HOWTO: Adding a diff lock to a D/E/J differential.

[someguy]

HOWTO: adding a diff lock to a D/E/J differential.

Caveat: I haven't done this yet.  I called Meritor and they explained this is how it would be done.  It took a while until I reached someone who a) understood what I wanted to do and b) knew how to do it.

Diff locks on truck differentials are controlled by an air solenoid on the diff carrier. 

The D/E/J buses use a differential from the RC23-160 family.  C = coach.   

Single axle heavy trucks use differentials from the RS23-160 family. S = single.   

The differential carrier (the piece that bolts into the front of a differential housing with the pinion, ring gear and diff lock) is interchangeable between the RS and RC families.  There are no bus specific differential carriers. 

When the diff is used with a front engine application, the differential carrier is mounted with the pinion high.   When the diff is used in a rear engine application, like a bus, the diff carrier is mounted with the pinion low.  This places the ring gear on the other side of the pinion and makes the axle shafts spin in the other direction.

Note: a diff from the rear of a tandem may also work.  They start with RR.  I have not confirmed that it will work.  Proceed with caution.

So the short answer to changing the gear ratio or adding a diff lock to  a D/E/J bus differential is to find the RS diff carrier with the features you want (ratio, locking/non locking) and bolt it into the diff housing.

However, there is a twist, with a sub twist.

The twist is that MCI buses use Quiet Ride ring and pinion sets.  So if you install a straight RS diff carrier, it won't have Quiet RIde and it will be noisier that the stock MCI differential.

So the cure for the lack of a Quiet Ride gearset in the RS diff carrier is to install the Quiet Ride ring and pinion from your coach into the RS diff carrier.

And here's where the sub twist comes in.   RS differentials use 2 different diff case halfs, depending on the gear ratio desired. (See attached MCI parts list.)

Case 1 is part 2L-3-74 and it works with 3.21 through 3.73 ratios. (Actually 3.08 to 3.73)
Case 2 is part 2L-3-77 and it works with 4.10 through 4.56 ratios.

You don't need to buy these parts, I'm just quoting the part number so you can see it in the attached parts list.  To get a diff carrier that will work with the QR ring and pinion set from your old carrier, you need to make sure the gear ratio of the new diff carrier has the right ratio to get a diff half that works with your ratio.

For example, the bus I'm looking at has a 3.21 ratio.  I can select any RS diff carrier that has a ratio from 3.07 to 3.373.   The MCI parts list doesn't list all the ratios for the diff half.  There is a 3.08 too.

And that's it.

Step 1: find the gear ratio of your bus

Step 2: figure out which diff half group your gear ratio is in

Step 3: find an RS diff carrier that has the right ratio for your ratio

Step 4: swap the QR gears into the new diff carrier. 

There are tutorials on doing this.  It is complicated, but can be done with some patience and tools. 

Step 5: install on the bus.

Wala: you have a new diff carrier with a "Driver Controlled Differential Lock" or DCDL as Meritor calls it.

Twist #2.  In some differentials, one of the axle shafts may be too long.  You may need to score a shorter axle shaft.  The diff I'm looking at is 46 spline.  You can verify your axle spline count when you pull the diff apart or from the MCI parts manual.

I hope this helps someone.

Edit: Some or all of this might apply to differentials earlier than the D/E/Js. I have not checked them out and didn't want to mislead anyone, so I didn't write about them.

[someguy]

More pics.

[Jim Blackwood]

That might be handy if you are planning on driving on soft ground but I suspect the loading on the front tires would still be the limiting factor. Probably intended for icy roads,

Jim

[chessie4905]

How about using those dash mounted levers they used to use, to modulate the brake on the side that isnt spinning?

[someguy]

How about using those dash mounted levers they used to use, to modulate the brake on the side that isnt spinning?

I think some of the newer coaches with the Electronic Stablility Control systems can do this.  I'm not sure though.

[TomC]

A bus drive axle is literally a truck differential rotated on its housing to face backwards. This is why the pinion is low on a truck and high on the bus-same differential. So using a locker truck pumpkin should be doable. Good Luck, TomC

[luvrbus]

How about using those dash mounted levers they used to use, to modulate the brake on the side that isnt spinning?

Chessie I have automatic traction control,or you can do it manually, with the switch on the dash I under that is the way it works