Syncro Transaxle failed 4th and mainshaft bearings (Pic Heavy

[tjet]

Doesn't Hyundai use plain bearings in their throwaway transmissions?

I'm not sure how long they would last without some oil pressure to float the shaft & remove heat.

[gears]

Howsight, I owe you. Thanks for taking the time to research that. You join a list of Samba guys (recently including Sodo and Waldi) who have helped me reach another ah ha moment (as usual, laying in bed in the middle of the night).

When VW bean counters removed a couple thrust washers in the transmission in order to save $2, they did us no favors. 1st gear thrust washer was removed, and then 4th gear thrust washer.

With a helical gear (as compared to a straight-cut spur gear), the idler is always fighting between staying in design mesh with the fixed gear, and cocking as contact moves from one side of the tooth to the other. If both gears halves were fixed on the shaft, this wouldn't be an issue .. but because the idler must be free floating on the shaft in an automotive transmission, it needs to run on needle bearings (or a bushing) and this requires clearance.

In drag racing, I was always amazed at the cocked wear on 1st gear idler, even though we ran on hand-packed loose needles, with as little bore clearance as we dared. The idler teeth were ALWAYS worn dramatically on one side, while barely contacting on the other.

With our 4th gears having such a small diameter thrust surface, the greater the bore clearance, the higher degree of cocking we'll see. It's a quandary, because bore clearance is required.

Anyhow, this seems the only explanation that accepts both my observation that the wear in question isn't the result of spinning action, and Waldi's insistence that not enough heat exists to cause damage to the gear. My mind was in a rut because of the extreme heat we'd see in Porsche racing, in which 300*+ oil temperature is the norm, and long gear life is anything greater than 30 hours.

So, will this new thrust washer help? I don't know. I think it will help a little .. but because it isn't fixed to the shaft, it isn't the perfect answer. I think erosion of the bearing will be reduced, but it won't be an absolute cure.

So, does this make cooling of 4th gear a wasted exercise? No, not at all. We're still removing heat from the second greatest heat source in the transaxle. Both Sodo and David Hines have reported a small spike in oil temperature when the pump is activated (followed of course by temperature reduction). So even though most guys aren't oiling the all-important pinion bearing, they're still cooling the oil and filtering out damaging particles that cause accelerated wear.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[gears]

It's funny you should bring that up, JB. That was another realization I had last night. That's where a gun-drilled mainshaft would be necessary. We had actually contemplated running ultra-low 3rd gears directly on the shaft with no bearing or bushing at all, as this has been done successfully before. Even the splitcase VW transaxle ran on cross-grooved bronze bushings, so it's far from a silly idea.

I'm going back to bed now ;^)
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Rjhdog]

[Sodo]

I have a hard time with 65mph, I like 70-74 mph. I wonder if there could be a resonance condition that occurs over 65..... and if you stay under 65mph your 4th gear/bearing/end-of-mainshaft area doesn't resonate. This phenomenon HAS to "show up" acoustically! I think we need to "listen" to this trans.

[Syncro Jael]

[Rjhdog]

[gears]

From what I learned in a conversation yesterday, I'll back off from my previous stance on moly oils. That said, another oil guy told us last year that he's seen inconsistency in Swepco products lately. I was referred to even another oil guy who I'll be talking to next week. I think I'll soon have a new oil recommendation for our vans.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Sodo]

I don't think THIS is an oil brand issue. Its too violent. Theres no oil in the world that can allow this kind of erosion while at the same time, lubricating satisfactorily on the rest of this (undersized) transmission.

Consequently, with such a condition you'd want the best oil, and cleanliness too. But oil isn't going to solve it. Is the best oil even 2% better than good oil? 1%? 5%? How many percent CAN you get from better oil? I bet....you get a LOT more from cool oil than from the best HOT oil. Its simply thicker.

This looks like a resonant condition between the elements of 4th gear and the mainshaft and the nearby bearings, housings. And heat makes it worse. I am repeating this in hopes of getting the attention of a drivetrain or lubrication engineer. But agreed you can't just conjure a good one up like a witch (for example).

I'd like to hear from some transmission builders wrt the conditions
---->when this erosion on the MS inner race is found. I understand this can be difficult as most trannies are trashed by the time this is unearthed. And have run thousands of miles in a horrible grinding metal soup.

1) 2wd or "4wd only"?
2) what ratios?
3) what engines?
4) is an eroded MS bearing ever in good shape (smooth rolling)?
5) the housing- is there evidence the M/S bearing is moving?
_________________


'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

[gears]

The oil comments were directed to Rj's question. I think you can give top oils FAR better than 1% improvement. In severe racing conditions, the better oils become VERY obvious. If you can postpone the snowball, general gear face and bearing wear can be delayed. (That said, I wouldn't consider building an oiling system without some sort of magnetic filter, thanks to your input, Sodo.)

Some photos were sent to me a day or two ago showing extreme wear on the engagement teeth of a relatively low mileage OE 4th gear. The builder surmised that too thin an oil was used. There could easily be another explanation, but I can't disregard the opinion of that particular builder.

I can say from experience that the most knowledgeable engineers surprisingly learn a lot from guys in the field. I've seen this time & again.

Yes, I've seen otherwise acceptable bearings with substantial erosion. The increased gap doesn't really bother me much .. but I'd never reuse a MS bearing once in there. Put it aside for a rainy day perhaps ..
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Rjhdog]

Thanks all.
So knowing what we know now at this point:::

Stick with Swepco 201

Or

Give 202 full synthetic a try?

[Howesight]

If one considers a gun-drilled mainshaft for pressure oiling the 3rd and 4th idler gears, and also JB's idea of using plain bearings (I presume for 3rd and 4th gears only), then:

1. should the plain bearing rotate with (ie, at the same speed as) the mainshaft so that the plain bearing slides against the idler gears' ID? or

2. should the bearing surface interface be at the mainshaft with the plain bearing fixed to the gear ID?

Since gears are cheaper to replace than mainshafts and a bearing affixed to the mainshaft (by a light press-fit) would prevent mainshaft surface wear, maybe #1 is the preferred approach? But approach #2 would allow for honing of the ID of the plain bearing after installation in the idler gear, making for a more precise fit and an easier/simpler machining and pressing operation. Maybe Weddle could be persuaded to manufacture and pre-install the plain bearings in these idler gears?

Plain bearings will also require more pressure in the gear oil pump than some of the electric pumps can reliably provide. This appears not to be a difficult challenge if you use Herman's clever idea of the VW power steering pump. Plain bearings and pressure lube might require avoiding the thicker gear oils. I use Swepco 210 in my non-cooler transaxle at present and I think that might be far too viscous.
_________________
'86 Syncro Westy SVX

[jberger]

I don't see a real need for 1-3rd gears to have a plain bearing installed as they don't seem to suffer the same damage. Also, 3rd gear would require a 2 piece bearing due to the splines for the 3-4 hub. 4th gear bearing should be completely doable, including a thrust surface (which will require a clearance ground main bearing).

[Howesight]

[gears]

Lol .. We could just make straight-cut gear sets like our early prototypes, to avoid the gear cocking issue altogether ;^ )
https://www.thesamba.com/vw/gallery/pix/1129657.jpg
Those are actually the 091 mainshafts for which we contemplated using a free-floating, two-piece, bronze bushing, to accommodate ultra-low 3rd gears.

But seriously .. the needle bearing area itself isn't a problem. From Rancho's report of seeing similar wear in the Berg Type I 5-speed, and their cure of the issue with added oiling, combined with Herman's report today of virtually no wear in his oiled trans, cooling oil directed onto 4th gear may have already solved the issue. Fingers crossed, anyhow ..
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Sodo]

[gears]

The bores certainly do vary. In fact, when installing loose needles (where you're installing almost double the number of needles), you'll always need to hone the gear for a bit more clearance. In doing so, you'll often find the bore to be a tapered shape .. tighter at one end than the other.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com