Diesel Suburbans for a minivan

Tell me about them. The numbers say they win at the minivan game. Similar room, similar fuel economy, easier maintenance, cheaper parts, better reliability, cheaper buy in.

Do the PMDs really fail because of heat on the 6.5s or is it more of the "This GM part failed at only 120K miles, it must be a terrible design!"?

Does the 700-R4 hold up ok in stock apps? I've only ever driven them modified, and then they're fine. They're stupid cheap to buy.

I am not concerned about power, so even the 6.2 is in. No complexity from the turbo et al either in that case.

This is for the fam, so the military versions are out, but the fire department versions could work. Super low miles on a lot of these too.

What rear/front end axles do these have? What real world mileage do they get? Anyone do veggie oil with one? I know Bryce has.

Any comments?

depends on if you get a 73-91 or 92+ and 1/2, 3/4, or 1 ton for the axles

tuna55 wrote: This is for the fam, so the military versions are out, but the fire department versions could work. Super low miles on a lot of these too.

I was cautioned by a fire chief against buying an old fire chiefs truck. The mileage will be low but the engine hours very high. Once on scene those things will idle for hours and hours.

Aside from that I'm also interested in this. A diesel 4x4 sub would be a good tow/camping rig. Though, I am puzzled about diesel sub's get the same fuel mileage as a minivan, statement. Newer minivans are pushing the high 20's a diesel suburban will be lucky to get 20. (for example: http://www.fuelly.com/driver/kartoon/suburban-2500)

A note about power, a friend had a 4x4 2500 chevy with the 6.2. It takes DAYS to get to 60mph. It would do it with a house behind it or not, but it still is a very slow vehicle. My 4x4 22r toyota with 32" mud tires and stock gearing was faster, and thats just sad.

Ignorant wrote:

tuna55 wrote: This is for the fam, so the military versions are out, but the fire department versions could work. Super low miles on a lot of these too.

I was cautioned by a fire chief against buying an old fire chiefs truck. The mileage will be low but the engine hours very high. Once on scene those things will idle for hours and hours.

Good to know

Though, I am puzzled about diesel sub's get the same fuel mileage as a minivan, statement. Newer minivans are pushing the high 20's a diesel suburban will be lucky to get 20. (for example: http://www.fuelly.com/driver/kartoon/suburban-2500)

They get very similar mileage to a minivan that I can buy for 4k-5k. I have heard of 6.2s getting near 23 mpg. Better than some minivans, which is wild.

The 6.5 turbos have cylinder block issues. If they have been rebuilt with ARP head studs and a crank girdle, apparently they are ok. The 6.2 is dead slow, and dead reliable in the earlier trucks, from what I've heard. Transmissions will last in inverse proportion to how badly you treat them, just like every other automatic.

i have an 86 suburban with the 6.2l. the thing is a freakin tank. it will pull anything you put behind it! but as stated wont do it very quickly.

my rig has: 6.2l tr400 (non overdrive) 4.56 rear end

so i can actually get to 65mph at a decent pace with a trailer. since its a non-overdrive and wiht that rear end, i limit myself to 65mph so i dont overheat the motor. but at 65 i get 15mpg with or without trailer.

growing up my family had an 82 6.2l with the 700R4 it would get 22-23 highway easily at 70mph. but in the 120k miles it went through 3 transmissions. that era 700r4 was not very beefy but from what ive read there has been a lot of development and that trans can be built to last now.

bottom line: its a diesel buy the best one you can find in your price range.

Friend had one in HS, 4x4 with the 700R4. We got 20mpgs all day and it was stone cold awesome! 6.2 btw. I want one so bad

I'm currently shopping for a '98-'99 1500 6.5

From what I gather, the brakes and axles in the 1500 6.5 ae the same as a 2500, but with a higher final drive... cuts the ability to tow a bit, but pushes the mileage above 20mpg. The 2500 is going to have one of two lower ratios, the 4.10 dropping mileage to about 16. So for bus duty, you'd want the 1500.

The stock PMD was a weak design and failed before 120k. Current replacements are supposed to be much better, but getting a cheap kit to mount it remotely seems to be the tick. Also allows for a quick, almost no tools roadside PMD swapout if necessary.

I'm having trouble finding a solid '98-99 with leather and under 150k at all... with most trucks I am finding pushing $10k. The really cheap trucks have 300k on them and you can see have been used commercially and usually beat up...

I know we (my 'rents) where GIVEN an 82 diesel 4x4 subraban back in the early 90's...

mom and dad kept amazing records of every car they owned... dad was real good about maintenance...

after 10 years when my dad finally sent the suburban off to the junkyard dad figured that he'd spent more on the FREE suburban then any car they'd owned including bought new(plymoth horizon ('87 model I think it was) that we had for 10 years before it was sold because of a move overseas... i'm sure by the time he gets rid of the chevy malibu it'll come out to less then the total cost of the suburban (well maybe not with gas costing 3-4x and he puts a lot more miles on the car then the suburban ever did.

i know we had the trans replaced/rebuilt 3x... the starter was replaced/rebuilt with regularity... note that I was a kid so I didn't pay attention to the little things...

having had mini vans the suburban seems a lot smaller inside... and like others said the 6.2 is dog slow... but it did average 18mpg no matter what it was doing lol.

if you like the burban then i'd go for it... but for practicality the mini van wins IMHO...

watch out for rear oil seals on 6.2s ....early ones leaked readily, as did some later ones. And if its been turbo'd, it'll blow the seal.

Go minivan, they win in the real world categories not just the statistical numbers one. A caravan with a 3.3 and a maintained transmission (meaning right fluid used and occasional changes) will go for a long time. The 3.8 should see the same results, a 3.0 won't, a 4 cylinder is a joke. GM minivans from 96 on used the 60* v6 with the intake manifold gaskets that crack and leak. though my 02 montana had 100k+ on it and the gasket was fine.

internetautomart wrote: GM minivans from 96 on used the 60* v6 with the intake manifold gaskets that crack and leak. though my 02 montana had 100k+ on it and the gasket was fine.

We had a Venture minivan (first year model IIRC) that we leased. Was also perfectly fine and got amazing gas mileage for something that could haul 7 people.

Of course, it was pretty lame. A turbo brick station wagon would be much cooler and get close to the same gas mileage with more smiles!

HiTempguy wrote: Of course, it was pretty lame. A turbo brick station wagon would be much cooler and get close to the same gas mileage with more smiles!

That's what I've got. Less mileage, won't carry the same amount of people/cargo and parts availability is unacceptable for a DD, especially one which the kids are required to be in every day.

tuna55 wrote: Do the PMDs really fail because of heat on the 6.5s or is it more of the "This GM part failed at only 120K miles, it must be a terrible design!"?

They fail mostly due to the heat. THere are relocation kits that mostly solve this problem... or just skip it an get a 6.2... or put the mechanical injection from a 6.2 on a 6.5.

Does the 700-R4 hold up ok in stock apps? I've only ever driven them modified, and then they're fine. They're stupid cheap to buy.

They don't hold up very well. But the good news is that you don't need them, especially with the stupid-low 1st gear. The diesel will make enough torque that a TH400 with 3.42 gears will be perfect. You could keep the same highway RPMs with a 700r4 and 4.10s, but the 3.06 first and 4.10 rear is more or less a granny gear. Maybe useful for heavy towing, but then you shouldn't be using a 700r4 anyway

What rear/front end axles do these have? What real world mileage do they get? Anyone do veggie oil with one? I know Bryce has.

Rear axle should be either a 9.5 SF 14-bolt or 10.5 FF 14 bolt. The 10.5 is preferred. Its bulletproof. Front will probably be an 8.5" on the lighter trucks and 12-bolt on heavier trucks. I used to get consistent 20+ mpg empty in my 98 6.5TD pickup. Towing 10k lbs was more like 13mpg.

If you're doing veggie, do it right, and go mechanical injection. Try swapping pre-chambers in the heads for best performance/least coking. Check on some veggie forums and chevy diesel forums, they have it all figured out.

Any comments?

Do it. Screw minivans... FWD, expensive to fix transmissions, impossible to change spark plugs, unibody boxes... not for me.

curtis73 wrote:

Does the 700-R4 hold up ok in stock apps? I've only ever driven them modified, and then they're fine. They're stupid cheap to buy.

They don't hold up very well. But the good news is that you don't need them, especially with the stupid-low 1st gear. The diesel will make enough torque that a TH400 with 3.42 gears will be perfect. You could keep the same highway RPMs with a 700r4 and 4.10s, but the 3.06 first and 4.10 rear is more or less a granny gear. Maybe useful for heavy towing, but then you shouldn't be using a 700r4 anyway

What about swapping the 6.2 style to the stick shift like the A833 (MY6) four speed OD manual tranny I put in my 72 that originally came in the diesel pickups? It sounds like a slam dunk.

Do it. Screw minivans... FWD, expensive to fix transmissions, impossible to change spark plugs, unibody boxes... not for me.

I needed that encouragement. The repair costs and ease of maintenance are biggies for me

What about swapping the 6.2 style to the stick shift like the A833 (MY6) four speed OD manual tranny I put in my 72 that originally came in the diesel pickups? It sounds like a slam dunk.

Yep. SM465 would be a good choice, NV3500 or 3550 would work well also.

curtis73 wrote:

What about swapping the 6.2 style to the stick shift like the A833 (MY6) four speed OD manual tranny I put in my 72 that originally came in the diesel pickups? It sounds like a slam dunk.

Yep. SM465 would be a good choice, NV3500 or 3550 would work well also.

OK, so I know I can easily get all of the stuff for a swap to stick for the earlier body style. Can the GMT400 trucks be converted as easily? I don't know about the availability of manuals in the truck siblings. I like the 6.2 style better for reliability and the manual conversion, but the wife likes the later trucks for their interiors, looks and handling (and I can't say I blame her in any of the three).

Availability of the manual was slim in the SUVs. Trucks could be found pretty regularly, but often in stripped-down, rubber floor form.

If I were doing it, I'd find the truck you want with a toasted motor, then a 6.2 will be an easy drop in. The manual can be added using junkyard donor parts. Starting with a diesel truck would be easiest just because the infrastructure will already be in place (fuel delivery, dual battery trays, battery cables, etc).

IIRC, all of the GMT400-480 trucks used hydraulic clutches, but I think the frames still have the provisions for the manual clutch linkage. Do some research before diving in so you don't end up trying to adapt a slave cylinder to an SM465 or something funky like that.

Nice thing is, the 6.2/6.5s have a standard chevy bellhousing pattern, so the sky is the limit on transmission choices. I was thinking about this earlier... the NV4500 came behind some 3/4 and 1 ton chevys, gas and diesel. If you are doing a 4x4, they are easily adaptable to NP231 and Dana 300 T-cases.

curtis73 wrote: If I were doing it, I'd find the truck you want with a toasted motor, then a 6.2 will be an easy drop in. The manual can be added using junkyard donor parts. Starting with a diesel truck would be easiest just because the infrastructure will already be in place (fuel delivery, dual battery trays, battery cables, etc).

If I do this I don't want a huge project. A little project, maybe, but not a big one. I'll consider it, though. I have swapped engines over a day and change, but changing types (6.5 to 6.2) might be weird, especially since I don't know a lot about diesels.

RE transmissions, I need an overdrive, so it's MY6, NV4500 or the internet-hated NV3500. I did do the math, the overdrive makes even the 4.10 lower than the lowest factory installed gears. Time to hit the yards, I guess.

She still likes the later ones better. I haven't found any good examples that stayed around for more than a day yet.

This one is nice. They've already dropped it from 8900 to 7500. You might be able to get them to deal. http://nashville.craigslist.org/cto/2140792496.html

If I do this I don't want a huge project. A little project, maybe, but not a big one. I'll consider it, though. I have swapped engines over a day and change, but changing types (6.5 to 6.2) might be weird, especially since I don't know a lot about diesels.

Good point... another suggestion is to find a GMT4 with a good 6.5TD that has a bad PMD. Swap it over to the 6.2 mechanicals - or repair the PMD and enjoy another 200k. People think the 6.5s suck, but they are actually wonderful designs... a bit dated, but wonderful.

RE transmissions, I need an overdrive, so it's MY6, NV4500 or the internet-hated NV3500. I did do the math, the overdrive makes even the 4.10 lower than the lowest factory installed gears. Time to hit the yards, I guess.

The NV3500 wasn't terrible, its just nothing to write home about. My commentary (having run transmission shops for a long time...)

You can't assume that torque = torque... a gas engine making 500 lb ft seems like the same as a diesel engine making 500 lb ft, right? Its not necessarily the case. Two things come into play. Gas engines make pulses of power that fade. Their harmonics are dictated by the lower compression they start with and a fast, but fading flame front. All of the intake charge is already there when ignition occurs, so its just a matter of the combustion "throwing" the piston and letting inertia work its magic. With a diesel, the initial compression is much higher, the light-off tends to be a bit more violent, and then fuel is injected through as much as 36 degrees of crank travel.

(I have to interject... my recent engine theories in other threads have come under scrutiny, so what I just said above is highly colloquial and not quantitative.)

What it ends up doing is creating a bit more violent harmonics than a gas engine... so a diesel with 500 lb ft will typically destroy a transmission much faster than a gas engine with 500 lb-ft.

If you had a big block gas engine, I would say that the 3500 or 3550 would be fine, but behind a diesel they won't last - doesn't matter how wimpy it is.

The other thing I'll throw out there... RPM is slightly less of a concern with diesel. In a very simplified example, in the gas engine, your right foot determines how much fuel is injected per cycle. If you increase the number of cycles (raise the RPM) you'll typically use more fuel. Given the diesel's rate of injection being more closely related to your right foot, its MPG is more closely related to your foot position than it is RPM. In a gas engine, I like to see highway RPMs about 500-1000 RPMs lower than peak torque for max MPG, but in a diesel, shoot for highway RPMs at the point where it requires the least "foot" to maintain speed. That's a bit difficult to calculate, but it often occurs at or above peak torque in a diesel.

She still likes the later ones better.

Sounds like you have two choices - hold out for a later model truck, or ditch her and get a later model girl

I just checked on NV4500 prices. Damn... they're still high these days.

Don't get me wrong they're worth it, but consider this...

As with any combo, you need a ratio spread - first gear low enough to get you moving, and a top gear that provides the highway RPMs you need. That doesn't necessitate OD, especially with the fat, flat torque curve of a diesel.

Some math...

Depending on your tire size, you probably want a final drive ratio of about 3:1 on the highway. In the NV3550, you need approximately 3.90 gears to achieve that.

NV3550 with 3.90 gears:
1st final drive = 15.64:1
2nd final drive = 9.09:1
5th final drive = 3.04:1

SM465 with 3.08 gears:
1st final drive = 20.17:1
2nd final drive = 11.03:1
4th final drive = 3.08:1

The NV3550 has a more reasonable spread, and closer ratios, which would be important if you didn't have the kansas-flat torque curve of a diesel... and if it wouldn't vibrate apart behind a diesel. The NV35-series is only rated to about 300 lb-ft and was designed for gas engines. Its not going to like a diesel.

I just want you to be happy. If it were my truck (and I understand that it isn't) I would honestly hold out for the NV4500... It is basically the strength and ratio spread of the SM465, but adds a .74 OD.

Just do some math. It can all be adjusted for tire size later, but go to http://www.novak-adapt.com/index.htm and poke around and find the ratios of the transmissions you're considering. Depending on tire size, I would shoot for about 12:1 final drive in first, and 3:1 final drive in the top gear. Flat torque curves need fewer ratio changes, like a diesel might only need a 4 speed. A high-winding 4 cylinder might need 8 speeds to keep it spinning in the sweet spot.

Clark 5 speed?

You can find bellhousings to fit anything on a clark, just takes some digging.

Ignorant wrote: Clark 5 speed? You can find bellhousings to fit anything on a clark, just takes some digging.

Insane overkill... I kind of like it.

tuna55 wrote:

Ignorant wrote: Clark 5 speed? You can find bellhousings to fit anything on a clark, just takes some digging.

Insane overkill... I kind of like it.

285v is the model you want I think. Dig around pirate4x4.com for some tech. The trans are like $200-$400..