My 1980 Datsun 720 diesel dually

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wayno
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Re: My 1980 Datsun 720 diesel dually

#221

Post by wayno » Wed Mar 06, 2019 10:27 am

DRIVEN wrote:
Wed Mar 06, 2019 5:35 am
Looks good to me. Interesting info about EGTs.
The EGT temps were an eye opener to me, I put the EGT gauge in my non-turbocharged 521 kingcab because I wanted to know how hot they ran without the turbo as the turbocharged 720 ran stinking hot all the time, this was before I figured everything out, after driving it for a while I concluded that I had likely came as close as one could to blowing up the 521 kingcab diesel engine when I drove it to LA right after getting the truck on the road, I had that engine floored for over a half hour going up the grapevine pass just north of LA, by the time I got to the top the engine was running real weird, I could see the smoke coming out of the tail pipe at night and it had no power, once it cooled down it felt normal again, the coolant temps were just to the red also, I was so lucky I didn't blow that engine up that night, I didn't have an EGT gauge back then so I have no idea how high they were, but if I were to guess it would not surprise me if they had climbed to 2000 degrees, whatever it was it was I am positive it was just below the melting point of aluminum pistons, I still do not know why this engine has not blown a headgasket yet with what I have put it thru in the past.
From what I have read climbing above 1400 degrees is real bad, it is not that it will melt something, it is when will it melt something, but I have read where others have drew the line at 1600 degrees in the larger domestic engines, I don't know what to think anymore, so I keep the diesel engines I have below 1400 degrees, the 521 kingcab engine never climbs that high much anymore, only when it is above 90 degrees outside and I am climbing a long uphill grade at 70+mph, but that was before I put the larger Volvo radiator in it, the water temps run much cooler now, I suspect that the radiator has very little effect on the EGT temps though, but I didn't have coolant temp issues before putting the turbocharger on it, well unless I was floored for over a half hour, but I suspect a lot of vehicles would have issues being floored for over a half hour, especially using a 1600cc radiator to cool a 2500cc engine.
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Re: My 1980 Datsun 720 diesel dually

#222

Post by wayno » Wed Mar 06, 2019 5:20 pm

I didn't do much today, my wrist is hurting bad, I suspect it's arthritis, but I put the EGT probe bung in.

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I don't know if that is the right place to put it, but the tube holding the turbocharger is thinner and it would make getting to the bolts harder and make it possible to break the probe if I slipped, so I centered it on the turbo mount tube.
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Re: My 1980 Datsun 720 diesel dually

#223

Post by wayno » Fri Mar 15, 2019 3:30 pm

Well I am tired of the noise and vibration in this 720 since putting them mobile home leafs on the truck, I have been trying to use angled shims to fix this issue, someone said to put the thick end towards the rear(lowering the nose/pinion flange of the axle), well it is not working, I think I am going to pull it apart again and try putting the thick end of the shim towards the front now.
The thick end of the shim is towards the back on my lowered 520(720 chassis) and it works great, but it is not working on this 720.
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Re: My 1980 Datsun 720 diesel dually

#224

Post by wayno » Fri Mar 15, 2019 8:32 pm

OK, I switched the angled wedges around so the thick end is to the front and I drove it, keep in mind that the carrier is raised almost 2 inches, it was slightly smoother while speeding up but still had vibration between 25mph and 35mph, but not terrible, so I put it back up in the air and put the carrier back to the stock position on the cross member, now picking up speed and slowing down it seems alright, but if I go a steady 40 to 50mph it vibrates something terrible and once it starts it will not stop until I slow way down or go really fast.
This evening just before I quit working on it I adjusted the the carrier rubber piece at a better angle but didn't test drive it, I will do that tomorrow, if not better I will raise the carrier again and test drive it, if not better then I will remove these leafs and put a set of 720 4X4 leafs I have on the truck.
One thing I noticed when I put these mobile home leafs on this truck was that actually had the centering holes maybe a half inch farther back than the stock 720 leafs which pulled the yoke in the transmission out that half inch, now I have had other vehicles that had the yoke pulled out a little without issues but they were one piece drive lines, my 521s have a slip yoke drive line while the 720 doesn't, but I wonder if this could be the issue.
I just remembered I have a 521 slip yoke rear drive line that might be around the same length as the stock 720 drive line that maybe I could use to let the yoke slide all the way back into the transmission, it's only about a half inch difference, I will look at that tomorrow before replacing the leafs.
I am going to figure this shit out eventually, the last test drive was making some weird squeaking noises which I didn't like, something didn't like the new position, I also checked the "U" joints and could not find anything that was loose.
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Re: My 1980 Datsun 720 diesel dually

#225

Post by DRIVEN » Sat Mar 16, 2019 4:25 am

Ahhh, new information. Having the yoke backed too far out of the transmission could certainly be causing that. As for your angles, you really should check them with an angle gauge like the one I posted a couple pages back. It's less than $5 and would remove a lot of guessing. Once the angles are dialed you can move on to other possibilities, if you still have a vibration.
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Re: My 1980 Datsun 720 diesel dually

#226

Post by wayno » Sat Mar 16, 2019 8:22 am

It really didn't seem that important to even mention before because it's only a half inch, it didn't even deform the carrier rubber piece.
Also how does one adjust or even measure 3 different angles when one cannot even get in there, I have 3 U joints which all have an angle, the one at the yoke in the transmission, the one at the carrier, and the one at the pinion flange.
I will get a photo of the yoke in a while when I measure the rear drive line piece.
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Re: My 1980 Datsun 720 diesel dually

#227

Post by DRIVEN » Sat Mar 16, 2019 8:41 am

This article gets into angle measurements about 2/3 down. https://www.google.com/amp/s/www.hotrod ... -tech/amp/

Basically, they say you should set the forward shaft level with the transmission, essentially making it en extension of the mainshaft. Then set your rear driveline and pinion angles to equal out to a zero sum.
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Re: My 1980 Datsun 720 diesel dually

#228

Post by wayno » Sat Mar 16, 2019 8:56 am

OK, I got under there with a 90/45 degree angle thing that normally is used to draw lines on wood/metal to make straight cuts, I had the rear 2 angles really close and it was as bad as ever.
Right now the front piece is in the stock position again, I will get under there and get a photo of the yoke when I measure the rear drive line piece.
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Re: My 1980 Datsun 720 diesel dually

#229

Post by wayno » Sat Mar 16, 2019 12:04 pm

So I got under the truck this morning and looked around, took a photo of the yoke, measured the rear drive line piece and then measured my extended 521 drive line piece from the 521 work truck chassis, it was around 3 inches too short.
I checked the drive line angles again and they were way off, but I had had the axle tilted the other way also without positive results.
Here is the yoke in the transmission.
Image
To me this doesn't look bad, it was only a half inch difference at the leaf mount holes between the 2 leafs.
So I looked at it some more, pulled and pushed on the yoke to see if it had any play, none, so I gave up and put the 720 4wd leafs in the truck and the issue went away, it appears that even though it was only a half inch difference at the leafs, it likely was an inch difference at the yoke, here is the yoke with the 720 4wd leafs installed.
Image
There are no shims or blocks dropping this axle, and the rear bumper is at least an inch lower with these 4wd leafs, but the mobile home leafs had also lowered the truck, so the 4wd leafs actually likely lowered the back of this truck at least 3 inches if not 4 inches from the height it was with the stock 720 leafs.
Fact is I think I need taller tires in the rear now, but I have so much money into these tires I am keeping them on this truck for a while.
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Re: My 1980 Datsun 720 diesel dually

#230

Post by DRIVEN » Sat Mar 16, 2019 4:27 pm

So, angles are the same and vibration is gone?
When the only tool you have is a hammer every problem starts to look like a hippy.

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Re: My 1980 Datsun 720 diesel dually

#231

Post by wayno » Sat Mar 16, 2019 4:45 pm

DRIVEN wrote:
Sat Mar 16, 2019 4:27 pm
So, angles are the same and vibration is gone?
The angles are the same as when I first put the mobile home leaf springs on and it vibrated on that trip to pay my water bill at the water bureau place, it has vibrated since, obviously because the yoke got pulled out if the transmission too far, at least it is obvious now.
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Re: My 1980 Datsun 720 diesel dually

#232

Post by wayno » Sat Mar 16, 2019 5:00 pm

I did connect the inter-cooler into the system this afternoon after I got the vibration thing figured out, everyone knows about how I was saying earlier that the turbo was clocked wrong and how the waste gate was at a weird angle and how I fixed it by drilling a hole in the middle of the bracket, I had to do that to get the outlet of the turbo discharge connected to the piping going to the intake, well when I piped in the inter-cooler today I had to undue what I had done as it was clocked perfect for the inter-cooler, before I didn't think there was the room to do it, but I made it work, it's tight but I got it all connected and took it for a test drive.

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The truck runs better than it ever has now on the 5 mile test drive I took it on, plenty of boost and quieter then has ever been, I gave it some pedal and got just over 70mph briefly(little tires) at around 8psi, and it never reached 1000 degrees(EGTs),and I seen 15psi a couple times getting on it, it was great, best it has ever been, but the 521 kingcab diesel is still better.

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Re: My 1980 Datsun 720 diesel dually

#233

Post by DRIVEN » Sat Mar 16, 2019 5:08 pm

That's awesome! Looks good under the hood. Well laid out considering the amount of room to work with.
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Re: My 1980 Datsun 720 diesel dually

#234

Post by wayno » Sat Mar 16, 2019 5:16 pm

Thanks, this one is starting to look like the engine compartment in the 521 kingcab now, no room to even work on it anymore, if the starter or alternator go bad I have to remove everything to get to them, but at least I can change the oil filter on this one without removing a bunch of stuff.

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