Aftermarket overdrive/gear splitter questions

[lonesome7.3]

I want to install an aftermarket over drive in my truck. First question is, is it an aftermarket over drive or a gear splitter? I have heard them called different things. Also, which one do you all recommend? The only two I know of are from Gear Venders and US Gear. I am leaning towards the Gear Venders model.

http://www.gearvendors.com/f2wd4s.html

http://www.usgear.com/dual_range.htm

Are there any other options out there I should consider? What should I know before entering into such an expense?

[NickKent]

US Gear claims downhill compression braking is not a problem on their site. I seem to remember reading years ago on here about one of these manufacturers having problems with their units and engine braking. But these were trucks with stick shifts too.

[lonesome7.3]

Thanks. That is a good point I will ask about when I call.

[SmokeyWren]

Not my area, but I've read that one of those brands works good with 4x4 and the other doesn't. So if you have 4x4, pay attention to which is which.

Originally Posted by lonesome7.3

First question is, is it an aftermarket over drive or a gear splitter? I have heard them called different things.

The formal name is auxiliary transmission. IOW, it's an extra transmission combined with the one you already have. Yes, it's a gear splitter, but it's also a double overdrive. Or depending on exactly which gear ratio you order in the auxiliary transmission, it can be an underdrive.

What should I know before entering into such an expense?

If you're doing it to save money in the long run, you'll be disappointed. If you're doing it to have a more pleasant cruise when unloaded, then you'll love it.

The normal reason folks want one is to convert a heavy-duty trailer hauler into a nice, quiet, low-reving freeway cruiser when unloaded. If you have a 4.88 rear axle ratio, a 20 percent double overdrive will give you the equivalent of a 3.90 rear end. Or if your F-350 dually has a 4.10 ratio, then the double overdrive would be equivalent to a 3.28 ratio. Now that's some long legs.

The gear splitter capability is useful for climbing steep grades with a heavy trailer. If third gear is a bit too long of a leg, then shift into 2nd on the tranny and OD on the auxiliary to get about a second-and-a-half gear and climb the mountain in style. Or if overdrive is slightly too long of a leg for hilly terrain, then kill the OD to get into direct drive, then shift the auxiliary into OD and you'll have somewhere between direct drive and normal OD.

The typical ratio for the auxiliary tranny is 20 percent overdrive. Your stock tranny has 29 percent overdrive. So the gear splitter won't work to exactly split the gears, but it's better than the stock gear ratios in the stock tranny.

One of our members has been working with one of the auxiliary tranny companies to develop a really-good gear splitter ratio for the serious (often overloaded per Ford's weight limits) commercial truckers with F-450 hot-shot rigs hauling in the Canadian Rockies. But I haven't heard from him in a few months. Maybe he'll see this and chime in.

The GearVendor's website has a chart that shows the various ratios available when you install a 22 percent GV overdrive. If you split every gear, then your 4R100 tranny ratio would be:

2.71
2.11
1.54
1.20
1.00 direct drive = tranny in 3rd with OD locked out
.78
.71
.55

That's a decent spread between gears except for that .78 to .71 ratio. I'd probably skip one of those.

That and more detail is available at
Gear Vendors Under/Overdrive Ford Truck 4-Speed and 5-Speed Automatics.

[lonesome7.3]

I do so I hope I find out which one.

[caryt]

GV..run hot and are not as good as a US gear which WILL allow 4x4..GV will not!
Why do you want-need one? You have a stick and could also upgrade to a 6speed for better gearing. Are you towing heavy? If so much better mods would be a BD brake, TW chip, IC, Tymar intake and Exhaust..and at least stage 1's. Will tow great and be much safer doing it.

[blackout]

First thing is do a little searching, this topic has been covered many, many times.
Here is a summary:

Gear Vendors
the good- shifts great, easy to split gears, supposedly low frictional losses (good for double overdrive), install is easier and cheaper
the bad- run hot, higher maintenance, real problem with reverse loading (engine braking in OD and low speed reverse not in OD, like backing your camper up a hill), costs more, have to lockout 4x4 to engage (should be no problem)

US Gear Dualrange
the good- built like a tank, 4x4 high and low no problem, reversing no problem, engine braking no problem, comes in either high or low versions (if you have 3.55 gears you would want the under drive version, 4.10 or higher you would probably want the over drive version), has a higher rating than GV
the bad- IS NOT BEING MANUFACTURED, shifts are not as easy and quick, has higher frictional losses, so DOD may not make sense for economy, 4x4 install requires moving the xfr case and messing with both driveshafts

Auxiliary transmissions

If the DualRange was still in production, I would recommend the underdrive and 3.55 gears.(this depends on your loads)
If you have 4.10 gears (and you have a 250 or 350), then the GV (this depends on your loads)

The best options (for economy highway speeds):
More gears in the transmission
-or-
a true 2 speed rear
Everytime a gear is engaged there are losses. Among others, there is a loss in the trans and a loss in the rear. The trick would be to get your preferred gear ration without introducing another loss, ie the overdrive.
So Smokey I hope your friend is building a 2 speed rear, cause this would be the best option.

[lonesome7.3]

Damn, some how I missed your post Smokey. Thanks, that was very helpful.

I plan on hauling heavy loads, that is why I am looking into this mod. If the US Gear one is no longer produced, I guess my options just got real limited.

Thank you for the side my side, that made a lot of sense and now has me questioning which direction I want to go.

[SmokeyWren]

Originally Posted by lonesome7.3

Damn, some how I missed your post Smokey.

My fault. I combined three of my posts into the first one - after you had already read it. Moderators have that power. But it may not have been a good idea just to reduce the clutter in the thread,

If the US Gear one is no longer produced, I guess my options just got real limited.

Not necessarily. It's still on the U.S. Gear Corporation Home Page - so if they stopped production it may be a temporary stop. But I'm mad at U.S.Gear, because they stopped production on my Cyclone fan, and stopped all factory support for it. So they let me down.

However, they produced thousands of the auxiliary transmissions, so their stocking dealers probably still have some in stock. Let your fingers do the walking and see if any are still in capivity at your nearest U.S.Gear dealer, or maybe they can locate one for you at another dealer. Probably under "truck bodies" or some such in the yellow pages. Or contact U.S.Gear and ask them where you can get one for your make/model truck.
Contact Information for U.S. Gear

[lonesome7.3]

Now that it is Monday I am going to try and give both of them a call. The time difference gets in the way though and sometimes I cannot get a line out.

But the way, I know this will make a difference. I am running 4:10 gears but my tires are 37 inches tall. Any thought?

[Jeremy]

People like Camping world may carry a few left over US gear units, they used to sell them. I've had mine for almost 10 years on my 2000 6 speed, I've never had any problems. Also US gear never made a unit for 2003 or newer trucks(i.e. 6.0's)

[LMJD]

I've had mine for almost 10 years on my 2000 6 speed, I've never had any problems.

I don't doubt it. The US gear unit, from a mechanical standpoint, is a much better (stronger) design than a GV design. Like stated on the US site, their unit operates similar to an Eaton 2 speed axle on mid-duty trucks---sliding gears, very reliable and bulletproof. On the other hand, the Gear Venders is a planetary unit type design.

[BP6.0]

People like Camping world may carry a few left over US gear units.

I just got back from camping world, and was checking out the US gear unit. They wanted $3800. installed.

[Nasty]

For now i will be driving mostly without a trailer or heavy load until i purchase another trailer. Would it be worth hooking it up. The dealer un hooked it for unknown reason and i have never used one before.

[lonesome7.3]

I did not think of checking out Camping World.