Hmm, 84 944 NA manual tranny experts?

[IdahoDoug]

So since I got this car, the tranny has made a noise on coast in 1st and 2nd gear easily heard and less so in other gears. I've never owned a 944 and its such a small car and with little sound insulation I was not sure if it was normal or not. It only has 60k on it and has been well treated.

I've put about 1500 miles on it and the noise seems to be increasing. I checked the level of the fresh Mobil 1 gear oil at about 1000 miles and yesterday I made a cork to fit and pulled the drain plug. No ferrous metal on the magnet, but I can see the oil contains enough gold sparkles I can tell something's amiss.

The only brass or bronze in the tranny are the synchronizer rings, which are in good shape operationally. No gear grinding, or other issues. So they do their job well.

What I'm suspecting is the sound I hear is the main or pinion bearings allowing the pinion shaft to shift forward and rearward with gas on/gas off. I suspect this misalignment is allowing the pinion shaft gears to nibble on the edge of the bronze synchronizers.

In research, this is supposed to be a stout tranny and I find nothing about an issue of this nature. Anybody have input on it, or know someone with strong knowledge I could call? Thanks in advance.

[Dimi 944]

It sounds as your back lash is out of spec. It happens due to worn out diff carrier bearings and pinion shaft bearings.

The transmission is more than likely due for a complete service.

Dimi P
Flying Horse Motorsport LLC
flyinghorsemotorsport@gmail.com

[IdahoDoug]

Dimi,

So what is the mechanism that is generating the brass glitter in the oil? When I got it 1500 miles ago, I pulled the tranny for a clutch and drained it for several weeks while I did the work. So when I refilled it with clean oil there would be small amounts of glitter, yes - but there is enough in the oil to show it is still generating brass filings and I'm NOT speed shifting and grinding gears.

What do you think is generating the brass?

[Dimi 944]

The only brass inside the transmission are the synchros.

Dimi P
Flying Horse Motorsport LLC
flyinghorsemotorsport@gmail.com

[IdahoDoug]

Yes, I know but thanks for confirming. So I will be doing this myself and I'm seeking understanding how a worn bearing is causing a synchro (which is activated/used only during a shift) to grind against something. I looked at diagrams of the synchros and they're buried inside the gear cluster between the gears and the hub, so I can't see anything hitting them. The only thing I can see is if there is longitudinal pressure along the main shaft or the pinion shaft that mashes the hub/synchro/gear together.

I'm asking because I'll be doing this myself and have also successfully done a very similar transaxle - a 1987 Vanagon Syncro (4WD) transaxle. It's problem was a similar sound but the loose pinion bearing and mainshaft bearing were allowing 4th gear/trans case contact. Since that was a known issue, I was able to order the parts in advance and open it up ready to go to work. I'm hoping to do the same here. So, if you can shed any light on what the mechanism that's causing accelerated bronze wear is, I'll use that knowledge to order the parts to correct it. Thanks!

What do you think?

[kdjones2000]

My money is on the differential carrier bearings being noisy.

Synchros are normal wear, I'll bet.

This is a hypoid type differential, and they are known to be a bit noisy. Probably doesn't explain your on/off behaviour, however.

Make sure to read the shop manual on setting preload and lash with the shims and such.

[djnolan]

I am sure Dimi knowas what he is talking about, but if you send an oil sample in for an oil analysis and they will be able to tell you if the wear is normal or not or to the point of no return. While you are at it send in an engine oil sample, too. You would be surprised at how much it can tell you.

[jcommin]

Catellus Engineering - Kevin Gross

Catellus Engineering, Inc.

[thomasryan]

the oil needs to be compatible with yellow metals AND hypoid type ring and pinions. Porsche has a list of compatible fluids but i cant find the screenshot.

901 and 915 transaxles are actually quite noisy with syncro rattle thus came the G50.

[IdahoDoug]

So, I'd really like to know if anybody knows why the trans is producing brass glitter. The gear oil is compatible, though I appreciate the input.

The diff bearings will get replaced, but that's not putting any pressure on the synchros. Any thoughts here? I put experts in the thread title for a reason - this is a technically daunting question. Thanks in advance.

Doug

[thomasryan]

The factory recommended lubrication.

I like the PTX especially during the cooler months.

[IdahoDoug]

Thanks, Thomas - I appreciate the input on the lubes. Mine is safe with yellow metals according to a guy who has decades of Porsche gear manufacturing and design. The fines in the oil would not be a symptom of yellow metal incompatibility. Thank you for running it down.

So, Dimi - I'd love to understand the mechanical mechanism why the synchros are experiencing stress in this transaxle. Any input on that? Thanks in advance.

[kevingross]

When warm, 944-series transmissions can make a sounds like chains dragging on a grate at low RPMs. Best theory is that it's the reverse gear idler, but I have also seen wear from fifth gear against the end plate (steel center section) due to undersized shim under the gear. It is nothing to worry about. I replace the reverse idler springs when rebuilding, and frequently find the fifth gear shim needs to go up a size.

The gold flakes in your fluid are probably unrelated -- probably but not definitely. As others have pointed out, the only bronze parts in the transmission are the synchros. Heavily worn or broken synchros can shed flakes, and you likely have that happening to you. How many miles on the transmission?

[IdahoDoug]

Kevin,

Thanks for chiming in. So it's got 59,000 well cared for miles on the entire vehicle. I got it about 1500 miles ago and drained good looking oil out of it and refilled. It makes the noise when the engine is slowing the vehicle or accelerating and it sounds like a metal box full of marbles. I can easily press slightly on the gas to give a "neutral torque" on the transaxle and its silent. Maximum sound is high RPM such as 3000rpm in 1st and you let off the gas to coast down with engine braking. Its not as loud on the accelerating side of the gears, as it is on the coasting/engine braking. As vehicle speed rises I can't really tell if I hear it in all gears, but I suspect so. Wind and road noise rise up so it's hard to be certain.

On the syncros, they work fine and there is no oddness in shifting whatsoever except for normal slight stiffness when the gear box is cold that changes to beautiful fluid shifts when its warm.

You are correct that there is no/little sound when its cold such as heading out from the 75 degree garage and the first few miles don't make this noise. The warmer the gearbox the more noise it makes, so if I come back from a few errands from around town I hear it in my neighborhood, but I don't hear it outbound with a cold car. I don't remember hearing it this winter (temps in the 30s) when I drove it around a bit. Seemed to appear with warmer weather.

On the theory that you'll assuage my concerns with your knowledge of some traditional sounds this box is known for (I have crazy acute hearing), and the further theory that the noise is in fact wear - how thick of an oil might I put in it as an experiment? If the hot/thinner oil can be helping cause the noise, I'm not opposed to a thicker summer oil as it will live in the garage all winter..

[IdahoDoug]

FYI, I drove it today specifically to confirm there is absolutely zero abnormal noise when the trans oil is cold (ambient 80 today). After about 15 mins of driving around town I can hear it.