M1008 overdrive switch?

[Enforced_Leo44]

Hi everyone,

Just got my hands on a '85 M1008, seems to run good and basically everything seems to be in good running order.
One thing that struck me and didn't really quite understand, is a supposed "overdrive switch" that the previous owner wired up into a floor switch near the pedals that looks like the highbeam floor switch that one can find on, say, a Humvee.
Supposedly the truck has a TH400 and the usual transfer case, which I think is a NP 205 since it has 2 sticks for its controls, so it should be bone stock, if not for a lift and bigger tires.
Is the PO just putting up some bs and making stuff up or is this "overdrive switch" something that actually makes sense? or maybe it has to do with the transfer case?

Any suggestion is gladly appreciated, thanks in advance.

This is a walkaround of the vehicle, the switch is not shown because it's in the lower left of the driver cowl.

 

[Mullaney]

Hi everyone,

Just got my hands on a '85 M1008, seems to run good and basically everything seems to be in good running order.
One thing that struck me and didn't really quite understand, is a supposed "overdrive switch" that the previous owner wired up into a floor switch near the pedals that looks like the highbeam floor switch that one can find on, say, a Humvee.
Supposedly the truck has a TH400 and the usual transfer case, which I think is a NP 205 since it has 2 sticks for its controls, so it should be bone stock, if not for a lift and bigger tires.
Is the PO just putting up some bs and making stuff up or is this "overdrive switch" something that actually makes sense? or maybe it has to do with the transfer case?

Any suggestion is gladly appreciated, thanks in advance.

This is a walkaround of the vehicle, the switch is not shown because it's in the lower left of the driver cowl.

.
It might be worth looking under the truck - where the wires would attach to the "overdrive switch" - and see where they go. Heck, it might be that he just installed the switch and called it that (never changing anything).

.

 

[Enforced_Leo44]

.
It might be worth looking under the truck - where the wires would attach to the "overdrive switch" - and see where they go. Heck, it might be that he just installed the switch and called it that (never changing anything).

.

Yeah that was my first thought as well, one thing that it's wired up to is a little green LED light on the right side of the dash, but that's about it, didn't look deeply under the truck yet

 

[vanaisa]

Well, then look. NP205 was not original transfer case, so it is swapped. Maybe you also have OD unit?

 

[Enforced_Leo44]

Well, then look. NP205 was not original transfer case, so it is swapped. Maybe you also have OD unit?

I’m not excluding that possibility, but what unit would need an external switch to engage overdrive?

 

[Enforced_Leo44]

Well, then look. NP205 was not original transfer case, so it is swapped. Maybe you also have OD unit?

Also, I’m not certain about it being a NP205, I’m just saying that based on the fact that it has a dual stick system

 

[Barrman]

Looking under the truck should be your next step. Engine, transmission with a bolted on transfer case. Then drive shafts to the rear and front. If there is another box bolted to the rear of the transfer case. Then you could have something like a GearVendors over drive unit on the rear drive shaft only.

 

[Enforced_Leo44]

Looking under the truck should be your next step. Engine, transmission with a bolted on transfer case. Then drive shafts to the rear and front. If there is another box bolted to the rear of the transfer case. Then you could have something like a GearVendors over drive unit on the rear drive shaft only.

That's a hint, the GV unit, I'll check under the truck for it next time I'll see it.

 

[Jeepadict]

Pics of the switch are worth 1000's of words.

Many xfer cases are capable of being twin stick'd. I suggest a through underbody inspection so you can better describe what you have so folks are able to actually help you.

Sent from my SM-G970U using Tapatalk

 

[nyoffroad]

Could be a lock up torque converter, if so NEVER have it locked and come to a stop! 6.2 has enough torque to overcome the lockup clutch and will burn it up in seconds. I think I still have the Tee shirt somewhere.
BTW it's not stock if it has twin sticks for the transfer case.

 

[Curtisje]

My M1008 had a gear vendors unit on it when I purchased it. It was controlled manually with a switch on the floor, a switch identical to those old high/low beam switches on older vehicles before they started putting that switch in the steering column.

Good luck. Should be easy to figure out. The GV unit bolts onto the rear of the transfercase.

 

[CARC686]

My M1008 had a gear vendors unit on it when I purchased it. It was controlled manually with a switch on the floor, a switch identical to those old high/low beam switches on older vehicles before they started putting that switch in the steering column.

Good luck. Should be easy to figure out. The GV unit bolts onto the rear of the transfercase.

That was my first thought. Those things are spendy, so it's a nice bonus if that's the case.

 

[Enforced_Leo44]

My M1008 had a gear vendors unit on it when I purchased it. It was controlled manually with a switch on the floor, a switch identical to those old high/low beam switches on older vehicles before they started putting that switch in the steering column.

Good luck. Should be easy to figure out. The GV unit bolts onto the rear of the transfercase.

Yeah I contacted the previous previous owner and he confirmed that it's a add-on overdrive unit, didn't specify the maker but I don't think that anyone other than GV makes such things

 

[chevymike]

This is a GV unit I put in (mine is a fixed yoke setup but most are slip yoke). This is what you are looking for, behind the transfer case.