1978 Chevy van 3/4 ton / 400 SBC / TH400

[Graham Piccinini]

Good day fellas,
Just bought a Chevy van with powertrain/drivetrain combo listed in thread title. Bought it mostly for the great interior: plaid seats, 4 swivel captain chairs with round table, and 2 bench seats in the rear with rectangular table, supposedly turns into bed, have yet to figure that out. Plus a mini fridge and a mini sink with some storage cabinets. Basically a conversion van for family trips.
Now to the fun part - I am 27, and all I know about carburetors is what I see in Roadkill episodes... My father hasn't touched a carburetor in about 15 years since Lada 21099 days, 1.5L 8 valve 4-cyl with SOLUS Carb... So there will be some learning to do for us both, plus my little brother if he wants to trip this van too... This one runs great, shifts great, no smoke/sputters/etc under any acceleration, and easily maxes out the 80mph speedometer. So with all this in mind - what are some great resources for DIY work on that van? Will buy a Haynes manual tonight after work, but am wondering if any of the old timers here can recommend other great resources? Maybe any easy upgrades that can be done in a day or two with engine in the van?
Currently all lighting has issues, so if you got leads to wiring diagrams or other DIYs for exterior lighting - that'd be great.


Thank you in advance, will post pictures soon if anyone wants to see it.

 

[BigCahuna]

I would bet that a vehicle that old has gone thru alot of owners who have had their hands in it. The good thing is it's old so that makes it alot simpler to work on. I would start with one item at a time. Bad , loose, or dirty ground will probably be most of your problems. Of course burned out bulbs are also a possibility. Fuses not making a god solid connection can drive you nuts, or plugs that are corroded. All you need is a cheap multi meter to read voltages and you should be able to geter done. I never cared for those probes that stick thru the insulation. My opinion is that over time, they allow moisture in the wire and it builds up that green corrosion. Corrosion is going to ad resistance to any circuits and reduces voltage that goes to any device.Your connections need to be clean and tight , with wires not twisted together wrapped with tape. Good luck.,,

 

[skyactiv]

If it has a Rochester Quadrojet, don't be talked into to replacing it with a Holly, Carter/Eldelbrock.

 

[Snagglefoot]

I would get the Haynes manual but use You Tube as a source. I particularly like A1 Auto videos for informative videos. I like the Rock Auto website to price parts.

 

[Graham Piccinini]

If it has a Rochester Quadrojet, don't be talked into to replacing it with a Holly, Carter/Eldelbrock.

You are the 4th person to tell me this, so I'm guessing it's quite a great unit.

 

[joegreen]

You are the 4th person to tell me this, so I'm guessing it's quite a great unit.

They are a misunderstood unit. They have Small primary for fuel economy and drivability and large secondary for power. Once people have problems with them they switch over to some other carb because the quadrajet can be hard to diagnose I believe.

 

[LenZee]

Excellent vehicle to swap to fuel injection.

 

[Graham Piccinini]

Excellent vehicle to swap to fuel injection.

While I love the idea - I don't have that budget...

 

[wrcsixeight]

While a Haynes or Chilton are helpful, they often leave one wanting more specific info rather than covering 15 model years.

Try and find a factory service manual specific to your model and year..

1978 chevy g van service manual in Car & Truck Manuals for sale | eBay

www.ebay.com

So many questions you will have in the future, can be answered by it.

Best resource you will find.

 

[Graham Piccinini]

While a Haynes or Chilton are helpful, they often leave one wanting more specific info rather than covering 15 model years.

Try and find a factory service manual specific to your model and year..

1978 chevy g van service manual in Car & Truck Manuals for sale | eBay

www.ebay.com

So many questions you will have in the future, can be answered by it.

Best resource you will find.

Thanks for that suggestion. I was able to find a full factory service manual in PDF form for free. Gotta love 21st century, for some things at least...

 

[Graham Piccinini]

#SurvivorsDoItBetter

 

[joegreen]

Excellent vehicle to swap to fuel injection.

Definitely keep it carbureted. There is nothing wrong with a carburetor and it's cheap and easy to get parts for. Plus not many mechanics are interested in diagnosing a vehicle that has been switched from carburetor to efi if there are some wiring issues.

 

[Graham Piccinini]

 

[Graham Piccinini]

Definitely keep it carbureted. There is nothing wrong with a carburetor and it's cheap and easy to get parts for. Plus not many mechanics are interested in diagnosing a vehicle that has been switched from carburetor to efi if there are some wiring issues.

That was my thought as well. Thankfully I was also able to find quite a few videos on Quadrajet rebuilds, so hopefully (if I ever have to) I could perform that task.

 

[R1jake]

Wow now that’s very cool, I’ve always had a van In my stable and also had a 78 blazer with that motor. That was a great engine and never gave me any issues. Had a nice 83 van kinda like yours here but it had the 305 in it which was a turd. Currently in a 94 ford E150 conversion van and it’s in absolute perfect condition and only 30,000 miles on it. Found it 2/3 years ago with 19,800 miles on it. Mine has the 5.8l 351 windsor. There is nothing better than a van for a road trip you can pull over sand sleep anytime you want. I’ll be going to the mountains in the TN/NC area later this month and looking forward to driving in comfort.

 

[supton]

A 3/4T with 5 lug wheels? I don't know enough about vans, but that looks like a 1/2T me, regardless of the G20 badge. Maybe it's completely legit--a light duty 3/4? heavy duty 1/2? Just making sure it is what it thinks it is.

 

[Chris142]

Couple things to check. Make sure that the vacuum advance on the distributer is working. Also take the cap and rotor off and make sure that the mechanical advance moves easily and not stuck.

The compression ratio is real low on that engine. You can crank in more initial timing and get more power,response and mpg.

 

[Graham Piccinini]

A 3/4T with 5 lug wheels? I don't know enough about vans, but that looks like a 1/2T me, regardless of the G20 badge. Maybe it's completely legit--a light duty 3/4? heavy duty 1/2? Just making sure it is what it thinks it is.

Had the same reaction. Had to find a 13 digit VIN decoder from GM. It is indeed a 5 lug 3/4 ton light duty truck. 400 SBC (6.6L) and TH400 3-speed, as mentioned earlier. Built in Lordstown, OH. That's all I was able to get from the VIN.


Cruise control does not work, brake light on dash is on. Brake master cylinder has two reservoirs, one is empty. Topped it off and it pushed all fluid out on the 1.5 hour drive home.

 

[Graham Piccinini]

Couple things to check. Make sure that the vacuum advance on the distributer is working. Also take the cap and rotor off and make sure that the mechanical advance moves easily and not stuck.

The compression ratio is real low on that engine. You can crank in more initial timing and get more power,response and mpg.

Thanks for that. That will be my next project after sorting out the brakes, lights, and few other maintenance items.

 

[Graham Piccinini]

Wow now that’s very cool, I’ve always had a van In my stable and also had a 78 blazer with that motor. That was a great engine and never gave me any issues. Had a nice 83 van kinda like yours here but it had the 305 in it which was a turd. Currently in a 94 ford E150 conversion van and it’s in absolute perfect condition and only 30,000 miles on it. Found it 2/3 years ago with 19,800 miles on it. Mine has the 5.8l 351 windsor. There is nothing better than a van for a road trip you can pull over sand sleep anytime you want. I’ll be going to the mountains in the TN/NC area later this month and looking forward to driving in comfort.

The reason I got this van is to explore the east coast later this month. It does not have working AC yet, so we will probably just explore the North East a bit more.