Bearing noise - need help diagnosing

SpyderMike · 03-22-2018, 07:06 AM

I have a 1985 with 250,000 miles on it that I have owned since 1989 or so. Most of the miles are mine and I know this car. I recently backdated - project thread here:

so this is how a backdate project starts...

So now I am driving it and at any stop with trans in neutral I hear a bearing noise. When I push the clutch in the noise goes away. This is a sign my trans needs refurb soon isn't it? I can't think of anything else to assign it to.

Ideas please!

Bob Kontak · Bob Kontak's Garage

I am guessing throwout bearing on pressure plate.

SpyderMike · 03-22-2018, 07:13 AM

So once the T/O Bearing is loaded the noise goes away, but unloaded it is still spinning and making this noise?

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by SpyderMike

So once the T/O Bearing is loaded the noise goes away, but unloaded it is still spinning and making this noise?

Let me research for a moment. You are loading the bearing when you push the clutch in. With clutch out it is just spinning unloaded.

Which way makes the noise? I may have it backwards. Looking now.

Edit: Read this over. it's short.

https://www.knowyourparts.com/technical-resources/drive-train/diagnosing-clutch-bearing-bushing-noise/

old man neri · 08:24 AM

Edit: My bad, I miss took the year of the car for the year of ownership. Disregard.

SpyderMike · 03-22-2018, 07:42 AM

When in neutral with clutch out it is noisy. When clutch pedal is pressed, it is quiet.

It is a 915 gearbox.

SpyderMike · 03-22-2018, 07:43 AM

from your link Bob, it is this scenario:

"A bearing noise that occurs when releasing the clutch pedal to engage the clutch while in neutral, but goes away when the pedal is depressed is caused by a bad transmission input shaft bearing."

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by SpyderMike

from your link Bob, it is this scenario:

"A bearing noise that occurs when releasing the clutch pedal to engage the clutch while in neutral, but goes away when the pedal is depressed is caused by a bad transmission input shaft bearing."

So if you are in first and release clutch car moves and no noise?

SpyderMike · 03-22-2018, 08:08 AM

I will have to see if I can detect that specific noise over all others when taking off in first.

During the backdate, I took out most of the sound insulation. I just really notice it at idle because all other noises are low.

KTL · 09:14 AM

Do you have an aftermarket shift coupler and/or aftermarket engine & transmission mounts installed? The shifter coupler and mounts can transmit a lot of noise when they've been replaced with aftermarket parts like WEVO or Stomski.

Edit: You can also test the release bearing by slightly pushing on the clutch to load it, but no so much that it actually disengages the engine from the transmission. By doing this you're putting some load into the release bearing but the transmission shafts are still spinning. This can tell you if it's a bearing issue internal to the transmission. The ball bearings that are fitted to the differential housing's retainer/tensioning plates are known to get sloppy with age. So I wouldn't be surprised if those bearings are causing your noise. The rest of the bearings in the trans (large roller bearings for the shafts, needle bearings for the gears) are pretty robust. Usually it's the roller bearing races installed in the case that can exhibit some wear on the contact surfaces. Those will show considerable graying and texture if they're going bad.

SpyderMike · 03-22-2018, 09:46 AM

I replaced all mounts, but with factory ones KTL. The shift coupler was replaced years ago. I don't think it is related.

I will try the partial load test as well next time the rain stops here.

Bob Kontak · Bob Kontak's Garage

I have nothing else to add because of my lack of experience with P cars. I just got my one.

However, with everyday cars, when the TO bearing goes to hell, it is an obnoxious noise.

T77911S · 03-22-2018, 10:46 AM

TO bearing most likely.

I bought a bmnw 325is that did the same thing and I thought the same thing. needless to say I found out the hard way that the was NO oil in the tranny. I must add they are WELL built.

probably your TOB

Targa Me · Targa Me's Garage

Throw out bearing.

adias · 03-22-2018, 12:49 PM

I have heard transmission rattling noise when stopped in neutral with a rebuilt transmission and new clutch and new TO bearing. Rattling goes away when pushing clutch pedal to the floor. This does not happen every time, as it depends on the last gear the transmission was in prior to stop. There are many posts documenting this rattling noise as normal. It seems odd to me, but that is what I learned and have been told.

uwanna · 02:16 PM

Quote:

Originally Posted by adias

I have heard transmission rattling noise when stopped in neutral with a rebuilt transmission and new clutch and new TO bearing. Rattling goes away when pushing clutch pedal to the floor. This does not happen every time, as it depends on the last gear the transmission was in prior to stop. There are many posts documenting this rattling noise as normal. It seems odd to me, but that is what I learned and have been told.

I have also read numerous threads about this rattling noise (do a search). Many seem to think it's normal. When you're in neutral, you have the input shaft turning as well as all five of the free wheeling
meshed gear sets. That's a lot of iron spinning. Ever been in a race car
with all insulation gutted, the noise is alarming! One thing I have noticed in my 915/70 45K mile trans (which does it all perfectly) is, when dead cold the neutral noise is not there, but if I drive for a while and warm it up the neutral noise appears when the clutch is active.
So for the OP, try your car when it's sat over night and see if it makes the noise.

SpyderMike · 03-22-2018, 05:46 PM

Thanks all! It will be sitting for a couple of weeks as I travel. I will try further diagnosis when I get back.

One more data point. I don't remember ever changing the oil in it in 28 years and 250,000 miles.
But then, I don't remember too much these days; "always looking forward" is my excuse.

safe · safe's Garage

TO bearing for sure. Doesn't need to be toast, if you removed sound dampening or just refreshed the mounts with new rubber the noise will be louder.
I noticed a significant increase in TOB sound when I installed the sport/cab transmission mounts.

SpyderMike · 03-23-2018, 07:27 AM

Why am I thinking the TO bearing should not be in play then...with transmission in neutral and clutch out? I thought it should not be interacting with the pressure plate then.

KTL · 03-23-2018, 07:49 AM

The TO bearing is always interacting with the pressure plate because it's always hard-connected to the pressure plate fingers and the release fork is always connected to the bearing.

Any time the engine is running, the pressure plate is spinning. If the pressure plate is spinning, that means the TO bearing is spinning too- regardless of whether the clutch pedal is depressed or not. However, when you depress the clutch pedal you are pulling on the TO bearing. That pulling effect changes its loading from simply spinning to being axially loaded and spinning. If the bearing is internally worn out it can make noise when unloaded- clutch pedal released/clutch engaged. The change in loading changes the sound it makes and in this case can make the sound go away.

Another diagnostic test you can do is listen how the sound changes as you press and release the clutch pedal. If you press the pedal all the way down and the sound goes away quickly, I think its related to the TO bearing. If you press the pedal all the way down and the sound slowly goes away, while the transmission mainshaft and the freewheeling gears on the pinion shaft take a short while to stop spinning, I think it's transmission bearings.

If you haven't changed the gear oil in forever? That oil might be black and full of bigtime sasquatch funkified stank. Which isn't doing your gears or bearings any favors.