1978 Chevy van 3/4 ton / 400 SBC / TH400
- Thread starter Graham Piccinini
- Start date
Got a year newer hightop campervan with the 350. I'd be more concerned with the gas tank on something that old. I rebuilt the carb twice after getting mine and it still ran lousy. The last time I did, I took off the top of the carburetor to check maybe the float was sticking or soaked, but instead found the gas was a bright orange color. Turns out the tank was quite rusty inside and was clogging the fuel filter pretty quickly. Replaced the tank and then it ran fine.
A lot of those 400's died early. I would not be suprized if it has a 350 in it now. I would be doubly suprized if it is still a 400!
The 400 with it`s siamesed cylinders will not tolerate poor maintenance. That said it is a good engine in that application. Hot rodders love that engine or at least the crank.
Who cares about the engine. Any small block will power that van.
I would swap the table for a pole. My$.02
In all seriousness, Chilton's has a good book so you can troubleshoot wiring. Keep the Q-jet and motor on.
I would swap the table for a pole. My$.02
In all seriousness, Chilton's has a good book so you can troubleshoot wiring. Keep the Q-jet and motor on.
How was the Transmission type decoded from a 13 digit VIN? Both the TH350 & TH400 carried the same M40 RPO code, The actual GVWR dictated what transmission it got. A 7,700 GVW G20 van would have a TH350, Even a small block C20 pick-up with a 7,700 GVW & 8-lug wheels would have a TH350.
All Big Blocks got the TH400 no matter the GVW.
Vladiator, one thing many people don't know or think of when staying on the road is showering. You can shower at trucks stops for a fee, sleep in your van and avoid hotels.
Great interior esp in the back. Any luck on sourcing a new grille?
You are correct, the transmission code did not come from the VIN. The previous owner swore up and down that it is a 400 Small Block with TH400 combo. Another Chevy guy I know also said that it must be a TH400 based on van size, so I haven't bothered to look yet. Plus didn't have a chance to get it up in the air yet since purchase... So based on what you are saying it could be a TH350, but once I get it up in the air I will refer to the trans pan gasket pattern picture posted above and will update.
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I got a few trucker relatives who have shower passes expire all the time... So I hope to get a few passes from them for the trip, and will use the portable pop-up shower for other times. I heard Linville waterfalls are pretty refreshing this time of year also...
The grill that came with it seems to be from a truck with 350 in it. Found a few examples online for the grill I actually need and it is priced in the $40-$60 range, so shouldn't be too hard to get.
Someone will correct me but I think the 400 SBC's have a different number of freeze plugs on the side? I want to say that the block can be told apart from the others on that basis. Not sure where the casting number is nor if it is viewable while installed in a van.
A book by Doug Roe is the book for the rochester carbs. He worked for GM at their proving grounds location. I have one of the last of the carbed 454 engines in my motorhome ( 1989 ). With a rebuild on the carb and a recurve on the distributor and headers, it's a beast.
Not all 400 SB's had 3 freeze plugs, Some had 2 & looked identical to other SB's & some had three bosses.....But only 2 machined for freeze plugs. If it has 3 freeze plugs or 3 bosses.....It's certainly a 400.
Engine aside: looks like I got a looot of work to do, as I doubt anyone done any of this stuff in the past couple decades...
The early 4 bolt main 400's had 3 freeze plugs per side. The later 2 bolt main 400's had 2 per side but still had the indention between them where the 3rd would be. A 78 would be a 2 bolt main. The 400 harmonic balancer will have a cut out for balance.
Not that there's anything wrong with a TH350, Probably the most well engineered light duty 3-speed auto's ever produced & doesn't have the parasitic spin losses associated with a TH400 as the Lo/Reverse Band always drags on the Reaction Carrier a little. The TH350 uses a Lo/Reverse Clutch that completely disengages. Hydramatic even adopted the design for the 700R4 & 4L60E. TH350 wasn't technically a Hydramatic unit & was developed jointly by the Buick & Chevrolet divisions.
If indeed you do have a small block 400 in your new van, make sure your cooling system is kept in tip top shape. The heads don't like to be overheated and if they are overheated, can develop cracks which makes them essentially worthless.
Just as an FYI, I had a 1973 Impala with the 400 small block and 100,000 miles when I got it in 1977. I put another 300,000 to 400,000 miles on it before getting rid of it in 1990. Great engine. I only wished it had a Quadrajet instead of the 2 barrel Rochester that was on it.
Just as an FYI, I had a 1973 Impala with the 400 small block and 100,000 miles when I got it in 1977. I put another 300,000 to 400,000 miles on it before getting rid of it in 1990. Great engine. I only wished it had a Quadrajet instead of the 2 barrel Rochester that was on it.
And it was the BIG Rochester 2-Barrel!, Got worse cruising MPG than a 396/402 Big Block TH400 & Quadrajet.
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