1978 Chevy C-30 and K-30 Frames

[Speed]

This truck is a '78 standard cab one ton dually,2 wheel drive,but the VIN from the frame,which it's Registered by,shows it to be a 1974 Chevy one ton crew cab 4WD. I'd like to settle,once and for all,how hard is it to make a K-30 into a C-30? I

ve heard everything from "Piece of cake-just slide the front suspension under the frame,bolt it in and change the steering box to the C-30 version and you're good to go." to "It can't be done without cutting,welding,lots of measuring,etc. etc. etc. So I don't know how this was accomplished. Its a good truck,and it has a 13 foot flatbed on it. Currently awaiting a 400 smallblock that I wanna change the timing chain to a new double roller set,a one piece oil pan gasket and a Holley square bore 4 barrel carb. The engine is from a '78 Motor home. It has an A/C compressor,so it'll be set up with on-board Air. The truck already has a 7 gallon air tank and most of the plumbing,which I intend to start fresh on,but I'll keep the air tank. Future inteny is an NV-4500and better seat,new windshield,a grille and more exterior lights.

[Moses Ludel]

Hi, Speed...In my view, the frames have some similarities.  The IFS on the C-chassis, however, requires a frame that will accommodate control arms and bulkier front crossmember for the lower IFS control arms.  The K-chassis has accommodations for leaf spring anchors and shackles to enable the front leaf springs to ride on the beam front drive axle. 

Steering gear and steering gear layout is different between the C- and K-models.  The C-model has a center link, two tie-rods, a pitman arm and an idler arm.  The K-model has a fore/aft pitman, a drag link, a one-piece tie-rod and a steering arm at each knuckle.  Gear output angle differs.

The easiest way to determine the frame's origin is to inspect the front crossmember attachments.  The crossmember should be riveted to the side rails.  If not, someone may have fitted the IFS crossmember, but it would be welded or bolted to the frame rails.  A simpler explanation is that the cab came from a 4WD (K-model), the frame from a 2WD (C-model), and someone registered the truck by its cab/dashboard and door jamb VIN(s).  On a truck of this vintage, nobody at DMV bothered to confirm the frame I.D.

On that note, there is a frame I.D. number.  Some quick research turned up this info for 1973-87 Chevrolet truck frames and the factory I.D. locations:  1) at the windshield tag, 2) the "SPID sticker" (assembled parts I.D.) on the front inner fender panel or in the glovebox, 3) the sticker at the door jamb and (as noted by this one source) 4) stamped at the top of the right frame beneath the cab and/or between the holes for the front bed bolts.  It's not clear how consistent this I.D. sequencing is for each year model.  Also, it's unclear whether the frame number matches the vehicle's VIN.  Presumably there's a numeric connection of sorts.

Here's a great resource for your truck's overall design, dimensions and equipment.  Note pages 123/124 regarding frame designs:

https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Chevrolet-Trucks/1978-Chevrolet-Truck.pdf

I'd download the PDF and use it as a reference...

Moses

[Speed]

I replied to it once,but it apparently didn't transfer. Okay-The cab I have is a 1978 C-10 cab with no  papers,but the frame had a Title that matched the Frame number. That number shows the truck to be a 1974 K-30 Crew Cab,but the truck is NOW a 1 1974 Chevy C-30 standard cab with a 13 foot flatbed. I never thought about looking at the crossmember attachment method. That'll explain a lot. Thanks Moses. Hope you and yours are healthy and happy.

    Speed

[Moses Ludel]

We're doing well, thanks...Trust everyone is getting ready for a bright spring and summer at Elko!  How's the snowpack in the Ruby Mountains?  We're at 70% in the Sierra and experiencing warmer weather much earlier than usual.  82 degrees F today, though dropping to a high of 43 on Monday.

[Speed]

Snowpack is pretty good,but I don't hold out much hope it'll be here for long. Glad your Clan is doing well. Safe Travels!

[Moses Ludel]

You as well, Speed!

Moses

[Speed]

Not sure this 400 engine is gonna be a runner. I turned the engine stand to one side,so the pistons are leveled,and gave that bank a good dose of PB Blaster,put the plugs back in and snugged them,and left it that way for 48 hours,then did the other bank the same way, but it still doesn't feel inclined to turn.  I have another engine stand with a longer "standoff",so if I swap it to that one,I think there's room for me to leave the flexplate on it that way I can use a couple of big screwdrivers on the ring gear and the arms of the engine stand to rock it back and forth and hopefully free it up to turn If I can get it freed up,I'll hook up a starter and battery and crank it that way,with plugs out,and see how  it sounds turning over. If it's not gonna be a runner,I'm looking for a 292 six cylinder for the one Ton. I think that with a three single throat carb set up with progressive linkage and a set of headers,2-1/2" pipes,turbo mufflers and stacks,it'll do pretty well. It'll get an HEI ignition too. What year did they start setting the sixes up for no-lead gas? I wanna make sure it's new enough to run fine on what they're calling gas these days. What do you think?

   Speed

   BTW-If I buy a Detroit Locker for this truck,would you be able to install it for me? That way I'll know it's done right and I wouldn't have to worry about it.

[Moses Ludel]

Good plan to test the condition of the 400, Speed...The 292 was a C/K20-30 and higher series engine.  Heads were induction hardened in the early seventies, sometimes you can tell whether they were factory induction hardened by the flame treatment.  After thorough cleaning and blasting if necessary, a Rockwell C test would confirm cast hardness. 

Standard practice for years, ever since the unleaded fuel era, has been replacement of exhaust valve seats with hardened steel seats—regardless of the cylinder head vintage.  Also, be aware of the cast-in later induction system ("manifold") and no opportunity to swap tri-power.  You'll need the earlier cylinder head if you want to follow through with the tri-power.  See whether Clifford or Offenhauser still offers 292 intake manifolds.  Clifford likes to use a single four-barrel.  Tri-power might be available elsewhere, as there is a market among hot rod and street truck builders of 230/250/292 inline GM sixes.

HEI is a good idea in any case.  1975-up should handle the ignition.  There is interchange with 230/250 distributors, which would increase the available sources.  Aftermarket HEI distributors are available, basically a knock-off of the '75-up units. 

Exhaust seats are the only real concern, some argue that doesn't make a difference.  I disagree.  If the seats are not induction hardened from GM, I install hard seats to avoid valve seat recession.  Be aware, too, that high temp cleaning processes by reman shops (procedures like a heat oven to burn off carbon) can "normalize"  (soften to original casting hardness) or essentially anneal hard cast seats.  If in doubt about a head's history, install hard steel exhaust seats.

As for a Detroit Locker, not a bad idea for a 2WD truck.  Know the handling/rear steer concerns with the Detroit.  On pavement, the truck will not handle like an open diff or even an "automatic" (multiplate) locker.  As for me installing your locker, sorry, that's not in the cards.  My projects take up all available space, the "fleet" now three vehicles that require routine service.  The latest is a 2003 VW Jetta TDI 1.9L (ALH) diesel A4 platform.  It's a one-owner car in excellent original condition that gets 45-plus mpg on the highway.  That's something only our motorcycles have done.  Toss in the 'Road Ready' YouTube channel episodes that I'm producing, and my shop is busy, busy, busy.

Moses