I was just on another site linked from here n found out that there is such a thing as a "overdrive conversion". They are made by Advance conversions and I am wondering if anyone knows anything about these? As I understand they are supposed to work like a splitter in a big truck but am wondering what it would do exactly in a '93 F-350 TD, 2WD, ZF5 w/ 4.10 rears. The one I seen made the truck go from 2400 @ 60 MPH to 1900 @ 60 MPH. Any help would be great guys.

 

Gear vendors builds both underdrive and overdrive to my knowledge.One is for higher ratio like 5:13/410 to decrease engine rpm, the other is for 3:55 etc to allow higher rpm for cruising and towing purposes. Never heard of Advance.........GV has the best reputation.

http://www.gearvendors.com/

 

I have looked at three different ones.
One was called a Ranger overdrive, it may have been made by Advance.
It required movint the transmission and transfer case back a couple of inches.(Mine is 4x4) Looked like a real hasle to install and rework everything to make it fit. Also it had a shift lever so I would have had three of them. I can also tell you from driving duplex transmissions in big trucks that splitting gears with two shifters is an art that many can not master. One hand for each shifter and the bicep on the steering wheel to drive plus a foot on the clutch and a foot on the throttle, it does get awkward on a winding road.

My opinion of this unit when I looked at it was it was for serious off roading or rock crawling. The under drive unit if you had high rear end gears: Shift while stopped, transfer case in low, Ranger in low, now you have super low gears for your main transmission so you can crawl the rocks. Or if you had supper low gears in the differential use the overdrive unit; Shift while stopped Ranger in high, transfer case in high, now you have gears in you main transmission that you could drive your rock crawler on the highway with.

www.usgear.com also makes one that looks like a good unit, shift is electric. The unit is big, so big it may require denting the floor pan up to get the install room it needs. It would probably not be to bad on a 2 wheel drive truck. But on a 4x4 the transfer case had to be relocated. So it was more than I wanted to deal with. I think it may be a better unit than the gear vendors unit since "I have heard" the gear vendors does not allow engine braking.
Please notice "I have heard" which may not be true.

www.gearvendors.com has a small unit that goes either on the back of the transmission or the back of the transfer case. Shift is electric. This looks like the simplest install of the bunch.

 

When I bought my 91 2wd on ebay last year (blown tranny) I was happy to find a gear vender overdrive unit installed (but not listed) any how it works great. I took it apart as I had to rebuild the tranny, It's simply a self contained planetary gear set up with wet clutches ie. shift on the fly. It has either direct drive, no change in speed or roughly a 30%? ratio increase when run through planetary. I love it In my truck lowers rpm by 300. I think I've got 4:10 gears. Gear vender does not! recommend using it as a double overdrive but its just the way you wire in the controller. Mine has engine breaking I can't speak for all models although the e40d does not allow engine breaking at idle in o/d position. I would recommend it in a heavy towing situation, I think they rate it good to 1500 horse power. Love it!!

 

farmnfly, do you have engine braking with the gear vendors in both positions?
I was going to get one of those till I heard the unit did not let the engine hold you back any. That would not be a good thing for me here in WV with the loads I pull across the mountains.

 

I stand corrected!! I had to look in the manual for this, It says when engine braking is nessary its reccommended to switch it off. It says that the angle the sun gears are cut helps push the carrier back against the clutch under load. Sounds like under heavy engine breaking this could push the carrier away from the clutch which could cause slippage. Where I live and drive usually empty and on flat land it has no effect. All I know is that in double overdrive and with the banks sidewinder it will push my f 250 to speeds I wont mention here!! Sorry for the missleading info

 

Thanks for the answer.
I had heard that it did not work, but now I know for sure.

 

Farmnfly,


I got a 91 Diesel, 4x4, E40D for which I got quotes for the Gear Vendor ($US 2,895)

I do a lot of empty running and my thinking is I might get an extra 2-3 miles per gallon with the second overdrive.

What kind of milage are you getting on your 91 truck the gear vendor in OD running around town, no load?

 

I'll be honest, I've never checked!! I work for a construction company and they give me off road diesel, so I just fill it up whenever I need. I really like it in my truck but as I stated eairlier it was just something I stumbled on I bought the truck on ebay 1991 f250 diesel bad tranny, I got it for $1250.00. Only when I went to pick it up I discovered the Gear Vender unit in the back of the bed. Then I almost fell over when I popped the hood and seen the Banks Sidewinder Turbo. The guy I bought it from obviously wasn't a diesel person and I know he bought it used buy the looking through the paper work in the glove box. Anyhow if I had to spend the $5000.00+ to buy a Gear Vender and Banks Sidewinder I probably wouldn't, but now that I have it I'll never sell it and I'll keep switching it from truck to truck as long as possible.
I drive about 25 expressway miles each way to work and that is where I run the double over. I would guess that I get high teens for milage on this strech. At less than 40 mph the truck shutters like a standard shift in too high of a gear. Its a nice setup up, there's a second dimmer switch that you step on to turn it on or off and you can shift any time any speed although it shifts very firmly and I had passengers say "what was that" when it slams in or out, even though it has a controller that unlocks the torque converter if you don't sequence it right you'll know when its shifting. If you have any other questions let me know.

 

This is great info guys, I really appreciate it. Is there anybody here that has this gear vendors unit installed in a ZF5?? I have that in mine and since I drive a highway tractor for my bread n butter, I am used to shifting without a clutch, therefore, I started using my ZF5 without a clutch and I am having no problems with it. If I had a Gear Vendors unit in there would I still need to use the clutch to make it work, or just let off the throttle to where there is no pressure on the driveline to make it shift?? What is yer experience?

 

You better be careful using the red stuff on the roads. Here's in Virginia, if DOT catches you, it's a huge fine.

 

Yes that is what I do with the automatic. But it does't make a difference the gear vender has wet type clutches that shift as an automatic tranny. The manual says to "play with it till you get used to it you can't hurt it". You would probably blow the tranny before you could dammage the gearvender if you tried to abused it!!

 

I know there is a chance of getting caught but in NY I drive 10 wheel and lowboy daily and in the last 10 years I've been dot stopped a couple dozen times and only once did they dip the tank. Also not that it would help any but the driver for our fuel supplier Hess said when he loads up from the depot there is only one tank they ad the dye if it is for offroad or heating oil. From their depot here they only have low sulfer. So I would be half legal, I would have low sulfer fuel I just didn,t pay the tax

 

I checked today on the way home from work with overdrive, at 2000 rpm my truck runs 59 mph in double overdrive at 2000 in runs 78 mph.

 

Wow, that is great, thanks for the information. If you do have a chance on day try to estimate your fuel consumption MPG. I would be really curious to see what you get.

If you think about it for someone that drives about 12,000 miles per year and saves about $1000 in fuel (a bit optimistic perhaps) with the GEAR VENDOR drive the unit could be paid of in 3 to 4 years.

It would really pay if you do a lot of empty highway driving where you would get the most benefit out of the double OD.

With Diesel prices the way they are going the above should only get better.

Also from what I have heard the GEAR VENDOR drive seems to be quite reliable given it is no more than a simple planetary drive which are typically indestructible.