The Stovebolt Site Forums The Parking Lot Big Bolts 50 gmc 300 drivetrain upgrade

I am struggling with which direction to go with my truck, it is a 29,000 miles truck without a spot of rust. I am a tile contractor and would like to use it daily as delivery truck that doubles as marketing tool. Id like it to be able carry 6 pallets of tile safely (2000LB ea) and dependably at modern speeds. Im leaning towards a 6bt cummins powertrain. My question is what rear axle would be best so that I can run 22.5" modern wheels and commercial tires and modern brakes. Dana s110-14? s135? Im not familiar with anything bigger so any help would be appreciated. Also would like to have front end upgrades to match. This has been a difficult choice to change anything as the truck is such a survivor.

6 X 2,000 lb is 12,000 lb. The 2 ton truck should have a safe GVW of 16,000lb (check tag in door) that leaves only 4,000 lb for the truck. I think the empty truck with a simple flat bed will weigh 5-8,000 depending on length and other details. How much do you really need to haul?

If your truck is really nice as is might just leave it as is. Or if making modifications just do bolt in stuff, no significant changes to the original that can't easily be undone.

The 6Bt will be far from bolt in, it is quite a bit longer than the GMC engine, check with your tape measure. A 4BT should fit without much if any sheet metal modifications. So will a 302 GMC, the simplest engine upgrade.

If you plan a different rear do you want it to match the front wheel bolt pattern? If so the start that decision process with what you'll do for the front axle/brakes. there is a fair amount of reading here already about such changes and swaps.

Grigg

Grigg, I've read in depth on this site about wheels and disc brakes etc. Lots of great info from lots of people. My truck is a long wheel base 1.5 ton as I understand it. Door tag reads FC 303 40849 with a gvw of 14,000b and gcw of 22,000. A full load of 12,000lb would be a rarity so i'd probably be better suited shooting for a 8,000lb max load. Also considering a dump bed as we do a lot of demo and haul off work as well. My truck has 5 lug Motor wheels front and back currently but I don't think keeping the same bolt pattern front and rear is necessary as long as the wheels are the same. As for the 4bt, EXPENSIVE. O considered the 302 but am concerned the truck will be underpowered and hard to maintain over the long run.

I really like the idea of 22.5" 2 hand hole steel wheels on my truck. Any one know of any rear end that would have a bolt pattern and final drive ratio that makes sense?

You probably have 5/10 bolt pattern, 22.5 wheels for these are getting rare, still have low rear gear ratio to match your original engine.

Any Diesel engine is going to be expensive, 6bt, while perhaps less expensive initially, is probably going to cost more interesting long run, no way will it fit in the engine compartment, much less fit an I'cooler, adequate capacity radiator.

Some Dana 80 axles and their associated front axle come with 6 lug modern bolt pattern, 22.5 wheels available with this pattern-Grigg did one-look on airport vans., modern gear ratios available.

Ed

There are just so many options and ways you could go with the rear axle. Hard to list and evaluate them all at once. This is a short version, not attempting to answer all the questions and considerations that each may bring.

If you want an original bolt pattern for these trucks yet hard to find 22.5" wheels you're looking for a Dana 70HD or Dana 80 from a GM P30, or 3500HD, 10 lugs on 7.25" bolt circle. These come with disc brakes only, and no parking brake.
As used in this project Picture Album

I'm unaware of anything better/newer for your actual original bolt pattern if it is 5 lug Motor wheel?
I have seen 6 lug Motor Wheel 22.5" wheels, and they might have made 5 lug, either would be exceedingly rare Picture

A more common bolt patern yet still reasonably old, would look almost appropriate on your model truck is 6 lug Budd stud centered. 22.5" wheels are pretty easy to find. Axle choices are plentiful. The smaller ones would be a few special/odd Dana 70HD and 80 again. Then larger stuff as found under school busses and other medium duty trucks. most of these older choices will have drum brakes and some later models with disc.
This shows a Dana 80 with this 6 lug Budd bolt pattern. Picture Album

Next if you don't care what wheels the most common these days will be hub piloted 8 or 10 lug as found on most every medium and heavy duty truck in the past 10-20 years (more or less). wheels are extremely easy to find, steel and aluminum, 19.5", 22.5" and larger.
I used a Rockwell Meritor RS-15-20 15,000 lb axle with 8 large lug hub centered pattern in this project Picture Album

Keep in mind if you put disc brakes in the rear you relaly should first have them up front.
If you use drum brakes in the rear and want a newer axle might have to search a little to find hydraulic drums instead of air drum brakes or hydraulic disc.


Planning the truck project you're contemplating is a lot of work and considerations, and worth doing before buying parts.
As to the cost, it'll be a lot if you want it done nice and tidy and safe, and even if you do all the labor. It's all the little stuff that adds up to make a very expensive project. The cost of the engine will be a small part of the whole project. Don't pick an engine that is harder to fit and deal with just because the right choice seemed to be "expensive" at the time, you can make up that difference in "savings" with time and aggravation pretty quick.

Grigg

My suggestion would be to buy a modern truck to use in your business. In Texas, a one ton with a gooseneck is the most feasible way to haul around 12k.

This old Emeryville weighs around 16,000 and I hardly noticed her back there.
I prefer 17.5 singles over 16" duals.

https://plus.google.com/u/0/1126369...1958631618&oid=112636930370126476644

I would leave the old truck intact and use it for advertising the way it is. If you do all the modifications yourself, you won't have time to run your business. If you have it done, it will be cheaper to buy a brand new truck. I operated trucks when 1950 models were still used every day. And we fixed something every day. And it was simpler then. We could go to any parts house and buy parts. Now if something breaks, you may well be stuck for quite a while hunting parts. I now own over a dozen old GMCs, but I realize that they are just toys these days
I recently jokingly posted on Facebook that someone parked my old 1950 520 in the ready line, but I realize that it has been obsolete as trying to make a buck with it for over half a century.
https://plus.google.com/11263693037...7132714818&oid=112636930370126476644

Crenwelge is right. Save the old GMC, maybe paint it up for your business. Time and dollars spent will easily buy the truck used you need for your business!

I expect you could even buy a new work truck for similar to what you'd have in building a nice clean reliable truck from scratch. I'm quite far along that path myself and haven't completed any body and paint work or interior, rubber, glass... it all adds up.