FG 140 4x4 Transmission Mod for Higher Top Speed?

D

Dirtastic

New member
Considering purchasing a 2005 or 2007 FG 140 4x4 but am concerned about the specification of top speed of 68-70 mph. With a manual transmission (and light load in 2wd) is it possible to put in a taller 5th gear to better keep up with traffic?

At least 75 mph is desired. 80-85 mph would be ideal (general highway speeds in Southern US are CRAZY FAST!)

I'm guessing this topic has been covered but searching on a mobile device is not cooperating.
 
A

Amesz00

Adventurer
Dirtastic said:
Considering purchasing a 2005 or 2007 FG 140 4x4 but am concerned about the specification of top speed of 68-70 mph. With a manual transmission (and light load in 2wd) is it possible to put in a taller 5th gear to better keep up with traffic?


At least 75 mph is desired. 80-85 mph would be ideal (general highway speeds in Southern US are CRAZY FAST!)

I'm guessing this topic has been covered but searching on a mobile device is not cooperating.
Click to expand...

Bigger tyres?
My fg84 (same as us spec 140) with 40" XZLs does 100km/h (62mph) at 2150. I think with 35s it's closer to 2500
(Ski freak?)
 
D

Dirtastic

New member
I've read about bigger tires and that's always an option for slight gains. Any good links to discussions on bigger tires: keeping existing *wheels* vs *bigger wheels* (19" or others?) and tires"?

But, aside from this, anybody pull the trigger on, or know about tranny mods for a manual? Any good reason not to simply put in a taller top gear?
 
westyss

westyss

Explorer
I am surprised that it hasn't been brought up before but while travelling about in Washington state I met a fellow who had an FG and had some type of Spicer transfer case installed that gave him several more gears which included top end gears, I didn't get much of a chance to have a look or get the particulars but there are options. I think he was in Leavenworth, Wa.
 
D

Dirtastic

New member
Spicer. Interesting.

I know nothing about automotive transmissions (but have rebuilt motorcycle transmissions) and my naive understanding is that in a 4x4 the transfer case simply takes the drive output and splits it, front rear.

This could multiply or reduce (such as 4wd high and low) but final output to wheels is applied equally to all.

My goal is simply to gave a tall highway gear in 2wd to get to remote areas. Obviously, when in 4wd the final gearing would affect all four wheels, but unless one were doing flat desert travel on hardback sand, it seems unlikely I'd ever use top gear in 4wd.

I wonder if Spicer offers a way to do this with a sort of ultra-high transfer that multiplies the output higher than OEM (and ideally in 2wd mode)?

Anybody with knowledge or experience with trannys and transfer cases? Clearly, I'm a n00b! :)
 
Czechsix

Czechsix

Watching you from a ridge
Brownie Box.

Funny thing is, I'm regearing lower for better slow speed torque. I'm willing to deal with 65-70mph top speed, even on our high speed freeways here.

ETA: Ok, too hot to work in the sun, so it's inside for now. Anyway, Spicer, Eaton, etc offer various solutions for this. Older companies like Fairey offered OD/UD boxes of various ratios too, and if it comes down to it building your own overdrive box isn't that hard to do. Back in the day there was a large truck OD/UD commonly referred to as a Brownie Box. It was a standalone unit that was added into the drivetrain as an aftermarket item. Think 40's, and 50's, that'll give you an idea of the time period.

If you're serious, I'd find your local heavy truck maintenance place and talk to the parts and service guys and see what they can dig up. You might also try on Pirate.
 
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SkiFreak

SkiFreak

Crazy Person
The biggest problem with this idea is that unless you plan on driving on the flats with no head winds, taller top end gearing will mean a lot of down shifting when you get to any hills.
These trucks are pretty well known for their lack of power/torque, so unless you can get more out of the engine too I don't see any advantage at all in taller gearing.
 
A

Amesz00

Adventurer
Actually, someone correct me if I'm wrong but I seem to recall the fg140 having 4.875 diffs instead of the Aus spec fg84 5.285??
 
D

Dirtastic

New member
Current US FG's are listed with top speed of 86 mph (instead of 68 mph for, say a 2004). So, now, a smaller motor and less torque than earlier versions but with higher top speed. Had to be gearing, but was this all done with solely the final ratio? Seems unlikely, but maybe?

Taller top end gearing for an older model might not be entirely mad since if this could be done it should have more power than a new model since the torque is higher. (Am I missing something obvious?) :-/

What year did the US motors get smaller?
 
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