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Old 02-21-2002, 05:15 AM   #1
hayden747
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Question 320 e21 DIFF problem, suggestions ?

Hi everyone, the problem I'm having started as soon as I upgraded the engine in my 1979 BMW E21 320. After installing a larger model engine, and programmable EFI I had problems with the diff. On the very first day I got the car going the diff LITERALLY exploded ( in second gear at full power) , the actual structure of the crownwheel & spider gear carrier sheared in half, leaving bolts, oil, and bits of broken metal all over the road.
I discovered this was due to 2 design faults, the main one being the way that the roll-pin which retains the main pin the spider gears sit on is installed. The hole for it is drilled parallel to the line of shear force ( creating a stress - riser ) rather than perpendicular to the line of shear force ( which minimises weakness, as in Nissan diffs )
I was thinking of maybe installing a LSD from a series 5 RX7, but this would involve a lot of modification of driveshafts and mounting points.
Any sensible suggestions on how to fix this problem would be appreciated. I have already got another second hand diff and am being careful not to use too much power. I had thought of grinding away the material from the outer side of the roll pin hole, to make a channel in the material, then getting that channel filled up by TIG welding, but I have been told that because the carrier is made of cast material it makes welding the material successfully very difficult.
Are there any other bmw diffs of diff parts that might be easy to fit without too much modification ?
Thanks.
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