72 F350 REAR END QUESTION

[1972yellowf350]

Hello Fellas,

This is my first post. I have searched over and over, with mixed results, so I said why am I going to these search engines when I can ask here. I have a 1972 F350 cab and chassis 4 speed with a 360, the rear end is way slow. My question is what rear end is a good replacement with minimum fab work? I have read that 1986-1997 Ford CNC's are pretty much a replacement, just a bit wider. Any help would be greatly appreciated. Josh, South Mississippi.

[Donnie]

why not just change your gear set? a lot less work & money too.....Donnie

[ToughOldFord]

What do you mean by way slow?

What ratio is in it now? What are your driving goals? Cruiser? Fuel economy? Towing? ???

[1972yellowf350]

Hey Guys,

Donnie: Could you point me in the right direction for a new gear set?

ToughOld Ford: The old F350 has 4:10 gears with a 4 speed tranny. Driving goals: Well it has a 360 in it so fuel economy is out the window, but 55 MPH is really stressing the old truck. I live in south Mississippi so we are limited on hills here. I am interested in cruising at least 65 MPH. As far as towing I have a 01 Cummins that does all my towing, but I have zero concerns about the towing abilities of the Ford. It has plenty of power.

Any info would be great. Thanks, Josh

[ToughOldFord]

Okay, I getcha. I know that the Dana 60 can go as low (numerically) as 3:55s which are a good freeway gear that still allows some towing.

Being an F350 I believe you have a Dana 70 and I don't really know what the gear options for that one are.

I'm not sure if you'll really see much/any fuel economy savings with a rear/gear swap though. When I had the 360 in the '69 it had 4:10s in it. I replaced them with 3:73s. That dropped the RPMs @ 65/70 MPH by 200 RPMs. Fuel economy didn't improve at all.

[1972yellowf350]

Thanks for the reply, yeah I figured that I wouldn't save any MPG's with the ol gas hog 360, but I am more interested in drivability. The Ol Dana 70 with the 4:10's really limit the speed. Its a nice truck, but it seems to like 50 mph, and 55 starts to stress it a bit. Im not in any hurry to go anywhere but 65 would be real sweet.

[ToughOldFord]

I wonder if you might have 4:56s in your truck? Reason I'm thinking about that is that with 4:10s I've never had a problem cruising at 65/70, the way you're describing it it sounds like your truck may be even lower.

Even if your door tag shows the 4:10s you may want to crawl under the truck and see if the tag is still on the rear to verify.

Hopefully someone that knows the D70 will chime in and let us know what the gearing options for it are.

[averagef250]

The pre-72 F-350 Dana 70's use an obsolete carrier offset. You're on the right track with replacing the whole axle with something more modern. You are correct that any axle from a 73-97 F-350 cab chassis bolts right under.

Most of those axles have 4.10's though.

[1972yellowf350]

Thanks Average F250. I'm gonna keep searching for a newer rear end, I may get lucky and find a 3:55 or a 3:73 for it. Thanks for the help. Josh

[gregamorton]

I lost a tooth in my rear on my 72 f350. I added a 73 f250 dana 60 3.73s and added 2" spacers on each side. I did have to cut perches off and weld new ones on in the right place.

[ToughOldFord]

Here's a FWIW. Got this from another conversation at a different forum:

you can find 3.55 gearing in the duallies,however from extensive searching,high,low and sideways,it appeared to me that the 92-97 9th gen drw trucks didn't offer 3.55 gearing at all.all 4.10's.the way i had to go was back into the 8th gen drw trucks (1st gen sterling 10.25) to find a drw pickup axle with 3.55's.

[1972yellowf350]

Thanks Tougholdford! I guess I'm on the lookout for a 8th gen rear end.

[TNIceWolf]

For what its worth I run my F350 dually with an identical setup as yours at 70 mph on the interstate on a regular basis. Yes the engine sounds like its coming through the hood. But the 360 or any other FE for that matter is a pretty darn durable engine.They have the ability to run that way.