Transmission Hum (Howl?)

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sped372
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Transmission Hum (Howl?)

Post by sped372 » Mon Sep 03, 2012 12:03 pm

I'm trying to diagnose a noise (in the bus) that seems to have crept up on me over the course of this summer. I'll try to be thorough, here are the symptoms:

Difficult to describe, somewhat loud humming noise that reverberates through the interior of the bus. Comes and goes but has been present more frequently as of late. I am almost 100% sure that I only hear it in 4th gear and with a load on it, coasting smooth and level without a headwind I don't really pick it up. As soon as I'm climbing an incline or accelerating it shows up. Seems to lessen on corners. Third gear on a severe hill (with a good load) I still can't seem to hear the noise. As soon as I'm into fourth there it is. In neutral coasting I think I hear a little bit of noise back there, but nowhere even close to under load. Based on these clues I think I've ruled out the wheel bearings or the engine/exhaust.

Is the infamous transmission howl?

Gear oil was changed about six years ago when I first bought the bus (I've since become much more educated and do all my own work). Shifting into third gear has always been a bit crunchy if I don't give it enough time or double clutch. I haven't really noticed any change in it's behavior, besides the noise. First might be a touch trickier to get into, but I'm not completely convinced it isn't just in my head.

I'm planning to change the gear oil again just as a good-faith effort. It doesn't pop out of any gears at this point. Am I just buying time until I can go for a rebuilt transmission or is there something else I should be checking into besides a gear oil change? Pressure plate, clutch, and throwout bearing were replaced about two years ago. I had to replace a broken clutch cable earlier this year and I feel confident I have it adjusted correctly (freeplay). I'm not sure what else to poke into.
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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hambone
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Re: Transmission Hum (Howl?)

Post by hambone » Mon Sep 03, 2012 1:26 pm

Could it be harmonics? I have a slight PP imbalance and it causes a vibration at 2700 rpm. Rev the engine slowly, and see if a certain rpm causes vibration.
They do get noisy/moany with age. Hal's was getting pretty bad too but he replaced it.
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sped372
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Re: Transmission Hum (Howl?)

Post by sped372 » Tue Sep 04, 2012 6:13 am

I don't think it's a harmonic imbalance in the engine but I can do a more thorough test while stationary. The fact that I really only hear it in fourth gear seems to rule out pretty much everything other than the trans. It's there in fourth no matter what speed I'm at, too, so it's not just a single rpm of the engine (and it's not there in other gears either).

I had even thought about something crazy like the top or rear rack vibrating at higher speeds but it seems to be load dependent in gear, not speed-of-the-vehicle dependent.
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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yondermtn
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Re: Transmission Hum (Howl?)

Post by yondermtn » Thu Sep 06, 2012 1:59 pm

fwiw, I had quite a trans howl ever since I bought my bus. In June I finally got around to changing the gear oil and the howl has quieted considerably. Lots of gunk on the drain plug and one gear tooth.
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1990 Vanagon MV 2.1 Auto

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sped372
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Re: Transmission Hum (Howl?)

Post by sped372 » Thu Sep 06, 2012 2:28 pm

Thanks for the input. I just picked up some gear oil and was planning on doing the change this weekend if time permits.
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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SlowLane
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Re: Transmission Hum (Howl?)

Post by SlowLane » Thu Sep 06, 2012 9:45 pm

In case you've never changed the gear oil before: remember to make sure you can unscrew the fill plug before unscrewing the drain plug. It can be terribly frustrating to drain the oil and then discover that the fill plug refuses to budge. :pale:
'81 Canadian Westfalia (2.0L, manual), now Californiated

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sped372
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Re: Transmission Hum (Howl?)

Post by sped372 » Fri Sep 07, 2012 5:12 am

I hear you! I was planning on checking that first. I picked up a 17mm hex-tipped socket so I can use a breaker bar on it. I figured that would be better than a stubby little L-key. My back is giving me problems right now so I'm not sure I'll get under there this weekend. Heal, dammit!
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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Amskeptic
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Re: Transmission Hum (Howl?)

Post by Amskeptic » Fri Sep 07, 2012 7:09 am

sped372 wrote:I hear you! I was planning on checking that first. I picked up a 17mm hex-tipped socket so I can use a breaker bar on it. I figured that would be better than a stubby little L-key. My back is giving me problems right now so I'm not sure I'll get under there this weekend. Heal, dammit!
Transaxle oil changes are easy on the back. Just lay down and use a pump available at your FLAPS.
These transmissions can last a long long time with clean oil and gentle driving. Chloe has been popping out of 3rd since I owned it. 16,000 miles later no deterioration noted with my new method of shifting into 3rd like I am laying a cracked egg down on a porcupine.
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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sped372
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Re: Transmission Hum (Howl?)

Post by sped372 » Fri Sep 07, 2012 7:26 am

Amskeptic wrote:Transaxle oil changes are easy on the back. Just lay down and use a pump available at your FLAPS.
That's the plan, I bought the pump since it was so inexpensive. I realize it isn't a heavy lifting job or anything but any sort of twisting or sit-up like motion is giving me pretty severe shooting pains right now. I took a knee to the side/chest playing volleyball and I think I have some bruised ribs. I'll probably give it a go but if the drain/fill plugs are stubborn I may have to wait.
Amskeptic wrote:These transmissions can last a long long time with clean oil and gentle driving. Chloe has been popping out of 3rd since I owned it. 16,000 miles later no deterioration noted with my new method of shifting into 3rd like I am laying a cracked egg down on a porcupine.
That's my into-third shifting method, too. It's a combination of quick and gentle. Fast across the throw to minimize loss-of-speed and then slow and gentle through the synchro.

My hope is that fresh oil will lengthen it's lifespan and also verify the noise was coming from the trans (if it quiets down). I still haven't experienced any popping out of gear so I don't think we're on the deathbed yet. This bus spends 90% of it's time in fourth gear since it's been primarily used for long distance traveling (even evidenced by the methodical log that came with it from previous owners) so I think maybe that's why 4th is starting to get noisy?
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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hambone
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Re: Transmission Hum (Howl?)

Post by hambone » Fri Sep 07, 2012 10:28 am

Has it ever happened where a "person" has destroyed the trans case removing a stuck plug? I worry about that. What is the case made of, magnesium?
Are there tips for when the plug just won't budge? A breaker seems like it may cause issues if used too vigorously.
Funny, mine now rarely pops out of 4th - but I must shift with "elan and verve".
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sped372
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Re: Transmission Hum (Howl?)

Post by sped372 » Fri Sep 07, 2012 1:56 pm

It's true that over-stressing a component is liable to damage it. My wimpy arms prefer a modest pull on a long bar opposed to a struggle with a short one. Lever action, baby.
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

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sped372
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Re: Transmission Hum (Howl?)

Post by sped372 » Mon Sep 24, 2012 5:55 am

Well my back finally healed well enough for me to get under there and change the gear oil. That pump was a joke, I just ended up squeezing directly from the bottles into the fill hole. I could only get each bottle half-empty but by marrying the remainders together I got 3.5 pints in there.

I didn't notice any *large* chunks in the old oil. Test drive *seemed* quieter but I won't really believe it for sure until I get some more miles on it.
1971 Karmann Ghia - 1600 DP
1984 Westfalia - 1.9 WBX

bigbore
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Re: Transmission Hum (Howl?)

Post by bigbore » Sat Oct 13, 2012 9:12 pm

sped372 if you are hearing more noise in 4th most of the time it is a main bearing getting tired (the first bearing in a bus to go) changing oil will help but its time is coming.

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DjEep
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Re: Transmission Hum (Howl?)

Post by DjEep » Sun Oct 14, 2012 10:56 am

SlowLane wrote:In case you've never changed the gear oil before: remember to make sure you can unscrew the fill plug before unscrewing the drain plug. It can be terribly frustrating to drain the oil and then discover that the fill plug refuses to budge. :pale:

That's no big deal. You just have to get 15 friends to help you tip the bus on it's side :geek:

But seriously, I'd just top off the oil and drive it until it explodes. Seen more than a couple of tired trannies go right after an oil change. I think the worn brass and such in the old oil actually helps cushion things that are hanging on for dear life. If it helps you sleep better, pull the plug for a few seconds to get any major chunks out, then put it back in and top off.
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hambone
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Re: Transmission Hum (Howl?)

Post by hambone » Sun Oct 14, 2012 1:54 pm

Chicken or the egg? Those tired transaxles might have died anyway. Seems that flushing out that tired old oil would do more good than harm. I like to imagine it that way anyway.
http://greencascadia.blogspot.com
http://pdxvolksfolks.blogspot.com
it balances on your head just like a mattress balances on a bottle of wine
your brand new leopard skin pillbox hat

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