A different kind of transmission noise

[DerrickB]

I searched the forums at length and found many references to a different set of transmission noises than those I am experiencing. I do hope I did not overlook an already provided thread on this.

I have a '73 Squareback with manual transmission. It was recently purchased from someone who took great pains to maintain the vehicle properly. It has a whine/whir/hum sound that occurs when the car is in gear and moving near the high end of the speed range for the given gear, whether the clutch is in or not.

It is most noticeable in reverse. I suspect that is because the high end of the speed range in reverse is such a low speed. I start backing up and the noise gets louder but does not change in pitch. I push the clutch in and the noise remains. I pop it into neutral and the noise goes away, even if i'm still moving.

It does it also in first gear. I thought it did it in second gear only when the clutch was in, but discoverd this morning that it was still making the noises - it was just hidden by the noise of the engine overriding it when the clutch was out.

I haven't confirmed that it does it in third or fourth gears because road noise tends to mask it.

Basically, having no knowledge of how this transmission works, it *seems* like something in the transmission related to how fast the car is moving compared to the gear the transmission is in (whether the clutch is engaged or not) is complaining.

By the way, I am referring to absolutely normal driving speeds here, not high-revving the engine. Drive in first, ready to shift to second, push in clutch and when the engine quiets down the noise is very obvious. Ready to shift from second to third? Push the clutch in and the noise can be heard when the engine quiets down. But the noise is, apparently, there even when the clutch is not pressed - you have to listen for it over the engine.

I was hoping to research this all myself. Any pointers/suggestions on where to look next?

[sjbartnik]

That would seem to me to indicate an issue in the final drive; either a bad bearing in the final drive or an issue with the differential. Does the loudness change when turning as opposed to driving straight?
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1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[DerrickB]

I got off work today determined to produce a more accurate description of the noise and the conditions under which it occurs. I even hijacked the assistance of a co-worker who we all tend to think of as mechanically inclined just because every car he owns is really old and beat up and breaks down often. I was then utterly and completely unable to reproduce the noise under any circumstances, despite it being fairly consistent in my mind previously.

I drove home, drove around the neighborhood a few times trying different gears, reversing in the middle of the road, basically looking like an old fool in an old car, and scratched my head.

The closest I could come to reproducing it was to go in reverse. You know how an old manual transmission has that "winding up" sound as you go faster in reverse? A similar sound was occurring in first and second gears, related entirely to the speed of the vehicle relative to the gear I was in. Clutch in or out did not affect it, but the instant it popped into neutral, it went away.

Only now it's gone and I cannot think of anything significantly different between this morning on the way to work and this afternoon after. It was low 60's last night and dry. It was humid this morning - the weatherman expected rain, but it never materialized. It is 80'ish this afternoon and very dry. The drive to work is about 10 miles with no hard work on the way and few stop lights/signs. The engine was probably similarly warmed up to and from.

If the problem recurs, I will get a more detailed description, and maybe some video.

In response to the previous response, the noise did not seem to be at all affected by turning versus going straight. The fact that the clutch did not affect the noise in any way said it's on the transmission side of the drive train. The fact that the noise was very dependent on the speed of the car relative to the gear it was in (ie. toward the higher end of the gear's speed range) says it could be anything between there and the tires, right? Except that putting it in neutral makes the noise go away immediately, so whatever is directly connected to the rear axle is not the issue...

I will post again if it recurs.

[Bobnotch]

Have you checked the gear lube level? You'll need a 17mm allen wrench to do so.
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[sjbartnik]

[DerrickB]

Okay, updates and feedback, unfortunately incomplete.

Thanks for the input regarding the final drive, sjbartnik. I don't know this stuff. I have the purple Volkswagen for Idiots book by John Muir, which I have been reading non-stop between service calls, so I'm catching up.

It did it again this morning (next day from original post) and I paid close attention. The noise occurs when the engine is in reverse, first or second gear while the car is moving, not when stopped. It is more obvious with the clutch in due to reduced engine noise. It may make it in higher gears - I can't hear it. When I shift to neutral, the noise goes away. When I put it back in gear, the noise returns.

The noise was quieter by the time I got to work than when left home. Heading home, the noise was initially faint, then gone entirely on arrival. Overnights here are very mild lately, 62 last night, 84 today. I assumed the manual transmission would "warm up" quickly while driving, but if it doesn't, that might explain the behavior. It only makes the noise when it's cold? 20 degrees makes the difference? (oil expanding/contracting at the critical moment of just becoming detectable by ear?)

I had to special order a 17mm allen wrench from the auto shop; it will be here tomorrow, along with a suction pump, and I can check and change the gear oil level then. While under the car to see where the ports were and what they looked like (and to see what kind of axle I had - double jointed), I saw that there appears to be oil leaking from axle-transmission seals. The entire engine, engine compartment, surrounding tins, accessories, rubber boots, etc. are very clean. The underside of the gearbox has a thin oily film with some small oil spots. The "constant velocity joints" have a very obvious dirty oil buildup all around. I would guess they have been leaking for some time in small amounts. I have no record of when the gear oil was last filled. I also read that I will need to learn how to pack those bearings :/

The auto shop offered me "GL-1" 90 weight mineral gear oil and asked if I wanted that or "GL-5" 80-90 weight and I said I don't know. What the blip is GL? Gonna internet that after this post. He also offered me some synthetic stuff. I'll need to know which to get when I go back for the allen wrench.

Thanks very much for the input. I will learn this thing yet!

[DerrickB]

I also want to clarify and apologize regarding the terminology I have been using. The "thing" that sits between the engine and the axles is called, variously, the transmission, the transaxle, and the gearbox. I assume this also serves the purpose of a differential. Are all of those referring to the same thing, and, if so, what is the "correct" term so I can begin using it? Or are there distinct components within the case that each have their own name?

[sjbartnik]

If you want to be technically correct, it's a transaxle.

But most people use transmission and gearbox interchangeably with transaxle.

The differential is incorporated into the transaxle housing which is what makes it a transaxle rather than just a transmission.
_________________
1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[Erik G]

you want GL4 (there are lots of arguments but it is safe for yellow metals)

I use this. It's cheap and excellent

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[W1K1]

redline lightweight shockproof gear oil has been a popular oil for aircooled transaxles for a while
http://www.redlineoil.com/product.aspx?pid=43&pcid=8
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1973 super
1965 squareback 1500E
1971 bay window westy- subi swap

[DerrickB]

Thanks for the oil recommendations. I got GL-4 Hypoid 85/90. I also picked up the drain plug wrench, then went home. I opened the filler port and stuck my finger in. If it was low at all, it was less than 1/4 inch. I drained it (icky, smelly, unpleasant and generally un-nice) and the oil that came out was black, but not gritty or seeming in any way heavily used. The magnetic plug had no metal shavings on it, but that's the same with my motorcycle; once the initial grinding is done, the metal shavings disappear.

This morning, I fired it up to go to work and the noise was right there. I did some experimenting. A noise is still present when in gear and driving, but it is very much more significant when the clutch is in. It isn't just drowned out by the engine noise when driving; it is significantly quieted.

The noise does not occur in neutral off of the top of 3rd gear - just 2nd, 1st and reverse. Sitting at a stop, in neutral, with the clutch out, I can get a similar noise by very gently pressing the gear shift into the gear channels of *any* gear, like just pushing toward it with my pinky, not really trying to push it into gear. By "a similar noise", I mean it's the same kind of hum/whine, but it's a different pitch and much quieter, but it's the same kind of noise. I don't know if that helps.

I've done some searching on the synchronizer for these transmi...axles and haven't found much, and I'm not at all sure if it's even worth investigating based on these symptoms. I can say that the gear oil level was not low, the oil was not dramatically bad, and that the noise is unchanged by replacement with new oil.

I'd be happy to perform whatever experiments may help in diagnosing this. I do not believe this is a "normal" noise, and I also believe it's getting worse/louder. As mentioned before, it is very definitely temperature sensitive, not in the engine or wheel bearings or brake pads or etc. Thanks in advance for any assistance. If I am able to figure it out on my own, I will post my results.

Derrick

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