What Size Are My Transmission Cooler Lines?

[TurboDiverArt]

Hi All,

I bought an X-Monitor for my 1999 Suburban Diesel. I still need to get the Tee adapter for the transmission line so that I can tap in the transmission temperature sensor. I contacted BD and they need to know the size of the lines that go to the cooler. They can look it up for the 6.5L TD P/U but are concerned that a Suburban might be different. I assume the lines are most likely 5/16 or 3/8. Anyone know for sure?

Thanks,
Art.

[TurboDiverArt]

I got under my truck tonight. Measured the outer diameter of the lines. They measure .375" OD (3/8") and the fitting nut size seems to be 3/4" unless it

[diesel65]

You have the 3/8 size lines, the tubing measured O.D.
The first generation 4L80e trans had the 5/16th size lines, In 1997 when GM came out with the 2nd generation 4L80E trans they moved up to the larger tubing.
The 2nd generation trans had the return line moved back on the case to the center bearing for improved lubrication.

[gmctd]

Tubing is o.d. - pipe is i.d.
Manual calls them pipes, but it's still to tubing specs.

[TurboDiverArt]

Thanks for the information! So, I've got 3/8" lines. BD power told me to tap into the forward most line, this would be the out to the cooler? Does this makes sense? Basically the hot side of the cooler?

Thanks!
Art.

[tanker]

Art and others, when cutting the cooler tubing lines, use a tubing cutter, (not a hack-saw) this provides a nice round tube for a good seal on the fittings, plus no metal particles in the fluid. Never use a brass compression type fitting. Use a hydraulic compression fitting (steel). Brass will fail and leak from vibration. Also the less threads etc, the less possibility of future leaks. Use proper fittings for a trouble free installation. I'm sure BD will get you the correct fitting for the job. smile.gif