The Stovebolt Site Forums The Shop Area Engine Shop Why isn't there any 8-lug support?

Have you guys noticed that you can buy just about anything for 5-lug or even 6-lug configurations, but pretty much zip for 8-lug configurations? Absolutely almost nothing.

A lot of people I know end up converting their 3/4 tons to 5-lug wheels, so that they can benefit from front disc brake conversions, tapered roller bearings, independent front suspensions, etc.
I have yet to find any support at all for the 3/4 ton end of things.

Anyone know something I don't? And why is that? If you've got a 3/4 ton, and if it's a GMC and not a Chevy, you really seem to be on your own there for restoration and upgrade stuff.

There were almost 3 times more 1/2 tons than 3/4 tons - maybe that's the reason? Still, that is a lot of 3/4 ton trucks from 47-55.

To add to those numbers, 3/4 tons were used as work trucks and many were simply run in the ground. And for many years many people stayed away from 3/4 tons because they rode rougher, used more gas and usually rattled more. Therefor many were crushed that would have possibly been restored today.

Boy Ken, I'll vouch for that, "rode rougher, used more gas and usually rattled more" I've been working for nearly three years to get mine to where it is and it still has a good ways to go. The rough I think I can help some with clean new springs, the gas mileage even with the stock sized radial tires and a 4.10 gear is right around 13mpg on the average and there is a cyclic vibration that comes in about 40mph that I just can't nail down. Taint tires, wheels, axles, driveshaft, center support or u-joint. All of them have been checked, spun, indicated and what not, and everything checks out OK. I truly believe it's some kind of harmonic flexing of the frame.

Nope you can't find much for the 3600 running gear, I've looked everywhere for the last three years and it's slim pickin's. My front brake drums are on size with about .008" or .010" wear and fit the shoes great, she stops on a dime but, when you brake you can feel a throbbing in the pedal so I'm pretty sure they are a little out of round. I'd replace them if I could find new ones but there just taint nothing out there. Turning to true them up would be fine but you can't find anyone around here anymore that will bond an over size lining to the shoes and arc them in.
But I do like how she sits nice and tall and kinda proud like, parked next to a half-ton.
Denny Graham
Sandwich, IL

Denny, as a backyard engine builder, it sounds more to me like your stovebolt engine is out of balance. Cyclic vibration at around 40 mph. It could also be an out-of-balance driveshaft. Sometimes that is called the "wobble of death". Or it could be tires out of balance.

You can isolate them. If it's the motor, you should be able to hold it at that rpm in park and tell if it's vibrating. Correct me if I'm wrong but it does seem like because of the low rpm range of the stock stovebolts, balancing the rotating assembly might not have been a priority in the 50's.
If it's the driveshaft, you should be able to coast at 40 mph with the tranny in neutral and the vibes should be gone.
Just some thoughts on how to get to the bottom of that.

I can vouch for the rough rider, rattle can quality of the 3600. It does seem like mine rides so rough. Part of that I think might have been the springs that were probably upgraded to handle an increased 3/4 ton load. And my long bed is beat to heck. You can tell this truck has had a hard life.

I might be forced to get parts off of a full-size passenger van with 8 lug wheels. If you think about it, you should even be able to get the 8 lug disk brakes too, as well as the IFS. They were almost always RWD, weren't they?
Anyway, I've been thinking about it.

And gee whiz, try to find some GMC parts in these restoration catalogues! You guys with Chevy's have a lot more available!
But it's a labor of love, right?

I think its as simple as supply and demand. There is not much demand for the 8-lug stuff. And many of the 1/2-ton products were developed when the economy was stronger. Now as more people seem interested in the 8-lug trucks, money to create products is tight.

Since I'm a hot rodder instead of a restorer, I am not real worried about parts availability as I build a 1-ton hot rod trailer puller based on a GMC.

So far I've been able to find everything I really need.

I repeat Dad, shut engine down at 40, still there, new u-joints (all three) and center support brg, drive shaft checked for balance, ok, tires are new Cooper Radials mounted on 1970 3/4-ton rims that have been blasted and repainted, no damage, the have been balanced at three different tire dealers and had them run up on a Hunter GSP9700 Road Force Machine, checks ok, Checked the wheels and tires myself on vehicle for run out and wobble with dial indicator, they’re with in specs.
Can’t imagine why coasting in neutral would eliminate a drive shaft problem, it’s still turning at forty, that might eliminate the engine, which it did as I mentioned in the first sentence.
I’ve looked at GMC’s and shied away because of the very reason, a serious lack of support.
Denny Graham
Sandwich, IL

( vibration ) I'm sorry for beating this horse again, but it's not dead yet.
I thought an out of round drum could cause a vibration as well as a pulse in the brake pedal. If so, how could it be diagnosed? I know that backing the adjusters off would eliminate the shoes from dragging, and that you can get the rear wheels up to speed on jack stands, but how could you find the vibration if it's in the front. You should be able to feel it in the steering wheel, right? Or are these old steering gearboxes loose enough that the 'shimmy' would be lost in the steering slop? I don't know - maybe I'm just over-thinking it. These old drums weren't balanced as well as the newer ones to begin with, right?

I bought a truck this spring. 3/4t 51 . Rides rough, rattles, not very fast at all, trys to run hot in the Texas sun, leaks oil. I love it. As far as I know it is the only one around here running and driving. I try to take it out as often as I can. Paint is rough, kind of rusty, Hell it's old and so am I. We seem to fit together like OJ's glove. But not much luck with the 8 lug parts. I did find a couple of rear drums from a fellow member here. The truck has 2 Ford van wheels on the back. Rest is original GMC.

OldGMCTrucks.com has some leads now and then for the 8 lugs.

Denny, just a though on your vibration problem. If I'm not mistaken, the original wheels are a relatively tight fit to the hub, which would make them a hub centric wheel. That would be the hub is what the wheel centers from, not the lugs. IIRC, the wheels you currently have on it do not fit tight to the hub. This could be the problem. I have run into this problem before. On the cars I deal with, adding a hub-centering ring solves the problem. However, I'm usually dealing with aftermarket custom wheels, so that wouldn't be a direct solution for you. But perhaps you could machine your own, sized to fit your hub and wheel opening. Aluminum would be a good choice, many of the aftarmarket rings I use are either aluminum or plastic.
Just a thought anyway.

Don’t know how you would check the balance of the drums Dave, but that thought had crossed my mind. The out of round drum only has to be out a few thousands to feel a pulsing in the pedal and it would still be in balance.
I’ve indicated the wheels for out of round runout and wobble, they are fine. I’ve been thinking about making up a set of rollers that I can run up the wheels with and watch to see if they start the hopping. Back in the day a lot of the gas stations had wheel balancrs that spun the wheel on the car, wish I could find one of those rollers.
I’ve had it up on the jacks and turn the back end up to speed and I didn’t get the throbbing that I fee when I’m on the road. That sure sounds like a wheel or tire problem but when we spun the tires up on the Hunter road force balancer they checked out just fine. That lead me to the axles and flanges, checked them with the indicator and they are true. I wouldn’t be talking about it if it were a common sense thing, over the last few years I’ve tried about everything and it has me absolutely baffled. I even went down to the lumber yard and bought 800lb of sand bags to see if some weight in the bed would make a difference, nota.
Denny Graham
Sandwich, IL

Denny -

Thanks for taking the time to answer my questions. I had even thought about a bad wheel bearing, but that usually gives a vibration that won't go away. It is a true mystery. This vibration is like Super-horse. I keep beating it, but nothing phases it.

Take care,
David

My '02 RAM vibrates under load but not when coasting or down shifting when the u-joints are going (Iknow you said your u-joints are new). This may explain why a driveshaft might vibrate under load but not coasting, or why it vibrates on the road but not on jack stands. Yeah I noticed you said it vibrated after the engine was off coasting. Just a thought. Not necessarily a coherent one.

Shouldn't this be two seperate topics?

The 8-lug issue and a new one discussing vibration?

Quote:
''and usually rattled more"


here is a trick i used on my bed pad blocks
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=9A-3.jpg

i also used a long strip of hard 2''x1/4''x14'' rubber under the cab. So imagine where the 2'' round or square rubber stock & replacement pad fits for the cab's two big front bolts, now go look at the under side of the cab and follow how the cab under bracing structure is. this long piece of rubber about 12-14'' fits on top of the frame wide support arms. the bolt holds one side while i used a big pop-rivit to secure the frame rail side, if needed use a bit of E6000 glue.
this allows a lot more support to the cab along a longer surface so in theory should help spread the weight over a greater area, whereas the round stock pad tended to have the major cab weight located in a small area which made it break down sooner.
sorry i don't have any pics of this but you'll see what i mean. soon