'63 GMC panel van needs new rims. Which modern rims fit?

Okay, I brought a 71 chevy van for it's 6.2 diesel, 700r4, and 3.79 posi rear for a transplant to my van. A family friend did the conversion and gets 31mpg, perfect for my van! The rims from the 71 van are 8 on 6 and a half with the same centre hole but are 16.5 inch rims.

The problem is my GMC step van had 18 inch rims originally and with the tyres side by side they have a 5 inch difference in overall height. This makes the front drop axle on my step van sit 2.5 inches lower to the ground on 16.5 rims, and this is only inches from the deck.

The local roads are beat to hell so I need more ground clearance. Do I flip the drop axle around or take the front clip from the chevy van and bolt that to my step van frame? Alternatively I could use 19.5 rims on the current step van front axle and use the chevy van 3.79 posi rear end with 19.5's on.

Looking for a reliable and cheap build...

Any thoughts?

 

i'd like to see pics of it's current state, especially with the low ride height.

 

The front axle sits about 7 inches from the dirt, on it's original 18" rims.
If we use the 16.5" rims/tire combo, it'll lose about 2.5 inches of clearance under the axle.



Tire height comparison

(P.S. This a father/son project, in case you were wondering why I responded with the pics)

 

one thing about conversion vehicles like step vans and busses the coachbuilders used "leftover parts" whenever they could. at one time i was going to purchase a 66' GMC bus and the dash was 54' chevrolet truck gauges. i was convinced it had the dash changed until seller produced brochure from coachbuilder that showed picture of dash.

 

I think the 19.5" wheels would be the way to go, however, the 3.79:1 gears may be too tall for that combo.

 

Quite possibly...

I'd estimate the best crusing rpm of the 6.2 diesel engine to be around 2/3 of its max RPM... I'd guess 1800-2000RPM is the figure to aim for at 60mph

With 3.79 gears, .7 overdrive and 33 inch tall tyres @ 60mph gives a crusing RPM of 1616rpm...

With 4.10 gears, .7 overdrive and 33 inch tall tyres @ 60mph gives a crusing RPM of 1753rpm...

With 3.79 gears, .7 overdrive and 28 inch tall tyres @ 60mph gives a crusing RPM of 1910rpm...

Thanks to: http://www.csgnetwork.com/multirpmcalc.html for the RPM Calculator.

My thoughts are to go with a 4.10 rear and 19.5's... at the cost of a posi rear

 

You're right on, 2000 RPM is a good cruise speed for the diesel. The 6.2 has tons of torque but only the HP of like a 305, so it will get you there, just not very fast necessarily.

 

X2 not true. I've had Fords with stock 16" one-piece wheels, and 16.5" on on '60s Dodge 3/4-tons with split rims and tubes. New Dodge 17" are one-piece.

 

Okay, today we worked out the rear axle is a 2.73 give or take a few points. With 19.5 tyres and the original Sm-420 trannys 1:1 final drive we can cruise at 65mph at 1800 Rpm. Does anyone know if a SM-420 tranny will bolt up to the 1985 GMC 6.2L diesel? This would allow us to get it on the road quickly with least fabrication, if it bolts up. We have the bellhousing to fit a chevy 350ci and the flywheel, clutch etc...

Any thoughts are greatly appreciated. Trying to work out our best option before we part with cash or time!

 

The bell pattern is regular old Chevy, so are the engine mounts, give-or-take year/style.

Flywheels for the 6.2l are not terribly common, as most were backed up by automatics. They are out there, but you might have to dig.

It has a unique number of teeth, which, if I remember correctly, is 139. It is the 'big' clutch. Depending on the 350 bell housing you have, the flywheel might not fit. If you have an OEM bell, check out the part number online and see.

There is no flywheel interchange with any gasoline engines. The clutch just has to be the right diameter and spline count. Totally do-able.

The bell on the back of the 327 is probably the right one for the large flywheel, but you should find the part number and check.

The starter on the 6.2l is block mounted (and unique to the diesels), and absolutely will not fit into the hole of a bell with a bell mounted starter, should you have one of those (some in that engine era did). I have tried.

The SM-420 is the common pattern, and should bolt to most bells. Early ones may have, or not have threads where they should or should not, but that is an easy obstacle to clear.

Get the starter from the donor vehicle. They are not cheap, and there is only one (also not cheap) aftermarket one I know of, from Powermaster. They are almost infinitely rebuild-able, but you have to have a core.

The Diesel requires a return fuel line to the tank, but that is easy. Diesel is an awesome solvent, so grab a few cheap fuel filters, and swap them out frequently, until you're sure the tank is clean.

My latest Diesel retrofit, PM's welcome:

 

Great info! Thanks

Any idea what the difference is between the 350 gas flywheel and the 6.2 diesel flywheel? Can the 350 flywheel be modded to fit?

 

The register hole is a different size, and the bolt circle is different. I suppose you could machine those, but you would never find a starter that would work. Nor would it balance, as the 6.2l native flywheel is a balanced, dual-mass unit.

The Diesel has 139 BIG teeth, and a monster starter (like 3-1/2 HP, and takes two batteries to turn), necessary to overcome the 22.5:1 compression on the 6.2l. A SBC flywheel will have 153 or 168 smaller teeth. Even if you could figure out how to get a SBC/BBC starter onto the 6.2, it would not have the cojones to spin the Diesel. Even if it did spin it, it might strip the teeth off the flywheel.

Everything you need is out there, and all bolt-on. There are used ones out there.

New flywheel:
http://www.rockauto.com/catalog/raf...47&parttype=5348&a=FRc1061547k1523578-7596099

$135-148 is not too bad for a new flywheel.

Except for some stray weird ones, the SM-420 has a ten-spline 1-1/8" input shaft, and so does the "normal" clutch for the 6.2l of that era.

http://www.rockauto.com/catalog/raf...47&parttype=5348&a=FRc1061547k1523578-7596099

After that, and so long as one of those bell housings are the right size to clear the flywheel, you might need a few bolts, and it is all done.

Check the current bell housing that is in the truck. It it has a starter that is mounted to it, you can't use it for this setup. If the starter is mounted on the block, you 'may' be able to use it.

If it is block mounted starter, look at the starter mounting bolts. If they are straight across from each other, on a line parallel with the back of the block, then it is a no-go. If the bolts are staggered, with the bolt closer to the block further forward than the other, then you should be able to use the bell housing, as-is.

 

Awesome and it's only 60 bucks to ship to the Canadian wilderness!

Thanks, Gimpy!

 

No problem. Always happy to help.

 

Oh, and don't forget to install a pilot bushing in the end of the crank, since the donor was an automatic. It is part of a full clutch kit.

 

Good point. Don't want that input shaft to be unsupported. It would kill the input shaft bearing in short order.

 

A 2.73 in a truck that big? Seems unlikely. I know with my O/T late model van I had to do some research when the RPO code showed it's 14-bolt semi-floater was a 3.23 to find out such a thing even existed. But it sure drives like it has a tall gear.

 

I was surprised at the numbers; I got under it last night with one wheel jacked off the ground and chalked the wheel and the pinion yoke and my best guess is the pinion went around 2 3/4 turns for one rev of the wheel.

 

Jack up and support both sides, and get a buddy to turn the other wheel at the same time you turn one.

 

Alright, we'll give that a whirl when I get off work.

 

It's a 5.13 after all, we turned both wheels this time. It's showing signs of wear and slop so it's being changed for the 3.79 posi axle from the camper van.

 

I suspected it was. The side and spider gears multiply the rotation of the ring gear by two, when you turn just one side.

 

I tried on a wheel from the 72 chevy camper:


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As you can see the centre bore is slightly larger on the camper rim than the hub on my 63. I hope to pull the wheel studs from the camper and re use the nuts so that it centres with the tapered nuts. Would this be a problem if it is not centring on the central bore as per the original split rims? I figure wheel studs have got to be grade 8 bolts...?