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Trans/clutch noise only when in Neutral


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I have a knock/rattle noise that sounds a little like when you have a pair of sneakers in the dryer.  Kind of an irregular knocking.  It is not very loud and only occurs when in neutral with the clutch engaged.  It is somewhat variable in volume and seems to be loudest after long highway trips.  It is louder outside the truck than inside.  When disengaging the clutch, it slows and then stops over a couple of seconds.  The transmission shifts smoothly, clutch works fine, and there is no noise or other problems in any gear at any speed, in 2wd or 4wd, other than the general loudness of the drivetrain in this 4x4.

 

I just put in fresh GL4 oil in the transmission a few months ago. There was one thin metal shaving in the oil about 1/4" wide by 1" long, nothing else.  Truck has 106,000 miles.  '86 KC 4x4 5 speed.

 

Things I am thinking it could be, admitting I am not the best at understanding transmission innards:

 

Clutch or input shaft bearing that is getting worn and rattles in neutral but not when in gear because it is stabilized by the forces moving through the driveline

 

Something outside of the transmission, like a mount, or exhaust component, that is loose and the vibrations in the transmission when engaged and in neutral are transmitting to this component and making it vibrate.  The fact that it is intermittent and more audible when the truck is hot/after high speed use seems to argue for an exhaust component.

 

What do you all think?

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Jack it up, get under it with a stethoscope or other listening device of your choice, have a helper reproduce the issue and have a listen. Use jack stands and be safe under there.

 

that should give you an idea if it’s in the tranny or something else. 

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If your reporting of the situation is 100% accurate, and it is a transmission problem, the only difference between when the truck is moving and when it is not, is that the input gear and layshaft/cluster gear are moving when the truck is not moving, but not the main shaft. When the truck is moving, the main shaft starts moving.

 

The pocket bearing inside the input gear of the transmission supports the main shaft of the trans and could be bad.

 

It's not very common for that pocket bearing to go bad, but if the trans sat for years with water in it, that would definitely cause it to fail.

 

Other causes of that noise inside the transmission could be a sticky synchro on the input gear, but not likely. Is your shift lever bound up or does it have any pressure on it from let's say a shift boot or anything else?

 

The noise could also be from a loose exhaust hanger or many other things.

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On 5/2/2021 at 7:48 AM, MaddieCycle said:

I have a knock/rattle noise....  It is not very loud and only occurs when in neutral with the clutch engaged....  When disengaging the clutch, it slows and then stops over a couple of seconds.  The transmission shifts smoothly, clutch works fine, and there is no noise or other problems in any gear at any speed,

 

 

 

 When clutch is disengaged the clutch disc, mainshaft drive, (and bearings) countershaft driven, (and bearings) and 1st, 2nd, 3rd and 5th driven gears loose on the mainshaft slow and stop. Almost for sure this is a bearing. It's quiet when driving because there is a load on it taking up any slack. The strip of metal is worrying as it could be one of the ball bearing cages that support and space the balls.

 

Did it look something like this???

 

o1doL87.jpg

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8 hours ago, Stoffregen Motorsports said:

If your reporting of the situation is 100% accurate, and it is a transmission problem, the only difference between when the truck is moving and when it is not, is that the input gear and layshaft/cluster gear are moving when the truck is not moving, but not the main shaft. When the truck is moving, the main shaft starts moving.

 

The pocket bearing inside the input gear of the transmission supports the main shaft of the trans and could be bad.

 

It's not very common for that pocket bearing to go bad, but if the trans sat for years with water in it, that would definitely cause it to fail.

 

Other causes of that noise inside the transmission could be a sticky synchro on the input gear, but not likely. Is your shift lever bound up or does it have any pressure on it from let's say a shift boot or anything else?

 

The noise could also be from a loose exhaust hanger or many other things.

Thanks.  I doubt this truck ever had water in the gearbox.  Shift lever moves like butter.

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6 hours ago, datzenmike said:

 

 When clutch is disengaged the clutch disc, mainshaft drive, (and bearings) countershaft driven, (and bearings) and 1st, 2nd, 3rd and 5th driven gears loose on the mainshaft slow and stop. Almost for sure this is a bearing. It's quiet when driving because there is a load on it taking up any slack. The strip of metal is worrying as it could be one of the ball bearing cages that support and space the balls.

 

Did it look something like this???

 

o1doL87.jpg

Hard to say, it didn't really have any form or distinguished markings. I did the oil change months ago and made a mental note of it but did not save the piece. It did have a curve to it. Agree never good to find a piece of metal in the gear oil.

I will get under it to verify the noise source, but my inspection thus far makes it seem like the tranny. Not good news.  Seems like if I do try to do something about this now it would make sense to go with a full rebuild + clutch replacement and rear main seal.  Truck is in great shape, I just put an entire new front end on it, many other repairs, I know it in and out, doesn't burn an ounce of oil and all 4 cyl compression is within spec.

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If clutch is not slipping or causing problems, and if the rear seal is not leaking oil... leave them alone. Don't fix what isn't broken.

 

 

This is likely where the metal strip came from. It spaces the balls and without it I'll bet it doesn't run right and will make noise.

 

s6fBNQU.jpg

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Maybe just drive it until I encounter driveability issues?  I want to avoid a catastrophic failure, also I only do a few thousand miles per year with this truck so it could limp along like this for a long time.  I had a Subaru that lost 4th gear and had all kinds of input shaft noise, drove it for a year and then sold it.

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My suggestion is sorce another trans and rebuild it swap the trans and sell the noisy one.  A properly rebuilt trans will out live you.

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Right now it's fixable. When it lets go it may be junk.... and it may leave you stranded.

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Agreed.  What kind of job is this? Seems straightforward.  Drop the trans, split the case, rebuild kit, re-install.  How many hours for a skilled transmission mechanic?

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If your lower cluster gear bearing has lost its cage it is only a matter of time before it explodes, right now you can pull the transmission and put a new bearing in it and put it back together, if it explodes a bearing can come out the front cover which normally happens, but I have had the bearing come out of the race on the gear side and go thru the front gears,.

I was only 8 blocks from home when it screeched, so I turned around and tried to make it home, while I was going thru the Safeway parking lot the truck dramatically shuddered(this is when the bearing went thru the gears), I kept going till I got home, I pulled into the neighbors driveway so I could back into mine and I had no reverse, I coasted backwards out of his driveway far enough to get it into my driveway forwards, I left a trail of gear lube from his driveway into mine and I broke out my pressure washer and cleaned it up the best I could.

The reason it shuddered was when the bearing went thru the gears in the front it broke the shaft on the back side of the middle plate where 5th and reverse are, 5th gear went thru the tail shaft case and all the gear oil leaked out between Safeway and my neighbors and my driveway, the transmission was destroyed but I made it home, I expect the tow would have cost more than the replacement transmission so it is a toss up on what I should have done when it screeched as it was a couple blocks after the screech before the bearing went thru the gears, I expect I could have just stopped, walked home and used another truck to get my trailer home and then towed the truck home, but................. I likely would have just towed the truck home without removing the drive line so the damage could have still occurred as the drive line is still turning the guts of the transmission even when in neutral, this happened suddenly, I had no warning like you have, if you continue driving it you only have one direction to go, are you feeling lucky???, right now your transmission is likely serviceable and only likely needing a bearing, if you fix it now you will likely only need a bearing, if a bearing gets out you might only need a front cover and bearing unless the race spins in the case, then you may need a front case and front cover.

Your best avenue is to stop driving it, remove the transmission which is a bitch in a 4wd and fix it while you still have something to fix, transmissions used to be cheap in wrecking yards, they are not cheap anymore if you can even find a good one, fix it now, it is less of as headache.

If the transmission quits making noise when you push the clutch in and put it in gear, take it out and fix it, or do you feel lucky?

 

I wrote this how to in the link below for folks that wanted to put a truck 5 speed in their 521, it shows one how to take the front case off and replace the lower bearing and then put the L case onto the Z transmission, it is not that hard to remove the front case, clean all the metal out and then install the bearing and put it back together, this is way easier to do than source another transmission, by the way buy the best bearing money can buy, US or Japanese made, don't buy any bearing made in Korea, China, or anywhere else unless you want to do this all over again, I have never found a good bearing in a auto parts store, as I recall I was paying $70.00+ for a good bearing from a bearing place, last time I bought bearings I was unable to find a 62mm(63MM?) bearing anymore, below are photos of the 56mm bears I found a while back(years???).

001.JPG.c4e5d37835e3844606f73ab06c332937.JPG

 

003.JPG.02a23283fb85057d96ba25a588a315f5.JPG

Edited by wayno
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Thanks Wayno that is wise advice. Looks like I need to call a couple of local transmission shops in the morning.  Besides fixing whatever is out of sorts in there, any other wear items that would be wise to fix, if I am going to go through the hassle of having someone pull the transmission? Seems crazy to not do the clutch while in there.

Edited by MaddieCycle
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If you've never rebuilt a transmission before, don't be scared, but be aware that there are a couple special tools you will need (bearing splitters, pullers, large wrench for tailshaft nut, snap ring pliers, roll pin punch, etc) and there is also a learning curve. Many first timers run into common problems, mostly by trying to cut corners and try to not disassemble the whole trans. Complete disassembly actually makes the job easier.

 

If you have a transmission repair shop near you, give them a shot. Back when I was rebuilding these for a living, a complete rebuild cost about $650, including parts. I have no idea what shops charge for them now, as parts have dried up and the knowledge is disappearing as well.

 

I don't think anyone sells a rebuild kit for these. Really all you need is bearings and a couple synchros. If I recall correctly, there are six bearings in there, including the pocket bearing. You don't always need all the synchros either. Second and third gear usually take the hardest hit when shifting, so even if you got just two synchros, you pick the best two used ones and use them. Seals, as Mike mentioned, should be left alone, unless you can find nice OEM seals. Gaskets, who needs gaskets? The right stuff rtv is my choice for transmissions, diffs, oil pans, etc, and will work just fine. Leaving the gaskets out helps tighten things up too. Especially on the front cover. Obviously you need to be careful of not using too much rtv, but don't skimp either.

 

As I said, there is a learning curve.

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4 minutes ago, Stoffregen Motorsports said:

If you've never rebuilt a transmission before, don't be scared, but be aware that there are a couple special tools you will need (bearing splitters, pullers, large wrench for tailshaft nut, snap ring pliers, roll pin punch, etc) and there is also a learning curve. Many first timers run into common problems, mostly by trying to cut corners and try to not disassemble the whole trans. Complete disassembly actually makes the job easier.

 

Thanks! I did the whole front end last summer on this truck and now I am building an off grid cabin.  At my home in the city I live on a hill and the truck does not fit in the garage.  No room, no time - gonna let a shop do this.  I have an appointment next week with a local reputable shop for a free estimate.  

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I can relate. When we moved to the country, the only place to put tools was in a goat shed. It took two years to build the shop, and during that time I had to work on my cars/trucks in the gravel.

 

Let us know how the appointment goes. I'm curious as to the state of mind of the modern transmission repair shops. I wonder how they will receive you, being a classic Datsun guy.

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I did the front end a block from my house in SF, just parked on the street where it is flat.  The truck was in various states of repair, on stands etc... for 3 weeks!

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So you're that guy. I always wondered what kind of guy would do that kind of repair in the heart of the city.

 

With parking at a premium, I don't blame you.

 

What part of the city?

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I have done rattle can paint jobs in abandon warehouse parking lots.  You get a lot of texture in you paint if the wind comes up.  When this happens it is Rhino Lined!!!  LOL

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On 5/5/2021 at 7:26 AM, Stoffregen Motorsports said:

So you're that guy. I always wondered what kind of guy would do that kind of repair in the heart of the city.

 

Lolz well I am a girl but other than that yeah that's me.  I rebuilt the top end of an old Honda XL125 on a block I used to live on that was flat, and my neighbors filed a complaint with 311. 🤣

 

Took it to a reputable local transmission shop.  They pulled it and found several problematic bearings. Gears, shafts, synchros are all good.  Clutch is showing some signs of wear so doing the clutch/flywheel/rear main seal while we are in there.  Will be 2k out the door parts and labor, and the shop is getting all Japanese bearings, he said they categorically will not put Chinese parts in any transmission.  The guy was cool about the truck and told me he's seen these engines go 400k miles.

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