Per information I've found, here is one procedure apparently from Manny T.

An easy way to calibrate the dip stick without removing the pan is :
Take the GMC out for a drive to get the oil hot and the torque
converter full of oil.

Remove the vacuum modulator and fill the tranny until the oil just
drips out of the hole from the vacuum modulator now mark your dip
stick at the full line.

Question I have is: What temperature should the oil be for this to
be accurate??? There is a huge difference when the oil is 140 degrees
vs 200 degrees. And how much time would I have to do this before all
of the oil drains back out of the converter??

Thanks

--
Ray Erspamer
78 Royale - "The Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMCRoyale@gmail.com
414-484-9431
Web Site: http://ray-lisa.page.tl/
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I may be sticking my neck out here, but I don't believe it matters whether the fluid is hot or cold for this procedure. Think about it, all you are doing is establishing the level for the dipstick reading. The fluid will be at the same level, at the bottom of the modulator hole, no matter what temperature it is. After you have calibrated the dipstick, and you are checking the actual fluid level, then is when you need to have the oil at operating temperature and the torque converter filled (engine running). For the purpose of simply calibrating the dipstick, the oil temperature is immaterial.

Actually it still Doesn't matter!

powerjon wrote on Fri, 07 November 2014 20:54

Actually it still Doesn't matter!

I'm kinda confused - the original question was "does it matter if the fluid is hot or cold when you check it?". JR suggests it doesn't matter, but then says you have to check it with the fluid hot (which was the point I was reinforcing by posting the expansion characteristics of the tranny fluid). Am I missing something?

I kind of look at it this way. If the torque converter has leaked down, there will be a deficit in fluid compared to when the engine is running and the converter is full, IF THE LEVEL is checked cold and leaked down. I want my transmission to have the correct volume of fluid in the system when it is operating. If you let the converter leak down and then pull the modulator, you will probably drain some fluid when you remove the modulator. If you have recently run the engine, the converter should be filled like it would be when you are operating the coach. Clear as mud,
right?
Jim Hupy
Salem, OR
78 GMC Royale 403

On Sat, Nov 8, 2014 at 12:22 PM, Matt Colie wrote:

This is not about checking the fluid level, but checking the level indicator for accuracy.

I think it will no matter if the transmission or fluid is hot or cold.
The fact is that the modulator hole is the desired level as has been stated here.

So, with things cleaned up so the spilled fluid might be reused and the coach at a more or less normal attitude, could not one just pull the modulator and let it drain into a clean pan (for an extended time if cold).
Note and mark the level on the stick and call that good??

Would that not provide effective calibration?

Matt