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Old 12-11-2006, 06:03 PM
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SM 465 - Bad Noises

I recently rebuilt the engine, transmission, and transfer case on my 78 chevy K20. It's been finished and running well for the last 4 days. Today the transmission started making a new and horrible whining sound. In top gear under cruise with no load it sometimes has a high pitch whine. It goes away under load. I'm used to the regular whines of this tranny, but this is disturbing because it is a lot louder than any whines before. It sounds like "doing damage loud". It is intermittant and maybe happens more when the transmission is cold. Like I said, it just started happening today.

This was the first transmission I've rebuilt; but I think I did a decent job and I didn't find it too difficult. I mostly just replaced the bearings and seals. What would cause this whining noise to appear after a few days of driving (probably a couple hundred miles)? If a bearing is failing is there any way to find out which one without tearing the whole thing apart? Any chance that it could be an oil issue? Would synthetic help any? It was filled with oil and there are no noticeable leaks so I'm assuming it's still full. I will check asap.

Any help is appreciated,
dh

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Old 12-11-2006, 07:32 PM
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It's possible that you could have a pinion bearing noise too. Gonna take some checking to figure it out.
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Old 12-12-2006, 06:14 PM
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SM 465-Bad Noises

I would guess differential also. Here is a trick I've used in the past.

Take a small tape recorder,using duct tape,mount it to the driveline component,where you think the noise is coming from.

Go for a short drive,then mount it on another driveline component,go for a ride.

This should help you dial in the noise. Good luck!
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Old 12-12-2006, 06:31 PM
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Thanks for the replies. It's very definitely coming from the transmission or transfer case. The truck doesn't have any sound insulation so all noises come through clear as a bell and it's easy to tell where they're coming from. I'm used to the normal transmission sounds, the new noise is just a lot louder than I'm used to. I think it would actually be best described as a screeching or squealing.

Today I determined that it only happens when the transmission is cold. After driving for a couple minutes it won't happen. I also checked the oil level and it is a bit below the fill plug on both the tranny and transfercase. I bought some lucas oil stabilizer and I'll put it in tonight. Hopefully it'll help. I'll update if anything changes,
thanks again,
dh
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Old 12-12-2006, 09:44 PM
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Maybe the throwout bearing is squeeling? Adjust a tad too tight?
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Old 12-17-2006, 12:49 AM
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Here's an update. I thought I had it figured out, but now I'm worried again.

It was only happening when the transmission was cold and in high gear, ok, no problem. I let it warm up before I went into high gear. That seemed to be ok and I didn't hear "the sound" for a few days. Then today it came back. I was on the freeway cruising at about 60 mph. The transmission was good and warm (I figure) because I was driving for about 30 minutes before getting on the freeway. After about 5 minutes on the freeway the noise starts. I've noticed there is a quiet clunk sound when the screeching starts. Then there is the same clunk when it stops. When it's making the sound I can sometimes get it to stop by letting off the gas. Then when I get back into it the sound comes back. I was in traffic today and couldn't do much accelerating/decelerating to try to get rid of the sound. After squeeling for about 30 seconds it started to make bad clunking sounds and make the truck stumble. It felt like an engine miss but it wasn't the engine. The transmission was catching up and making my truck kick and stumble. This happened for about 30 seconds and then it went away and was fine. I've since driven it about 50 miles today with no problems. I figure the screeching was a bearing heating up and the kicking was it grabbing. Does that sound plausible? Does anybody think this could be something else? What would screech so bad then go away? I was planning on putting synthetic oil in it but now I don't know. Maybe I'll try it anyway.
thanks for any help,
dh
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Old 12-17-2006, 12:51 AM
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Quote:
Originally Posted by Jmark
Maybe the throwout bearing is squeeling? Adjust a tad too tight?
Would this happen in only high gear? It seems to be gear (or output shaft speed) dependant.
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