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620 Neutral Noise, with Idle Speed Drop When the Clutch Pedal is Up


hovdat

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I have a '77 Datsun KC 5-speed. I replaced the clutch, bearing and pilot bushing very recently, but am concerned about the noise it makes when in neutral and the clutch pedal is up.

 

After putting in the correctly-lubricated new clutch, when I pushed the clutch all the way to the floor you could hear the bearing up against the fingers of the clutch plate (I think, or I really hope it wasn't the fingers being pushed against the springs on the clutch disc), so I adjusted it out as far as it could go, then just today I shortened the pushrod of the slave cylinder so there was a little play in the fork (previous teenage owners were suspect, seemed to in slap whatever they had access to on so it would run, including a plastic bottle "gastank" under the hood, for example, so an incorrect slave cylinder is not out of the question). I was hoping the noise was related (maybe not disengaging completely?) but it's still there. Here's as best I can describe it:

 

When in neutral, I can push the pedal to the floor and shift easily throught the gears (less finger noise with a shortened pushrod but still there somewhat). When I let the pedal up I can hear more whirring/whooshing-like noise along with a drop in the engine idling speed, like the engine is under some kind of stress or pulling on something.

 

Is there a break-in period for a new clutch and bearing? Will this noise and draw on the engine go away with time? What is pulling on the engine?! There is less than a mile on the new clutch but lots of idling time while checking other engine/running items (not on the road yet except for a few unregistered joyrides through the neighborhood, and am I wrong or have we ALL done that?!). Did Autozone sell me the wrong pressure plate/bearing combo (have read lots of threads on bearing collar height, matching pressure plate to bearings, etc.)?

 

Just wondering if anyone has had the same issues. Thanks for your time and thoughts!

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. When I let the pedal up I can hear more whirring/whooshing-like noise along with a drop in the engine idling speed, like the engine is under some kind of stress or pulling on something.

 

When the clutch pedal is let up, even in neutral, the input shaft of the transmission begins turning. It is full time gear connected to the counter shaft and it's bearings and these to all four forward speed and reverse gears above it on the mainshaft. Pretty much everything is spinning and on top of this, they are in a bath of oil. Worn bearings will make some noise and the oil will require some engine power to splash out of the way.

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If you have noise when the transmission is in neutral, and the clutch is out, and then when you press the clutch pedal in and put it in gear and all the noise goes away, keep in mind that you are just sitting in a driveway, that would be transmission bearings more than likely.

It would be in your best interest to stop driving the truck and fix the issue before you have to be towed home because the bearing exploded and took out the front case.

The reason the noise goes away is that when you push the clutch pedal in and put it in gear, nothing in the transmission is turning anymore.

If you still have noise when you push the clutch in and put it in gear in your driveway while not moving, then it is likely something else other than the transmission.

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Dang, fast replies!  Datzenmike, that makes sense, and given that it's been pretty cold here in New Mexico I might understand that it'd drag the engine down a bit, especially with just idling and no driving to warm the crankcase oil.  But wayno, now I'm worried.... it hasn't been driven for 10 years, but I did flush and fill with the correct viscosity yellow-metal safe oil (differential too, and golly but that didn't take a LONG time to find the right oil).

 

How pricey is bearing replacement on a 5-speed KC?  Is that something a regular transmission shop could do or do I need to find a Datsun specialist?  I know there's a regular Ratsun member lurking that has talked about seeking out "old mechanics in the Albuquerque area" but I don't find any of his posts now.... he might know where I could take it, if I can track him down!

 

Is it possible to post links to Youtube clips in these forums?  I'm wondering if I can get a good video of the sound it makes just so you can see/hear what I'm talking about, and if it's unusual or worrisome... I take my son to the DMV tomorrow to get his Learner's Permit, and this 620 will be his DD.... eventually.  And not if I can let go of it once it's back on the road!

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You can replace the front counter shaft bearing your self if you are able to remove and replace the transmission, it's not that hard to do.

But we have to be sure that is is the transmission first, does the noise go away completely when you push the clutch in and put it in gear in your driveway without moving, even when you rev the engine?

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