Best Overdrive Unit???

[johnnyb1]

My next project is an overdrive for the C6. I found a Doug Nash unit and I found a few Gearvender units out there. The D.N. has an asking price of $650 which is cheaper than any of the GV units so far. Price is not really my concern though. Does either one seem to be better than the other?

 

[icanfixall]

Well asking this question can really open up a crap storm here. Some really like the Gear Vendors but they too have their own problems. Towact has seen them explode but I have not. I have seen the pics he has posted too. Now the GV units are hydraulicilly driven. So you have to reach about 20 mph before they operate in 1st gear. If they break its usually felt they wont leave you stranded like the US gear units will. The US gear is a direct drive and if they fail your broken down right there. The GV just wont have the OD but you can continue driving. Doug Nash is similar to the US gear but I think its location is between the trans and the flywheel. Finding parts for the US or Doug Nash is really tuff but the Gear Vendors is made completely in house now. They no longer buy from England and modify to fit a us built car or truck. They also are found on some drag cars and salt flat cars along with the Calloway Vets.

 

[The Warden]

IMHO the Doug Nash is a stronger unit and will hold up better. Also, it'll mount between the transmission and the transfer case, so you can use it in 4 wheel drive if you wish.

HOWEVER...there are two major issues with the Doug Nash unit. First, has a very firm shift, and requires some manipulation of the accelerator pedal to shift properly...while it'll bolt to and work with a C6, the Doug Nash unit was really designed for a manual transmission where you can use the clutch to relax driveline pressure to aid in shifting. Again, it is possible to shift a Doug Nash with a C6, but it takes some finesse and understanding how the shift mechanism works.

Second, and more importantly, finding parts for a Doug Nash unit is considerably more difficult. Doug Nash was bought by U.S. Gear, which was in turn bought by another company who has ceased all product support. John (jaluhn on here) has been working on finding alternative parts sources, but this is a potentially serious problem.

GearVendors units, OTOH, use a planetary gear setup that make the shifting more similar to that of an automatic transmission, and IMHO are more auto-friendly. GV also still exists and offers product support. However, IMHO it's not as strong (shouldn't really be an issue with an IDI, but take a look around OB for carnage pics), and (if this matters to you) it mounts behind the transfer case, so you can only use it if the front axle's not engaged. Also, while you can split every gear with the Doug Nash, the GV really only provides an overdrive gear at the top...so, your 3 speed turns into a 4 speed, instead of the 6 speed you get with the Doug Nash.

Hope this helps a bit...given that you have an automatic, unless you want the flexibility of using the OD in 4x4, I think the GV's going to be a better bet for you.

Best of luck whichever route you go with

 

[icanfixall]

Tim thats not completely correct about the GV units. I can't take off from the start in GV over or under but... Once I reach about 20 mph I get the GV to shift to 1st over. So I start out in 1st. Then reach 20 mph and I get the od gear. Then I peddle the V and manually shift into 2nd. Then speed up and shift the GV into 2nd over. And so on till I'm around 85 mph in double overdrive turning 1850 engine rpm. So I get 8 forward gears. Its amazingly quite at 85 mph turning 1850 rpm....

 

[The Warden]

Tim thats not completely correct about the GV units. I can't take off from the start in GV over or under but... Once I reach about 20 mph I get the GV to shift to 1st over. So I start out in 1st. Then reach 20 mph and I get the od gear. Then I peddle the V and manually shift into 2nd. Then speed up and shift the GV into 2nd over. And so on till I'm around 85 mph in double overdrive turning 1850 engine rpm. So I get 8 forward gears. Its amazingly quite at 85 mph turning 1850 rpm....

I stand corrected in that regard...I thought you couldn't shift the GV below 25 to 30 mph and had to run it manually to split the other gears.

I do have to ask you, though...you said that the Doug Nash/U.S. Gear will leave you stranded if it fails? I'm open to be corrected, but unless it's a catastrophic failure (which would take out either of them and leave you just as stranded), what failure mode on a Doug Nash would leave you stranded? Unless the shift motor fails mid-shift, it seems to me that the worst-case scenario is that you'd be stuck in whatever gear you were last in...

 

[icanfixall]

When the gears fail in them you get stranded because they need to drive thru the gear box to work. The Gv will continue to operate jast as a non overdrive unit so you can continue on your travels. The GV is a cone clutch powered by hydraulic pressure when the speed of around 20 mph is reached. It got an eccentric lift pump driven very similar to the mechanical lift pumps on our rigs. Very reliable. Most of the times the friction material on the cone fails. Then it will shift but no overdrive happens cause it slips.

 

[towcat]

When the gears fail in them you get stranded because they need to drive thru the gear box to work. The Gv will continue to operate jast as a non overdrive unit so you can continue on your travels. The GV is a cone clutch powered by hydraulic pressure when the speed of around 20 mph is reached. It got an eccentric lift pump driven very similar to the mechanical lift pumps on our rigs. Very reliable. Most of the times the friction material on the cone fails. Then it will shift but no overdrive happens cause it slips.

wrong.
with a broken input shaft in the GV, you are going nowhere.
here's the post and pics of the latest GV carnage.
www.oilburners.net/forums/showthread.php?60778-GV-carnage-very-ugly-pics
here's the post of the orig install.
www.oilburners.net/forums/showthread.php?55942-double-OD-and-other-nonsense
enjoy

 

[johnnyb1]

Thanks for all the input guys. The GV sounds like what I want. Just an OD on the highway. I may pull a camper or car occasionally but that's about it. If I'm in 4x4 I don't need OD anyway. E40D was suggested but I like the C6. Thanks again. Keep everyone posted.

 

[Agnem]

I have 2 GV units. Bought the first one new, and it's been under the Moose Truck for probably 18 years. Never had a problem with it. The second is under the Lady Moose, and bought it used. The front seal leaks a tad, so I top if off now and then. But it pulls the camper all over the place, and we've also never had a problem with that one. I think Towcat's experiences are genuine, but in a very heavy duty application on tow trucks and roll backs, and possibly with abusive drivers. I'm sure Gear Vendor units aren't the only thing that breaks on his Ford and Chevy IDI's.

 

[chris142]

Some day when I'm not broke I'd like to add an Overdrive to my truck to help with hwy mpg. I see no reason to put it between the trans and transfercase. If I'm in 4x4 i'm in low range and 1st or 2nd gear. Any faster than that and I'll be in 2wd.

 

[laserjock]

Some of us in snowy climates need to drive at "highway speed" in 4x4. Probably not 80 mph but not 25 either. For some its a consideration.

 

[chris142]

No way that I would ever drive that fast on snow! I'm terrified @ 25mph on the stuff.

 

[laserjock]

From all of us who are not terrified of the stuff, we would appreciate it if those of you that are would please stay home and out of our way.


I lived in Nashville for a few years. An inch of wet snow crippled the place and God the time we got about 8" you would have thought it was 8 feet and the apocalypse.


Sent from my iPhone using Tapatalk - now Free

 

[chris142]

Maybe our snow is slippier than yours? Theres no way to safely drive hwy speeds here when it snows. My truck and jeep are literly all over the road and unsafe at faster speeds. They even close the schools when it snows 1/2 inch because the school busses get stuck at bus stops or end up in a ditch.

I do enjoy watching the fools with chains on the wrone end though. I watched a guy in a rwd Mustang with chains on the front try to drive

 

[GOOSE]

How is the shifting on the GV units? Is there a lag at lower gears because the hydraulic fluid isn't as pressurized on account of the lower speeds? I am under the impression that you can shift these without letting off of the go pedal....

The only one I have seen in action is in Big Ed. Darrin's unique combo of a Cummins powerplant, C6 auto and a GV Od along with 3:55 gears worked great together, I was very impressed. Darrin wound out the Cummins power pretty good as we were hungry to get to some grub at that point in time. I do only remember him shifting at about 50mph or so using the GV more for an extra gear rather than splitting 1, 2 and 3rd gear.

Also don't forget the old Brownie units. They are quite different requiring an extra shifter in the cab but give very good results and are built stout!!