nk993

I recently got my gearbox rebuilt and it has been a ****ty nightmare since then. In some of my other threads you can see my posts about sloppy shifting and the loud squealing noise on cold start. I had the theory that the input shaft had issues. After fighting with the shop that built it for a couple months (who did not believe me about the symptoms) they eventually got some sound equipment out and agreed with my assessment of an internal gearbox issue and stripped the gearbox for a 2nd time.

They've discovered I was correct. They discovered the sleeve that the input shaft bearing sits on has heat marks on it. The input shaft bearing is fine and is correctly sized. The input shaft itself, however, turned out to have been too small due to bad machining at the factory. It is 2 microns too small, therefore causing the sleeve to spin on the shaft (when it should not be moving at all). This manifests itself with very sloppy shifting when cold and a very loud squealing noise on cold start (see video).

The ****s at Porsche seem to think this is not their fault and that 2 microns is within tolerance. Which is bull**** given the symptoms and the evidence provided. Does anyone have any advice on this and how to handle this? I am honestly getting sick of Porsche ownership when the quality control has been so bad and the support from the company even worse.

Gbos1

.....and why I have an awesome “Independent Mechanic” who knows 993s / Air-cooled 911s extremely well. He re-geared / rebuilt my transmission with zero issues. He built many Porsche Race Cars over the years and is an old Air Cooled Porsche Mechanic back in the day. I would never take my 993 to a Porsche Dealership... never. You need to find yourself a good Indy.

Todynot

You realize a micron is equivalent to .000039"? You have some pretty sophisticated inspection equipment on your hands to be accurately making that assessment.

71-3.0-911

Thats what I was thinking. He probably meant two mils.

nk993

This was an independent. Issue is with Porsche-supplied part.

I didn't make the measurement, they did. I am basing it on what they said on the phone. He definitely didn't mean 2mm, that is huge.

71-3.0-911

A mil isn't a millimeter. I'm guessing this is part of your problem. This may help: A mil is a measurement that equals one-thousandth of an inch, or 0.001 inch. One mil also equals 0.0254 mm (millimeter). Thus a mil is not the same thickness as a millimeter

Here is a breakdown comparison:Mil is a unit of measurement in the English system. 1 Mil is 1/1,000 of an inch or .001

Micron is a unit of measurement in the Metric system. 1 Micron is equal to 1/1,000 of a millimeter.

If you need to convert one to the other, 25.4 Microns equals 1 Mil.

The formula to covert Mils to Microns: (Number of Microns) x 25.4 = Mils So if it’s .75 Mils it’s .75 x 25.4 or 19 Microns.

The formula to covert Microns to Mils: (Number of Microns)/25.4 = Microns So if it’s 12 Microns it’s 12/25.4 or .47 Mils.

nk993

ok regardless, I am using metric, not the weird one. On the phone they said microns, so lets stick to that.

Gbos1

[QUOTE=nk993;17274811]This was an independent. Issue is with Porsche-supplied part.



My bad... yeah seems like that isn’t your problem with the part. Better take a closer look at your Indy and the work that was performed.

nk993

What should I check for? i definitely have my doubts

Gbos1

Honestly no idea not seeing the box apart. I can tell you, my Indy has seen and fixed many F ups regarding gear box rebuilds over his 40+ years working on them.

INTMD8

So the shaft is .000078 in undersized?

I don't think we can just stick to that. As others have mentioned, this isn't adding up.

nk993

Ya it doesnt....

boomboomthump

First, a "mil" can be measured with normal dial calipers. Second, a "micron" does not require sophisticated equipment, just a micrometer that any shop would have in various size ranges if they perform any sort of engine or transmission rebuilds. I'm a hobbyist and have these myself for Harley rebuilds, etc. They can measure within .001 millimeters.


That said, since you say the shaft should not spin in the bearing, is it supposed to be press-fit on there? Something is not adding up here. I have not dabbled in any Porsche gearboxes or motor builds (yet) but the variance noted is not going to influence perceivable "sloppy shifting". Something undersized by a micron or two will not change the "press-fit" status of something (if this should even be press fit so as not to spin). If we're talking 1 to 2 mils (.001", not mm), yes that may change both slip-fit or press-fit mating but again I wouldn't immediately think one could translate that to sloppy shifting.

Hopefully some experts with experience in gear box rebuilds on our cars can chime in but something seems amiss in your video given the problem disappears when you depress the clutch pedal but is present when release, yet trans is in neutral.

nk993

So this is based on my phone convo with the client guy, but what I understood was: The input shaft bearing sits on a sleeve. This sleeve is press fit onto the input shaft. The sleeve is not supposed to spin at all. It is spinning due to the input shaft being too small. I also don't have any experience with a 993 gearbox so I can't really comment on that.

The video did imply something wrong with the input shaft bearing since the problem is not there when the input shaft isnt spinning (clutch depressed).

Agree it does not explain the sloppy shifting. A bent input shaft would have helped explain the sloppy shifting, but they measured that too and it was straight.

IainM

It’s pretty obvious when you press fit an item if it’s loose or not. These guys aren’t calling it straight. Maybe the client guy doesn’t know mechanics but sounds like they’re trying to pass the blame and not redo their work