tr7triumph.com

They are the same transmissions with the following exception:
1981 onward have a lower 5th gear.
TR7 & TR8 ID numbers are different but the parts and casting numbers for the gearboxes are the same.

A bit of warning- Because a transmission in good in a TR7 with 90lbs of torque from the 4cly. does not always mean when used in a TR8 with 150+lbs of torque that it will be fine. I have had then actually grind and have notchy gears! It is like going into shock! The torque difference when applied to bearings and shafts can either be fine or make you pull the gearbox back out!

What helps is flushing the gearbox out and using the synchromesh gear lube. There are some threads on this in the forum. Also check the imput shaft for excessive play that can tell you if there is any wear on the main front end bearing of the gearbox. Replacing the pump on the back casing will prevent future failure of the aged and fragile pump parts. Good Luck![;)]

Michael
1980 TR8 FHC/Works Rally Project

If it is broken then fix it....if it is not then make it faster!"

There's one single, but BIG difference between the two versions: The LT77 out of a TR7 have a white
7 tooth speedo drive gear, and the LT77 out of a TR8 have a black 8 tooth drive gear. If you just
swap the gearboxes out without adressing this little quirk your speedometer (and odometer) will
read roughly 14% out...

Also worth mentioning is the early gearbox had a smaller input shaft brg and different input shaft. Box #CL22477C up got the larger shaft & brg. If you are useing an 80 gearbox, it should have the heavier components.
As Michael says, good idea to at least put a new set of pump gears in. They are made of some sort of composite material (plastic) and get chewed up from metal bits floating around in the box. If it fails completely you will toast the gearbox.

72 MGB BRG
80 TR8 Persian Aqua
If women don't find you handsome, they should at least find you handy.