How do I ID rear axle?

[Trask]

I thought this would be easy, but now I'm not so sure. I'm trying to figure out which rear axle my truck has. It's 1992 W250 Cummins 4WD with Gertrag 5 speed. VIN 3B7KM23C2NM543708, axle ratios 3. 5

There are no visible numbers anywhere on the axle housing.



Has 2 1/2" by 12" brake shoes on it.

The actual machined brake area in the drums is 3 1/2" wide.

Inner bearing is # 28682 and most parts books show that for a Dana 70

Outer bearing is # LM104948

Grease seal is 28746

Axle shaft is 1 3/8" diameter.



When I reverse check these parts - some show for Dana 60s, some for Dana 70s, and most for brake systems with 3" X 12", not 2 1/2" X 12" like I have.



Is is possible somebody put in the wrong shoes before I had it|?

How can I tell for sure (without pulling the cover off) what this is?

 

[Philip]

Your truck came with 2. 5" shoes from the factory. Just replace with the 3" shoes and don't worry about it.



The axle is a Dana 70HD. That was the only axle used in the CTD trucks.

 

[JTsokalas]

Trask,

Philip is right on the money. The rear is a 3. 54 ratio and most if not all of them came with the 2 1/2 inch brake shoes on the 3/4 ton or the 250 series. You can go ahead and replace the shoes with 3 inch and you essentially have what the one tons, or 350's had.

John

 

[Trask]

Thanks for the replies. As I understand it, this thing has the drums made for 3" brakes but only came with 2 1/2" shoes, correct?



I see that according to the parts listings, 2 1/2" shoes use wheel cylinders with 1" bores, but 3" shoes use wheel cylinders with 1 1/8" bores.

Right now - mine are the smaller 1".



So, if I install 3" shoes, seems I ought to put in the larger wheel cylinders also? I'm going to replace them anyway, and the prices don't change much. That's if the bigger wheel cylinders bolt in with no problems. A shoe with more surface area needs a larger bore wheel cylinder to maintain the same force - I assume.



I'm not trying to be nit-picker here. But, I've run into this sort of mixing of parts before with my GMs or Fords. Since I'm fixing it anyway, I'd like the get the most brakes I can as long as all is a bolt-in fit.

 

[KOG]

Shouldn't need to change the cylinders, but you will need to have the drums turned because they'll be worn at 2-1/2" now.

 

[cerberusiam]

So, if I install 3" shoes, seems I ought to put in the larger wheel cylinders also? I'm going to replace them anyway, and the prices don't change much. That's if the bigger wheel cylinders bolt in with no problems. A shoe with more surface area needs a larger bore wheel cylinder to maintain the same force - I assume.

Yep, you got it right.



All the parts bolt in with no issues.