear and takes off much better. And gets much better mpg. It is a larger coach and is fuel injected, so that makes a difference too. With a 3 something gear it might even do worse on the mpg, as you will be deeper in the throttle to keep it rolling.

Chuck