nzporsche944s2

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Car was driving normally then very suddenly at about 25mph (40kmh) the forward motion stopped and it sounded like ice cubes in a blender coming from back end. At low rpm and slipping the clutch it was possible to crawl forward without noise but then if the clutch is fully released or the revs rise then the noise starts again. Noise is in all gears. I towed it immediately to my garage and did the following;

Checked CV bolts - they are ok
Jacked car up and disconnected Torque Tube from Transaxle and then started engine - no noises and clutch operates normally.
Drained gearbox oil and strained through a stocking - absolutely no metal at all and very clean oil (I changed it about 6,000 miles ago). I was expecting fragments and shavings but...nothing
With the back of the car jacked up the diff seems to be operating normally by hand - rotation of one wheel turns the opposite wheel the other direction (this is a non LSD gearbox)

Tomorrow I will pull off the CV joint and open the inspection panel on the side of the gearbox to look at the pinion gear and ring.

Is there anything I am missing?

Would a bad CV cause similar noise and lack of forward motion? What is the easiest way to diagnose it?

mikemyers924s

The situation you first described sounds exactly like a ring and pinion failure. There are a couple other threads on this that describe the exact same thing, I will try to find them and post the link for you. I don't think a bad CV would cause the symptoms you described.

nzporsche944s2

Thanks Mike for the reply - i did do some fairly thorough searching on this forum and it threw up a lot of info. The part that threw me is that there are no shavings at all. The oil is as clean as the day it went in.
Opening the side panel tonight should determine if it's the ring gear.

Makis

I would say catastrophic failure of pinion gear will leave metal bits in the oil and you will be able to see them when you remove the oil. On the S2 pinion gear is quite reliable so you may be lucky is not that. I would recheck the CV. Also lift the rear and rotate the wheels to see if everything is working as it should.

harrisonrick

If the r & p failed, you should see chunks in there. BUT, don't forget on the side panel there is a magnet that may have caught some smaller pieces of the pinion gear, and you'll find out when you open the side. When my r & p was whining, there were no metal pieces in the oil...just those stuck to the magnet on the side panel. Of course, there was a 1 inch hunk rolling between the r & p causing the noise.

2nd guess is a CV joint has failed and its grinding together. Do they have up/down play? They should have side-to-side play, but NOT up/down.

Good luck.

whalebird

Check the axle stub shaft on the wheel side of the axle. Rule out a wheel bearing/stub axle failure before pulling the diff housing. I too would expect to see metal in the fluid.
I hope it's external of the trans. You'll be on the road in no time.

tifosiman

I agree that it sounds like an R&P failure. Although the S2 R&P is stronger than the N/A R&P it does happen sometimes.

I am surprised that there aren't shavings in the oil but it is possible you broke off a couple of big chunks of the ring and they haven't been ground up into little shavings that made it down to the drain hole. Although I would expect at least a few of the small shavings.

I know you spun the wheels while it was up on jacks, but did you spin them completely thru a few revolutions? Generally you'll be able to get crunchiness and skippage if you do that with a busted R&P.

mikemyers924s

I'm fairly confident we can rule out CV joints because you wouldn't have been able to drive the car at all (like seriously it wouldn't move at all) if you had sheared the bolts or broken the joint itself, but it wouldn't take your more than two minutes to double check both sides and make sure they aren't sheared or broken. That would be nice as it's a relatively easy fix.
I think we can rule out clutch failure because you got the car to move a bit.
If it's not CV's and it's not clutch it's somewhere in between and we all know where that is.
Have you gotten around to pulling off the inspection plate yet? What you see in there should confirm or unconfirm our suspicions. Don't forget that magnet that may have collected some broken metal shavings/chunks.

nzporsche944s2

Thanks all for your replies and suggestions - here is where it gets stranger....

Last night I checked all CV joints for any up-down movement. None at all - they are very tight.
I took off the inspection plate and the ring and pinion gear are perfect. No visible wear on any of the spider gears or ring or pinion. Definitely not the catastrophic failure I was expecting. The magnet inside the plate had some very, very fine metal fuzz on it but I would think nothing more than general wear.

So I have now removed the gearbox and I am pondering my next move.

I still strongly suspect some sort of gearbox failure. When the car was making the initial noises you could see the flanged shafts that connect to the inner CV joints 'trying' to move while the "ice cubes in a blender" noise was going on.

I'll study the porsche manual and see how easy it is to do some exploratory disassembly. Has anyone here pulled the end cover off the gearbox "just to have a look". Anything to watch out for? e.g springloaded things?

lovemyp-car

honestly that sounds extraordinarily similar to when i had a cv bearing cage shred. Since you have pulled the transaxle i'd assume that you would have seen something along those lines if that were the case...but when my axle first blew the car would move a bit, then the rest of the axle got all chopped up and the thing would not move...when i rolled the car forward or put the car in gear and released the clutch it would make the most horrific sound (ice cubes in a blender fits it perfectly). I also drained the fluid, and it was very clean.

Question: does your car have a limited slip differential? If it does, is it possible that one of your axles exploded, and your lsd clutches are slipping a bit, giving you some forward motion, but not a normal amount?

good luck!

nzporsche944s2

lovemyp-car - thanks for that. I don't have an LSD ( I was hoping I might as I don't have the option codes sticker in the car but alas no limited slip diff).

Good suggestion though.

harrisonrick

ahhh.


Could be the differential carrier bearings are toasted, and grinding.

Lemming

Interesting and confusing as it originally sounded like R&P. Have you ruled out that it is not the clutch and that you were in limp mode? You state that when you disconnect the TT from the transaxle everything is fine, but there is also no load on the clutch. Just an thought before tearing into you gears.

harrisonrick

...ooh, Lemming has a very good point. We might be looking in the wrong place.

Yet another possibility.

nzporsche944s2

Lemming / Harrisonrick - yes that thought had occurred to me but head under the back of the car with my hand on the gearbox while it was making the noise - the vibration and grinding felt like it was right under the palm of my hand. If it were the clutch then that vibration would have to be transferring down the TT (and the noise too). It is possible and I can't rule it out.

I did take out the clutch inspection bung and feel around for rubber debris but nothing. If the rubber centre had collapsed then wouldn't there be a clonking noise as it comes on and off the 3 dog tabs?

From here I will probably give the gearbox to a reputable Porsche shop to have them inspect the internals and at the very least reseal it (it had a very minor weep from the front input seal and another at the gasket between the cast iron housing and the rear aluminium casting.

I'm still lost a bit becasue there isn't the 'smoking gun' that would have made the diagnosis so much easier...

Thanks for all your suggestions so far...keep them coming