coolwildflower

my boyfriend wants to help me with the rear end, on my 73 240 z. he thinks it may be a R200 in there, how can we be sure that we need a new rear end, and how can we be sure if it is a R180 vs R 200, etc. any help on rebuilding rear end please. i tols hi, that i was driving on freeway about 75 mph and suddenly i lost power and could not get the car to go any faster than 35-40 mph, it just all of a sudden had no power . i drove it all the way home in 3rd gear. he said it sounds like the rear end. took offthe rear brakes and found them both worn down. any advice?