My 1980 Datsun 720 diesel dually

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Re: My 1980 Datsun 720 diesel dually

#241

Post by DRIVEN » Mon Mar 25, 2019 9:10 am

^^Agreed. Leverage.^^
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Re: My 1980 Datsun 720 diesel dually

#242

Post by wayno » Mon Mar 25, 2019 4:20 pm

I guess I look at it a different way in more than one way, first there are 2 tires on the ground and they want to be flat(both want to touch as all the rear tires were bought at the same time), second if I were to use a 2 foot adapter(exaggerated) I would not be worried about the bearing, I would be worried that the axle would break at the bearing.
As for the 4 inch adapter/spacer causing bearing issues, if they didn't have bearing issues on Datsun Motorhomes using the adapter on the left in the photos below, that 4 inch spacer on the right that is on my truck now is not likely going to be an issue, and yes they are a different type of adapter.

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Yes I get it, but the H190 axle has a bearing in the center of the axle on the carrier, and a bearing on the outer part of the axle, these bearings are far apart, I will always come back to the axle itself.
Have you ever seen some of the loads I have hauled on my work truck before I switched over to the dually axle(floating), if they didn't fail doing that to them, well they must be over built.

I know nothing about Hondas and their bearings, but if they had a crazy offset wheel, I would imagine them 2 bearings being so close to each other that they would not like it, that is a different kind of pressure that I don't have a word for right now.
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Re: My 1980 Datsun 720 diesel dually

#243

Post by Laecaon » Mon Mar 25, 2019 9:04 pm

One can think of it anyway they want to. But there is only one correct way to think about it*...

The wheel is mounted to the spacer, mounted to the flange of the axle. The axle is supported at the end of the axle housing by a roller ball bearing. And then supported at the diff.

The weight of the truck in the rear is applied to the leaf springs. The leaf springs sit within inches of the wheel bearing, but on the axle housing. The weight gets transferred to the wheel which puts weight down on the ground, and the ground pushes back.


You are bolting the wheel to the flange of the axle. Immediately you will have increased load on the studs of the flange (where your wheel used to mate). And of course there is more radial load upwards at the weld point between the flange and axle. This upward force is sent down the axle to the wheel bearing. This wheel bearing is taking all of the load, and at the diff, there is most likely an opposite force (downwards) and not as extreme.

Now you extend you wheel out. There will be more force applied upwards on the wheel bearing. Say the flange of the axle is 4 inches from the bearing, and you add a 4 inch spacer, so now you are mounting the wheel 8 inches from the wheel bearing. You are doubling the forces applied upwards on the wheel bearing. And of course that means the bearing has to push back with the same force.

Roller Ball Bearings are fairly good at radial forces.

With all that said. Everything is made with a margin of error. And its pretty obvious Nissan over Engineered these cars. My guess, you are now at the upper end of what the bearing is rated for. No it will not fail immediately. It will shorten its service life. By how much? Well that is another discussion.

What I think is, you need an inch less spacer to make it look right.


*Not saying that I am thinking about it correctly necessarily.

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Re: My 1980 Datsun 720 diesel dually

#244

Post by wayno » Mon Mar 25, 2019 11:04 pm

I agree that it it would look better with an inch less sticking out, i already mentioned this a few posts back but it is what it is, and I would never try to modify these spacers/adapters as my welding is not up to that caliber and it never will be.
I also agree that the 4 inch from the bearing has a certain force, I expect that 8 inches away from the bearing more than doubles the force, but the force we are talking about doesn't make the truck weigh more, if there was a 1000lbs(just a number) on the rear bearing without the spacer/adapter, there is still just a 1000lbs on the bearing with the spacer/adapter.
Now what I ask is where does that force go, I think it goes into the studs, flange, and the part of the axle that sticks out past the bearing, although some of that force will be pushing down at the gearset spider gear in the middle which the bearings holding the carrier in place take up that force, so basically I believe that the axle bows more because the axle has been extended past the bearing farther which is basically leverage, it's easier to bow the axle the farther out you go from the bearing, but that bearing still only has a 1000 pounds on it, even if you put solid lead rims and tires on it there is still only a 1000lbs of weight resting on that bearing.
Right now I believe that the weak spots are the studs and flange, the H190 axles in the trucks are quite beefy, I do not know if the 2 wheels bolted together help or make things worse, I expect it doesn't make it worse unless I drive just the outer tire up onto the curb and have the inner tire hanging in the air, that could possibly triple or more the stress on the studs/flange and bow the axle more on the inner side of the axle bearing, but there is still only a 1000lbs of weight on that bearing.
Now if the bow in the axle is enough to angle the inner race on the axle differently than the outer race in the housing then this could be an issue, round bearings would start to wear the sides of the races, bearings shaped like barrels would also have issues, I don't remember the type the H190 has, but I suspect the barrel type, either way if that axle bows enough that could be a problem.
I do not ever plan to use this truck to haul weight, it was not safe for weight with the adapters I had on it for at least 10 years now, and it still is not safe for weight with these adapters, and the tires are so close to to rubbing the fenders now that it could ruin the fenders if the tires hit them.
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Re: My 1980 Datsun 720 diesel dually

#245

Post by wayno » Mon Apr 01, 2019 2:53 pm

I cannot seem to get this truck to go down the road smoothly, I am thinking about putting the stock leafs back on.
I will try looking at the drive line angles again.
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Re: My 1980 Datsun 720 diesel dually

#246

Post by wayno » Mon Apr 01, 2019 4:53 pm

Well I am going the right direction, 2 degree wedge in the rear and an inch spacer between the carrier cross member and the carrier, it's smoother than it was, it was shaking the whole truck some, but the shift lever was doing a dance at certain speeds, that is better also, but not there yet, I am done messing with it today.
I lifted it up as high as I could get it, then I lowered the rear axle onto some stands till they took almost all the weight of the truck, then I would get under there and check the angles, with the spacer under the carrier it basically made the driveline almost straight from the transmission yoke to the pinion flange, all I had to do then was get the rear axle close, but now I wonder if you want the driveline from front to back perfectly straight, maybe I need angles to stabilize things instead of it trying to act like a noodle.
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Re: My 1980 Datsun 720 diesel dually

#247

Post by DRIVEN » Mon Apr 01, 2019 5:51 pm

There should be a slight angle at the carrier and the rearend. 1-2 degrees is ideal. Front driveline should be level to the engine/transmission.
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Re: My 1980 Datsun 720 diesel dually

#248

Post by wayno » Mon Apr 01, 2019 7:31 pm

That is the issue, when the carrier is in the stock position the front driveline is angled down, this angle makes it difficult to figure out what the angles should be on the 2nd and 3rd u-joints, #1 is the yoke, #2 is the carrier, #3 is the pinion flange, right now the shift lever still shakes a little at a certain speed, if I speed the truck up over 50mph it smooths out.
3 u-joints/angles are confusing me, so all I could do was raise the carrier so there was no angle at the yoke, and then get the pinion angle as close as I could to straight like the carrier is, it is close to straight the whole length now.
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Re: My 1980 Datsun 720 diesel dually

#249

Post by wayno » Sat Apr 20, 2019 7:03 pm

I had most everything I needed to make one last log exhaust manifold, I have not yet mounted the turbocharger pipe/mount or the pyrometer bung, I will do that when I decide to use it, I cannot see to weld so my welds look like shit.

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The 2 middle pipes are really close together, I think I got on between them when I welded it together, if it leaks I will take it off and weld the pipes together from one end to the other on both sides, that will stop it from leaking.

I am driving this truck all the time now, it goes pretty good, but I will be parking it next weekend as I am going to start driving the 521 kingcab, it's finally starting to warm up and I would rather drive it.
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Re: My 1980 Datsun 720 diesel dually

#250

Post by wayno » Wed May 15, 2019 2:34 pm

I am sick of the sound this truck makes since changing out the rear leafs, it still vibrates a little at certain speeds but that I can live with as it is mostly smooth on the freeway, but going thru the gears around town blows.
So I think I am going to put the stock leaf springs back on it as it was smooth when it had the flatbed on it with these wheels, I don't remember how smooth it was when I put the stock type box with dually fenders back on it, all I know is that now it is terrible with all these minor vibrations and the sound it makes, I have tilted the axle up to 6 degrees one way and 4 degrees the other way, I have raised the carrier as high as 3 inches, all this without any significant positive results, yes it is better than it was but I am just about done screwing around with it.
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Re: My 1980 Datsun 720 diesel dually

#251

Post by wayno » Fri May 17, 2019 12:26 pm

It has the stock leafs back in it now and it is way better, it appears that the 720 leafs also moved the axle back a little as when I changed the driver side out I had to loosen the passenger side so I could slide the driver side forward maybe close to an inch.
My theory is that the lowering leafs are pulling the drive line out of the back of the transmission and it don't like it, it's a custom drive line that is around 16 inches longer than stock as that is how much I lengthened the frame to have a kingcab/long box truck, but for some reason the locating pins in the leafs I have used are farther back than the stock leafs, so if I want to lower it any it appears I will have use lowering/drop blocks as the usual way I do it is not working for me.
I took it for a test drive and didn't even get 20 percent of the normal test drive done before I turned around and went back home as it was back to normal, I got it up to 60mph once when I stopped and turned around as all appeared to be good now.
I suppose I could make a 1/2" thick plate with 2 holes in it to keep the axle forward where it is now, but I just looked at it and decided it is good the way it is, I can haul a little weight in it now as when it is lowered the axle is very close to the frame as the bump stops have been removed, I have no idea why it sits so low in the rear without drop blocks, these stock leafs appear to be almost straight.

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