Transmission Conversion
 

I have a 68 Dually flatbed with a four speed, (granny gear 1st). I am never going to pull a lot with this truck, the heaviest thing may be the cab from another truck to the media blaster.
I have been considering swapping a 400 Turbo in place of the standard.
Is this common, or, are their more issues than makes it worthwhile?
Top end in this truck is about 60 with the current gearing, and I never use first gear. I realize I may have to change the rear end gearing as well, but I am just looking for basic information here.
Thanks, so much to all!
hexter01

Re: Transmission Conversion
 

I did this swap years ago in a 72 3\4 ton. You will need a automatic crossmember from an automatic equiped truck as well as a column and shift linkage out of a automatic equiped truck note the th400 and th350 shift linkages are different where they mount to the frame but I think either will work. You will have to knock out the 4 speed crossmember after you remove the transmission. Final drive ratio won't change it's 1 to 1 on both the 4 speed and the th400. You will also have to change the drive shaft and you will need a th400 slip yoke.
Ugly 61

Re: Transmission Conversion
 

Thanks, to Ugly61! I can't believe I got a reply, so fast.
I may just use a Lokar floor shifter, since this isn't a show truck, only a worker.
Thanks again!!
hexter01

Re: Transmission Conversion
 

Don't forget to change the manual trans flywheel to an auto trans flexplate.

You'll also need to swap nosecones on your starter to an engine block mount type rather than the bellhousing mount type you currently have.

Re: Transmission Conversion
 

Keep in mind that it's about the same work and not much more $$ to go with a OD tranny.
That would give you an advantage and might save you a rear gear change.

Re: Transmission Conversion
 

your so close to installing a np4500 why not go that rout?

Re: Transmission Conversion
 

He's probably tired of that high clutch in trucks. With my bad back the hip rotation on a bad day for me in a clutch single cab is brutal. I like my cars with manuals and hydraulic clutches. But I'll stick to auto trucks.

Re: Transmission Conversion
 

Dont forger adding a cooler & cooler lines

Re: Transmission Conversion
 

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If you still like shifting a manual like I do here is what I did with my C30 Dually....

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

LockDoc

Re: Transmission Conversion
 

I just read that whole thread on the nv4500 conversion. That's incredible work, really smart. My only question is after using the stock bell clutch and linkage what about the drive shaft? did that remain stock or did it have to be shortened? my trucks a 71 C20 with the sm465 and has the slip yoke behind the center bearing on a two piece. I'm assuming that's how your truck was?

Re: Transmission Conversion
 

Thanks.

Yes, mine is a two piece. I had to shorten the front driveshaft.

LockDoc

Re: Transmission Conversion
 

You could get a floor shifter, bm/hearst and wont need all the extra linkage, it comes in the box.

Re: Transmission Conversion
 

Thanks so much to all for all of the replys.
I am 65 and the thought of a long trip shifting gears did cross my mind. I am considering the overdrive transmission, but to me having a TH 400 grabbing gears, as a 60's guy, there's nothing better.
Again, thanks everyone, I will reread all of your posts, and try to come up with a solution that works best for me, that I can handle, skill wise.
hexter01