I dropped the pan on my Buick TH400 -72 and changed filter. I figure I should as well change the fluid in the whole transmission as well. A common way to get the fluid out of the torque converter etc seems to be to loosen the lines to the oil cooler and utilize these. Do both of the lines to the oil cooler have pressure above atmosphere? If not, I suppose I could put the low pressure line in a container of new oil, and the high pressure line to a waste bucket and just run the engine? Otherwise if both lines have a base pressure above atmospheric I suppose I drop both lines in a waste bucket and refill the regular way as I go? How about flow and pressure, is this like a firehose with oil all over the place or do I have some respite here?
No pressure in the lines without the engine running. Fill the pan with fresh fluid. Then disconnect the top line at the radiator. Slip a piece of 3/8" fuel line over the line end and run it into a white bucket. Have a helper start the engine and you watch the color of the fluid coming out of the line. When it changes color from dark to bright red, signal your helper to shut the engine off. You have now flushed the converter. You can do this more than once to be sure, but I think it is unnecessary.
Alright! And I suppose that while doing that I have to be pretty quick replenishing fluid simultaneously as we go so nothing goes dry?
You likely won't get it done in one pan full. Fill the pan up, connect a hose to the disconnected top line, connect a hose to the top of the cooler by using a short length of tubing, put both ends in a bucket, have a helper start the engine, run engine until the absolute first hint of running low on fluid and immediately shut the engine off. Rinse and repeat. You can do this by yourself if you lines are long enough. Keep going until the fluid is clean. You'll want to be hooked up to both the cooler in the radiator and the line you removed because you won't be 100% assured that someone didn't cross the lines or you'll have a mess of epic proportions. IIRC, the flow from most older GM vehicles was out of the top of the radiator cooler. There is a lot of fluid in the converter. It takes a lot of fluid to push it all out. 8-12 quarts total is not usual to use depending on how dark it is.
It happened the new oil had the exact same color as the old one, sampling from oil I drained out prior to the filter change. But the gearbox anyway now has gotten a good dose of brand new fluid. Another question, should we normally expect the fluid level to rise above the level where the little flange on the inlet tube contacts the gear box? Or is that a symptom of overfill? I am asking because my refill tube is a bit crooked at the end and it doesn't seal 100% at the bottom. I could see liquid seeping out there the other day. But if we don't expect fluid up to there, I figure that leak can just as well remain there as an overfill protection.
When you shut the engine down, fluid drains back out of the converter, raising the level in the pan. That is normal. There is an O ring that seals the fill tube to the case. That is a common leak point. https://www.rockauto.com/en/catalog...matic,dipstick+/+fluid+filler+tube+seal,10970
Sounds normal. With the engine running, oil level is below the pan sealing surface. When off, the torque converter drains into the pan, so then you'll find interesting leaks like pan or dipstick tube. So, at rest it will continue to drip until you get the tube aligned with the trans case properly, maybe a new o-ring too. No other sealant should be necessary if alignment is correct and the end of the tube is round and not deformed. Sometimes the upper tube mounting bracket becomes distorted during handling or previous removal/installation, so that may be a source of misalignment to investigate. Devon
Alright! Just ordered a new o-ring seal, lets hope this is the last annoying leak on this vehicle I will have to deal with for a while.
Fiiiiiinally there is no transmission fluid leaking anymore. at least not since yesterday. Feels so good! I trued up the end of the filler tube as well as I could. Then I mounted the stock o-ring and checked with a ruler that it was thick enough that it would protrude outside the diameter of the tube all the way around. It didn't, so I ordered a bunch of NBR o-rings with various thicknesses. An o-ring with a 13 m.m inner diameter and 3 m.m. thick (0.5 m.m. thicker than the stock one) was enough in my case. With some patience and force it got in. This was a pretty sneaky error. Oil was dripping everywhere and running along the newly installed pan gasket, so I thought that was failing too. I almost ripped the pan off while at it, but adhered to some good advice I got. A leak generally flows downwards, as we already knew. So just stay calm and fix suspected or confirmed at the top first before working downwards. This is so obvious when you think of it, but still, when having all tools out and starting to get a bit desperate it can easily happen that more stuff come off than necessary.
