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The AC Valve-Train was taken directly from the THM400 Transmission (which serviced both Cars and Trucks).
Being that the 4L80E was only going to service Trucks...
The One of Two different Spring to Valve Locations was chosen for it's ability to easily soften the 1-2 Shift with a Firmer Spring.
I am sure that I am the first to say that the Accumulator Circuit does not have any great affect on the 1-2 Shift...
But that is just as it is configured in it's Original arrangement.
It could be made to firm up the 1-2 Shift...
But honestly doing so is easily achievable without the help of a reconfigured Accumulator Valve-Train.
i meant the oversized ACV. I have messed with another 4L80E since this thread and also got low vac readings. i see sonnax makes an oversized valve, but the reamer and fixture are $$$
so I had a peek at my crib sheet for vac test numbers for ya
I like to see at least 15"Hg at the end of the valve (big chamber) and 16.5"Hg in the L-shaped cavity and it should easily stroke that valve with vac on that cavity. Any less than that and you can see weird stuff like slow reverse psi rise.
I don't have to tool to go OS on that valve. If I get a VB that doesnt test well in that area I wont use it in a stock-ish application. If that VB tests well everywhere else I mark and save it for builds that delete all accumulators
the L shaped cavity has NO role in the line rise in reverse
and the only reason the other end of the valve has anything to do with line rise in reverse, is because it's active tq signal oil.
So if there is a leak, it will have low tq signal oil to the boost valve.
The leak doesn't have a large effect in fwd ranges because the leak can't cross tq signal to exhaust, it will cross it with drive pressure...so if anything, a small leak at that valve will increase line pressure in fwd gears.
FYI fixed line setups this typically is a non issue even if the valve checks very poorly.
overall the accumulator valve from GM on these 80e units is pretty crappy. Do better next time @vorteciroc
These are the THM400 Accumulator Valve-Train variations.
(To reference the 4L80E... Omit Detent Fluid, and change Modulator Fluid to Torque-Signal Fluid).
For Automatic shifting, these go from my least preferred arrangements to my most:
Does the ABOVE look familiar?
the screw adjustable was a neat concept. Seen them loads of times
The valve layout is different in a couple ways, but yes it gets its roots from th400
The couple of differences in the 4l80e make it worse than the th400
But, for reference here to the topic of this thread...I wouldn't personally waste any time on the accumulator valvetrain.
If you're worried about it leading to epc issues such as abnormally high line in drive and low line rise in reverse, there are a couple solutions easier than reaming and replacing a pretty unimportant valve in the grand scheme of things
A. really shrink down (via peening) 14c/14d holes to restrict tq signal to the valve
B. most don't realize...but an accumulator block off plate will actually block 14c/14d entirely and makes the 1-2 accum balance oil inactive as well. So the epc issues go away but you then need to rethink your 1-2 shift (I bet people didn't know a 3/4 accum block off plate would affect the 1-2 shift!)
C. get another core VB in better condition
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