68 Chev 3/4 4x4 overdrive trans swap

[Daimler]

Hello, I have a 68 Chev 3/4 ton 4x4 with a 350 and the stock 4 spd trans and stock transfer case. Both were rebuilt when I installed 1985 4:11 one ton diffs front and dually rear. (the original diffs were 4:56) I was wondering if a modern 1 ton 5 speed overdrive manual transmission can be fitted. (I remember a Torque Flyt auxilary tranny that could be placed between the existing tranny and the bell housing. It was 7 1/4 inches long and was rated for about 7500 GVW. It gave about 30% overdrive. I do believe another shift stick in the cab is great but I am not sure they are available any longer. Changing the drive shaft lengths is no issue.) I suppose it may be possible to swap the tranny and transfer case together to make it all a little easier, but I want to find out if a modern heavy duty 5 speed can be fitted to the original transfer case. Maybe someone here has done this swap? Presently I get 9 to 12 miles/gallon loaded.

[Bigdav160]

I think the short answer is "no easy swaps".

A popular swap is a New Venture 4500 (NV4500). GM and Dodge both used this transmission. You can search this forum to find more details. I think the NP205 might need to be changed to a TH400 version. The transmission is longer so there will be more modifications will be necessary.

I never heard of an overdrive unit in place of the bell housing. I'm surprised there's enough available input shaft length to drive it.

I've heard of people putting a gears vendor unit behind the NP205 but I do not know what's entailed.

edit, with the tranmission change you might be able to improve your mileage a couple miles a gallon. It's not enough for a lot of people.

[Daimler]

Thanks for your reply. Back in the mid eighties an outfit called Torque Flight (Flyt?) sold this seven and a quarter inch long 30% overdrive tranny with a stick shift. It bolted to the bell housing and the tranny then bolted to it. I may still have the brochure they sent me back then but it would take some digging. When I search for them I usually only find Gear Vendors. I phoned them back then and the Gentleman told me he would make me one for my 54 Power Wagon with the 5:88 diffs for 2500.00 us.

[LockDoc]

-
Here is how I installed an NV4500 5 speed overdrive trans in my C30 Dually, and used all of the stock linkage and bell housing mounts. I don't have a clue on the 4x4 part though. I'm sure it could be figured out.

http://67-72chevytrucks.com/vboard/s...d.php?t=673588

So far this is working great for me.

LockDoc

[HO455]

Novak is a good source for info. They are Jeep folks but have a great website with lots of information.
https://www.novak-adapt.com

[Bigdav160]

Does a '68 Suburban have a NP205? It doesn't, does it?

It should have a Rockwell T221. I think you have even fewer choices.

[olblue60@aol.com]

No, 1968 is not a 205. I have that in my 72. I should remember whats in my 68, but I seem to be having a morning moment . Sorry I can't offer more.

[Daimler]

Thanks Lockdoc, great info!

[Daimler]

Just a thought, has no one else ever heard of this Torque Flyt O.D. tranny? If I remember it, maybe someone else does too? It was for sale in the mid eighties, not sure if they are still out there.

[1972RedNeck]

Originally Posted by Daimler

Just a thought, has no one else ever heard of this Torque Flyt O.D. tranny? If I remember it, maybe someone else does too? It was for sale in the mid eighties, not sure if they are still out there.

I haven't heard of any Torque Flights outside of Chrysler's automatics. I have been intrigued by Ranger Torque Splitters for a number of years though...



Sounds exactly like what you're describing.

http://www.advanceadapters.com/categ...lete-units/91/

[B. W.]

Early ranger (cast iron)

[landy]

The stock t-case in a '68 is a Rockwell as previous poster noted. Since parts are getting hard to find, some swap out the Rockwell for a 205, which would provide for more options.

[Daimler]

When I first posted this question I did not realize i was posting in the wrong category. I should have posted under pickup trucks and not suburbans and panels. I believe the drive lines would be the same though?

[LockDoc]

Originally Posted by Daimler

When I first posted this question I did not realize i was posting in the wrong category. I should have posted under pickup trucks and not suburbans and panels. I believe the drive lines would be the same though?

I wasn't sure what you had so I left it alone. I can move it for you.

LockDoc

[Bigdav160]

Yes same drivetrain but the truck section gets a lot more traffic

[Daimler]

Thanks Lockdoc, it is a 1968 3/4 ton 4X4 that has a stock transmission and transfer case. The dually diff stuff was installed to improve handling for a 11 1/2 foot camper which seemed a little iffy on the original diffs and the 35's that were on it. Step side fenders were placed along side the fleet side and cut to fit so the xtra dually tire would be fendered.

[El Dorado Jim]

try posting this in the 4x4 section, may get a few more responses.

[olblue60@aol.com]

In my "Chevrolet Pickup Redbook" it has an option listed "M10 overdrive transmission" . I'm not familiar with it.

[Daimler]

Thanks Redneck, that is exactly what I am was asking about. Its been a long time for me so I must have a jumbled memory. And B.W., those pictures of the installation thrill the **** out of me! Twenty years ago I got side tracked into Jags when my Dad needed a new Cadillac. He drove them all his life but Cads had since turned to junk. I met Geoff while looking for hub caps for a 68 Daimler Jaguar and discovered he was installing the Chev V-8's into Jags. Talked it over with Dad and he went for it. Built Dad the car and ended up working with Geoff on Jags on for twenty years. I kept the 500 out of Dad's /74 Sedan De Ville for my truck. Maybe now I can finally get back to finishing off the 68. ( just retired) I included some pictures of my truck. Longest trip was Calgary to Big Sur California with the camper and towing a borrowed Goldwing. 9 to 13 mpg on that trip. As a point of interest the running boards I rigged up are hollow aluminum hand rails removed from the Saddledome when they renovated. I found them in the scrapyard at a price per pound. Could not at that time afford to modify a couple of sets of correct stepside panels so ran these to blend the rear fenders.

[57taskforce]

Originally Posted by Daimler

Thanks Redneck, that is exactly what I am was asking about. Its been a long time for me so I must have a jumbled memory. And B.W., those pictures of the installation thrill the **** out of me! Twenty years ago I got side tracked into Jags when my Dad needed a new Cadillac. He drove them all his life but Cads had since turned to junk. I met Geoff while looking for hub caps for a 68 Daimler Jaguar and discovered he was installing the Chev V-8's into Jags. Talked it over with Dad and he went for it. Built Dad the car and ended up working with Geoff on Jags on for twenty years. I kept the 500 out of Dad's /74 Sedan De Ville for my truck. Maybe now I can finally get back to finishing off the 68. ( just retired) I included some pictures of my truck. Longest trip was Calgary to Big Sur California with the camper and towing a borrowed Goldwing. 9 to 13 mpg on that trip. As a point of interest the running boards I rigged up are hollow aluminum hand rails removed from the Saddledome when they renovated. I found them in the scrapyard at a price per pound. Could not at that time afford to modify a couple of sets of correct stepside panels so ran these to blend the rear fenders.

Man that's a good looking truck!

[BLT gmc]

The T/C shifter really becomes a problem with the seat when you push it back 7" for the overdrive. Linkage has to be re-engineered!! But I agree, having more sticks in the cab is cool. I want people to look at that bamboo jungle and ask how the he** do you drive that!!!
Posted via Mobile Device

[B. W.]

Originally Posted by BLT gmc

The T/C shifter really becomes a problem with the seat when you push it back 7" for the overdrive. Linkage has to be re-engineered!! But I agree, having more sticks in the cab is cool. I want people to look at that bamboo jungle and ask how the he** do you drive that!!!
Posted via Mobile Device

Yep, you gotta move it. I moved mine forward, it sits in front of the stock position now, may move it back a little. I welded a tab on & cut off the stock linkage hole so it would line up better.

[Daimler]

Thanks Taskforce, I have been looking for a more modern truck with maybe a 454 4X4 and stick and thought why not continue with the 68 - so I thought I would ask around. This site has definitely renewed my interest.

[franken]

An NV4500 and NP205 or NP241 is probably the same or less money than a separate overdrive.

[Daimler]

I've been thinking, working from a cruise rpm of 3000 with the 411's and stock four speed - why not both. Use the 27% drop with the Ranger to 2190 rpm. Then pull the O.D. on the NV4500 for another 25% - dropping to 1625 rpm. Dad's V-8 Jaguar weighs 4500 lbs. With the 700R4 he is turning about 1650 RPM at 65 MPH. Although the motor is 'built' he gets 28 to 34 mpg on the hiway. If the 500 Caddy motor was mildly tweaked the truck would also have the power to push the truck at these rpm's? Basically the same power to weight ratio? All i have to do is knock off a bank.