Ok a buddy replaced his passenger front axel but it never engaged into the c clip. He drove about a block then started to freewheel no transmission engagement. We removed the axel and can now see a roll pin in the spline shaft which is in front of the c clip. Tried pushing it up with a long screw driver but it seems stuck. Can anyone shed some light on this for me please.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Those C clips can squish and actually hold it out not in. When you put the axle in make sure the gap in the c-clip is facing down. This will help ensure it engages proper. I saw a good u-tube video on this not that long ago. If you are installing an axle always look at the orientation of the c clip. Forgive the crude drawing attempt with letters but I think it will help the point. The C clip should be orientated like: n(good) - C(bad) - )(bad) - U (bad). I hope this makes sense and helps.