Difference in Years?

[79Betty]

Can anyone tell me all the differences from 1977 to 1978, and 1979? I need wiring and chassis differences. I know essentially they're the same from 1973-1980 but i need those 3 years exactly as i have my 1977 c30 and 1978 k20 and 1979 k10 titled and all but need help!

[ray_mcavoy]

As far as wiring is concerned, the three biggest differences I can think of are:

(1) For trucks with gauge clusters, 1977 was the last year to use a mechanical oil gauge. 1978-up oil gauges are electric. As a result, the instrument cluster pin-out changed quite a bit for gauge clusters between 77 & 78.

(2) 1978 was the year they changed to the fusebox that takes the plastic ATO/ATC type fuses instead of glass fuses. There were also a number of wire colors that changed for 78. I believe these might have been mid-year changes so there might be some early 78's with the glass fuses & older wire color coding. They also added a ground buss connector near the parking brake in 78.

(3) 1978 was the first year for the permanent magnet type wiper motor. The wiring is a bit different because there is a separate connector for the parking switch. The 73-77 wiper motors had the parking switch wired internally in the motor.

Chassis wise, I believe 78 was the first year to have added some extra strut bracing from the engine mounts to the transmission & transfer case on the 4x4 trucks.

The seat belts were changed in 78 as well. The 78-up seatbelts have the retractors for both the lap & shoulder belts built into one assembly that's bolted to the floor beside the seat. While 77 had separate retractors and the one for the shoulder belts mounts to the door latch pillar portion of the cab (and interferes with mounting the factory type cab corner speakers). The cab floor is shaped slightly different where the seatbelts mount and the rear halves of the sill plates are different in that area too.

[79Betty]

Ray that is some good info that helps. Trying to also distinguish of brake parts will interchange as i have a 77 c 30 wiring harness, cab n doghouse, 78 k20 chassis and 79 k10 axles n suspension so it's hectic as hell trying to order the right parts.

[LONGHAIR]

That is right in the time period where the front axle changed from Dana44 over to the Corporate 10 bolt. It wasn't a clean "instant" change, it took quite some time before they all got 10 bolts.....must have been a supply issue?

[79Betty]

That would also mean a difference in brakes... Be a good note.

[motornut]

compareing my 78 and 79s
my 78 has early glass fuses,both 79s blade
NSS wire colours are different
high/low beam wire colours different
78 no charcoal,79 yes
78 two line fuel,79 three(1/4 return)
78 Idiot oil,moved holes when changed to gauges
not sure about inner /outer hood release...78 no, 79s yes
and the "Fat lip" hood edge? some think 79

[ray_mcavoy]

Originally Posted by 79Betty

That would also mean a difference in brakes... Be a good note.

Actually, the front brake parts will interchange between the Dana44 and GM 10-bolt front ends. So will most of the other parts on the "wheel ends" of both axles. There were some differences in the steering knuckles and the steering stabilizer mounting that affect the tie rod ends but I think those changes were outside of the 77-79 year range. And speaking of brakes, the calipers did change over to metric threaded banjo bolts sometime around 78 or 79.

Originally Posted by motornut

NSS wire colours are different
high/low beam wire colours different

Yes, some of the other wires that changed color around this time include the fuel sender wire (changed from tan to pink) and the oil pressure light/sender wire (changed from dark blue to tan).

Originally Posted by motornut

78 no charcoal,79 yes
78 two line fuel,79 three(1/4 return)

The charcoal canister requirement was based on GVW. Some trucks got them as early as 1970. But the GVW cut-off point kept getting raised over the years so more and more trucks started getting the canisters (along with other emissions equipment).

I believe the 2 vs. 3 fuel line difference has more to do with the original engine/drivetrain configuration than the year. Both my dad's 77 and my 77 have the 3-line setup with the 1/4" return.

Originally Posted by motornut

not sure about inner /outer hood release...78 no, 79s yes

The inside hood release was an option. I think 77 was the first year for it.

Originally Posted by motornut

and the "Fat lip" hood edge? some think 79

Yeah, 79 sounds about right for that slightly raised "style panel" on the hood lip. I know the 78 sales brochures show the "flat front" hood but I suppose it could have been a late-year addition in 78.

Also, the headlight bezels, lower grille molding, and change from exposed fuel cap to filler doors.

There are a bunch of cosmetic changes on the interiors too. Like a different style of instrument panel bezel for 75-77 vs. 78-80. And the higher trim level trucks had woodgrain accent panels on the dash & doors with about 3 different woodgrain styles used over the 73-77 year range. Then they changed to brushed aluminum in 78.

And that reminds me ... the location of the VIN tag moved from the door jamb to the dash in 79 so a cut-out "window" was added to the dash pad.

[motornut]

I wondered if the 3 line pump helped with fuel boiling?

[ray_mcavoy]

Originally Posted by motornut

I wondered if the 3 line pump helped with fuel boiling?

Yes, from what I understand the addition of the return line was intended to help prevent vapor lock.

[79Betty]

Well 1978 and older has standard threads on brakes and 79 and up has metric > guess i'll just keep it all 1979 k10 then since the only thing non then is the wiring (1977) and core support (1974). Just trying to get my ducks in a row. Now i gotta find a 1979 wiring harness.

[77 ChevySport]

AFAIK the 77 was the lat year Chevy offered a engine that ran on regular gas. Mine is a LS9
H/D emission. No smog pump and single fuel line, (No vapor line)Larry
P.S. No cat. converter.

[ray_mcavoy]

Originally Posted by 77 ChevySport

AFAIK the 77 was the lat year Chevy offered a engine that ran on regular gas. Mine is a LS9
H/D emission. No smog pump and single fuel line, (No vapor line)Larry
P.S. No cat. converter.

It was all based on GVW. In 77, 6001 lbs & above was considered HD.

My 77 K15 has the LS9 H/D emission like yours, no smog pump, factory dual exhaust with no cat converter, and no vapor canister. But it does have the 3-line fuel pump, in/out/return with 2 lines (feed/return) along the frame. Dad's 77 K15 has the same setup but with the LF4 400 engine.

I think the light vs. heavy duty emission cut-off point was still at the 6001 lbs point for 1978. Except in California where it was 8,501 lbs. Then in 79 it was upped to the 8,501 lbs.

So the regular gas (no cat converter) engines were still available for a while after 77. But they became increasingly limited to heavier trucks as the years went by. And the laws changed requiring converters on more and more vehicles.

[buddy_1]

Originally Posted by 77 ChevySport

AFAIK the 77 was the lat year Chevy offered a engine that ran on regular gas. Mine is a LS9
H/D emission. No smog pump and single fuel line, (No vapor line)Larry
P.S. No cat. converter.

My 78 was leaded gas truck. It is a C2500 HD.

[79Betty]

Maybe someone ca help again. Anyone know what are the right fuses for a 79 wiring harness? I found mine but i have no fuses. I have to wire in pretty much everything except the headlight switch... Should be fun!

[motornut]

Originally Posted by 79Betty

Maybe someone ca help again. Anyone know what are the right fuses for a 79 wiring harness? I found mine but i have no fuses. I have to wire in pretty much everything except the headlight switch... Should be fun!

my 79 4X2 non AC,writting kinda worn tho

[79Betty]

Reviving a thread... Trying to figure out what it is between a 1974 and 1977 now... I know the core support... Know 76 n down had door panel difference... I need wiring diagrams dangit... If i can get it titled as early as possible the better... But i don't want to have to order brake parts for 8 different years lol

[79Betty]

My79 was unleaded cat truck, 78 k20 and 77 c30 both leaded and not cat's. Need to get it titled as 74 only problem is it has a 79 k10 front axle (metric brakes) and 77 wiring... Just hope i can find out what the real differences are!!

[ray_mcavoy]

Originally Posted by 79Betty

Need to get it titled as 74 ...

Unless your state goes by something different, I have a feeling that you'll have to get it titled according to the VIN.

[79Betty]

Was "told" to get a state issued VIN because of the cab swap. If not i have a 74 cab now i can swap, but that sounds so much easier. Need to get to the BMV but i hate them so much... So very very much...

[buddy_1]

In Texas, when you get the VIN reassigned they go by the frame. Whatever the frame VIN is will be the truck you will have. Look at my avatar. 78 frame, 85 body, 90 grille & core support w/ carburated 95 engine. Went through all the inspections, paperwork and hoops. Still titled as a 78 with a DOT sticker in the door jam showing the original VIN.