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From the time I first gazed at a NAPCO-converted '57 GMC short box, V-8 powered pickup to our last two Suburban K2500 beam front axle models, vintage G.M. beam front axle K-trucks have held my attention...I recall test driving an early press fleet '88 Chevrolet Silverado (GMC Sierra) 4WD IFS pickup in its first release to the media in the spring of 1987—wondering, "What is G.M. thinking here!"

 

G.M. hit stride in the 'sixties and 'seventies, setting a benchmark for 4x4 trucks. Our 1973 Chevrolet K10 short bed with a 350 V-8 and 465 Muncie truck box was among the best vehicles we've ever owned.  Even our Dodge Ram 3500 was purchased largely for its beam front axle—a design that G.M. trucks taught everyone to value.

 

I know what works for G.M. beam axle trucks...Do you have questions?  Want to share what today's "built" G.M. beam axle truck is all about?  Join the forums and get the conversation going!

 

Moses

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  • 8 months later...

Well, perhaps I can pose a question or two.

I'm seriously considering swapping the entire drivetrain from my 1986 2500 GMC into a 1982 K5 Blazer.

The GMC has a 454/SM465/New Process case, with the 'semi-float 14 bolt rear, and 10 bolt front.

I know that I'll be moving spring pads to get the rearend from the pickup mounted into the K5 chassis. Any surprises with swapping the front in? I intend to move the entire brake and steering systems over to the K5 chassis, and the cooling system, as well.

I guess the biggest concern that I have concerns the 3/4 ton 'semi float' rear end. I've hauled some fairly substantial loads for fair distances with it in the pickup, it makes no noise, the brakes are good, the bearings, as well. Am I perhaps just a bit paranoid about this rearend, or would I be better off trying to source a 'full floater'?

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This is a very straightforward swap.  The spring perches for 1/2 and 3/4 ton GM trucks are close if not identical during this vintage, and the K5 is like the 1/2-ton.  You will find that the rest of your '86 donor and the Blazer has essentially the same layout, too.  Each model has a chain drive transfer case, the 454 3/4-ton model should be a beefier transfer case.  The 454 will fit the Blazer engine bay, the SM465 was available in the Blazer, and since you're doing front and rear axles, the wheel bolt pattern will be identical (8-stud).  Shift linkage needs sorting and the steering column if automatic to stick.

 

You will need improved cooling, and the '86 radiator could be a bolt-in (core support pieces, too).  The steering linkage needs a close look, may be the same.  Motor mounts, driveshaft splines and such are a consideration, the driveline will need fabrication for length of the tube.  Frame should require no modifications, possibly a need to adjust the location of the rear cross member.

 

I've seen this setup under many Blazer K5s from the beam axle era.  It will be exceedingly rugged.  I've rebuilt the Corporate 14-bolt axles, the Gov-Loc is a somewhat worthless limited slip that may plague your '86 axle.  The semi-floating axle shafts are a non-issue with this weight vehicle, they should work very well if in good condition.

 

You're going carbureted to carbureted, so there's no fuel pump or delivery system issue.   ('86 is the last GM V-8 year with a carburetor and a mechanical fuel pump.)  The 454 should be an HEI with minimal emission constraints if a "Federal" engine and emission package.  You might need to sort out the EVAP system.  Sounds good to me!

 

Moses

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  • 2 months later...

Sorry to have taken so long to reply.  Much to do after renters left our other home in a shambles...Anyhow, a bit of history on the components.

 

The 454 originated in a 1974 "Heavy Half" Suburban that had a Turbo 400 behind it, two wheel drive, of course.  I installed a new flywheel, clutch assembly, pilot bushing, and put it in front of the 465 where a 350 gas engine had previously been.  The 350 had a connecting rod hanging out the side of the block, courtesy of one of my sons who had an "enthusiastic" driving style.  

 

Prior to installing the 454, I replaced the timing set with Cloyes double roller timing set, and while it was on the engine stand, I removed the oil pan, R&R'd both front and rear main seals, inspected the bearings, and put in a new Melling HV/HP oil pump and drive.  Other new parts installed were water pump, thermostat, Accel HEI distributor, coil, plug wires, fuel pump, power steering pump, and I removed the remote engine oil cooler adapter from the block that I never could get to seal.  I should have replaced the cam, lifters, springs and retainers, and also should have had a valve job done, but it ran really well prior to removing it, so I figured why...

 

 Another son with the same right foot affliction as the other, soon revealed why the original valve operating system was inadequate!  It now has lifter noise in at least a couple or three lifters.  For now, it's just an annoying 'tick', but I won't let that get too far along before I remedy it.  Also purchased new and installed into the GMC was new motor mounts, intake manifold and exhaust manifold gaskets, a new, properly sized and rated "big block" aluminum radiator and mounting pads, as well as new hoses.

 

I "kitted" the "Quadraflush" carburetor, which starts, and runs great, seems to be quite capable when 'wheeling, and has yet to develop the "overnight fuel dump" that every other Quadrajet I've owned has eventually developed.  I do have a 650 Edelbrock carburetor that I had been running on a small block, and I'm going to swap that for the Q-jet to see if there's any difference in performance or mileage before I get to yanking and swapping drivetrains.

 

The 3/4 ton axles are geared 3.73, and both are "open" differentials.  Both have had new rotors/drums/pads/shoes/bearings installed within 10K miles, with no noise, vibration, leakage or other distractions noticed in operation.

 

As I plan to 'gut' the pickup to acquire the parts to make the swap, the pedal assembly, steering column, and all the other little parts that can be aggravating to find are 'right there' and work, so I'm not anticipating a big parts search, with one glaring exception...I'd love to dump the NP208, and install the NP205 that I have sitting in the corner of the garage.  Problem is that the 205 came from  a  Dodge 3/4 ton, (transmission unknown) and I'm not sure about compatability.  I may end up putting it in the paper with an offer to trade for the 'right' GM case.

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Rocket Doctor...I've had huge success with Quadrajet carburetors, kitting and 'blueprinting' them, adding a brass float in the process.  Despite the complexities and myriad adjustments to properly tune this carburetor, the Q-Jet is the most refined and altitude compensating 4-barrel carburetor ever built.  Running on the primaries will deliver respectable fuel efficiency. 

 

Aftermarket replacement carburetors require tuning and tweaking, and some are benchmarked for a specific displacement engine.  Generic carburetors are troublesome to re-jet and tune.  If you have the 454 Quadrajet with its original jets and metering rods, and if it's a Federal design without electronic feedback, be grateful.

 

The NP205 gear drive transfer case might work if the input spline count and shaft length are the same.  Flange bolt circle is common.  A quick answer would be a call to the Advance Adapters' tech line at 1-800-350-2223.  They can quickly note any differences between the Dodge and GM applications for the 205.

 

A gear drive NP205 is, quite frankly, the most rugged OEM transfer case ever built for a light truck.  The only other consideration would be an Atlas II from Advance Adapters.  The 4-speed Atlas is even more trick.  See the magazine's video coverage of both the 2- and 4-speed Atlas designs.

 

Moses

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Moses, this particular Q-Jet is indeed the "48" state version, the truck it originated in had a high enough GVW to exempt it from much of the nonsense that was happening, and was to follow.

 

I'll give A-A a call, a description, and what I can make out on what's left of the data tag, and see if we can't figure out what it is for certain.

 

I'd almost contemplate using the Turbo 400 that originally came from behind that 454 this NP205 could (and I'm sure the parts are out there somewhere to do it) be used.  

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I'm partial to the Q-Jet—with a brass float replacement.   Consider that option if you get into the carb again, the phenolic OE floats are terrible, especially after setting up dry.

 

Provide the data tag numbers.  I have a Mitchell interchange book that covers that era and may demystify.  Advance Adapters should be helpful, too!

 

We had the Turbo 400 in each of our K2500 Suburban 4x4s (1986 and 1987).  The '86 had the Federal 49-State non-feedback carburetor, and I really liked it.  No fuel restrictor for unleaded, either, all stock.  The '87 was the first TBI, and it had charm, too.  Both trucks were far better built than any Suburban after 1991.  IFS 4WD was not a good direction for GM on the light-duty trucks, especially the K2500 and K3500.  They persisted with the design from the 1987 pickups onward.

 

Moses

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