[subwoofer88]

I just got a 1993 D250 that has the 9.25" rear that I want to swap for a dana 70, and I have two questions.

1- If I swap a first gen axle with a different gear ratio will I need to do anything, or will the computer compensate?

2- If I can only find a 2nd Gen dana 70 will the speed sensor even work? Not worried about axle width and all that stuff if this can work.

I spent some time looking around and no one has really ever brought this up it seems.

 

[u2slow]

Speed(ometer) sensor is in the transmission. An axle ratio change will affect your speedo.

The sensor in the axle is used for ABS. It doesn't care about ratio.

Is the plug the same between the 2 diffs? I swapped my 93 (w250 w/Dana 70) to a Dana 80 and don't remember anything weird. It may have simply plugged in.

 

[subwoofer88]

Ah, well I feel dumb. Thanks for the education.

 

[moparmike72]

Speed(ometer) sensor is in the transmission. An axle ratio change will affect your speedo.

The sensor in the axle is used for ABS. It doesn't care about ratio.

Is the plug the same between the 2 diffs? I swapped my 93 (w250 w/Dana 70) to a Dana 80 and don't remember anything weird. It may have simply plugged in.

The axle sensor on My '98 3/4 ton dodge company pickup also drives the speedometer, when I first got it the wire was pulled out of the sensor and the speedo was dead, the ABS light was on. Replaced the sensor, repaired the wire and the speedo works and the light is off. There's no speedo drive on My transfer case, only a blank space where they used to machine the hole for one.

 

[u2slow]

The axle sensor on My '98 3/4 ton dodge company pickup also drives the speedometer

That came later. OP has a '93.

 

[subwoofer88]

Yeah I had to take step back after typing that. Not sure why I thought that was the speedometer sensor in the axle. I did look into it either way and the same ABS sensor is used from 1990 up to 1997. I can clearly see the plug on the side of the transmission with three wires sticking out.

So I guess a better question to ask is how interchangeable are the reluctor wheels inside the transmissions? Does it matter which 4 speed auto it comes out of (A518, 47RH, etc.), does the year matter, or do I have to find one from a 90' to 93' transmission? They all have a near identical architecture on the inside even into the 2nd Gen trucks. I am stuck with going to a 4.10/4.11 gearing since no Dana 70's ever came with 3.90 gears, and no on makes 3.90 gears for them. Not like it makes that big of a difference cruising down the freeway of course. Just a 0.20 gearing difference.
I have another 93' A518 that worked fine, but could use a rebuild since it has 250,000 miles on it. I can do all the work to that one and swap it in.

 

[u2slow]

No reluctor wheel inside a '93 trans. Its a worm gear. The conversion to electric happens outside the trans with a transducer. Axle ratio is fine tuned with a mechanical ratio adapter.

How the Speedometer Sending Assembly works - Dodge Diesel - Diesel Truck Resource Forums

1st Gen. Ram - All Topics - How the Speedometer Sending Assembly works - How the VSS assembly works and goes together.( pictures will be added once uploaded and aproved) Since this seems to be a common question, and troubleshooting issue, I thought it might be helpful to explain what parts make...

www.dieseltruckresource.com

 

[subwoofer88]

Okay thank you that cleared up a lot. So just to be clear it looks like I just need to change out the pinion gear (short shaft type). PATC sells the right style gear, and their calculator says I need a 35-tooth count pinion gear.

I have a 1992 service manual that doesn't say anything about this. Yet my 1977 service manual gives you all of this information and more.