1978 Suburban Ambulance - looking for resources


I just became the owner of an old suburban. I am looking for the best online resources and groups for folks talking about parts, repair and maintenance for this old thing. It is a 1978 15 (sometimes listed as “C-15”) series Fulltime 4WD 1/2 ton Suburban (V8). I don’t know if that means it is a GMC Sierra 1500, or what. I am most immediately trying to figure out the exact specs for it – the body has been stamped with “GMC series 15 Sierra”, but the VIN indicates that it is a Chevy Suburban. I know its possible for it to be both, but I need to know if I have a Light duty truck or a heavy duty emission truck in order to get the right spark plugs and fuel filter and such. I also need badly to verify if I have a 350 or a 400-4 or a 454. The engine seems to hold more than 4 qts of oil, and the VIN indicates that its a 400-4. There are some numbers on the crankcase/manifold, but I’m not sure how to use them. The previous owner told me it has a 350, but I don’t trust it. Also, I’d like to tow a decent sized trailer for 2,000 miles, and I’m wondering if it will make it. I have the original owner’s manual, but it is not clear on the towing capacity, and says a couple of different things. I have many other questions. This rig used to be an ambulance (has a modified hi-top)and it has two alternators, two batteries, a kill switch, and some other strange modifications. I also need the best and most comprehensive repair/maintenence shop manual available for this vehicle (for overhauling, teardown and rebuild) and don’t know where to find one. Is this the right place to look for help?


For the actual truck parts, any GMC/Chevy truck manual relevant to the model year will do. As for finding a service manual for the ambulance part, you can probably forget about it. If you know what company actually did the conversion, you might be able to find something, but chances are no.

I know there are antique “service vehicle” enthusiasts out there who are into old hearses, ambulances, limos, etc. I’m not sure if they have a website or a forum, but that might be worth looking into.

For problems with the truck parts, this forum should be able to help you, or else there are lots of Chevy/GMC truck forums out there. We may even be able to help out with some of the the ambulance parts if you do a good job explaining the problem.

And yes, it is possible for it to be both a GMC and a Chevy. The two Suburbans are identical all the way up to the badges. You occasionally hear stories about GMC’s that come from the factory with a stray bowtie somewhere. However, its more likely that the conversion company mixed and matched parts.


The 454 had much wider valve covers than the 350 or 400. As to differentiation between the 350 and 400 the block nos. would have to be known.

For parts and manuals you might consider these guys.

Hope that helps you a little bit anyway.