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Hi All,

I'm contemplating the transmission changeover to transynd and am wondering if I can borrow the technique I use to flush brake lines. I happen to have a good vacuum pump on hand and I've made up a simple jar arrangement that I can hook onto the brake bleeder nipple. I use this to pull brake fluid through the lines and it makes those flushes really effective and easy.

I'm wondering if this technique can be applied to drain the remaining fluid in the cooler, lines, and torque converter of the transmission. I could easily create a 5-gallon bucket version of the vacuum jar and hook it to one of the cooler lines. I'd regulate the vacuum down to negative 1-2PSI by bleeding excess vacuum off. This would just put a gentle pull on the fluid and allows it to come out slowly.

Has anyone done it like this? Are either of the cooler lines plumbed internally so that they would actually pull fluid from the TC?

Not saying this is how I'm going to do it... just pondering the idea.
 

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Hi All,

I'm contemplating the transmission changeover to transynd and am wondering if I can borrow the technique I use to flush brake lines. I happen to have a good vacuum pump on hand and I've made up a simple jar arrangement that I can hook onto the brake bleeder nipple. I use this to pull brake fluid through the lines and it makes those flushes really effective and easy.

I'm wondering if this technique can be applied to drain the remaining fluid in the cooler, lines, and torque converter of the transmission. I could easily create a 5-gallon bucket version of the vacuum jar and hook it to one of the cooler lines. I'd regulate the vacuum down to negative 1-2PSI by bleeding excess vacuum off. This would just put a gentle pull on the fluid and allows it to come out slowly.

Has anyone done it like this? Are either of the cooler lines plumbed internally so that they would actually pull fluid from the TC?

Not saying this is how I'm going to do it... just pondering the idea.
I can't speak from experience but I don't see any way for this to work. If simply removing the hose or drain plug doesn't drain the entire volume (it doesn't), attaching a vacuum pump to it won't either. In brake lines, the system is completely filled with fluid (and there's no physical barrier between the lowest point of fluid and the bleeder), and therefore opening the bleeder valve causes flow throughout the entire system. The vacuum pump simply increases the rate of flow, and therefore the rate at which you draw fresh fluid into the system. Because there are parts of the transmission/TC that won't gravity-drain (due to physical barriers above the lowest point of fluid), I think you'll only get out as much as you would from a gravity drain. The difference would be that it might come out faster, but I don't see much of an advantage there.

Search "double drain" -- that seems to be the most common way of changing out transmission fluid in an Allison.
 

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Discussion Starter #3
jdwarren;12046067Because there are parts of the transmission/TC that won't gravity-drain (due to physical barriers above the lowest point of fluid)[/QUOTE said:
This actually gets straight to the heart of my question. In the areas that cannot gravity drain, there must be inlets and outlets so the pump can circulate fluid and the outlet/pickup is likely at a low point. Is it possible, through the cooler lines, to apply a vacuum to that pickup line so it pulls fluid from the TC? I'm still planning on doing the two change swap so I'm mainly just curios at this point.
 

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This actually gets straight to the heart of my question. In the areas that cannot gravity drain, there must be inlets and outlets so the pump can circulate fluid and the outlet/pickup is likely at a low point. Is it possible, through the cooler lines, to apply a vacuum to that pickup line so it pulls fluid from the TC? I'm still planning on doing the two change swap so I'm mainly just curios at this point.
Good question -- and the answer lies beyond the scope of my knowledge.

Any thoughts, @Mike L.?
 
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