1971 B300 1 Ton Chassis Rear Axle

[87Itasca]

Hi all,


Anyone know the rear axle used in these applications? It's a full floater, Dana 70? It has a removable pumpkin, and while we are unsure of the rear ratio, we're betting something like a 4.56. This engine is screaming at 55-60 MPH.


Is there a tag or number etched in these somewhere to tell?


We want to drop the ratio down a bit, but don't want to go to low. 3.42 maybe? I'd imagine a 2.75 would be great for the highway, but it would be a pig elsewhere.

[Rickf1985]

You will find it is a Dana 60 with 4.56 gears. you should have 19.5 tires and the rpms will be around 2800 if I remember correctly at that speed. There is a calculator on here for that, I will edit it in when I find it.


You say this has a removable third member? That would not be a Dana 60 or 70. Can you get a picture of it? The ratio is always marked on the gears if you are that far into it. The tooth count is etched into the ring gear. If all else fails divide the ring gear by the pinion and that is your ratio. With 19.5 tires you would not want to go below 4.56 or you will drop out of the power band and you will go nowhere at all, plus you 6-8 MPG will become 4-6 MPG!


I KEEP looking at your signature to see what vehicle you have and I keep forgetting that you are working on something else. That would have been a Dodge corporation rear. Ratio should be on a tag on the rear. most vans had 4.11 gears in the 300-350 series.

[87Itasca]

Sorry Rick. It is a 1972 Tioga, that is a 1971 Dodge B300 Sportsman 1 ton with a 5.9 and a 727.


The issue we are having is that it just runs out of steam at 50-52 MPH. It feels like we drop out of the powerband right around there. At 60, the engine sounds like it will explode. We wanted to gear it down a bit to where they can take it on the highway at 65 or so for prolonged distances and not blow the engine. Honestly, they'd just like to be able to keep up with the RH lane traffic. It does fine at 45-50, but there is a noticeable drop in power after that point. It doesn't feel like its not getting enough fuel or anything, it just feels like it is no longer in the powerband and is losing steam. We figured we could change the gearing and improve this.


I don't know about the pumkpin, that's what I was told by a gentleman here who used to work on these older rigs back in the day. He could be mistaken. I have not actually gotten under it yet to verify.

[Rickf1985]

Sorry, My power went out when I was replying to this the other day and I never got to add the link. power just came back.This will tell you where you are at. You need to be at least around 2600 rpm plus to push that kind of mass at speed.


http://spicerparts.com/calculators/engine-rpm-calculator