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Slippin Tranny????


OgreBattle

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Hey all, 

 

This is a pretty difficult issue to describe adequately through written text but I'm going to give it a go and see what ya'll think

 

So I've been using my 620 pretty frequently recently. I deliver pizzas as a side gig while I'm in grad school and I normally use my primary vehicle but last night I thought fuck it lets see if the Datsun can handle it!

 

I took about 12 deliveries all over town, probably put about 50 to 70 miles within a few hours. Starting and stopping the engine all night like a mad man. 

And I must say, the old bag did very well. Didn't give me a single issue, and I made like 100 bucks for night.I was incredibly proud of the trucks performance to say the least.

 

Tonight, though, I was driving my friend home, first time I drove the truck all day, and it was kind of bucking, or lurching forward while driving in first through third gears. Then i tried to start into first on a hill, and the truck stalled out on me and wouldn't start back up. I let it roll backwards in neutral down the hill into a parking lot. There was an overwhelming smell of something burning, almost like burnt rubber. I popped the hood and checked it out and there were no noticeable leaks or smoke coming from anywhere.

 

Tried to start it again and it started right up. But the bucking persisted. Now this bucking has been happening on and off recently, but it is a minor occurrence for the most part, that does not persist. The night I did all those deliveries, for example, I had no issue whatsover. But tonight the bucking was much more violent and eventually resulted in me stalling out again at a traffic light. Tried to start it again with no luck. I pushed it through the traffic light and slid into a parking lot. I tried to get her running but there was no starting for about 15 minutes; the engine would turn but it just would keep chugging and chugging without firing on.  I decided to try one more time before leaving her in the parking lot and it started right up. 

 

But, again, this bucking is still persists, especially if i'm not hitting the gas hard. And i can only assume I'm going to stall out again at another traffic light or stop sign or something

 

 

So my first thought is, obviously, my tranny is slipping and its either because its blown out or possibly my clutch is bad which would explain the smell? 

However, my mechanical skills/knowledge is quite limited, so I'm hoping the pros can guide me in the right direction. 

 

Is there a list of things I should check before bringing it into a transmission shop?

If it is the clutch (which makes sense to me because all the gears had this bucking problem) why the stalling? and why the inability to start again?

 

As always, i appreciate any assistance yall provide.

 

 

 

 

 

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Start the truck, put it in 5th. Rev it up a bit. Dump the clutch. If the engine does die immediately, the clutch is slipping.

 

Make sure you have nothing in front of the truck of course.. cause that could end bad.

 

Second, if it's dying and not starting for a bit, that's a different issue.

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Pull the 2 wire plug off the matchbox distributor and clean the male plug ends on the distributor, do what you can to clean the female plug end also and see if that fixes the issue.

I have bucking and stalling on my work truck a long time ago, it turned out to be this connection, what was happening was every time the engine shifted position like when I let off the pedal I would lose power, and the moment it kicked even once it made a good connection again until it happened again.

I figured my issue out on the road, it died on me while slowing down to make a left turn into a recycling place, the police showed up and told me they were calling a tow truck, I said give me a few minutes and I would get it started, he wasn't having any of that, so I said if I get it off the road will that be good and he said yes, so I waited for oncoming traffic to quit, I put it in 2nd gear and I used the starter to move my loaded truck and trailer around 60 feet off the road, he left after shaking his head in disbelief, I had it started a couple minutes later.

Bucking was the engine missing because of inconsistent power to the distributor, it made the whole truck jerk badly. 

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It sounds to me like your engine flooded (carb problem) by parking on a hill, and the result is fouled plugs that won't clear up.  Spend the $100 you made on plugs, cap, rotor, and plug wires.  I bet the clutch has nothing to do with it, unless you're not mentioning a rear main seal oil leak that could have sprayed the clutch disc with oil?  That would stink.  

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A slipping clutch is not violent. It's more of a revving of the engine with reduced acceleration.

 

1/ Bucking sounds more like an electrical problem, like the ignition turning off and on. If it backfired out the exhaust it's definitely that.

 

2/ To a lesser extent, loss of fuel like the carb running dry, will cause a lurching or stuttering of the engine but not nearly so pronounced.

 

 

For now go with an electrical problem. Look for anything on the coil or distributor wiring that might be lose. Wiggle the wires while engine running but NOT the high tension lead!  Next, engine off, go over the high tension lead from the coil to the distributor. It should be firmly seated into coil and distributor, no rust or corrosion. Lift the cap off and inspect the rotor.... it has to conduct that spark and point it to the correct cylinders. On top of the rotor is a springy metal contact that touches a spring loaded carbon contact on the underside of the cap that could be worn away.

 

Sometimes just checking connections makes the connection and the problem disappears.

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Horrible smell of burned rubber/plastic accompanied by awful running.  Fried alternator?  Check battery voltage.  Down to 10-11V and it'll likely start and run - but very poorly.  

 

Start sniffing around the engine bay until you find the smell.  Alternator, distributor, etc... until you spot it.  Then you found your smoking gun.  Could be as simple as a bad coil wire which Is why I suggested a basic tune-up for starters.  Bad plug wires also force a coil to overheat (and potentially spill its burned internal oil).  

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You guys are awesome, seriously. 

 

I drove it around the day after the night i had the issue, and it was going normal and smooth for a while, then is started bucking slightly , but it would stop when I really gassed it. 

The little bucking persisted, however it was nowhere as bad as the other night, and the truck did not shutoff at any point. I also have had no problem starting it at all, and the smell has not come back at all.

 

I checked the distributor coil and wiring. It is all relatively new (motor was rebuilt about 4000 miles ago) and there is no corrosion or looseness. 

However there is one single wire that runs from a wiring harness behind the driver side lights to the bottom half of the distributor; that wire is very old and a little loose. 

I fastened it on best I could.

 

Does the fact that I could drive normally  for most of the ride before anything going wrong confirm that it is an electrical issue?

I'm going to get the battery checked tomorrow regardless because it is fairly old. 

 

Also, who wants to provide a brief tutorial on 620 carburetor adjustment?

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The '79 should have a Blue and a Black/White and possibly a Black wire going to the distributor. Two wires at least. There should be a small thin black box on the side about 2" square. Be sure the two wire going to it are securely in place.

 

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I just went and looked at both my rigs with matchbox distributors, the 520 has an L20b and has the black ground wire going to the spade next to the "T" plug wiring(1980 wiring harness).

My 521 work truck has an LZ23 and the ground wire has never been connected to that distributor ever since I have owned the truck and converted over to an L20b, that's over 20 years ago, but it is the only one that has ever had issues with the distributor wiring(story in previous post), I should probably make a ground wire for it, it has the 1971 wiring harness it came with but it's messed up, I can pull every fuse and it keeps right on running like the energizer bunny, but when I turn the key off it dies, so I don't care.

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I agree.

 

Only an automatic transmission could possibly slip. Or a clutch.

 


But, again, this bucking is still persists, especially if i'm not hitting the gas hard. And i can only assume I'm going to stall out again at another traffic light or stop sign or something

 

 

 

Generally a plugged fuel filter is more noticeable when more fuel is demanded. It's like running out of gas. A part blocked jet will give mushy performance but once into the secondary it will go just fine. If really jerky like the ignition being turned on and off... could be electrical.

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The fact that the issue comes and goes confirms its not clutch, nor likely transmission unless its seriously low on oil. Could have just been debris in your carb? Do you have any gauges to see what actual oil pressure, water temp, or trans temp were?

 

I do not have a gauge for anything besides temp. And speed, I have an oil pressure gauge that came with the truck but I havnt tackled installing it yet

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