3/4ton WC diff repair HELP!

[kw573]

Hello,

I am helping a mate assemble a dodge diff with new bearings.
I am familiar with setting up diffs, done quite a few. But this diff, with a pair of bearings at the drive shaft end of the pinion, has got me stumped.

The question is: how do you set the preload of a set of three tapered roller bearings?

Further, it is being fitted to a 1/2ton Dodge WC21 which I believe originally had much the same diff, but with the conventional two bearing pinion.

The TM instructions make no sense at all. We are considering assembling it with two bearings only.

Comments from those more knowledgeable that we are will be very welcome.

Thanks.
Sam.

[kw573]

Still lost!!

Is there no one who understands and has set up one of these diffs?

The lack of adjustments on the pinion is perplexing. There are 3 bearings, but only one set of shims (between the 2 smaller bearings on the drive shaft end). The diff is giving inconsistent results with the adjustments of the shims. Very confusing.
There seems to be no control over the critical pre-load on the bearing at the inner end?!?

Who has re-bearing-ed one of these? The diff seems to have been previously assembled without any shims = incorrectly.

HELP!

Sam.

[motto]

I have recently built two of the heavy WC differentials of the type you describe using new 4.89 crown wheels and pinions. The instructions in the applicable TM s describe the process very well.
Obviously the bit that has you tricked is the pinion double bearing set up. The preload on this is established by doing a test run placing the spacer ring BETWEEN the two cones and testing the torque required to rotate the pinion with the cone in the middle acting as no more than a spacer. It is not in contact with the cup. You are in fact treating it as if there were only two bearings supporting the pinion. There are a range of the spacer rings supplied in .002" increments IIRC. Ross has the spacer ring sets. When you get the rotating torque correct with the appropriate thickness spacer you then take it all apart and move the spacer ring to the other side of the middle cone and assemble with nothing between the two cones of the double bearing.
The main problem I had was setting the preload on the carrier bearings, measurement of which is achieved through calculating the amount of distortion of the housing. I didn't have access to a large enough micrometer and made up a device like a 'G' clamp used in conjunction with feeler gauges.

Dave

[kw573]

Hi Dave,

Thanks for that. I've made quite a bit of progress today on the diff.

The first issue was to realize that the bearings that we have for the double cup are not the correct Dodge bearings. Although they are the same size, they do not have the extended inner housing that gives the correct pre-load when the two of them come together in the double cup! Therefore, the instructions about shims made no sense because our shims were in a different place on the pinion.
So the first step was to remove the cup (from the housing) for the third bearing so that we could assemble the double cup bearings with shims on the pinion to get a good pre-load without the interference of the third bearing. The shim thickness was about 0.273".
That was as far as we got today. Also, the instruction about putting the shim on the wrong side of the bearing to do the pre-load now makes sense, as it takes the middle bearing pre-load out of the picture. That is what we'll be doing tomorrow, hopefully.

We also had help from Ross P. and Jay A.

Onward and upward!
Sam.

[kw573]

Hi all,

With the double-bearing pre-load sorted, we could now set the pinion main bearing pre-load according to the TM, as explained by Motto and Jay.
This was a straightforward exercise, re-postitioning the spacer (a very thick shim = 0.193"), test the pre-load, then changing it for a thinner one to give a good pre-load. Then re-assemble the pinion with the spacer in the correct position. Wolah!!!

Then we fitted the crownwheel assembly, adjusted the pre-load on its' bearings, followed by the backlash (looseness between the crownwheel teeth and pinion teeth). Now, if I had my clever hat on, we would have first set the crownwheel bearings pre-load without the pinion in the housing = much easier.

Lastly, using an enamel paint, we took a "mark" to show the point of contact on the crownwheel teeth. This is the critical adjustment in "setting up" a diff. With 0.005" backlash, we had to move the crownwheel away from the pinion to move the mark off the 'toe' of the teeth a bit, but not enough to exceed the backlash limit (0.010"). One increment of adjustment gave 0.011" backlash and only a very slight improvement in the contact mark. Clearly, there was nowhere to go from there.

Darren decided to take it to a local diff specialist for an opinion. The opinion given was "it is a very old diff that has done a lot of work, so that is probably as good as it is going to get". Darren is happy with that.

Hopefully, end of saga!!

Have a nice day.
Sam.