I was bombing around in that desolate area between my ears and this came to mind.

Can you use a current production 5 or 6 speed manual transmission in an application that would reverse the direction of the input shaft? This assumes you want the output direction reversed as well.

I don't see there being an issue with the helical gears since they work the same in either direction. My concern would be thrust on the shafts.

Would lubrication be an issue?

I understand that some manual transmissions are using sprags that prevent reverse rotation so those would be out of the question.

I have never heard of a manual transmission that had this feature. It's possible that some twin-clutch boxes could, but that's way too new and expensive for me to think about.

Thrust would have to be taken into consideration, as it would be reversed and there may not be thrust provisions in sides that normally don't get thrust. I'm thinking about the countershaft.
Then there may be problems with oiling hole orientation and if the transmission has its own little oil pump inside (most don't, but I believe Gear Vendors overdrives do), it'd pump backwards.

What is this, create a V8 out of two Honda 4s?

R.

This would be a real one-off situation where the transmission would be mounted remotely and facing the wrong way.

The brainstorm involves something way out in left field so I won't bring that up.

Look up the Boxster and 911 transaxle very similar but reversed. Also the 928 transaxles.

On the Boxster pretty much everything but the bellhousing of the trans is behind the centerline.

Can't speak for 5-speeds but just thinking about trannys in general I can't see why they wouldn't work in reverse. In and 833, there is a thrust washer on either end of the cluster and I doubt it cares which way the thrust is going. As for those Porsche transaxles, they get run in reverse all the time for use with mid engines as opposed to rear engines - the issue with those is the oiling but otherwise they don't care which way they run.

Aren't there some 413/426 industrial motors that rotate opposite of normal rotation when running? You'd be all set for one of those!

trying to do the Sierra RS200 setup?

Feets wants to turn the Imp into a wheel stander.

Also with the same input direction the boxster has an opposite output as the 911.
The Boxster should also be the same, in terms of rotation, as a 944 trans which you can buy for around $200 but they are very weak. Also known as Audi 016 trans.
A 968 trans should also be the same and its a stronger 6-speed. Same transaxle used in Audis up to the 2000s.

There is/was (not sure if he's still kickin)a guy here in town who was a transmission builder. He had a 40 Ford, 2 door sedan with a small block Chevy and a Turbo 400 in it. Nice car too. Behind the Turbo 400, he mounted some kind of a 3 spd straight drive transmission backwards. Slip yokes of each transmission shared the same u joint. I can' remember much about how the driveshaft was hooked to the original input shaft of the 3 spd, other than it looked like a round plate welded to the shaft. Plate was close to the trans case, and had a cv joint/slip yoke combo thingy on it. He used it as an overdrive. Don't ask me how, but it sort of made sense when he explained it to me 30 years ago. Word on the street is, that the setup is still in the car and working. I saw it with my own eyes when I was in my early 20's,and the car is still here local. Next time I see it at a cruise in, I'll ask the dude that owns it now if I can peek under it to see if it's really still in there.

I remember way back when Feets claimed to have seen a functioning /6 mounted on it's side & I thought for sure that he had went off his meds & was in dire need of some hands on adult supervision but that was not the case as lo & behold he produced (& posted) a pic of it (it was powering a boat iirc)

Some transmission cases have cast-in ledges that direct lube to bearings...these ledges depend on lube thrown off of gears turning in a specific direction.

Just had a thought if you want a strong, cheaper transaxle that can easily handle V8 power. Look for a snailshell transaxle from a 931, 924 turbo.

Don't know your application but yrs ago when we were building old woods rigs and needed very very low gears , we would couple up two old three speed transmissions with a short jack shaft and put the two transmissions in reverse and you would end up with a super low gear .