Transmission Conversion - The 1947 - Present Chevrolet & GMC Truck Message Board Network

hexter01 · 07-19-2016, 06:57 AM

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

Ugly 61 · 07-19-2016, 10:41 AM

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

hexter01 · 07-19-2016, 12:25 PM

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

Shady Rascal · 07-19-2016, 03:48 PM

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.

PanelDeland · 07-19-2016, 03:53 PM

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.

mike16 · 07-19-2016, 07:38 PM

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

TrkEnvy · 07-20-2016, 02:19 AM

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.

scooterpimp · 07-20-2016, 05:32 AM

Dont forger adding a cooler & cooler lines

**LockDoc** · 07-20-2016, 09:32 AM

-
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

old Chevy guy · 07-20-2016, 10:17 AM

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?

**LockDoc** · 07-21-2016, 01:30 AM

Quote:

Originally Posted by old Chevy guy

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?

Thanks.

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

LockDoc

mooseboy84 · 07-21-2016, 01:44 AM

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

hexter01 · 07-21-2016, 04:42 AM

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

07-19-2016, 06:57 AM	#1
hexter01 Registered User Join Date: Jul 2016 Location: Ostrander Posts: 3	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

07-19-2016, 10:41 AM	#2
Ugly 61 Registered User Join Date: Jan 2015 Location: Clyde KS Posts: 91	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

07-19-2016, 12:25 PM	#3
hexter01 Registered User Join Date: Jul 2016 Location: Ostrander Posts: 3	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

07-19-2016, 03:48 PM	#4
Shady Rascal Registered User Join Date: Feb 2016 Location: Weatherford Texas Posts: 306	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.

07-19-2016, 03:53 PM	#5
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	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. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

07-19-2016, 07:38 PM	#6
mike16 Registered User Join Date: Dec 2009 Location: bisbee, arizona Posts: 1,529	Re: Transmission Conversion your so close to installing a np4500 why not go that rout?

07-20-2016, 02:19 AM	#7
TrkEnvy Registered User Join Date: Apr 2011 Location: Las Vegas, NV Posts: 264	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. __________________ 1971 C10 - LWB shortened to SWB, welded in my C notch, reinforced trailing arms with 3/16 plate, new cpp 5" rear drop springs, 2" drop blocks, ece super panhard kit. Cpp drop spindles, 2 inch front springs, 5.3/4L80E I call it Bruce Banner..

07-20-2016, 05:32 AM	#8
scooterpimp Registered User Join Date: Dec 2015 Location: Newark ,Delaware Posts: 158	Re: Transmission Conversion Dont forger adding a cooler & cooler lines

07-20-2016, 09:32 AM	#9
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,345	Re: Transmission Conversion - 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 __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

07-20-2016, 10:17 AM	#10
old Chevy guy Registered User Join Date: Apr 2007 Location: Foster Rhode Island Posts: 1,176	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?

07-21-2016, 01:44 AM	#12
mooseboy84 Registered User Join Date: Feb 2012 Location: Bay Area Posts: 35	Re: Transmission Conversion You could get a floor shifter, bm/hearst and wont need all the extra linkage, it comes in the box.

07-21-2016, 04:42 AM	#13
hexter01 Registered User Join Date: Jul 2016 Location: Ostrander Posts: 3	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



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