what rpm is your motor turning at 60mph? if it's around 2500 rpm, then I go with brian's diagnosis, if it's around 1500rpm then you likely have a 224 or a 247 diff... which would be odd, as it would require changing the yoke to make it fit...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!