Q&A: December 5, 2019 Edition

Q. A couple of years ago I bought a 1973 Jaguar XJ-12 hot rod. It was a professional build back in 1998. It had been in storage for many years and still looks like new. I have been told that the frame was shortened and a 1986 XJ-6 body and interior was installed. The engine is a modified LT4 originally dedicated to an Impala SS and the transmission is a Tremec T56 six-speed manual. My question: I have seen and read about many LT1/XJ-6 swaps, but they were all hooked to an automatic transmission. The LT4 makes it unusual but have you ever heard of another Jaguar/V8 swap with a manual transmission?
— David Kennedy, via email

A. I haven’t, but maybe our readers have. I’m curious about the shortened frame, as I believe that XJ-series Jaguars use unibody construction. What’s your wheelbase? Early XJs were 108.8 inches. The long (112.8-inch) wheelbase model was introduced in 1972, and beginning with the Series 3 XJ cars in 1979, I believe, it became standard. The XJ-12 cars were introduced in July 1972 and it appears they were available with either wheelbase until the Series 2 cars came out in late 1973 as 1974 models. All Series 2 XJ-12s seem to have been long-wheelbase.

Q. A number of years ago we explored the topic of tire date codes in Q&A. The original question was aimed at determining the history of a 1929 Buick, rather than establishing if its tires were safe. In researching the question, I discovered that DOT date coding started in 1971, and was originally a three-digit code identifying the week and year of a tire’s manufacture. The year was a single digit, as it was assumed that no one would use a tire for more than a decade. It became apparent that people do keep tires longer than 10 years, so in 2000 the code was changed to four digits, the last two designating the 21st century year of manufacture. Not included in my answer was the guidance (albeit not a regulation) that tires should not be used for more than 10 years, regardless of appearance or tread condition.

A. This was brought home to me recently, fortunately not in a disastrous way. As I’ve often mentioned, I own a 1995 Chevrolet Suburban. I bought it in 2005 with tires that were less than a year old. Over the last couple of years I have replaced those tires, two-by-two, with new ones. Until then, from time to time I would use the spare tire, which had good tread and showed no external signs of deterioration, on the road.

Some months ago I opened the cargo doors to put something into the ’Burb, and was confronted by the situation you see here. The tire, which was fastened vertically in the cargo space, had burst its cords right at the top, where it nestles up to the side window. At the time it was uncovered, so we can blame sunstroke, but for most of the 14 years I’ve owned the truck the spare has been under a factory fabric cover. The next generation of Suburbans moved the spare under the rear of the vehicle, eliminating all chance of sun damage. However, it created another problem: spares seldom used became prone to rusting in place, a real problem if you had a flat on the road.

Looking further at my blown tire, I found the date code to be 065, the sixth week of 1995 (at the newest). In other words it was the original spare, a 24-year-old Firestone Steeltex Radial, and it had self-destructed. Thank goodness it did so in its cradle, not on the road. I now have a brand new spare. You might want to check the age of the tires, particularly the spare, on your beloved collector car.