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Discussion Starter #1
Figured I'd start a build thread on here, found myself a very nice 1986 GMC K30, and have decided to do a rebuild and build up on it. It has a factory 6.2/SM465 combo, and I'm gonna tear that gutless wonder out in favor of a 1997 12 valve from a parts truck I've purchased. The GMC is a full load, AC, cruise, tilt steering, power doors, and in not too bad a shape.
 

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So the 12 valve is for sure going in, but not too sure I want to use the 47Rh from the donor truck. I'm always partial to the NV5600, but have been researching running a 68Rfe with an aftermarket controller. Still deciding on that. In the meantime, found some king ranch seats in a junkyard, so those may well make their way into the build at some point
 

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Nice! Sounds like a good build! I don't remember seeing anyone do the 68 RFE, so that'll be interesting for sure!
 

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68 would be really cool! I have seen one done but not many around. What gears are in the chevy?
 

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Discussion Starter #7
68 would be really cool! I have seen one done but not many around. What gears are in the chevy?
It's 4.10 right now, but i'd like to regear with 3.73s. I've been trying without much luck to find info on swaps behind a 12 valve, but it hasn't been documented very well. I know at least one guy makes what looks to be a decent controller, but it's way more electronics than I ever hoped to have on this thing. We'll have to see. I do love my NV5600s :confused013:
 

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4.10 is perfect with a 68. I hate electronics more than most but I did enjoy the 68 in my 4th gen.
 

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Discussion Starter #11
4.10 is perfect with a 68. I hate electronics more than most but I did enjoy the 68 in my 4th gen.


Yeah, I guess they’re a double overdrive, eh? Reckon I could try it before regearing. I’ve owned a lot of 4.10 trucks with the cummins, and I just associate them with poor highway cursing rpms


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That's a sweet GMC! I think the NV5600 would be a cool idea if you don't mind adding in another pedal.
What do you plan on using the truck for?
 

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Discussion Starter #13
That's a sweet GMC! I think the NV5600 would be a cool idea if you don't mind adding in another pedal.

What do you plan on using the truck for?


The truck is already pretty much tailor made for a 5600. It’s already got a hydraulic clutch set up for the 465 that’s In it. For usage it’s going to see a lot of road trips, light to moderate off road, with a box camper. I hope to daily it


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Yeah, I guess they’re a double overdrive, eh? Reckon I could try it before regearing. I’ve owned a lot of 4.10 trucks with the cummins, and I just associate them with poor highway cursing rpms


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Correct,

68RFE ratios's
1st 3.23:1.
2nd 1.83:1.
3rd 1.41:1.
4th 1.00:1.
5th 0.81:1.
6th 0.62:1.
Reverse 4.44:1

NV5600 Ratios
1st 5.63 : 1
2nd 3.38 : 1
3rd 2.04 : 1
4th 1.39 : 1
5th 1.00 : 1
6th 0.73 : 1
R 5.63 : 1


If you plan on doing any real towing or off roading, the 5600 would be my choice, if it's more of a daily with medium to light towing, i could see the 68RFE. But, if you really want to play with numbers...check out this site, they have an amazing calculator set up for all the ratios so you can see where you will be RPM and speed wise based off tranny and rear end and everything. definitely worth playing with to help make a decision based off your needs

Gear Ratio Calculator
 

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Discussion Starter #15
Correct,



68RFE ratios's

1st 3.23:1.

2nd 1.83:1.

3rd 1.41:1.

4th 1.00:1.

5th 0.81:1.

6th 0.62:1.

Reverse 4.44:1



NV5600 Ratios

1st 5.63 : 1

2nd 3.38 : 1

3rd 2.04 : 1

4th 1.39 : 1

5th 1.00 : 1

6th 0.73 : 1

R 5.63 : 1





If you plan on doing any real towing or off roading, the 5600 would be my choice, if it's more of a daily with medium to light towing, i could see the 68RFE. But, if you really want to play with numbers...check out this site, they have an amazing calculator set up for all the ratios so you can see where you will be RPM and speed wise based off tranny and rear end and everything. definitely worth playing with to help make a decision based off your needs



Gear Ratio Calculator


I’ve used that calculator a lot over the years, haha. The main purpose of the truck is going to be daily driving and road trips and travelling on the highway. I’ve got other rigs for any serious off roading or camping, and towing. If this truck goes off road at all, it’ll be logging roads and established trails. I love the 5600, but would also like the convenience of an auto. And then the wife can drive it too


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Rear Admiral Rickard Onmi
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kinda sounds like the 68 is the right tranny for the job then. You could always look around for an allison too if you are going to be running a controller anyways
 

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Discussion Starter #17
kinda sounds like the 68 is the right tranny for the job then. You could always look around for an allison too if you are going to be running a controller anyways


I’ve also looked into the Allison, but the conversion parts needed turned me off. And as I don’t plan on pushing stupid horsepower or modify either transmission, I would think the 68 would do me fine


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I have a built Allison and the full conversion kit for sale, but its a 2wd
 

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Discussion Starter #19
I’d like to apologize for the lack of updates, went overseas for work for 4 months and hired some folks to build a garage on my property. Came back to find a snow covered concrete footing, and nuts to working outside in the Edmonton winter. I’m going away for work again and the next few months will be spent buying conversion parts online so they’ll be waiting for me when I get back. In the meantime I’ve located a 5600 about 3 hours south of me, it needs a 4th gear synchro but I’ve rebuilt one before for my first gen so I’m not too concerned about it.

This is how the truck sits now, the 6.2 has actually been really reliable, I’ve used this truck to jump start the various projects I have around the property. Next to it is my ‘79 crew cab, also waiting for attention. I’d like to put a 6V Detroit and twin sticks into it, but those are rarer than hens teeth around here, so it’ll get the 6.2 from the red crew for the time being. Thanks for following!




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Discussion Starter #20
New
Made what I think to be the 3rd biggest purchase on this project, found me a 5600. I was looking for a core to rebuild, but a buddy hooked me up with a running take out for a fraction more than a blown up core



I’m still going to take it apart and check the bearings and things, and adjust the shaft free play, as I’ve read they do better with a a tighter clearance on the main and countershafts, and the last one I built like that is still going strong. I’ll also get the case sandblasted and painted, and make it look all pretty. I was going to go the core route and rebuild, but I’m quite pleased I won’t have to mess around with pressing the shafts apart to do syncros now



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