2004 Express 3500 Axle Swap

[JayY]

Long story short, I picked up a 2004 3500 axle thinking it was a AAM 11.5" from a 2004 Silverado 3500. Upon inspecting the axle, it's actually a Dana Super 70 (70S) from a 2004 Express 3500. Originally, I planned to do the swap to a GMT800 axle to address the uneven front to rear track width and not have to run spacers on the rear of the truck. Another benefit was the rear disc brakes, so I could address a soft brake pedal and eventually add Hydroboost to my 1997 K2500 5.7.

I've measured the axle and it appears that it's the same width I was wanting to achieve with the GMT800 axle. I was already planning on moving the spring perches and shock mounts, so no big surprises there.

My main question is, since I've never even heard of a Super 70, who else has swapped one of these into a GMT400 pickup, if any? It appears the ring gear is 1/4" larger than a standard 70, which I found interesting. It only came in HD Ford and GM vans as far as I can tell, and only offered with 4:10's or 4:56's. Mine is 4:10 limited slip, so I plan to re-gear it to 4:56 and add the factory trac-lok to keep my 5.7 in the powerband with 35's.

Any additional info that can be provided on this axle would be greatly appreciated!
Thanks!

 

[b454rat]

I think the axles are fine, they are just as strong as the GM 14b ff. Not many people use em because the GM axle is so plentiful, and a Detroit locker is cheap and simple to install. And since it's GM, the limited slip is actually the infamous Govlock. On the smaller axles there's a reason they call em grenadelocks, but on the 14ff they are alot stronger, so one would think it would be the same strength on the 70.....

 

[stutaeng]

Yeah, some of vans are different as the trucks on the axles. I've actually started looking at getting one of these 2500 or 3500 Express vans and noted the differential cover has like 12 bolts! I'm curious now, because I was recently reading a thread on a different forum on towing with these vans and the guys there were recommending the G80? Not sure if they switched to 14b or what on the vans. I wouldn't think the G80 would fit in a 70S? Dunno.

Also, I believe some of the early GMT400s trucks also have a Dana70.

There's a website that "ranks" the strength of rear axles and the Dana 70 is ranked just a hair lower than the 14b, IIRC. But probably marginally. I would not worry about strength of these axles. At this point if you already have the 70S, I would just run it.

Edit: What's the difference in Wheel Mounting Surface (WMS) on the 70S vs. your existing 14BSF? WMS = track width.

 

[JayY]

Yeah, some of vans are different as the trucks on the axles. I've actually started looking at getting one of these 2500 or 3500 Express vans and noted the differential cover has like 12 bolts! I'm curious now, because I was recently reading a thread on a different forum on towing with these vans and the guys there were recommending the G80? Not sure if they switched to 14b or what on the vans. I wouldn't think the G80 would fit in a 70S? Dunno.

Also, I believe some of the early GMT400s trucks also have a Dana70.

There's a website that "ranks" the strength of rear axles and the Dana 70 is ranked just a hair lower than the 14b, IIRC. But probably marginally. I would not worry about strength of these axles. At this point if you already have the 70S, I would just run it.

Edit: What's the difference in Wheel Mounting Surface (WMS) on the 70S vs. your existing 14BSF? WMS = track width.

Its about 3" overall. Just enough to where it would make the wheels flush with the body lines

 

[b454rat]

In 88 GM used the Dana 70 3HD. I think it was just 1 ton 4wds with the 454, I've seen more than a handful of 1 tons with the semi float rear, 2wd mostly. I don't remember all the specs on it, but used an offset carrier. They only used the axle for a couple years, I had an 88 and an 89 with it. Highest (numerically) gears factory was 4:10, I had one with 3:42s. Higher gears take some thought, don't even remember what they were. Another reason why many went with the 14ff. Van rears were always wider, so makes it cheap an easy to match the trackwidth of the front. I used an 80 van rear is an 89 CC dually I converted to a short box and 4wd, tires had the same track width front/rear. I have an 02 IIRC Sierra van rear thats eventually going in my Yukon when I SAS it. In 03 when they went to LS motors is when they went with the Dana rears. There were 2 side by side at a local yard, one a 2500, had a Dana 60 semi float, the other a 3500 had the Dana 70 full float. Both were disc's, I'm pretty sure both were Govlock, but I know for sure the 60 did cause I pulled the cover. Was hoping for a tracklok or even better a powerlok, what a let down lol

 

[stutaeng]

Its about 3" overall. Just enough to where it would make the wheels flush with the body lines

Okay, gotcha. Here's a pretty lengthy thread that talks about the locker of some of these vans:

https://www.cheaprvliving.com/forums/showthread.php?tid=25715

I think they get hung up on the LSD vs locker rambling though...Curious as to what LSD yours has...

 

[454cid]

In 88 GM used the Dana 70 3HD. I think it was just 1 ton 4wds with the 454...

A guy I used to work with had the Dana axle in his dually 6.5L.

 

[454cid]

I'm curious now, because I was recently reading a thread on a different forum on towing with these vans and the guys there were recommending the G80? Not sure if they switched to 14b or what on the vans. I wouldn't think the G80 would fit in a 70S? Dunno.

G80 is just an RPO code.

 

[stutaeng]

G80 is just an RPO code.

Yeah, you are right. I should have said, "What locker is in OPs Dana Super 70?"

 

[JayY]

Thanks everyone for the detailed replies! @stutaeng I'll do a little digging and see what I can come up with