1979 Ford F-150 u-joints

Maintenance/Repairs
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I have a 1979 Ford F150. I changed the u-joints recently and had a very curious experience that I hope you may be able to explain. After I removed the two old u-joints and dropped the drive shaft, I went to the local parts store and bought a pair of new u-joints for the truck. Back in my garage, the front u-joint went in as it should. The fit seemed to be good and the front u-joint replacement was a success. When I started on the rear u-joint, the part that I had purchased (1979) was too large. It didnā€™t fit. I tried to force it in place but my better judgement told me that this is likely a bad idea. So, I went back to the parts store with the idea that maybe they could educate me. Was I doing something wrong? The parts guy told me to try a pair of 1978 u-joint for the same F150 model. I thought, ā€œWhat the heck?ā€ But I bought the parts and went back to the garage to attempt the rear u-joint replacement again. Much to my surprise the 1978 part fit perfectly. I was shocked! How could this be? Was my beloved truck on the Ford production line at the time they shifted their manufacturing lines to the 1979 models? Is she a 1978 or a 1979? What gives? Do you have any ideas? Itā€™s an oddity, but more importantly Iā€™m wondering if Iā€™ll find other items on the truck that are of a different model year. But most importantly, I donā€™t know when to celebrate my truckā€™s birthday. Enjoy your show! Thanks for all the years of good advice and levity.

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International would change part specifications during a model year run, perhaps Ford does this too.

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Many times the manufactures make design changes throughout the year. Most times the affected parts will be posted when they are sold. Most changes occured in July. Thats why you can sometimes have to order parts depending on if they are made in the early or late part of the year. Many times you can even look on the door and see that the vehicle was built in Nov. Of 2004, but the VIN states that it is 2005.

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There are 3 different universal joints for that truck, not unusual for pick up trucks of that era, you need to know the cap size and cross section width to order the correct joints.