Making Rear Axle Shims

[Steve_69]

As I have previously stated, for me, the roadster is about the journey, more so than the finished product. The latest adventure is my attempt to make rear axle shims. I started off by using a micrometer to measure the old shims that were pretty badly torn. On both sides, I measured a 0.006” and a 0.004” shim, making 0.010” at each wheel. I know that replacing my bearings and locking collars will more than likely change that dimension, so I will use a feeler gauge to verify during assembly.

I knew that cutting and drilling thin shim material would be a bear, and sure enough, my attempts to do so were a failure. I decided to sandwich some shim stock between layers of plywood to drill and cut. Though my results are usable, they are not pretty. I learned some things in the process such that when I make some more, I will do a much better job.

I sandwiched shim stock between two pieces of smooth plywood and drilled and bolted them together. I measured the dimensions of the good shim with vernier calipers, so I have the correct measurements if I need them. I taped the good shim to the wood and traced it out. I drilled the 21/64” bolt holes (5/16” bolts) and installed counter sunk screws with nuts to be sure that the shim stock would not move around during cutting and so the jigsaw will pass over the fasteners. I put a 2-1/2” hole saw into the drill press and cut the center hole. I clamped the assembly onto a work surface and started with the jigsaw. 1st lesson learned, the jigsaw could not make the tight bends, so I had to do some additional hand-drilling to simplify. Next time I would drill these with the drill press before I start with the jigsaw. Next, the jigsaw left some ragged edges. Next time, I would either belt-sand (I don’t have one) or file the edges before I take the assembly apart. Finally, I would counter sink the nuts on the wood so that it would be easier to clamp down for cutting. With these changes, I feel I could make some pretty good shims. We will find out someday soon.

[Habitat.pat]

Looks better than the shims I cut. I freehanded the cutting with scissors.

Peace,
Pat

[theunz]

Nice write up Steve, especially your thoughts on improving your process. I simply cut some out of some gasket paper. Much easier to do, and I figured better than nothing.

[COS1969]

What specifically do the rear axle shims do? I mean I understand the idea of a shim, but for this application, what is the purpose?

[Habitat.pat]

I have never heard a definitive answer to this question. Since the bearings are not roller bearings they don’t require end load adjustment, the only thing I can figure is that since the machining tolerances of the day weren’t as good as now, the bearings sat slightly proud of the housing & shims we’re used to snug up the bearings on the housing. On my car one bearing sat flush with the face of the housing so I didn’t put in any shims. The other side was a about .006 proud, so I added a .005 shim.

Peace,
Pat

[spyder]

Read this thread from way back. I don't see any use for shims with captive bearings. I had a 520 truck with roller bearings and shims were definitely needed to set the lash.

viewtopic.php?p=238913#p238913

[Habitat.pat]

Read this thread from way back. I don't see any use for shims with captive bearings. I had a 520 truck with roller bearings and shims were definitely needed to set the lash.

viewtopic.php?p=238913#p238913

Since Tom Walter was mentioned in the above link I decided to ask him about it when I spoke with him this morning. He said that the shims have nothing to do with axle end pre-load, but are used to set the tightness of the wheel bearing outer race side clearance in the axle housing. The axle tubes were not all that accurately machined, but were machined for the outer bearing race to be flush with the flange, or protruding slightly. The shims are used to space the backing plate out (if needed) to take up the space between the axle flange & the backing plate with the bearing fully seated.

Peace,
Pat

[tcslc]

I put this off for so long, but now I need ‘em for my resto and didn’t want to skip shimming the axles even if it can probably be safely omitted. Steve’s plans were a great idea, and it only took about 2 hours to make all the shims I’ll need.

[ted heaton]

NOS axle shims.
.003".
Parts manual shows 2 on each side.
The explanation above (quoted below) is to my knowledge the correct reason for the shims.
The measurements were confirmed by Datrock. The bearing sits slightly proud when installed.

Since Tom Walter was mentioned in the above link I decided to ask him about it when I spoke with him this morning. He said that the shims have nothing to do with axle end pre-load, but are used to set the tightness of the wheel bearing outer race side clearance in the axle housing. The axle tubes were not all that accurately machined, but were machined for the outer bearing race to be flush with the flange, or protruding slightly. The shims are used to space the backing plate out (if needed) to take up the space between the axle flange & the backing plate with the bearing fully seated.

Ted

IMG_20231208_171649.jpg

IMG_20231208_171727.jpg

[tcslc]

Given the original condition of my car and lowish mileage, I’d venture that the rear axle was never apart. When I disassembled mine there were 4 shims on the passenger side and 3 on the drivers. If the repair manual states two each side, then I suppose the factory was slightly more precise in its measurements. i made 7 shims, all stacked and looking like one big shim in the photo above, but each is correct thickness. Coincidentially, that’s all that I could squeeze out of the shim stock I had on hand. I stamped the axles as they came out for L\R, so it’ll be interesting to see how many are needed per side on reassembly with new bearings.

[redroadster]

It's a variable , as the ring gears aren't exactly the same and can be set differently the main thing is to keep the shaft from hitting the pinion pin , most come close ..050
Here's what is needed to make steel ones
https://youtu.be/xVZZfx9KPlc?si=vm3WAam2L8Y-vBso

[tcslc]

How is the shaft to pinion pin measurement made in the garage? I was simply going to replace the number of shims that came from each side (3 left, 4 right). I marked my axles during removal. Would be nice to be able to be more precise.

[redroadster]

There was a special tool , after I did 2 another tech said there was one ,kept in parts dept , it was close to a Axle but modified you put it in and it hit the pinion pin , you turned the thumb bolt to just contact the Axle, then it had fine thread thumb bolts that you turned to move it out in mm then dial calipered the bolt difference from just touching to moving the Axle back the desire distance ,which needed to be the shims thickness ...it not all that critical IMO as long as the Axle is away from the pin a 1/16 '
I'd say on a 311 as long as it's got some clearance 1/16 " ,it fine , on muscle cars esp.big block high hp type the splines could twist which on drag race accel could throw the whole Axle out of the housing , I drag raced at KCIR my 70 charger 440 r/t vs the owners nephews fury 426 dual tunnel ram , I won easily as it thru it out in 1st gear

[rbsails]

This may be too simple, but I put the old shim on wide packing tape, (clear) and put the shim material on another piece of tape, stuck them together, and cut them out with scissors. I used .001 steel shim material, and punched the holes out with a large paper punch. They are perfect. They do require patience to get apart.The shims are required to prevent wear on the gears in the center section.
Blaise