Paulz

It's fixed, at least temporarily. The wheel bearing nut was tight so that didn't cause it. While playing with the locking hub I noticed in the lock position it does not push the gear out flush with the mounting surface of the hub. Pulled the other side, same thing but on that side the gear on the axle stick out farther. I pulled the locking mechanism apart and found a shim to put behind the gear so it extends flush with the mounting surface. Bingo, no more clunk. Nice to at least know where it was coming from. I'm a bit surprised though, I would have thought that gear slipping teeth would cause a ratcheting sound, not the one big clunk, catch, clunk, catch it was doing. Anyway I guess I need to find out if the gear in the locking hub is in fact supposed to come out flush. The gear or the axle is surprisingly thing, less than a quarter inch I'd say, surprising. Still don't know why one side sticks out more. Again thanks for the help.

I pulled it off, the snap ring is there but I noticed the gear behind it is barely sticking out past the hub so it is only engaging in the locking mechanism a small amount. I pulled the other side, that gear sticks out the width of the gear. Somehow I need to figure out how to make that come out farther, or make the one in the locking hub stick out more. Thanks for the help

Hey sorry I just noticed I got some replies. Still have the truck and the problem. I don't think it's the U-joints, it actually skips and catches, in 4high or low, under load, along with a loud jerk and clunk. The end of the shaft, is that what I can see when I pull the locking hub off?

Ha, no but that's an idea. Or clean it. The valves I'm used to fooling with are open at idle but I believe there are some that have restrictions at various vacuums. I'll have a look, thanks.

I don't know the mileage or history but it appears to have a fairly fresh head. Doesn't smoke under acceleration, deceleration or cruising, just idle, and not all the time. Like flipping a switch, one minute it's fine, the next puffing badly. But since I disconnected the pcv that has stopped too. No blowby out the valve cover breather, air cleaner is dry. Very confusing. It's like oil is getting slung up to the area where the pcv tube enters the crankcase, which is why I asked where that is.

My 1980 720 pickup, which has the L20, was puffing blue smoke if left idling. I disconnected the PCV valve, smoking stopped. The pipe from the manifold runs underneath, where does it pull crankcase air from? Anyone had this issue before?

Bumping an old thread because I've got a clunking going on in my '80, only when in 4wd either turning or going down hill, seems to be skipping with a loud lurch and clunk. Sounds like right front axle. Can't find anything for sale.

I picked up the one I ordered at Oreilly yesterday. It's just like the one on there, the bleeder port on the bottom but the hole must lead to the top I'm guessing. I didn't get the cheapest one they had, it was $24, but still probably China. Going out to my cabin today to put it on.

My understanding is 1980 is an oddball year for the 4x4, maybe they just used what was around. In any case I have to decide whether to use a side port with the bleeder up top or an end port, which I assume also has the bleeder on top. I can't tell where the torsion bar is in the photo, looks to me like either would work.

Mike! The plot thickens, of course. Went to the auto parts this morning, the one they show for a 1980 4x4 is just like the one on there, side ports and bleeder on the bottom. The two wheel drive one has the end connections. Unfortunately my truck is not here, neither is the manual, and I need to get it ordered for tomorrow. I don't even remember if it has torsion bars, I guess so, or how much room there is around it, seemed like plenty. Here's links to the two they have. Oh, oh, just remembered I took a photo of it yesterday. https://www.oreillyauto.com/detail/b/power-torque-4688/engine-parts---mounts-16774/transmission---transaxle-16780/clutch-parts-16462/clutch-slave-cylinder-11336/808c079b207c/power-torque-clutch-slave-cylinder/cs2094/4670887/1983/nissan/720-pickup?q=Clutch+Slave+Cylinder&pos=1 https://www.oreillyauto.com/detail/b/power-torque-4688/engine-parts---mounts-16774/transmission---transaxle-16780/clutch-parts-16462/clutch-slave-cylinder-11336/808c079b207c/power-torque-clutch-slave-cylinder/cs2093/4670886/1983/nissan/720-pickup?q=Clutch+Slave+Cylinder&pos=0

Understood, thank you!

Mine has gone out. The replacements I'm seeing have the inlet and bleeder on the end, mine has them on the side, with the bleeder curiously below the inlet. What's right? It's a 4x4 if that makes a dif. Thanks!

I'm back. I put the carb back on today, ran it some more and believe I've discovered the vacuum leak is at the throttle shaft. Here is a video. That's starting fluid I'm spraying. The idle mixture screw does work, it almost stalls out when all the way in and picks up at a turn or so out but from there on out stays the same. Vacuum is about 16 at rough idle and 20 when I spray the shaft area. The funky sound is the unhooked smog pump valve but it does well do show the stumble.

Thanks again. I'm away until Thursday, I'll get the carb back on and report back.

Thanks guys. I have found one thing: I held an unlit propane torch around the carb and at the base that faces the engine, idle speed increased. Sprayed some ether there, same thing. Pulled the carb thinking I'd find something but the gaskets and the insulator block look fine. Had to quit for the day but there is a vacuum leak there somewhere. It's not the throttle shafts, they are tight. My original post was confusing. When I first got this truck it wouldn't idle at all and vacuum was way low. By disconnecting some of the vacuum driven smog components I was able to raise the vacuum and get an idle, albeit rough. The diaphragms in those components, like my advance can, are shot. If I can get it to idle smooth and lower the HC then I'll start reconnecting the smog stuff. I'm not in the smog license class at the college, the teacher just showed me how to use the sniffer in manual mode. I'm taking auto body.. I'll try and get to the root of this carb base leak tomorrow and report back. Thanks again. Edit: Flatcat just saw your post. Since it runs well at high speeds and under load I have not suspected ignition components but I will have a look.