Thread: Are a 99 and 01 HD trans the same?

I found a 01 HD trans for sale locally and I was wondering if it would bolt in my 99 GTP. Also is there a way to tell if the trans is a HD trans by looking at it?

The 01 trans will work in your 99 car as long as it really IS a correct code HD trans from a GS or GTP, other car lines with the HD trans may work as well but there are a few variations. You will have to change the cooler lines on the 01 trans as all 00+ used a quick connect type cooler line and the 97-99 used a threaded end line. Some 99 cases used the threaded end fittings and had the correct thread to go into the newer cases but most 97-99 require getting a new feed fitting as the thread size is different going into the case.

Originally Posted by Trannyman95

The 01 trans will work in your 99 car as long as it really IS a correct code HD trans from a GS or GTP, other car lines with the HD trans may work as well but there are a few variations. You will have to change the cooler lines on the 01 trans as all 00+ used a quick connect type cooler line and the 97-99 used a threaded end line. Some 99 cases used the threaded end fittings and had the correct thread to go into the newer cases but most 97-99 require getting a new feed fitting as the thread size is different going into the case.

How do I know if it is a correct code trans? The trans is not in a car and isn't connected to an engine.

There is an ID tag on the back side of the trans case. It is roughly 3.5x1.5" and should be white or pink in color. In the center of the tag there are two larger letters than the rest of the letters on the tag and this is the code that is needed. Just above or next to the letters will be a number that is also larger than the rest of the letters but not as large as the two larger letters and this designates the year. XA or XB are the codes for the GTP and GS until the 04 and then there were a few different ones used.