Found my 915 noise source, lots of questions

[Peter Zimmermann]

Originally Posted by yelcab1

Thanks Pete

How about a dissambly sequence for the transaxle. Anything specific to keep in mind so that it all comes back with the same backlash and shim pack ?

Many years ago, I had a shop replace a cracked transaxle housing on a different 915, it broke 3 times after that. My guess is they never did the shim pack right. I don't want that for this time.

All that you have to do is:

1. Remove both diff carrier bearing races (mark them somehow if you're going to re-use them),
2. Remove the side cover o-ring,
3. Remove both axle flange seals (housing & cover),
4. Remove the TOB guide tube,
5. Remove the M/S bearing outer race,
6. Remove all of the clutch release parts (shaft, fork, etc.) but don't remove the black, plastic tube.

No need to send the old P/S bearing race, all that EMS needs is the race for the new bearing. Do not remove the clamping plate studs.

That's about it. Put your pinion depth shims together and secure them with a ty-rap. Do not remove the diff carrier bearings unless you're going to replace them. If you replace them do one at a time so you can't mix up the pre-load shims, and be prepared to check/set bearing pre-load when you're ready for assembly.

[yelcab1]

Originally Posted by Peter Zimmermann

Regarding your gears, a camera just can't replace eyes. If there is any tooth root wear (through the hardened surface, usually found on the smaller gear of each gear set) that gear set is a throw-away. .

Peter, how can I tell if the gears have worn through the hardened surface? Is it polished, or rough? does it have wear patterns? Does it ???

[Matt Monson]

Originally Posted by yelcab1

Peter, how can I tell if the gears have worn through the hardened surface? Is it polished, or rough? does it have wear patterns? Does it ???

You will generally see pitting. If it's really bad the pits start to connect into a straight line. It's most commonly down near the root of the tooth on the running surface. You need to look at every tooth on every gear in addition to the ring and pinion. Sometimes it will only be on a single tooth, but if a single tooth breaks off, it will still usually do catastrophic damage.

Also, regarding your case issues, we've developed another methodology of repairing it other than the shim method. We use oversize bearing races. We take the case and machine it round (it is currently out of round, which is why it hangs at some points and is loose at others when you spin the race). Then we install the oversize bearing race and it's as good as new.

Bearing plates like Guard sells are only good as a preventative. There's a number of shops that will tell you it's a fix for the case bearing problem. It is not. It can reduce the wear and tear and prevent the problem from happening, but once it's happened it's too late. I only mention this because while it hasn't been said in this thread, if you start making phone calls, certain shops will try to sell you the plate as a fix and convince you to peen the case or loctite it, along with the plate. That's a bad idea.

[Peter Zimmermann]

Good info from Matt. My top pic shows the beginning of root wear/tooth failure on the bottom/middle tooth. The middle picture shows extreme wear, and the lower picture (poor) shows the flash hitting and bouncing off of root wear. Think of root wear as a cavity in one of your teeth - it starts small, then turns ugly.

[yelcab1]

Peter

Sorry for being dense, you mean the fuzziness in the circle? that is root wear? Or the little pits all over the surface of the gear tooth?

[Peter Zimmermann]

I'm not able to draw circles/arrows, etc. on pictures but here are a couple of new pics... hopefully they will show you what you need to know!

[Peter Zimmermann]

oops! Hit the wrong button... here's one more.

[yelcab1]

Thanks, got it. I don't have any of that, thank God. The only wear that looks like that is at the roller bearing on the main shaft. The hard to see picture at the very top of this post shows that. And then the idler shaft. They are both junk.

Your pictures of the second gear set look like they have been through acid.

[Mahler9th]

Nice pictures. Street car or race car or in between? Looks like you are on the right track. I have a clutch disk if you still need one, and a need to visit RWC/San Carlos area this week.

If you need to do something about the main case or final drive housing in terms of machining, perhaps WEVO have what you need. I bought their main case a few years ago. I also have their shifter and coupler and retaining plate. They make excellent products and also do exceptional work. Cannot recommend them highly enough.

[yelcab1]

Mike, I have a clutch disc coming, so thank you.

I talked to Wevo and they charge $1000 for the case reinforcement. That is a little more than I want to spend for this weekend toy. I drive it hard but I don't race it or anything.

[Joe Bob]

Case reinforcement? Is that the bearing shell removal and pressing in a sleeve? I think I paid $300 with Aase.

[coollx]

Matt said,

Also, regarding your case issues, we've developed another methodology of repairing it other than the shim method. We use oversize bearing races. We take the case and machine it round (it is currently out of round, which is why it hangs at some points and is loose at others when you spin the race). Then we install the oversize bearing race and it's as good as new.

I had looked into having oversize bearing races made but it's very specialized machining and is cost prohibitive.

Just wondering Matt where you found oversize bearing races? Are they from a specific application and, if so, which one?

Thanks

[Peter Zimmermann]

Originally Posted by yelcab1

Your pictures of the second gear set look like they have been through acid.

From a 3.2 Carrera with about 200K miles. The trans had been opened, I have a hunch more than once, and a real doofus had done some horrible things in there. That said, it's one of the worst gears I've ever seen that didn't break.

[Matt Monson]

Originally Posted by coollx

Matt said,



I had looked into having oversize bearing races made but it's very specialized machining and is cost prohibitive.

Just wondering Matt where you found oversize bearing races? Are they from a specific application and, if so, which one?

Thanks

I know that you guys hate these words but it's a "trade secret". My builder, who used to be PHII's builder, came up with this solution about 10 years ago. He's always been very hush hush about it and won't let me tell the exact details of how we do it.

But I'm working on him and he seems to be wearing down. I might be cleared to talk about it pretty shortly. I'm trying to convince him that the community will be better served by more people knowing how to make this repair using what we consider a better way than the shim method. It's not always about making money. However it does require some specialized equipment to do it, and we do the whole process in house. We've got our own CNC mill, among other things.

I do sincerely apologize for not being able to spill the beans. I try to keep business clear of my posts here and just participate on technical aspects. I almost didn't say anything at all, but thought the OP would be better served by knowing all options and since it doesn't compete with Wayne's business I felt it was ok to say something.

[yelcab1]

Originally Posted by mikez

Case reinforcement? Is that the bearing shell removal and pressing in a sleeve? I think I paid $300 with Aase.

Aase brothers are out of the bidness (so the song goes).

[coollx]

Matt,

In my mind, using a race with an oversized O/D makes a bit more sense than inserting a shim/sleeve if for no other reason than it doesn't reduce the amount of remaining aluminum casting between the input & pinion shaft bearings as much. Plus, pressing one thin metal shim inside another just doesn't seem like its a permanent solution...maybe I'm wrong.

Based on the research I've done thus far, it's probably fairly safe to assume your builder is not making the races or having them made. They are probably from another existing automotive application.

Perhaps some day soon you'll get the green light to share the "trade secret."

Thanks for your response.

[Fishcop]

Matt, at the risk of taking you somewhere you don't want to go .... but my guess would be that a plating technique is used to enlarge the outside only dimension of the bearing race (hard chrome?) as the size increase needed is minimal. But as you suggest the, specialist machining required to bring the case back to round would not be for the average home machinist!

Cheers

[Porsche_monkey]

I don't think hard chroming can build up 0.002" evenly. A few tenths is the limit I think. Beyond that you would need to go oversize and then grind it.

And there is no guarantee that the bore is round, it likely isn't, so it still needs to be machined...

[sc_rufctr]

I have read in other threads about hard chroming the OEM race to make it slightly bigger... (temporary fix at best IMO)

To be honest I'm a bit dubious about all fixes except for the WEVO option.

After all the main reason (but not the only one) the PS shaft bearing becomes shagged out is because of the amount
of material between the PS and input shaft bearings.

Porsche fixed the problem by installing a smaller bearing on the input shaft...
Result = More alloy between the two bearings which fixes the problem. (credit to Peter Z about this subject in many different posts)

So what we need is for someone to develop a solution the mimics the Porsche solution... And that already exists ~ The WEVO option
But could it be done at a more reasonable price?

A suggestion for a permanent fix...
1. Machine and install a steel reinforcing ring on the PS shaft bearing. (most recommended fix)
2. Machine and weld in an alloy ring in the "input shaft bearing area that fits the smaller bearing from the later 915.

Funny thing is it starting to sounds like a lesser version of the WEVO fix.

Something to consider which hasn't been mentioned is the tendency of the lower five studs that hold the PS bearings
retaining plate to become slightly loose. These studs are constantly submerged in tranny oil and the locking compounds
Porsche used 20+ years ago are not the same as the ones available to us today.

I would check all 9 studs before rebuilding the trans.

It's easy to do... Lock two nuts on the lowest stud and check how much force it takes to rotate that stud... Lock two nuts on the upper most stud and compare the two.

If they are loose... Re secure them. Remove studs, Clean the stud hole and stud with acrylic thinners,
Reinstall the the studs using "Loktite Red" to re secure (apologies for being obvious in advance)

[Fishcop]

Just puttin' in out there