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Manual gearbox mounted backwards?

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White Trash CVP

Oct 14, 2020, 6:01 AM

Post #1 of 4 (391 views)
Manual gearbox mounted backwards? Sign In

More of a silly general question and curious as to various opinions.

I know that there are off the shelf solutions.

And I know manual box designs and applications vary widely, straight cut and hypoid, synchro and not.

But do you think that a manual box in rough theory could be mounted in reverse to work as an auxiliary OD unit - (divorced behind a normal transmission) that is the output shaft becomes the input?

I know it would work for an hour, lol .. but what failure and wear modes might be considered?

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Oct 14, 2020, 10:07 AM

Post #2 of 4 (380 views)
Re: Manual gearbox mounted backwards? Sign In

My opinion is the gear ratio would be much too high as the input side RPM is much higher in most gears than the output side and the most you could slow it down would be a 1:1 ratio and then there would be no point in having it at all.

I don't understand what the goal of this would even be.


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White Trash CVP

Oct 15, 2020, 6:04 AM

Post #3 of 4 (348 views)
Re: Manual gearbox mounted backwards? Sign In

Again, yeah .. more of a musing than a plan. Hadn't even considered ratios but was thinking they might "mix" like driving an old 5+4 (even if the rear shifter were a foot behind the cab and backwards, lol)

In the case of say a pair of old Muncie 465's the first trans in 4th and the backwards one in 3rd would give ~ .3 overdrive, etc.

Wouldn't be difficult to divorce a 465 in a square box chevy frame - although matching "input" splines to a driveshaft yoke...

Again, I know Gear Vendors etc have reasonably priced off the shelf units .. Just wondering if a manual box would survive long being driven backwards. Thinking that gear thrust would be an issue as the force from the reverse direction was never intended.

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Oct 15, 2020, 6:42 AM

Post #4 of 4 (347 views)
Re: Manual gearbox mounted backwards? Sign In

Just a thought that would be a stopper I'm almost sure but may not be all types? Not my specialty, never was still owned and cared for many using similar ideas road vehicles or assorted machines with a running engine or thing of some sort not always an engine.
The input and output shafts need a neutral spot so a shaft spins in gear oil.
I'm asking I don't do this notice that "gearcases" of all type place oil level such that it's "splashing" to keep they all lubed. Doesn't that mean if the proper shaft isn't spinning from source end/input it's not splashing from just the rear?

That's as old as thing with gear boxes, before engines as we know them at all was done. Common ones didn't pump gear lube/oil they splash it so that ends the game of using over the counter transmissions backwards IMO out of the gate.

If you filled one full it would foam out the vent(s) up top or just gush out.

Just for thought doubt you could do it without a design re-do how it gets lubed??

Said, just a though that would stop the show,


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