Fixed transmission leak. Engine sounds better too. Explain?

[handjammer]

Hi. New-ish syncro owner, fixing up this van as a side hobby. Haven't had a reason to post because there is such a wealth of information on this forum, it's incredible.

But a curious thing happened and I can't wrap my head around it. I fixed a transmission leak recently, using this amazing trick posted here: https://www.thesamba.com/vw/forum/viewtopic.php?t=344159.
The hose on the little top bleeder vent was kinked. When I unkinked the hose, there was an audible sound of air escaping like someone trying to hide a fart. Took her out for a test drive and right away I noticed the exhaust was significantly less loud when I released the throttle (Is the sound of backpressure? Still learning). It was quite loud before, I was even considering a new muffler. And now it just purrs softly. So nice.

So what's going on? I mean it's awesome, I killed the two proverbial birds. But what's the relationship between the transmission leak and engine sound on throttle depress? Do I need to be concerned about possible damage while the vent was closed, assuming increased pressure in the tranny case caused the leak?

thanks, just want to learn all I can!

oh almost forgot to mention an important detail: its got an EJ22.

[zuhandenheit]

My first thought was that there's no connection -- it's a coincidence or you're imagining things. But, for fun, I've thought seriously about whether there could be a connection --

Let's say your transmission has a problem such that it increases the load on the engine (i.e., was harder to turn), that would make your exhaust louder at the same speed / rate of acceleration. It's therefore possible for a change in the transmission to change the sound of the exhaust.

Your transmission was leaking because the clogged vent caused the pressure within the case to increase. Normally, as the oil temperature increases, it expands, and the air (which of course also expands as it heats) is displaced and escapes the trans by way of the vent. When it's clogged, the air becomes compressed increases and it exerts pressure on the oil (which will also be slightly more compressed), and so the oil is pushed through the seals. The increased pressure of the oil will increase resistance -- the gears will be harder to turn.

So, in theory, i figure it would be possible to change the exhaust note of an engine by increasing pressure in the transmission case.

However, I can't believe that the pressure would have increased enough, in your case!

Yes, your oil should have a lower pressure now that you fixed the vent, but I'm thinking the difference is certainly insignificant. The difference in the thickness of the oil is I'm sure a lot greater between cold and hot.

By the way, keep in mind that even if the oil was incompressible, a clogged vent can still result in leaks. As the air in the trans heats, it would apply pressure to the oil, which will be pushed out the seals without itself being compressed. I mention this to make the point that it would be a mistake to think the leaks are an indication of the pressure of the oil. (Pressure against and pressure within are different -- if you push a solid ball through a pipe, you're not increasing pressure inside the ball; and hydraulic fluid is supposed to be incompressible: it allows pressure at one point to be exerted at another point, though the fluid is not itself pressurized.)

The weird thing about this is that it seems nearly impossible for there to be a connection between your transmission repair and the exhaust, but I think it would in theory be possible to effect a change to the exhaust note by changing the pressure within the trans -- and you did!

[Sodo]

[Mellow Yellow 74]

It's kind of like the placebo effect - you do work on your van and it seems to go better even though the work you did doesn't really explain why
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1962 Karmann Ghia
1974 Deluxe Microbus
1985 Caravelle (Vanagon)

[handjammer]

I almost didn't pose the question because I knew I couldn't rule out the possibility of coincidence. But I made no other modifications to the van. I simply pulled on a hose with some pliers until the sound of air came out. All things are as equal as they can get.

I want to reiterate that the noise drop only applies to throttle depress while in gear. The engine was always quiet when giving it some gas, pre- and post-fix. It's a manual transmission, if that wasn't obvious. 1st and 2nd was especially loud prior to the fix, 3rd and 4th saw less change in noise but still noticeable.

If I were a full-time vanagon hacking devotee, I would re-pinch the vent hose and make some comparison videos. Unfortunately, intentionally breaking things is not exactly on my to-do list right now. Believe me, the difference is profound.

I'll accept that it's a coincidence provided there's some other explanation of why the sound has decreased. Stuck rock theory seems plausible I guess, just kind of unsatisfying.

[Sodo]

I agree it would be interesting to find a physical reason that releasing pressure allows the trans to turn more freely. But it's not feasible. A little less friction from removing contamination from your lubricant,,,,, now THAT's up my alley.

Whenever I vacuum and wash the windows the van is quieter and has a little more power.
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[IdahoDoug]

Agree - placebo effect! NTTIAWWT, of course as my vehicles run smoother when washed and vacuumed as well.

You could pressurize the transaxle to 150psi and it would not affect internal friction in a measurable way outside of a NASA grade measuring capacity.

I vote for the jacking up and dealing with the clogged hose having caused some drivetrain flex and moved an exhaust that was barely contacting a frame, or a rock was allowed to fall out that was jammed against a frame or engine mount.

Or placebo effect - extremely powerful.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[Waldi]

Nothing to do with your observation, but you say leak, did you check oil lvl.

[zuhandenheit]