Vote for The Forward Look Network on the Mopar Top 100 Sites 


From: Mopar Randy
Remote Name:
Date: November 01, 2003


Perhaps I'll have another shot at explaining this. When you install the axle into the tube, you then drive the "race", as you call it, or the "cup" as I call it, into the tube afterwards as you said in an earlier post. When you drive the race into the tube, for the sake of illustration here, drive it in only half way at first. Pull the axle in and out. You'll notice it moves in and out about 3/8 of an inch or so. That's your "end play" (Again, this is for illustration only) Now, drive the race on until it is ALMOST flush with the tube, say about .020 out. Check this with a feeler gauge. Now, move the axle in and out. You'll notice you now have about .020 of movement, or "end play". Now, measure your axle shims with a caliper. The total thickness should be on the order of .015. Put the shims on the axle and notice that they (the shims) do not contact the bearing race you just drove in. Now, look at the back of the backing plate. You'll see that the hole in the backing plate is small enough to contact the bearing race and the shims both. Install the backing plate and torque the nuts to 35 ft/lbs. You will probably have detected some resistance right at the end of the tightening process. This resistance is the backing plate contacting and drawing inward the bearing race that you left hanging out the .020 earlier on. The backing plate has now drawn up against the shims and reached torque. Now, with your trusty dial indicator, move the axle shaft in and out and measure the movement, or end play. Given my hypothetical scenario, it should be about .015. So, how does the backing plate hold the axle in? It does this by holding the RACE in place. The bearing can not move on the axle because it is pressed on against the machined step, which makes the axle and bearing "as one" The bearing/axle also can not move through the race, so, by holding the race in place (with the backing plate), you hold the axle in place as well. And the shims allow the race the "slop" of their thickness for setting the end play. Remember, the race will naturally be forced outward against the backing plate when the vehicle is driven because of the taper of the race and rollers. Even though you have to "drive" the race in at installation, the bouncing, torquing, and turning of the car will instantly force the race out against the backing plate during actual operation. So, to recap, the backing plate holds the race in the tube at the distance of the shim pack, thus retaining the entire axle assembly at the proper "end play", which should be roughly the thickness of those shims. Just one final note: When you drive the race into the tube, you probably drive it in until it "seats" and then try to move the axle. Of course, with the race seated against the bearing, it won't move at all. To check "end play", you need to assemble the backing plate with shims onto the tube and then either drive the car around for a bit, or apply pulling force to the axle shaft with tool# C-499 to draw the race out into contact with the backing plate. Then jack up the car and check the end play. Sorry this was so long. Mopar Randy


Last changed: July 19, 2018