Noise, what is it?

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Noise, what is it?

Post by impulsive » Fri Sep 06, 2013 8:51 am

OK, since getting the 87 4ZC1-T back on the road, I have noticed a noise I don't much like.

Scenario: Shifter in neutral, clutch engaged (pedal out), I hear a distinct whirring sound. Push clutch pedal in, whirring goes away.

I've done a bunch of reading, and it seems that this sound is directly associated with the input shaft bearing. The sound is not violent, not crunchy or poppy, just a whirrrrrrrrr. I got the motor back from the machine shop, and iirc, the input shaft bearing and pilot bearings were already installed by them. These parts were also new.

I made a video too:


http://www.youtube.com/watch?v=KM60mSqV3uc

What do you guys think? Input shaft bearing? Throw out bearing? A bearing inside the trans? I'm nucking futs and it's nothing to worry about?

I don't have any ill behaviors related to this sound. It doesn't lurch or cause a drop in RPMs when I let off the pedal. It just whirrs and I don't like it.

When I had the car apart, I drained the trans and it sat. I resealed the front and rear of the trans with new seals and torqued everything to spec. I did not open the trans or do any work inside it. I refilled it with 5W Redline oil.

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Post by IZU069 » Fri Sep 06, 2013 7:35 pm

If it's also quiet in 4th gear but not others, then it's the mainshaft's center bearing - a needle bearing with worn inner & outer shaft surfaces.
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Post by impulsive » Sat Sep 07, 2013 1:23 am

IZU069 wrote:If it's also quiet in 4th gear but not others, then it's the mainshaft's center bearing - a needle bearing with worn inner & outer shaft surfaces.
Well, I don't really notice any noise at all in any other gears. I really only hear it when I am in neutral and my foot is off the pedal. In the video it sounds a lot louder than it actually is. When I am driving, if there is any noise it is inaudible to me. I don't notice any growling or grinding in any gears while driving, and no bad behavior when shifting, etc.

Let me ask this, what is the most favorable oil and weight to run in these 5-speeds? I might try changing the lube again and see if it quiets down. This is the only thing I did between the rebuild and now. I drained and pulled the trans, it sat on blocks for about 2 years, then it went back and got filled with Redline 5W synthetic and the noise was immediately there.

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Post by Ghost » Sat Sep 07, 2013 9:10 am

IZU069 wrote:If it's also quiet in 4th gear but not others, then it's the mainshaft's center bearing - a needle bearing with worn inner & outer shaft surfaces.
Sounds like the same issue my friends gearbox was having, I think thats the same conclusion we came to as well.
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Post by IZU069 » Sat Sep 07, 2013 12:36 pm

Thanks Ghost. 4th and clutch-in is the only time that bearing does not spin. With amusement I watched another forum (of which I was once a member) spend pages of suggestions but not one mentioned the center mainshaft bearing. Yet is is one of the known weak points of those MSG(?) gearboxes - the hardening is not that good. (The other weaky being 2nd gear & its synchro.)


As to gearbox oil, it should be the same (mineral) oil as the engine - typically 20W-50.
It may be the synthetic that caused the noise. I've never considered synths for gearboxes. (Why?)

Some use thicker oils and claim improvement of bad synchros, but heavier oil wrecks good synchros - not that they'll be noticed with the heavier oil, but those boxes are not designed for heavier oils (eg, the old 80W-90 gearbox oils). It increases resistance though probably adds noise dampening.
Maybe the latter will help cover the center-bearing noise.
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Post by impulsive » Sat Sep 07, 2013 12:49 pm

An Isuzu guru i talked to suggested Shell Rotella 5w40 heavyweight oil. I might try that.

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Post by IZU069 » Sat Sep 07, 2013 2:36 pm

If he is a guru, then fine. Otherwise I'd recommend against something as low as 5W, even 10W, and if it's a synthetic oil, I'd advise against that unless someone knows better (for gearboxes).

That series of boxes was originally designed for SAE30W which is the now 20W-50. A straight SEA40W might be ok as a thicker oil, but I know many "supposed gurus" (who are anything but!) on some Isuzu forums advocate 80W & 90W etc gearbox & diff oils which is definitely wrong for good gearboxes.

Whilst the impact of thicker oils in "our" engines is well known - eg, seizing of twincams and other G-series engines at high RPM using performance 50W oils - gearbox impacts are less well understood or noticeable.

As to synthetics, I recall my gurus questioning their suitability for G- and 4Z-series engines, let alone any advantage that they may have. The general consensus seemed to be to stick with modern 20W-50 mineral oils (eg, Castrol GTX or GTX-2 for "cleaned" engines) and change oil and filter every 10,000km (even for the "change oil every 2,000 miles" G-OHV engines). To change less often thanks to extended synthetic oil life was asking for trouble - "our" engines were not of that technology and did not have suitable filtering.

But 90W oils went out with the synchro on first gear boxes that started circa 1966 for Isuzu passenger vehicles.

Granted, I used heavy gearbox oil in one of my G-OHV engines, but that was a crapped out smoker with zero oil pressure at idle. But never for gearboxes, and that included my rally years, and later years with my 400Nm (300Nm@2,000RPM) G200W.
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Post by impulsive » Sun Sep 08, 2013 3:28 am

Thanks for the input, I will see what I can find.

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Post by impulsive » Tue Sep 10, 2013 1:42 am

Well, I found some Shell Rotella SAE 30 straight grade. I drained and refilled with that. So far, no change. Noise is still there, and no change to functionality.

Do you think this SAE 30 is safe to use?

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Post by ImpulseRocket89 » Sat Oct 19, 2013 4:11 pm

Bart, if you ever get to the point you want to try a different transmission, I still have my stock one sitting around. It's got over 100k on the clock, but as far as I knew it was in good order before it was pulled. I've never really shipped anything of that size for freight, but I'm sure I could figure that out easy enough.
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Post by IZU069 » Mon Oct 21, 2013 3:40 pm

Hopefully synth won't be used next time.
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