Syncro Transaxle failed 4th and mainshaft bearings (Pic Heavy

[jberger]

[jberger]

Gears

So these pics are of two different wasted mainshafts, three mainshaft bearings (maybe 4) two 4th gears, 3-4 hubs...

1, My first transaxle rebuild was due to mainshaft bearing migrating forward in bore. You could hear it faintly in top gear against the highway barrier. That was then sleeved and all bearings replaced.

2, My second transaxle rebuild was due to breaking a pinion tooth at SDM in 2011. I have the sound on video.. from shock loading the transaxle. Had I drained the oil I may have saved that box but didn't know about it until a year later when it wouldn't shift. The insides were effed.

3, Other transaxle build, unit stuck in 4th gear. Broken Hub, 4th gear needle cage melted general carnage. Pressed in new main bearing (pressed in very hard) using Proper Loctite cylindrical surface.

4, Other transaxle build, Same unit above, main bearing moved in bore and friend did not care to listen for another 12k miles. Melted 4th gear needle cage, general carnage.

5, Sand blasted 4th gear above returned from Rancho on a client's box.. thrust surface looks good, but has marks from needle bearings in inner race. I measured the marks and the needle bearing last night, none of the surfaces match or make sense. The spacing is too close to be from the contact point of each needle, almost too perfectly spaced to be from two 4th gear vibrating\overheat events...

6, Mainshaft bearing pics above, three show obvious rotational damage (along with 3\4 hub). These were from the melted 4th needle bearing boxes. The one mainshaft bearing that is similar to the ones you are talking about when zoomed in (and I looked under magnifying glass) also show rotational damage. Like it was turned in a lathe.

7, I will look for other pics from when I disassembled these boxes years ago as some of those failed parts are no longer in my shop, to see if 4th\mainshaft bearing contact is visible.

[Sodo]

JBerger, I'd have to say that post is very hard to 'read'. Can you edit post#1 and and put a caption under each pic? I think you'll be hard pressed to get readers without a caption under each pic. Some pics are so similar I can't tell what you want the reader to notice between the pics.

It's too hard to respond.

Great pics though, lots of 'action'! This 'erosion' on the mainshaft bearing race is a very important subject.

Here's a pic I made to __help__ folks understand whats happening at that idler/bearing interface. Most still won't understand it from a pic I think most would have to see the parts (in an opened trans) to understand this problem.

Plz let me know if theres any problem with this image.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[jberger]

Sodo,

Very accurate pic of the 4th gear setup. I definitely do not have the patience to do that. I totally understand your comment on me editing the pics.. however this was meant as a continuation of the off topic discussion in SJ's thread. I did not want to muck up Jael's thread with my pics and these items have been kicking around in my garage for years. I know the dirty 4th gear, one of the main shafts and one of the 3/4 hubs are mine, but the other items have lost their familiar connections in my brain. This is a response to Gears's comments but I do not think he wants to discuss the issue. I have spent quite a few hours yesterday and today reading the Porsche forums (when I should have been doing other things) in order to find the Ah Ha info he has referred to several times. Still searching.

I feel kind of silly because I really don't have a horse in this race. My last build from 2012, mated up to several different custom water boxers is still going strong and I am not nice to this thing. Redline shifts, 5000rpm long pulls in third. Overloaded... The only thing I don't do is cruise at 70mph, unless empty. The only mods I did were welding the main bearing thrust retainer ring to add a bit of crush, omit gasket at LG housing, splash plates, Early type input shaft bearing, sleeved mainshaft bearing and all steel cage needle bearings.

[Sodo]

That erosion is a puzzlement to many. Otherwise someone would post and explain it. I can't yet fathom the heat/metal transfer aspect that Paul/gears has arrived at. It seems like that would happen elsewhere and be a known issue, but it seems to be ONLY in a Syncro transdaxle (?) Why can't Waldi explain it? We need a drivetrain engineer, or a Lubrication engineer.

Consider 3700RPM while in 4th gear. The 4th gear idler is turning 3700RPM = 62 RPSec. There are 50 teeth, so that gear is "singing" at 50x62=3100Hz. Here's 3100Hz.

The geartooth pulsations of 3100Hz is moving the gear like an orbital sander within the slop of the needle bearing and the slop of the mainshaft bearing. Both of which increase over time. At 3700RPM, and HOT, if the oil does not replenish (a theory) the oil boils away at that interface (and is thrown by centrifugal force). Now you have 3100Hz rubbing that dry gear against the bearing like an orbital sander. It could abrade by Fretting (Wikipedia article). Perhaps faster at higher temperatures.

The erosion could be a combination of several different things. Perhaps idling + welding + fretting. One thing is ---- you KNOW that volume of "lost steel" is circulating in your oil causing all sorts of deviltry.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[jberger]

Debris is bad, no doubt.

I have not seen any issues with 4th gear teeth themselves... so oil must be carried up by the driven gear (pinion) and delivered to the mesh point. Even when the needle bearing is melted the teeth are untouched.

[gears]

It isn't that I don't want to discuss the issue, it's just that I'm certain of what I'm seeing. Melted cages are a symptom, not a cause. Steel caged bearing are never a bad idea (I must have sold 1,000 steel caged conversion sets in Porsche world), but they aren't a solution. They are a band-aid, just like splash plates are.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[jberger]

[gears]

The ONLY time a circular wear pattern appears on the eroded surface is when end float has been lost. Any other time, the eroded surface has actually increased the side clearance.

Once you realize that the erosion isn't from the gear spinning against the bearing, you understand that it's the result of heat transfer from gear to bearing race. Ah ha ..
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Howesight]

I accept Gears' theory that heat is the cause and the melted needle cage is a symptom. One of the pics in JBerger's post shows what appears to be false brinelling in the 4th gear idler bore.

That got me thinking. At first blush, it seems impossible that two thrust surfaces rotating at exactly the same speed could not possibly "rub against each other" and therefore, any damage or metal transfer at that thrust interface must have some other cause. Makes sense, right?

But then I thought, maybe those two thrust surfaces are not moving about the same centre of rotation. Is it possible, in addition to the overheated condition of 4th gear idler, that precession and smearing at the thrust surfaces are occurring? My thought on this, looking at JBerger's pics is:

1. the locked 4th idler gear soon expels the trapped gear oil;
2. this is compounded by the gear temp which essentially boils off the small amount of gear oil and gear oil fractions that remain, (almost like a cracking reactor in a refinery);
3. the idler gear ID expands with heat;
4. as a result of the pressure of the gear mesh and the absence of gear oil to fill the needle bearing clearance space, the idler gear is now moving in precession. But, as suggested below, the mainshaft bearing inner race is not moving in precession.
5. To visualize this, think of a Spirograph gear inside a Spirograph geared circle almost the same size. The outer circle represents the idler gear. The inner circle is stationary and represents the mainshaft bore. The 4th gear set is designed and intended to have both the splined gear and the idler gear remain concentric with their respective shafts, but due to factors 1 to 4 above, this does not happen and instead, the idler gear is forced to rotate about the main shaft in a motion that is not concentric. Here's a link to a GIF illustrating the movement I am referring to: https://commons.wikimedia.org/wiki/File:Animation_of_mechanical_precession.gif

6. Meanwhile, the crappy mainshaft bearing is still strong enough to keep the mainshaft itself concentric with the bore that locates it and the bearing remains tight enough, due to lubrication and due to rotating, to remain concentric in its bore.

7. Now what happens is the same as though you held the mainshaft bearing in a fixed position, but rubbed the 4th idler against it axially in an elliptical motion, thus causing the metal smearing and metal transfer.

8. The metal bits oxidize and quickly become even more abrasive in the movement between the mainshaft bearing and the 4th idler and then further add to the heat load.


Here's a link to a bit that the good folks over at SKF have to say about smearing:

http://www.skf.com/cn/en/products/bearings-units-h...index.html

The photos in the SKF article show metal transfer similar in appearance to what JBerger and Gears found in their pics of the thrust surfaces on the idler gears and the mainshaft bearing. The motion between these thrust surfaces is sufficient to cause localized heating sufficient to achieve metal transfer, but possibly not sufficient to distort the entire idler gear or even show the classic overheat bluing, for example, of a crankshaft bearing journal after a failed con rod bearing event.

A method of maintaining the oil film in the idler gear and also cooling it might prevent the events which I posit in 1 -4 above. This seems to suggest gun drilling and pressure lube to the 4th gear idler rollers might be the only long-term solution in this undersized gear train.

Comments, Herman?
_________________
'86 Syncro Westy SVX

[gears]

That's probably a good explanation of what's occurring. The extent of erosion is definitely increased by higher horsepower engines, heavier vehicles, longer high speed freeway drives, and IMO most synthetic gear lubes .. all the same factors that cause higher heat in that area. Whatever the exact mechanics of the wear, I expect it will be cured with the various upgrades. (Herman may very well have already cured it.)

What seems counterintuitive is that the harder material (the bearing) is what's eroding.

I don't believe gun drilling and feeding oil through the needles will be the cure. In fact, packing the gear with loose needles (like we used to do for drag race boxes) might be more productive.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Alaskaberrys]

Wow. We may need to say "pic heavy" and "heavy mental lifting may be required" for those of us whose knowledge of transmisions end at the knob on the end of the stick thingy

[Syncro Jael]

[jberger]

[tjet]

That sucks. I had some concerns on the condition of my original Syncro trans (with 220k miles) before I drove cross-country a few months ago. I was going to install a fill/drain plug plumbing kit from Sodo, but decided to just flush it & refill it with Swepco 201 after talking to Sodo about it.

No issues so far. When I topped it off, I did jack up the front of the van so I could overfill it.

Averaged 65-72 MPH loaded heavy 3300 miles. 28" tires, original 4.86, & driveshaft removed

I'm going to drain it at 6000 miles to check the condition of the lube.

[Sodo]

[tjet]

jberger, do you have a decoupler installed?

[jberger]

[jberger]

[jberger]

Some chat about plain bearings taking over the roll of rollers..

http://machinedesign.com/technologies/plain-bearings-outperform-rolling-element-bearings

Flanged bushing example

https://www.ggbearings.com/en/products/metal-polymer/dp31