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My 1966 R60/2 "failed" 2 of the rivets that hold the drive spline in the rear wheel. The spline was loose on the hub and could be rotated a bit. It was obvious that continued use would shear the remaining rivets. This is a summary of my observations and progress. To use these fasteners it is necessary to ream the spline flange holes to .249" with a carbide reamer (the material is hard). It is also necessary to ream the hub to .249". This is best done using the flange as a guide. Index mark the hub and flange to assure proper reassembly.

I cut the head diameter on the screws to .350" to clear the exterior of the spline and get rid of excess metal hanging in space above the flange. I recut the angle of the head to match the holes in the spline flange (approx. 100 degrees included). This modified fastener sits with its head approximately .120"(3mm) above the flange. This allows about .080"(2mm) between the head and the drive casting.

The eight screws pass through the flange and the hub. Two flat washers are added to the bolt end to cover the remainder of the unthreaded portion of the screw. The assembly is secured with a grade 8.8 nut and Loctite then torqued to acceptable levels. The exposed screw threads are cut off to provide a professional appearance to the installation. As a final inspection it is possible to insert a gage pin between the machined central hub and the machined tip of the spline tooth. My hub has a space of .126" between these 2 objects and is concentric within .002" at all points. This concentricity should be no problem to achieve as the spline is located by a closely machined diameter in the hub.

As a first comment

If I felt confident that I could find the correct material and shape of rivet for this application I might have attempted replacing the original rivets. Even then I would be somewhat doubtful of my ability to evenly peen over the rivet and obtain the intimate contact that would guarantee that there would be NO RADIAL MOVEMENT each time the throttle was opened or closed. If the rivet is loose or the wrong material early failure will be the consequence.

 

On the other hand I am comfortable with machine tools and processes and feel that this repair will outlast the brake drum.

This is the female drive spline removed from the hub. This part was heat treated. I’m not sure whether it was a case or through hardened. The first attempt at reaming the holes to 0.249” destroyed the High Speed Steel tool bit. This unit was reamed with Carbide tooling.

Inside of brake drum with female drive spline removed. The hub has already been reamed to 0.249” using the drive spline as a fixture. The spline is bolted in place and the holes are reamed through the spline. The spline has an index mark added so it will be easy to replace it to the same rotation after reaming is complete. NOTE: the hub has a step machined inside the bolt circle. This step is concentric with the axle and fits the machined diameter inside the drive spline. This assures the assembly will be concentric to the axle.

This is a close up of the drive spline flange. These holes are already reamed out to 0.249” (a bit over 6mm). Note that because of the 100 degree chamfer on the hole that there is only about 2mm of straight bore. This would be the amount of thread available if the original ring were tapped for a bolt coming in from the back side of the drum. The ring was hard and would be difficult to thread. 2mm of thread is not sufficient for correctly fastening this ring.

Alloy Flat Head Socket Cap Screws in 1/4-20 threading and 1 3/4" length. *Yield 140,000 PSI

“Raw Material” at the top and “Finished Product” at the bottom. Socket Head Screws are made of  a fairly strong alloy, and certainly have a higher PSI yield* than the original rivets. This ¼=20 screw had sufficient unthreaded length to pass through both the flange and the hub before the threaded portion began. The bolt body diameters were all very close to 0.249” diameter. The extra head diameter was removed as it served no purpose and interfered with the spline protrusion. The underside of the head was dressed to approximately 100 degrees to match the countersunk holes in the drive spline flange. The excess length was removed as it served no purpose.

The screws were a light tap fit through the spline and drum. I added high strength cylindrical retaining compound Loctite to fill any gaps that would allow any wiggle. An important issue on this installation is the clearance between the spline flange and the rear drive cover. I take modeling clay and stick it to one part with critical clearances. I then assemble the wheel to the drive (but do not rotate it). I then remove the wheel from the drive and measure the “squeezed thickness” of the modeling clay. This gives a reasonably accurate measurement of space available.

 

In this instance there is ONLY 0.200” (5mm) between the top of the flange and the “drip catch lip” on the rear drive cover. Therefore any fastener installed in this system must have a head height lower than 0.200” (ZERO CLEARANCE) above the spline flange. Since mine sit in the countersink they are much lower and clearance isn’t a problem.

 

You can check the concentricity of the assembly by inserting an appropriate drill shank between the spline bore and the bearing hub. The same pin should fit anywhere around the circle. My finished assembly showed less than 0.002 total eccentricity.

This is the back side of the installation. I used 2 washers under each nut to clear the last bit of unthreaded fastener body. I used a common washer figuring they would deform enough to conform well to the rough casting. The nuts are alloy steel and tightened to 11 ft/lbs. The same Loctite is applied at assembly.
In a "have to do" situation if you bought a 6mm carbide tipped reamer you could make the required changes in hole diameter on the spline flange and hub using an electric hand drill and some forethought. The bolt head diameter could be reduced with a file while spinning the bolts with the same electric drill. The head angle is not super critical as the load is "shear" not tension. Finally a hack saw could be used to cut the bolt length down, or this could be skipped as it is hidden behind the wheel cover.

The "saving grace" is the fact that the location of the spline is established by its fit on the machined protrusion on the hub. To do the job with simple tools remove the remaining rivets. Pin flange in a couple of places for location. Ream a hole and install a bolt/nut, ream opposite hole and install a bolt/nut, and dance your way around the flange this way. Mark the flange & hub so it assembles the same way next try and you are set.

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