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Discussion Starter · #1 ·
While inspecting my rt1150 final drive after the usual large-bearing failure, I detected what seemed to be excessive ring-pinion backlash. Investigationon the net indicated that the lash should be measured at 49.5 mm radius, so I threw together a quick jig to obtain that distance. To minimize rocking of the ring while 'pressing firmly', I turned a bearing substitute ring with about .05 mm clearance, both internal and external. The installed tapered bearing shim miked at 2.40 mm. I then pressed the bearing on, measuring with feeler gages to get the required distance to attain the specified .005" (approx.) backlash, and obtained the following values:

'shim space' backlash
2.2mm .050
2.0 .030
1.7 .030
1.5 .020
1,2 .012
1,0 .002

Since the shims don't come less than 1.9mm, clearly something is really amiss - either my measure technique or some component. I could fabricate a shim of the appropriate size, but I'm really hesitant to do so without understanding why these readings are so far from nominal.

Any suggestions?
 

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I think you need to be careful with your "bearing substitute ring". The axial dimension of the actual bearing is a function of the groove and balls, it is not just the dimension of the width of the race.
How this might have affected your backlash calculations I haven't really spent time thinking about, but it might have thrown your measurements off.
I have referred to the BMW Service Manual method when checking backlash; I've never felt a need to change the tooth contact pattern or gear lash on any of the K1200LT final drives I've rebuilt. It doesn't seem to be a common area of concern.

ldwilson46 said:
While inspecting my rt1150 final drive after the usual large-bearing failure, I detected what seemed to be excessive ring-pinion backlash. Investigationon the net indicated that the lash should be measured at 49.5 mm radius, so I threw together a quick jig to obtain that distance. To minimize rocking of the ring while 'pressing firmly', I turned a bearing substitute ring with about .05 mm clearance, both internal and external. The installed tapered bearing shim miked at 2.40 mm. I then pressed the bearing on, measuring with feeler gages to get the required distance to attain the specified .005" (approx.) backlash, and obtained the following values:

'shim space' backlash
2.2mm .050
2.0 .030
1.7 .030
1.5 .020
1,2 .012
1,0 .002

Since the shims don't come less than 1.9mm, clearly something is really amiss - either my measure technique or some component. I could fabricate a shim of the appropriate size, but I'm really hesitant to do so without understanding why these readings are so far from nominal.

Any suggestions?
 
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