Help me identify a 10mm hex 'drain' plug?

Is it in this pic? This is what I use to change my PSD fluid. red is coolant drain, blue is PSD drain and green is PSD fill. Hopefully someone else can comment on your 'other' plug, not sure what it may be. Hobbit has this pic and many other helpful Prius pics at: Hobbit's techie-rants

 

Looks like the end of the transmission oil pump cover sub-assembly. Could be the 'fluid pump cover plug', which is removed to inspect the oil pressure. If removed, it should be replaced with a new O-ring and torqued to 65 inch-pounds/7.4 newton-metres.

The manual doesn't say anything about a ball and cylinder in there, though. It doesn't show the oil pump cover from that angle - there's another lump which could be a different bolt, possibly the one you removed.

 

May be a pressure relief valve but this is an uneducated Aussie guess. Looks like the end plate for the lube oil pump.

 

For some reason, All Data is vague on this part. It *is* part of the oil pump.

I'm going with Pat's guess it's the pressure relief in the oil pump. You should be able to clean and replace the sleeve, ball and spring, and tighten down the plug again

Of course, if this is the relief sleeve, ball/spring, get it in wrong and you could ruin the mechanical parts of the transaxle ...

 

From the TCH FSM, there is no ball bearing in the transaxial oil pump pressure release valve, only a spring and a cylinder. I will be very careful to put the pieces back in the correct order.
You mentioned the ball bearing came out first, I would suspect this will go in last, cylinder-spring-ball-bolt.

 

We need somebody to chime in who actually has a Techinfo subscription. Not available to Canadians, I should sue for discrimination

 

I looked at the Toyota repair manual section that deals with the transaxle. None of the exploded parts diagrams show this sleeve, spring, or ball.

 

Hmmm. I thought that maybe All Data might have been missing something. So the Techinfo has nothing?

The information provided when you click on a detail of that end of the transaxle is pretty vague. I wonder if on purpose?

 

Leaving aside why you'd go for a hex fitting so high up on the
transaxle when looking for the *drain* plug, especially when the
right plug is visible in your picture, what you wound up at is
clearly part of the transaxle-fluid circulation path and is one
of the passages to/from the pump. The ball and spring is probably
a check valve. I would suggest giving the area a hard look to
determine which surface the ball would be most likely to seat
against to make a seal, and insert it and the spring in the
correct order to restore that functionality. I went through
a batch of my old training-session pictures and unfortunately
I don't have anything detailed enough for that end of the transaxle
although I *did* spend a bit of time trying to figure out the
actual circulation path that the pump drives. For the most part
it's up into the end of the shafts assembly and down its center
hole, seeping out along the way into various bearings, if that
helps identify the correct flow direction at all.
.
_H*

 

Since these parts do not appear in the transaxle exploded parts diagram, my guess is that the OP should insert the parts in this order: first the ball, then the spring, then the sleeve, and then insert and tighten the bolt (along with the O-ring). As Hobbit said, the OP should inspect the hole with a bright light to determine how the ball is intended to create a seal.

My further guess is that the sleeve is intended to have an "interference fit" with the hole that it came out of, but the OPs transaxle has a larger hole (or the sleeve has a smaller outer diameter) than designed, so the parts fell out. Maybe the OP can comment on whether this theory seems to fit his visual inspection of the parts.

 

Well, s*** happens, I wouldn't get too fired up over it.

I like your plan of checking out your father's Prius. I'm sure you will be extra, *extra* careful not to have parts flying off, like that time when I was a kid and managed to lose the metering rod hanger on my Dad's Impala

I'd never use contacts working around vehicles. If you have a pair of real glasses, use them, they can actually save your eyes from oil or chemical splashes

 

My favorite is when you turn on a bolt and it doesn't back out, so you turn some more, and then you hear something fall off inside...

Tom

 

Oh, that's happened to you too?

Picture the bald 800 lb gorilla hearing that distinctive noise, realizing the "simple" repair job just turned into a major disassembly process, and then screaming the F Bomb at whatever that bolt was attached to.

Then picture the 800 lb gorilla shaking the ratchet at the bolt in a threatening manner, as if *that* would ever fix anything ...

 

I laughed so hard at this I have tears in my eyes. My stars, I have done exactly that on many occasions. I don't swear a lot, but I have a long chained-together litany of cussing that rolls freely from my tongue when something like this happens. My wife just looks at me and says "Jesus! Get a grip. It's not that important." She doesn't understand the cussedness of inanimate things.

Tom