Differential swap

[Bulldawg1981]

I just recently purchased a 94 CH613 and it has the Eaton DS402 diffs with 4.33 gearing on Mack air ride. I’d like to swap out to higher gear (lower numerically) to have better rpm’s at highway speeds and I would like to replace the Eaton rears with Mack top loaders (personal preference) if it’s not too much of a hassle. Will the Mack rears bolt right where the eatons currently are or are the mounting brackets totally different to where I’d have to have a complete cut off installed? I can’t seem to find this info anywhere and was hoping someone in here could point me in the right direction! Thank you.

[Joey Mack]

I would think you would need to buy an air ride back half and so the swap. If i remember right the 'Z' springs are different and the hangers and torque arms as well.  Do you have an air ride truck to look at and take measurements ? I did a 96 CH-613 many years ago, but it was a Camelback truck. 

[Geoff Weeks]

If it is the Mack Clone of Hendrickson, I believe all the parts with the exception of the brackets that clamp around the axle housing, and may be torque arms the rest of the parts are the same. The clamping brackets set the shaft angle, on an Eaton it pitched "nose up" and Mack toploaders are level.

 I found out that Eaton housings are made that DS (single speed) housings will accept DT and DC  (two speed and Traction Control) center sections.

If your not changing the whole rear suspension, it seams like a lot of work and money to change axles housings for no gain. You can re ratio by just changing center drop out, and if you want more flexibility, add 2 spd centers for less work than whole cut off and change all the parts IMO.

Edited yesterday at 01:03 PM by Geoff Weeks

[Joey Mack]

Re gearing would do it. GW do you think 3.90:1 would do ? Theres a lot of DS 404+405's around.  Of course i dont know the fine points of Eaton's model numbers. 

[Geoff Weeks]

404 and 405 are different I'm not sure all the differences but I don't think they bolt into 402 housings. To new for a person like me!

As to what ratio, you have to run the math on what you have now, the transmission gearing and start ability on a hill with load, and make a selection that is the best for your needs.

You can build DT's to 3.70, I'd have to look but DS might go below that. DT's all take the same "carrier" while DS can use differing carriers for different ratios.

I'd rather put my money in getting the ratio right then the preferred maker of the axle. Unless there is a real problem with the design (Rockwell SQHD's were known for weak powerdividers) I just don't see what is to gain by switching makers. Most made in the last few decades are good, some do better in one area, but I can't think of a "bad" diff made in the last few decades.

I've run IHC (now sold as Spicer) Rockwell and Eaton, and can't say one is better or worse than the other.

When I changed from DS 402's to DT 402's the same driveline bolted right back up. When you switch makers you are going to have to make driveline changes as well adding to the cost for no gain.

[Joseph Cummings]

I'm never a fan of putting faster ratios in. It never seems to save the amount of fuel everyone thinks it's going to. What do you use the truck for? What engine and transmission? Tire size? 

[Lmackattack]

If you want mack rears and you currently have eaton then a complete axle swap is going to be cheaper in the long run.  only thing to check at that point is if the axle tubes are the same size to accept any parts that clamp down on them to hold it to the suspension.  

My opinion is to stay with eaton. far easier to get parts for these days. 20 years ago id dissagree with my current statement.

[Geoff Weeks]

58 minutes ago, Lmackattack said:

only thing to check at that point is if the axle tubes are the same size to accept any parts that clamp down on them to hold it to the suspension.  

 

I have the complete manual for the suspension on my DT402, it shows the angle on the axle tubes for various axles, Rockwell and Eaton were something like 2-5 deg angle and Mack was 0, I think that would apply no matter what suspension you use because of the axle design and how the  power flows through.

From what I remember working on my Hendrickson clone, the axle seats are what sets the angle and the forward axle is different than the rear. I would think Mack top loaders would be the same as the Neway (0 deg angle) my DT 402s are on.

Kind of a long way around to say I think they would fit the axle tube but be wrong for the angle needed for Mack top loaders.

[Joey Mack]

Theres a 3 degree wedge under the u-bolt clamp plate on Mack rears that are air ride, and as im typing this, i am forgetting which axle... Sad time for me again.. I think its the rear, to compensate for suspension movement as it keeps and angle on the intermediate drive shaft for proper u-joint bearing rotation..

[Geoff Weeks]

Good reason to look up the parts book, and see what is required. I think the parts will be different for Mack rears vs. Eaton but am open to being corrected.

[Joey Mack]

Yep.  Im away from my library right now, so maybe he will study on it and see the difference between the set ups..  I dont want to dissrespect him, but i would stay with the current set up and swap parts in it. And JC made a point about fuel mileage after a gear swap as well. And Eaton Rears are everywhere, and in every salvage yard..