Manual transmission in a HMMWV

[1993]

I've searched but haven't really found any substantial info about installing a manual transmission into a stock 1993 6.2 M998.
What manual transmission would fit with the least modifications required?
Any threads out there that describe a swap like this in more detail?
Thanks!

 

[Awol]

My guess would be an SM465 4 speed out of a GM truck. They came behind the 6.2 / 6.5, so I would imagine it would be rather straight forward. You'd have to figure out a solution for the clutch pedal and related parts, but I cant imagine it be that difficult.

 

[SETOYOTA]

Why would you want the manual?

 

[TOBASH]

Why would you want the manual?

Just as there are those on this forum who want stock vehicles and others who want to modify, there are different kinds of collectors and drivers.

Automatic vs manual has long been one of those forever debates WITHOUT a winner.

Manual is reliable and easy to troubleshoot. The right stout unit with solid gears can last a lifetime. Just look up the old GM "rock crushers" behind a Buick 455 (and some Pontiac GTO blocks)...Bulletproof!

TH400 Automatics are sought after by others for ease of use, but ALSO by experienced drag-racers and rock-crawlers. Quicker in the quarter mile than a 4-speed, and easier to crawl without a manual clutch. Simple mechanical and easy to use.

700R4K adds an overdrive but is not as robust, even when rebuilt for racing. It is totally mechanical.

4 speed electric also has an overdrive and is plenty robust, but potentially susceptible to electrical issues with a harness and controller that are quite expensive.

SO... Many flavors of transmission, each with their own risks and benefits.

Rather than ask "why", a better question is "what will you be using the vehicle for", or "what is the current transmission lacking?"

Best,

T

 

[SETOYOTA]

So TOBASH do you often answer questions directed at other individuals or is this a one time thing? I'm am familiar with the GM transmissions you have described and don't need the tutorial. And for the original poster I would still like to know why a manual? Don't have an opinion either way. If you own it feel free to do anything to it . And with enough time and money just about any kind of modification you can dream up can be accomplished .

 

[TOBASH]

So TOBASH do you often answer questions directed at other individuals or is this a one time thing?

Well, I've noticed that occasionally on the more trafficked forums that posting allows multiple persons to view and comment on the written items.

If I understand this newfangled technology correctly, PM's usually are a more private communication allowing one-on-one communication.

:/

Not sure why you're being so hostile.

T

 

[1993]

Well, I've noticed that occasionally on the more trafficked forums that posting allows multiple persons to view and comment on the written items.

If I understand this newfangled technology correctly, PM's usually are a more private communication allowing one-on-one communication.

:/

Not sure why you're being so hostile.

T

Yes, I do like to think that any question I ask will not only serve me but also anyone else who has it.
And the more people that get use or entertainment from it the merrier!

Btw, that was a great synopsis Tobash, Thanks!
All of my vehicles,(except for the riding mower..) are manual.
Maybe I have issues with being in control, I don't know, can't afford a psychologist yet..
But I do know that I get amazing MPGs when doing my own shifting. much better than what the vehicles I drive are rated at.

In New York state there really isn't anywhere that I know of for rock climbing, so I can take that off the list of reasons to have an automatic.
But considering the cost of buying a replacement tranny, and including labor, it's probably more than what I will save in fuel anytime soon.
So, as much as I like to mess around with the idea, for now it seems I am going to stick with what I've got(unless I start making some major bank soon...), after all, this truck has less than 8,000miles and for the most part it looks/runs like I imagine it did just off the assembly line.

Hey Tobash, do you have a HMMWV? do you drive it in the Brooklyn area?
I was thinking of driving mine down there someday, those pot holes can be a lot like rock crawling, especially right after winter. I've had some close calls where I'm sure I would have totaled my Jetta.
Actually I was in Greenpoint just two days ago, Manhattan Ave. looks excellent for an offroad experience. They ripped off the top layer for resurfacing so low cars can now scratch their bellies on the manhole covers.

 

[wheelspinner]

My only recommendation against it would be unless you have three legs, using the Torsen (sp?) diffs properly would be just about impossible as they require brake/acceleration application simultaneously. Adding a clutch into the equation will make this about impossible.

 

[1993]

My only recommendation against it would be unless you have three legs, using the Torsen (sp?) diffs properly would be just about impossible as they require brake/acceleration application simultaneously. Adding a clutch into the equation will make this about impossible.

Not quite understanding here. confused actually.
Are you saying that the differentials on the M998 require brakes and throttle at the same time? is that only in certain settings?
How is it that others have been successful?

Just looked up Torsen Differential.
It doesn't seem to involve brakes in any way.
Here is a great video. SUPER clear explanation.
https://www.youtube.com/watch?v=JEiSTzK-A2A

 

[riderdan]

Brake throttle modulation is your friend if you're stuck. Tricky to do with a clutch in the mix.

 

[Action]

Not quite understanding here. confused actually.
Are you saying that the differentials on the M998 require brakes and throttle at the same time? is that only in certain settings?
How is it that others have been successful?

Just looked up Torsen Differential.
It doesn't seem to involve brakes in any way.
Here is a great video. SUPER clear explanation.
https://www.youtube.com/watch?v=JEiSTzK-A2A

If one of your tires loses traction or gets in the air, all of the power will spin that wheel. Using your brake with the left foot stops this. If you have your right foot on the throttle, left on brake, What do you push the clutch with?

 

[1993]

Brake throttle modulation is your friend if you're stuck. Tricky to do with a clutch in the mix.

True, I started driving farm tractors early on, tractors actually have a left and right brake for this purpose.
But that's why in a HMMWV there is an option to lock the differential? I think it's the "L" selection on the left shifter?
Or does that only work while the automatic transmission is installed?

 

[Wire Fox]

True, I started driving farm tractors early on, tractors actually have a left and right brake for this purpose.
But that's why in a HMMWV there is an option to lock the differential? I think it's the "L" selection on the left shifter?
Or does that only work while the automatic transmission is installed?

That lock mode locks the front and rear differentials together. Nothing more. That means that the left and right wheel at each differential can still lose power if you aren't using BTM, but each differential will have exactly 50% of the transmission's power going to it.

 

[kcobean]

If one of your tires loses traction or gets in the air, all of the power will spin that wheel. Using your brake with the left foot stops this. If you have your right foot on the throttle, left on brake, What do you push the clutch with?

According to that video (which is awesome) it is the slippage itself that transfers power to the non-slipping wheel via the spur gears. How is the application of the brake used to gain traction? I'm not understanding.


That said, I had a manual Jeep Wrangler a few years ago. I did some rock crawling with it and one of the reasons I got rid of it was because of the difficulty in (or more accurately the inability to) operating throttle and brake at the same time, which is critical when trying to be precise about putting a tire on top of a rock,

 

[1993]

According to that video (which is awesome) it is the slippage itself that transfers power to the non-slipping wheel via the spur gears. How is the application of the brake used to gain traction? I'm not understanding.

That said, I had a manual Jeep Wrangler a few years ago. I did some rock crawling with it and one of the reasons I got rid of it was because of the difficulty in (or more accurately the inability to) operating throttle and brake at the same time, which is critical when trying to be precise about putting a tire on top of a rock,

Yes, I agree, that video shows how the Torsen differential gets rid of the discussed slippage problem all together, so no need for brakes for that application.

And I do agree that a manual transmission is a pain in the butt when rock crawling as well as in NYC traffic. However I do not plan to do either of these things often with this truck. not that I wouldn't want to, just that it's not conveniently near by.I guess the manual transmission is really just a daydream. Unless if at some point I pick up another M998 but with a shot drive train that "needs" the transmission replaced lol!
However my truck really just seems too perfect to even touch the paint job

I rescind my inquiry. the original transmission is staying in there for now!

 

[kcobean]

Yes, I agree, that video shows how the Torsen differential gets rid of the discussed slippage problem all together, so no need for brakes for that application.

And I do agree that a manual transmission is a pain in the butt when rock crawling as well as in NYC traffic. However I do not plan to do either of these things often with this truck. not that I wouldn't want to, just that it's not conveniently near by.I guess the manual transmission is really just a daydream. Unless if at some point I pick up another M998 but with a shot drive train that "needs" the transmission replaced lol!
However my truck really just seems too perfect to even touch the paint job

I rescind my inquiry. the original transmission is staying in there for now!

When I ready your initial post, all I could think of were my days in the Dodge Viper Club, where every now and again someone would inquire about putting an auto transmission into a Viper, usually because of a physical impairment that made running a clutch difficult. The responses were usually similar too...."why the heck would you wanna do that?!" LOL

 

[riderdan]

The torsion diff isn't a true locker. So as Action mentioned, if one wheel is slipping, more power goes to that (faster turning) wheel.

I was taught BTM when I went through the driver course in the Army. I've used it occasionally to get unstuck. My (very limited) understanding is that when you apply the brakes, the spinning wheel is slowed down (hopefully) allowing power to go to the wheel that actually has traction.

 

[patracy]

I'd rather have a auto for the torsion diff from personal experience in snow. But that is purely my opinion.

Now, what about the shift tower itself. Wouldn't the shifter end basically behind your reach and high? I mean think, we sit beside the exhaust manifold and that doghouse has basically the back of the engine under it. Most shifters would end up at an uncomfortable/weird angle if you did manage to install it.

 

[kcobean]

The torsion diff isn't a true locker. So as Action mentioned, if one wheel is slipping, more power goes to that (faster turning) wheel.

I was taught BTM when I went through the driver course in the Army. I've used it occasionally to get unstuck. My (very limited) understanding is that when you apply the brakes, the spinning wheel is slowed down (hopefully) allowing power to go to the wheel that actually has traction.

In a traditional differential, your understanding is absolutely correct. With traditional open differentials, engine power goes where there is the least resistance, i.e. the slipping wheel. Using the brakes to provide "artificial traction" to the slipping wheel (the drivetrain doesn't know the difference between brake friction and ground friction), you increase resistance to that side, which means now there is no "path of no resistance" and since the power has to go somewhere, it is transmitted to both sides more evenly. The tire with traction gets it's share of the power that it wasn't getting before. You are effectively implementing a "poor mans LSD".

With a Torsen diff, I think it's the opposite. The beautiful simplicity of the worm gear/worm wheel/spur gear interface means that as the slipping side turns faster than the non-slipping side, its power will be re-transferred to the other side via a gear mechanism that naturally "locks up" when the power is applied in that direction. It effectively creates a "hard link" between the two axles when their speeds are different in an unbalanced way.

Applying the brakes on a Torsen differential just reduces the amount of power available.

That said, if it's a method that was taught in the Army (I was a Huey crew chief so I played with different toys back then) there may be "strategic" advantages to BTM in a 4WD system and/or by just lowering wheel speeds to aid in traction while still getting the engine power needed to get through the obstacle.

Differentials are fascinating things.

 

[StackJ]

I was wondering about clutch placement too.