cds72911

Hi All,

I've got a pretty serious grinding sound on my 3 -> 2 downshift, while driving.

The higher the RPM, the more it grinds. It does not grind upshifting 1 -> 2. It does not grind in any other shift up or down while driving. The car shifts cleanly in all gears when running, parked, not driving. It does not "pop out" of second gear.

I assume it is my second gear synchro going out, but I want to make sure I'm not missing something more obvious.

Some background:

• The car is new to me, and I'm just getting it on the road, so I don't know if this is new behavior or not.
• When I had the engine out last month, I drained and replaced the fluid with exactly 2.7 liters of Motul 300 75w90.
• There was no indication of metal bits, flakes, or glitter in the gear oil that I drained out (neither steel nor brass).
• I upgraded motor mounts (Function First) and transmission mount (Rennline) last month.
• I put a Numeric shifter in the car, but am using original stock cables, installed at the same position that I marked upon removal.
• I have a new clutch/flywheel/pressure plate, arm, pivot, inout seal, etc. in the car.
• I flushed/bled the clutch line, and there isn't any air in the system.

To reiterate, other than this one symptom, the car shifts great up and down in all gears, and up into 2nd fine.

The kinds of things I think I need to consider based on reading RL and googling:

• Motor mounts/transmission mount
• Shifter alignment
• Fluid level
• Clutch bleeding
• Worn synchro
• Bent shift fork

Motor and transmission mounts are brand new, so I don't suspect them at all.

The Numeric "seems" aligned right, but I don't have any way to measure it. It is easy enough to adjust if it might help. Moving in the same direction, the 3 -> 4 shift doesn't have any issues, so I am not sure it makes sense to mess with it.

I don't know if I should add more gear oil - I put in exactly 2.7 liters, but the way the factory manual is written, it seems like there may be an additional step to ensure it is filled correctly. I've got .3 liters of fluid that I can do this with. Anybody done this and seen a difference in the shifting (especially 1 -> 2)?

With it not popping out of gear, I don't suspect the bent shift fork, but only a teardown would really tell me for sure.

If it does end up being a synchro, any tips, tricks, advice, links, etc. for that project? I've torn down and rebuilt transmissions in the past on other cars (VWs), so I'm not especially scared of the work (not excited about it, but not dreading it). Any other things to fix while I have it apart?

Thanks in advance.

strathconaman

I have heard that synthetic non-porsche 75w90 is too slippery for the synchros. The easy (if not inexpensive) option is to re-fill the case with Porsche 75w90.

B-ran

I had the same problem. Shifts were all good except downshifting to 2nd. According internet experts my synchro for 2nd was shot. Drained and replaced the trans fluid and I freaked out because it was still grinding. After a few drives the grinding stopped. It's been a year and twenty thousand miles since and no grinding gear changes whatsoever, so I would assume the synchros being shot idea was rather incorrect.

gnat

Our 01's synchro was bald when we rebuilt our transmission. Not knowing anything about transmissions I didn't see the problem because it was so uniformly smooth, until he grabbed the new one to show me side by side

It did not exhibit what is described here. There wasn't really grinding unless you let the clutch out too early, just hard to get it into 2nd. It was also going up, not down (could have been some going down, but not enough to make an impression). It was the worst when the car was cold and after a mile or 2 it would become much easier though still nothing like the rest of the gears.

My suggestions would be to check the cables. There is one that likes to pop out of it's clip and makes shifting a challenge (forget which are the common gears).

I'd also suggest going back to the factory shifter or at least have someone verify the Numeric is installed and adjusted correctly.

As already mentioned, changing the fluid (and using the Porsche oil) is another good step.

Doubt the mounts have anything to do with it. I've never heard of any shifting issues due to bad mounts anyway. Ours were terrible when we changed them and it had no effect on shifting.

cds72911

Thanks all.

I visually verified that the lower end of the cables are in place (I have them safety wired and it was intact).

The Numeric is definitely installed correctly and functions well, but I can can easily mess with the adjustment of the cable ends to see if it has any impact. I kept the center console out until I get this all dialed in, so it is all readily accessible. The top ends are firmly in their spots, no popping out. The ends are firmly attached to the shifter (the numeric replaces that little black plastic retention pip on the left side one with a washer and screw).

I'll verify the fluid level since that is easy. But it sounds like Porsche gear oil is in my future. That'll teach me to try to save a buck.

Thanks again.

dporto

I've got Liqui-Moly 75w-90 (Not Porsche, but I'm pretty sure it is Porsche certified) in mine, and it shifts perfectly... Gear oil too slippery? Hmmm... sounds weird to me.

rockhouse66

I disagree. I think the synthetic is an issue in this case.

Ahsai

Yes, our transmission is famous of being picky on oil.
OP, have you checked the magnet inside the transmission drain hole (use your pinky).
I suggest you fill it with genuine fluid until the oil drips out of the fill hole (with the trans being level). Should be ~2.7L. If that doesn't solve the problem, you can drain the oil and reuse it after transmission rebuild.

Triple Black

I had the exact same issue recently. All shifts were fine except for the 3 to 2 downshift at higher revs. Even in normal around town driving it was fine, but I don't do much of that. I chalked it up to abuse - lots of downshifting at higher revs really makes the synchro work hard. I had my indie open it up - not only was the synchro worn, but so were most of the gears. So, after a big repair bill, I now have a gearbox with mostly new gears and it works flawlessly. I also got him to put in a limited slip diff at the same time - you know, while you're in there

cds72911

And that is precisely what I’m concerned about.

Schnell Gelb

Until the O.P. is sure the correct Porsche gearbox oil (made by Shell) is used and to level, other options are moot.
We've discussed the gearbox lube issue and no, sadly there is no alternative to the correct Porsche dealer supplied lube.
Lots in Search "Markus"

cds72911

Thank you.

I don't believe have a magnet in my early transmission (in my research, my understanding is that the magnet came in later evolutions of the transmission).

However, there were no materials in the old fluid that I drained. I put in a later model magnetic plug, and there are no materials on the magnet.

Exactly 2.7 liters didn't bring me to the point where the oil dripped out, so perhaps I'll just try to top it off to see if that matters.

I'm hopeful but not optimistic. I'm running out of driving season, so this may end up being done in the spring. I need to drive it it recreate the behavior.

Thanks!

cds72911

Yup, all options point to this as a likely culprit. I'm going to try topping it off with the Motul, and if I get more driving weather, try that before draining and refilling with the good Porsche labelled stuff.

You say "to level" - what is your technique - fill until it starts to drip out the fill hole?

rockhouse66

Personally, I wouldn't obsess over the oil level. Unlike an engine that relies on oil level to keep the pump pickup submerged, the transmission just churns the stuff around. Close to full is fine IMO.

I suspect others here will strongly disagree but think about it.

cds72911