i'm seriously thinking to bolt one of these gear vendor behind my th-400 . with a rear end ratio of 3.73 , this should be a dandy , the strenght of the 400 and the under and over at wish on all the gears . what's your thaughts ??? be good phil

 

I don't see an issue if you're okay with the cost...well, maybe clearance under the tunnel and your drive shaft will be a lot shorter.

 

for an o/drive I think .70 is fine, 30% engine speed reduction, ans with a automatic you far better off going the bolt in 200 4r route, and it's a much cleaner install, and cheeeeeeeper, and then you have the lockup converter.....

so instead of cruising 80mph at 4k rpm, you doing 2800.....much more livable....
the GV unit gives you a 18% engine speed reduction....just over 1/2 as much, and for that PRICE....forgetaboutit....

 

Have no idea if it will fit, but did run some numbers for 3.73 axle, 70 mph and 27 inch tires.

Turbo 400 / Gear Vendors (.78 o/d) = about 2700 rpm (includes approximate converter slip)
700R4 (.70 o/d) = 2275 rpm (with lockup converter)
2004R (.67 o/d) = 2177 rpm (with lockup converter)






22%

 

Wow that's an impressive way to look at it.

Hey, will you do me a favor and run the same 70 MPH numbers for me between a TH350, and a TH2004R, and 3.08:1 gears? Same tire size. Thanks.

 

Just install an OD tranny. Same price, 1/2 the weight.

 

I helped a friend install one on his big block nova behind his th400 - it was fairly straightforward, though required some tunnel mods to make fit proper. He loves it.

I tried to talk him into the od tranny route for weight purposes but he was having none of it. he loved the strength and shift quality of the 400.

 

Turbo 350 (1:1) = about 2800 (with approximate converter slip)
Turbo 350 w/ GV (.78) = about 2200 (with approximate converter slip)
2004R (.67) = 1798 rpm (with lockup converter)

 

Beautiful. I have a TH350 in my Vette now and I have a TH2004R getting ready to go in when I install the 405. I can certainly live with almost a full 1000 RPM drop at 70 MPH.

Thanks.

 

phil, I just recently completed a self-install of a GV unit in my '69 Camaro; 454, TH400, 3:73 rears, and I love it.
it has dropped my cruising rpm as much as 1000rpm on a flat stretch, and having the ability to manually operate the unit in and out of overdrive on the fly is an added plus.
as they advertise, the unit itself is about the size of a 2-pound coffee can, and should add a length of about 17" overall to your trans-assembly.
on the downside: they sent an incorrect front yoke; it wasn't grooved for the snaprings to hold the joint in, added a week to the install waiting on correct part. (brainfart on my part: check all parts thoroughly upon receipt).
the electrical switchbox is cheesy, at best. I had to install it under my dash, but this winter, I intend to find a way to separate the switch and lights and incorporate them into the dash itself somehow.
the small "computer" control unit presents a challenge for an install location. I took my dash cover off and ended up mounting the unit on top of the ashtray housing; a Corvette is going to present a thought~process, at least.
it required a complete overhaul of the exhaust system (headers). my crosspipe was exactly where it didn't need to be, so I had a muffler shop re-fab the tubes from the collectors to the mufflers, and relocating the crosspipe.
I had many opinions and advisors when I considered the GV option. my goal was to gain an overdrive gear, allowing me to have the uumphh of the TH 400/3:73 combo, with a "road gear". the other options were 700R4, 200-4r, and 4L60e. when I sat down and compared gains and costs, against simply adding to what I already had, the GV was my obvious choice. I think my final tally was just short of $3G, all numbers in. compare that to the cost of a replacement O.D.trans, torque convertor, electrical, driveshaft modification and exhaust modification; I think you'll see the numbers
the install process is relatively easy (if you have a lift, like I do)
I was in no hurry to complete the job, but it's NOT a 4~5 hour install, like advertised.
good luck in your choice

 

With a GV unit in a Vette the trans cross member would have to be modified right?

The drive shaft would resemble a half shaft after the length of the GV unit so the angles would have to be perfect.

B&M makes a controller for the TH2004R and th700R4 that gives you push button on/off control and you can dictate when you want it on and off and the control box is small and very easy to mount.

Based on the speed to RPM ratios above I would go with an OD transmission as the others have noted.

 

Why not just go with the 4L80E it has the guts of a Turbo 400 with an overdrive.

http://www.transmissioncenter.net/4L80E.htm

 

Beat me to it, and then it has a lockup converter to boot.....

the factory autos or for sticks the o/drive units are the way to go.....

and at less than 1/2 the price of a GV od unit.....


bolt that tranny in and save the grief and get a better install to boot....

years ago when O/D was not available there simply was no choice but a GV unit....today, totally dated machinery, no longer necessary....

 

..my daddy used to say: "a wise man will change his mind; a fool seldom does"...
had both cars on the lift today; the '69 Camaro and the '82 Corvette.
a Gear Vendors unit, in a C3 ('82) Corvette, will present several body modification/drivetrain challenges, probably not worth the monetary expenditure required to accomplish a similar goal, by utilizing today's (not dated ) technologies of overdrive~equipped automatic transmission assemblies.

 

humm . these facts are very usefull at least . thanks everybody .may be i'l go the 4l/80e way . did you heard of someone who made a kit for the installation of that trans in a c-3 , since i think i need a drive shaft mod ??

 

Here you go search is your friend lol.

http://forums.corvetteforum.com/show...ighlight=4L80E

http://forums.corvetteforum.com/show...ighlight=4L80E