Re: 78 K20 modernization project
 

I had been mulling over my plans to change the 78 K20 to an overdrive automatic, installing a newer motor, converting it to EFI and upgrading it to power windows & locks and adding sport mirrors to it.

The truck has been so reliable and solid I had second thoughts about tearing it apart. I found a 74 K10 on CL for a reasonable amount of money that was missing the drive train.

I picked it up on Thursday and it came with an extra front clip and another set of axles & tires attached to the Blazer they were on because the kid didn't feel like taking them off of it to give me what was in the ad.

The 74 is a bare cab with nothing under the dash but it had factory A/C so it will be much easier to install than putting A/C into my heater only 78 K20. It also has the auto trans 4x4 tunnel so I won't have to fill that hole where the shifter goes through on the K20 and it has a sliding rear window the K20 also does not have.

The Blazer floors are really rusty and it has had some metal fatigue issues in the door jambs so I am just going to part it out and put the best stuff from the two onto the 74 K10 and scrap the rest of it. I thought about making it an off road beater with all the serviceable parts that come off of the other two trucks but don't feel like spending the money to make it safe to drive or put a drive train into it.

One of the clips that came with the new acquisition is a near perfect 70's vintage set that is painted exactly like my 78 K20 so that will be going onto the 78 to fix the damaged driver side fender and cancer infected passenger side fender. I may take the driver side door off of the Blazer to put onto the K20 if my attempt to straighten out the damaged edge on the current one doesn't turn out.

Pics of the clip swap on the 78 K20 to follow after I get the K10 and K5 merged into one and the carnage cleaned up.

Re: 78 K20 modernization project
 

i wish i was closer i'm in need of a cab lol my 73 is rotting like no tomorrow... po did some stuff to it that mother nature loved

Re: 78 K20 modernization project
 

The clutch fork broke so I ended up yanking the whole drive train, resealing the leaky transfer case and the transmission adapter, and upgrading the engine to a high volume pump and installing new rod & main bearings.

http://67-72chevytrucks.com/vboard/s...t=clutch+broke

Re: 78 K20 modernization project
 

The day after I got the whole drive train back into the truck, got it assembled and back onto the road the ignition mechanism failed.

http://67-72chevytrucks.com/vboard/s...=1#post4004633

It seemed quite coincidental to have something break right after I did all that work but nothing I did was even close to the failed part so it was purely bad luck. At least it failed in the morning when I was going it warm it up prior to heading off to work instead of failing at work and stranding me with a broke truck and no tools or parts to fix it with.

It is now back on the road and runs & drives better than it has since I owned it. It shifts smoothly into all gears with little to no effort and the clutch works with minimal pedal movement instead of having to push the pedal to the floor all the way to be able to shift as before. It is much nicer to drive now but the clutch still kills my knee to use it.

Now I can get back on the 67 C-10 to K10 conversion project after a couple week delay fixing the K20.

Re: 78 K20 modernization project
 

Scored a great retrofit shifter boot for the NP205 shifter out of a wrecked Saturn with a manual trans that fits the NP205 boot retainer ring perfectly.

http://67-72chevytrucks.com/vboard/s...77#post4209677

Looks great, won't let in any noise, fumes or moisture like the damaged old one did.

Plenty of height for full range of motion with no binding.

The price was right too at only $3.

Re: 78 K20 modernization project
 

Scored a delay wiper switch & delay module with pigtail at the wrecking yard today.

Just have to dig in and see how the wiring is different between the delay module connector and the non-delay switch.

http://67-72chevytrucks.com/vboard/s...45#post4209745

Hopefully it won't take any funny business wiring wise to make them work.

Delay wipers are a tough thing to live without after you have had them for so long. Not having them is the worst thing about driving the K20 in bad weather.

Scored a tach cluster small fuel gauge too from the same truck the delay wipers parts came out of. Unfortunately the tach was gone and the hack that took it busted the housing & damaged the circuit board getting the tach out.

Just have to make a new overlay for the Camaro tach now that uses the 80 psi oil pressure gauge to match my engine so I can complete the tach cluster I am building and change it out on the truck.

Re: 78 K20 modernization project
 

I put the delay switch in and it has a mind of its own so either the switch or delay module or both have issues unless there is something different with the wiring.

I couldn't find where I stashed the other two switches I have to test them too so I will have to dig into this again at a later date.

Anybody have a wiring diagram that shows the delay module wiring? I have one with the standard 2-speed motor only.

Re: 78 K20 modernization project
 

Since I had the dash panel off to access the wiper switch I took the opportunity to replace all the general lighting bulbs with 168 bulbs and checked to make sure they all worked while I had it apart.

I am going to retrofit the truck with TBI so I needed to install a newer speedo with the optical VSS capabilities into the stock housing. Amazingly the 78 housing had a hole pretty close to the right size for the optical sensor to go through. All I had to do was enlarge it a little to make room to get the plug through and create clearance for it to sit right with the speedo in place.

Used a hacksaw blade to open the existing hole up just enough to clear.

I also reset the mileage on the optical VSS speedo to match the K20 to within a 1/10th of a mile before I put it in.

Road tested and both the speedo and mileage counter work correctly.

Re: 78 K20 modernization project
 

I also replace the 60 psi oil pressure gauge with an 80 psi gauge from a diesel square body since after I installed new rod & main bearings and a high volume oil pump I have more than 60 psi oil pressure so the stock gauge is pegged 99% of the time.

I didn't like the mismatched gauge fonts & band colors so I swapped out the rest of the gauges for newer ones to match the oil pressure gauge & VSS speedo. I used a diesel water temp gauge that only goes up to 240 degrees too since I always hated the C-H temp gauges. How hot is H? Fixed a problem with the temp gauge too while I was at it. One of the clips came half way out of the housing and made the temp gauge only work part of the time. I was able to snap it back into the housing securely and the new gauge works properly now.

I repainted all the gauge needles with Chevy orange since I had some on hand. I've used it in the past and it works very well against the black gauge faces. In bright light it changes to more of a fluorescent color but in the shade it becomes the orange color that stands out very well against the black. You can see this in the middle pic. All the needles were painted with the same paint so the direct sunlight makes the needles brighter.

Couldn't find my plastic polish so I had to put the clear cover plate back on with just a washing off.

Re: 78 K20 modernization project
 

Next up will be to finish assembling the Camaro tach cluster. I finally got another printed circuit to replace the damaged one on the housing I modified to fit the third gen Camaro tach so now I can go forward with the assembly & wiring on it.

This thread got me started on it about a year ago.

http://67-72chevytrucks.com/vboard/s...ht=camaro+tach

I also picked up a spare Camaro tach face with the 80 psi oil pressure gauge I need to I can finish the overlay with an 80 psi range to match. The newer tach out of an 89 Camaro has a smooth face too where the gauge is not separate so it will lend itself better to a full gauge overlay like I did playing around with the speedo.

I may try to make the tach overlay look more like a stock speedo face with the circular stripe in the middle if I can make it fit so it would match up better with a stock speedo.

I think doing it this way and keeping the Camaro oil pressure gauge in place and just making your own fuel level gauge to go in the stock truck oil pressure gauge location is much easier and looks better too.

I may mess around with a stock oil pressure gauge and see if I can make it function as a fuel level gauge without having to change out the mechanism.

Re: 78 K20 modernization project
 

Good looking project. Did you have to swap the sending unit to use the 80 psi oil gauge?

Re: 78 K20 modernization project
 

Yes. I installed the 80 psi sender to match. They are marked on the hex section at the base of the sender with a 60 or 80 so you can tell them apart.

I still need to change out the temp sender but didn't have a 1/2-NPT to 3/8-NPT reducer handy. The diesel sender is smaller than the older small block sender. The newer heads have smaller sender bosses so it would bolt right into a newer engine with the lighter casting scalloped edge cylinder heads.

Re: 78 K20 modernization project
 

Good looking project

Re: 78 K20 modernization project
 

Just a note, Idle mixture screws do not change the over all air fuel mixture off idle.

Re: 78 K20 modernization project
 

That is what the wide band oxygen sensor bosses on my exhaust are for.

The wide band gauge is the best tuning tool I ever purchased.

I need to put it on this truck and get the jetting dialed in but it is too darn cold to go outside to play.

Re: 78 K20 modernization project
 

I hear that, I gotta go move some stuff around today so I can get my neighbors car in to change his fan clutch. Its cold and rainy.

Re: 78 K20 modernization project
 

I like the mods your making, looks great.

Re: 78 K20 modernization project
 

Thanks.

I haven't been able to drive the truck in over a month. We got rear ended while stopped at a red light and I really messed up my clutch foot. I can't even put the clutch in far enough to get it started without large amounts of pain.

I did clean it up and wash the mud out of the floor mats and off the rubber floor mat this weekend at least so it doesn't feel completely neglected.

I fired it up and let it run for a while using my right foot on the clutch. That was kind of awkward but at least it didn't hurt. Definitely couldn't drive it that way though.

Re: 78 K20 modernization project
 

Started putting the truck back to stock and fixing the little things that it needs.

Got the stock iron intake cleaned up & painted Chevy orange to match the engine. Scored a nice condition Q-Jet to go on it and put the choke parts from the old 78 K20 crusty Q-Jet on it so the choke can function properly.

Dusted off the stock air cleaner and fit it with a new filter element.

Debating putting on a set of fenders I have that have the front cup clipped off for large tire clearance but have no rust or other body damage.

Re: 78 K20 modernization project
 

I scored a 4.10 posi FF 14-bolt and the Dana-44 in the front of my 69 C20 that was half way converted to a 4x4 by a PO is geared to match it to the 5.13 gears in the 78 K20 are going away.

I picked up a set of K20 spindles & brake parts to upgrade the Dana-44 to 8-lug so I can clean up the 4.10 geared axle assemblies and paint them before they go into the truck.

I am keeping the 5.13 axles in the truck until the future owner has a chance to drive the truck with them in place so he can see they run quietly and have no problems. Once we can get together for the test drive I will swap out the axles and deliver them to him.

This should make a huge improvement in the functionality of the truck and add some much needed fuel economy too. It's no fun shifting every two seconds and 7 mpg just plain sucks.

Re: 78 K20 modernization project
 

I can't imagine having to drive anywhere other than around town with 5.13s and no overdrive.

Re: 78 K20 modernization project
 

Luckily I don't need to take it anywhere on the freeway. It is an absolute beast down low with those gears but being over 4000 rpm at freeway speeds gets old in a hurry.

The original owner had them put in when the truck was only a month old because it didn't have enough pulling power with the stock gearing.

Re: 78 K20 modernization project
 

Started taking apart the spare 4.09 geared Dana-44 front axle I have to get it ready to go into the 78 K20 and ran into a snag. Can't get the pinion gear out. Is there any trick to get it to come out?

http://67-72chevytrucks.com/vboard/s...51#post4815851

I'm afraid it is welded to the forward pinion bearing due to the heat discoloration on the yoke.

I may have to try to split the race with it in the housing still. I hope I can get it apart without damaging the pinion gear.

Any help would be appreciated.

Re: 78 K20 modernization project
 

Pics of the pinion spline & forward bearing area.

Re: 78 K20 modernization project
 

I got the pinion out. Took nearly three hours but I got it out without hurting the rear end housing or doing any additional damage to the pinion gear.

The pinion gear is heat discolored for about an inch rearward of the forward bearing. I don't know if it is enough to weaken the pinion gear or not. Most likely it will fail under heavy load so I am going to look for a better set of gears.

The roller bearings were hammered and not rolling too well if at all.

I will try to get the inner race off without hurting the pinion gear and see how it looks. It is being pretty stubborn.