Hello Challenger fans, awhile back I bought a spare differential to put the new richmond 3.55 ring and pinion in.....after a long and educational experience...I got it put together. WARNING !!!! IF YOU DAMAGE THE PINION BEARING taking it off the original pinion....YOU CAN NOT GET A NEW ONE-----PERIOD! Since Dodge owes Mercedes some money...due to the Bankruptcy...there is a LOCK OUT on the sale of that bearing. Oh there is a number on that bearing...you just can't get it.....Dodge can't get it for you. The good news is there is a bearing that is reeeeal close..but machining to the pinion and diff housing is required.It's a great swap for performance...just prepare yourself for the extra work