Hello friends!

[Thurmond1317]

Hello all, my name is Jay and I'm the new owner of a shortie bus! It's a 1979 GMC P30 Chassis bus that's been fully stripped. Unfortunately some of the striping(Like all of the electrical systems) was done by the old owner, so nothing except the engine works No brake lights, headlights, fans, just engine power. I definitely have my work cut out for me.

Anywho, the intent of this bus is to be a home on wheels for me(way down the road), with the space for entertaining/traveling with a few friends. I'm extremely new to this world so I might ask some dumb questions, but super excited to learn and do something I've never done before. I've got some interesting ideas for arranging the interior but first bracing and insulation.
It's a tad goofy looking from the side but adds to the character imo.

Some odd info about it: Its a dualy in the back which isn't the weirdest; But it has a transfer case for 4wd, just no front drivetrain?

 

[Cheezewhiz]

Hello!

I've got a stepvan based on that chassis, with a cummins 4bt and a stickshift.

What motor have you got in there?

And that is kinda strange, is the front axle for 4wd and is just missing the driveshaft? Or is it only a steering axle up there?

 

[PorchDog]

Or a "Gear Vendors" overdrive unit?

 

[Thurmond1317]

Sweet! Wouldn't mind a cummins in this haha.
I'm not sure where I would find what engine name but it's a 5.7 diesel 350 4bbl.
And right! It's odd. Just the transfer case, the front is only steering, no diff in sight.

 

[Thurmond1317]

I've never actually heard of this. Will have to look into it for sure.
I just assumed transfer case because that's what the seller said it was. And to my untrained eye, it made sense to be one. Are there any obvious indicators if it's a od unit?

 

[PorchDog]

I doubt it is a gear vendor unit-- if it has a place to attach the front drive shaft-- it's a transfer case.

 

[Albatross]

That might be the Oldsmobile (350N? 350DX?) diesel that was optional for GM trucks prior to the 6.2L Chevy-by-Detroit engines like the one I've got.



IIRC, correctly, that was the engine that had so many issues that it broke American's trust in diesel motors, which is why so many of our cars are gassers, while euro cars and light trucks are easier to find smaller turbo-diesels in. I think one of the main engineers basically begged Chevy to not release the engine as it was developed too quickly, and wasn't "ready; he got canned and they released it anyways, and it had a lot of problems IIRC.


I've heard that to do it right you'll need to beef up the timing (kind of standard for GM anything), replace the head studs with ARP studs, and add an aftermarket water-separator at the very least. And that's besides all the electrical work you've got to do now.



As for the transfer case, I would look into the "New Process NP205" (https://www.motortrend.com/features/1406-transfer-case-spotters-guide/) and see if that bolt pattern matches up to what you're seeing. Considering that the drivetrain on that P30 is essentially just a beefed-up 1-ton on thicker framerails, it's possible that you've got yourself a factory 4WD on it. Or someone was trying to put one there. There were a few different transfer cases used by GM in that time, and they're all pretty tough.


Your drivetrain and wiring should be almost identical to a 1979 CUCV, the "military" squarebody pickups.

 

[Thurmond1317]

That's somewhat concerning. Once there's a day without rain over here I'll try and find any indicators as to what I actually have.

I do work on cars as a hobby so I'm confident I'll be able to do most of the work myself. Would just take a while to do the research and make sure I'm doing it right.

Will definitely give that a look. Would be awesome to have 4wd in this so I can take it snowboarding sometime.

 

[Albatross]

Would be awesome to have 4wd in this so I can take it snowboarding sometime.

Yeah.... That's partially why I got mine, but the primary reason is that the P30 chassis is essentially so familiar to anyone who has done any work on an engine, and that parts for it should be pretty much anywhere, without having to wait a week to get them in.


But after thinking on it for awhile, I also kind of decided that if you do wind up getting stuck in 15,000 lbs bus with 4WD, who the **** are you going to be able to call to come and get you out? Then again, I wasn't really thinking about trying to get up snow-covered hills, either, but rather mud and swamps.

 

[Thurmond1317]

That's a pretty good reason. I didn't realize how many of them are still on the road in so many different types of rigs.

Yah know, very fair point. I doubt my little 4matic Mercedes would cut it XD
Good thing about building the skoolie though is if I get stuck, I can just sleep in the back till someone rescues me or the snow melts haha.

Also forgot to mention prior, but I possibly have a spare engine in the back. Old owner said it came from a ambulance that got rammed by a logging truck, but I haven't found the numbers on both to verify. Would be extremely conveniently to have that spare engine already in the back though if that is actually the case.

 

[Cheezewhiz]

That might be the Oldsmobile (350N? 350DX?) diesel that was optional for GM trucks prior to the 6.2L Chevy-by-Detroit engines like the one I've got.



IIRC, correctly, that was the engine that had so many issues that it broke American's trust in diesel motors, which is why so many of our cars are gassers, while euro cars and light trucks are easier to find smaller turbo-diesels in. I think one of the main engineers basically begged Chevy to not release the engine as it was developed too quickly, and wasn't "ready; he got canned and they released it anyways, and it had a lot of problems IIRC.


I've heard that to do it right you'll need to beef up the timing (kind of standard for GM anything), replace the head studs with ARP studs, and add an aftermarket water-separator at the very least. And that's besides all the electrical work you've got to do now.



As for the transfer case, I would look into the "New Process NP205" (https://www.motortrend.com/features/1406-transfer-case-spotters-guide/) and see if that bolt pattern matches up to what you're seeing. Considering that the drivetrain on that P30 is essentially just a beefed-up 1-ton on thicker framerails, it's possible that you've got yourself a factory 4WD on it. Or someone was trying to put one there. There were a few different transfer cases used by GM in that time, and they're all pretty tough.


Your drivetrain and wiring should be almost identical to a 1979 CUCV, the "military" squarebody pickups.

Just to add to the veracity, my transmission in the P30 is just... GM. Like everything I've found out about it is just , "yep, that's an old GM trani, it got a granny gear in it? Oh yeah, they made em like that."


Like, I was trying to figure how to make the ********** run faster than 50mph, you know, so it wasn't exactly helpful

 

[Cheezewhiz]

Hey also, pics of the motor?

 

[Albatross]

Just to add to the veracity, my transmission in the P30 is just... GM. Like everything I've found out about it is just , "yep, that's an old GM trani, it got a granny gear in it? Oh yeah, they made em like that."

That sounds like an SM420 or an SM465:
https://www.offroaders.com/tech/jeep/transmission-ID-gm-sm420.htm
https://www.novak-adapt.com/knowledge/transmissions/manual/sm465/

That's a pretty good reason. I didn't realize how many of them are still on the road in so many different types of rigs.

Well, they may not all be on the roads, but there are still a ton of classic truck guys, redneck beaters that just don't quit, and hod-rodders and 4WD/mudders that still drive those, and the worst experience I've had is the part isn't at the store I walked into, but it can be that afternoon, or the next morning. But the point is still the same, you can generally put hands-on replacement parts in less than 24 hours, if not that-day.

 

[Thurmond1317]

Hey also, pics of the motor?

Yes! I'll try and grab some of both tomorrow provided its not raining.

the worst experience I've had is the part isn't at the store I walked into, but it can be that afternoon, or the next morning. But the point is still the same, you can generally put hands-on replacement parts in less than 24 hours, if not that-day.

You're not wrong. I've seen some videos of some crazy builds but haven't personally ventured off the road in quite some time. Probably some gems out there. And I quite like the sound of that. It's always frustrating working on something, realize you're missing/broke/need to replace an important part and you have to wait a week for it to ship.

 

[Albatross]

You're not wrong. I've seen some videos of some crazy builds but haven't personally ventured off the road in quite some time. Probably some gems out there. And I quite like the sound of that. It's always frustrating working on something, realize you're missing/broke/need to replace an important part and you have to wait a week for it to ship.

Well, if you do in fact have the diesel that I think you do, you will still face some issues for engine parts, as there were never a whole lot made, and there are even fewer surviving this far down the line. Some of your more common components might still be easy enough to find, but I would probably bet that most of your stuff isn't going to be easily found. And honestly, because the P30 is just a beefed-up version of the C/K 30, a lot of the steering/suspension components are less likely to be found, too; NAPA and Oreillys seem to be the places to find them more often than not. But you can still save a lot of money ordering the parts online.



I would also keep in mind that GM/Chevy sold Bluebird what is essentially a moving platform: a frame, and engine and transmission, with a gas tank, a seat, and a steering wheel. Those are the "GM" components, and everything else is by Bluebird or your bus company.

 

[Thurmond1317]

Well after further inspection I have quite a bit of news. Also I apologize in advance if formatting is all over the place, I’m writing this on my phone.

So I got the casting numbers off each of the engines and was quite surprised with what I found. So the engine that is powering the bus has the casting number 12555506 which I could not find anything similar to the year that the bus was supposed to be(also I was mistaken, the bus is a 78* not 79) I kept seeing casting numbers for newer engines and specifically, two forum posts with the same casting numbers, talking about some sort of larger engine. I was so confused. Taking a look at the paperwork I got with the original title, was even more confused to see the mileage. The bus itself currently reads 454,xxx but the paperwork in late 2019 was 45,xxx. I thought maybe they were just missing a number. Then another service record in 2021 at 101,xxx miles. Confused yet again. Then I found a document with some mechanic notes saying the vehicle was retrofitted with a “mid 90s 395 GMC engine” That report was stamped beginning of 2019 with a 35822 odometer reading. So now the engine situation makes more sense, I believe I have a 6.5L diesel and if I’m reading it’s C089 casting date right, should be a March 8, 99 production date.

Now that leaves me with questions like what is the actual mileage of the engine? When was it replaced? Should I be worrying about water separators still or was that only an older engine problem? At least I know the old owners took it to the shop a bit and the engine swap was hopefully done by professionals. That also means the transmission and transfer case are probably different as well then too?

Also the spare engine unfortunately had a separate casting number that I’m having a harder time tracking down. That one reads 14022666 although I’m not 100% on those digits. Was pretty dirty and checked it at night as was the only time it wasn’t raining lol. Also no casting date that I could see.

 

[Albatross]

That would be the later big brother to the engine that I have.



The 6.5L fixed a lot of problems that were had on the 6.2L, and itself only had a few major issues that are relatively easily sorted out--other than the absolute "main" problem of that line which was a complete and total lack of "balls" for a diesel engine. But that is chiefly because it is a diesel engine that was made for light-medium -duty working trucks, coming out of the OPEC oil crisis, with a national speed limit of 55 MPH, and was made for economy and reliability instead of "moar power!!". They were used in the C30/K30 trucks, as well as the CUCV (military version, has more BHP and much more torque), as well as the breadbox trucks, RVs, and the (military) humvee.


The water separation issue was only a problem on that old Buick engine, and has essentially been fixed on all but probably the most recent of engines. The main issue on the 6.5L was the factory placement of (heat-sensitive) electronics directly over the head/engine manifold, which would cause a nasty breakdown of the like I've really only seen engineered by companies like (Cr)Apple computers on their hardware since Steve Jobs died. There is a water-separation filter on these engines, and they work pretty good.


Frankly, they were a good engine, IMHO, but there were some core design failures that, other than the crankshaft and the harmonic-balancer are all fairly-easy to solve. Here's some more info:

https://chevytrucks.org/6-5l-detroit-diesel-engine-guide/
https://www.dieselhub.com/maintenance/6.5-diesel-pmd-relocation.html

 

[Albatross]

Oh, and your transmission is likely the same, assuming that it's a 3-spd +granny gear. Might even be original.

 

[Thurmond1317]

That would be the later big brother to the engine that I have.
...the absolute "main" problem of that line which was a complete and total lack of "balls" for a diesel engine

Haha, yeah it's not the quickest machine in the world but I don't mind it. It's a good reminder not to rush things and enjoy what's here before moving on to the next thing.

Oh, and your transmission is likely the same, assuming that it's a 3-spd +granny gear. Might even be original.

I do recall it being a lower amount of gears. I used them when getting up the steep grade the town I bought the bus from had so they definitely work and shift as they should. It did get a little warm though if the temp gauge is to be believed but held up like a champ.

Also It's been struggling to start lately. Could be the 30 degree weather but when I first bought it, they used the two batteries, a jump box, and a jump from a truck to get it started. It's been cranking for me but always seems to run out of power before catching when I've been trying to start it myself. Do I need bigger batteries maybe?

 

[Albatross]

For me, the military-version of the Detroit-by-Chevy 6.5L is probably one of the best diesels every made, with a few changes and upgrades--like replacing the DB4 electronic fuel pump with the Stanadyne DB2 mechanical one, adding a Banks turbocharger designed for it, and maybe eventually getting around to adding a beefier crankshaft. Other than that, the engine actually likes a little bit of old motor oil or tranny fluid in the fuel tank to really keep it running.



Sure, it won't like the cold, because diesel, but a block heater might make it easier for you. Your electrical system is likely needing some work, and it's possible that they just threw some batteries in it to get it moving after sitting for awhile. I would throw an algaecide in the tank, change all your fluids--maybe after adding some Seafoam to them to break up some gunk and getting it running around the block for about 5-10 miles, and I would test your batteries and your alternator. There could also be an issue with the starter, or the power or the ground to it that would cause that kind of an issue.



If you're running out of power, I would definitely consider having three batteries, but unless the ones you have are 6 months old or newer, I would not just add another battery to the system and expect to not have any problems. If the batteries are of an unknown usage, you can usually find out on the labels, and if they're older than two years, I would buy a whole new set of three of them, and I would also check your alternator after doing that. Bad batteries have a tendency to make your alternator go bad, too. If the batteries are still good, I would try to find a way to recycle them into some other kind of project, or see if I can get $50 or whatever for them. You might also look into upgrading the batteries, too--since you have the space for it.


Crappy battery cables can also cause some issues, but when you're using that (2/0) 00-gauge or better, they generally don't go bad all too often. When I got mine, I replaced all of my cabling just because, and I used 0000-gauge (4/0) welding wire with some custom connections I bought. I "soldered" mine using a propane torch and a bench-vise, and probably something like 1/2 a pound of the thickest solder I could find. It was technically plumbing solder, because I couldn't find any electrical-rated solder thick enough in that town. Technically, it's all just lead and zinc, and when the ratio is correct, it's all the same. I couldn't find eutectic solder, which I prefer, but the normal 60/40 is close enough.


Now that I'm really thinking about it, you might also have an issue with your glow plugs, too... My 6.2L had an issue with that for a while, and there still might be one or two that are not quite 100%.