Do these sypmtoms sound like Ring and Pinion failure?

[nzporsche944s2]

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?

[John_AZ]

No metal slivers?? Interesting. There is a magnetic plate attached to the inspection plate that may have caught a few slivers.

Remove the bolts to the transaxle to torque tube coupler.
Get a very expensive metric hex to avoid damaging the 2 hex bolts.

Slide the coupler to the rear.

Start the car and listen......If the noise is gone....your assumption is correct.

GL
John

[Rasta Monsta]

This is what my 914 did when a CV exploded.

[nzporsche944s2]

Thanks for the replies

John_AZ - that procedure you described is exactly what I did and there is no noise but...if it was a CV causing the problem then disconnecting the coupler would have exactly the same result wouldn't it?

Rasta Monsta - how did you diagnose the wrecked CV. Do I have to remove all four and physically inspect or is there a general check first? From the outside they look good. Boots intact and no grease leaks. I had heard that if you can "stir" them then they are bad. They should have in-out movement in the gearbox to hub direction but no lateral movement. Does this sound right?

[Rasta Monsta]

They should move in and out, but have zero rotational play.

My diagnosis: I put the car in gear and let the clutch out. The car did not move. I then got out and looked under the arse end of the car. One axle was spinning! That ain't right! D'OH!

[John_AZ]

Originally Posted by nzporsche944s2

Thanks for the replies

John_AZ - that procedure you described is exactly what I did and there is no noise but...if it was a CV causing the problem then disconnecting the coupler would have exactly the same result wouldn't it?

Yes.

Follow Rastas info and then proceed to remove the inspection plate if not CVs.

GL
John

[Rasta Monsta]

P.S. If an outer broke, an axle will be turning. If an inner broke, a flange at the trans will be turning. This test should be done with WHEELS CHOCKED and HANDBRAKE PULLED!

[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?

[Kiwi944s2]

Having had some experience with having a gearbox rebuilt i would not advise disassembling it yourself. My mechanic could not rebuild it and had to send it out to a specialist who then cocked it up and put too many shims in it. My advice would be to take it to Peter Booth at Motorscience in Grey Lynn what he doesn't know is not worth knowing.

[nzporsche944s2]

Kiwi944S2 - I'm glad you popped up as I remember you had yours rebuilt but I couldn't find your contact details! If I remember correctly yours cost around NZD$8,000 all up is that right?
Of that do you know how much of that was Motorscience's bill? (given that I now have the gearbox out)

[matthewb]

If you are pretty confident that something is destroyed in there (and it sounds like you are) then why pay someone else to take it apart. Pull the bolts between the bell section and the cast iron section and see what's in there. It should come right apart and you will be able to see 1-4 and reverse in there.

Go for it.

[Kiwi944s2]

Unfortuneately Motorscience didn't rebuild my gearbox i now wish they had as they know so much about them.

However the pin that connects the gearshift rods to the gearbox disintegrated the week before xmas and i sent the car to Motorscience to repair ($1,000 in towing fees as the car was in Pauanui) They dropped the box pulled apart and fixed, then pulled it apart a second time to find a ticking noise and the bill including a couple of CV boots was $2,300. What impressed me is they know these cars like the back of their hands and they build 911 and 944 race cars.

They are cheaper than Contis and Giltrap and did not charge me for every minute.

[nzporsche944s2]

Update
I dropped the gearbox off for checking at Motorscience but at the same time i decided to keep going and check the clutch out. I had a nagging doubt that it may be the clutch and if it wasn't then at the very least I could replace the rear main seal and any other worn parts. What the hey I was half way there anyway....

So finally tonight we got the clutch out and there it was clear as day catastrophic rubber centred clutch failure!
This was a little odd because the symptoms didn't exactly match other clutch failures posted here in the forums. What I can see now is that entire second layer of the rubber disc furthest from the plate had disintegrated. This gave the centre of the clutch so much movement that the 3 metal dogs couldn't do their job properly and were slipping inder the tabs under power and load. This was giving the "ice cube in a blender" sound!

In a way I'm relieved because at least I can quantify the problem now and start ordering the parts. Up until now it was an unknown.

Over the next few days I'll take the flywheel off and and get to the rear main seal and start getting my order together.

I'll post a pic of the car-nage tomorrow.

Thanks for all your help along my journey....

[shinrai]

The same thing happened to me a few years back. No motion fwd or reverse. I too thought it was R&P failure. The problem occurred under hard acceleration. Here's some pics:

[ERAU944]

That's what I expected and would have been my first try, having a peek in the clutch inspection hole.

I had lots of drivetrain lash and difficulty shifting in my '84 for about a month (yes, I drove on the limp-home tabs for a MONTH)! FWIW I also suspected R&P issues first... Hindsight is 20/20!

I'm glad you found the problem!

[nzporsche944s2]

Pic as promised - very similar to yours shinrai. And that tab sliding under the tag - exactly what I had!