Vanagon 4th Gear and Mainshaft Ball Bearing wear issues

[gears]

Unlike early Type 1 VWs which utilize a 4th gear thrust washer, the Vanagon's 4th idler gear thrusts directly against the inner race of the mainshaft ball bearing. In our 5,000+ pound Syncro Vanagons, many of which are equipped with high horsepower conversion TDi and SVX engines (some held at 75+mph up hills and/or long distance freeway driving), this causes a REAL problem .. erosion of the inner bearing race thrust surface.

In the photo below, take special note of the lack of any circular wear marks. Instead, the splotchy & burned wear pattern closely resembles interrupted spot welds. This pattern is evidence that the erosion is NOT from a lack of lubrication, but rather a previously misunderstood oscillating friction between the two steel surfaces.

Enough material eroded from this race to leave a .011” step

What's really occurring is illustrated by this sketch of a cocking helical 4th gear ..

.. and this link
Mechanical Precession https://commons.wikimedia.org/wiki/File:Animation_of_mechanical_precession.gif
(a HUGE shoutout to Howsite Ron for illuminating me on this subject)

I was going to present another link showing linear friction welding, but that isn't quite what's happening here. Instead, merely take a look at the spattering of material stuck to the 4th idler gear ..

The spatter marks above are literally traces of hardened steel torn from the bearing's inner race, which are then thrown outward by the constantly spinning mainshaft. Some material sticks to the gear, most is thrown out into the oil, and of course some passes directly through the mainshaft ball bearing .. one of the two most critical bearings in our transaxle.

Again, keep in mind that none of this wear is happening while the gear is freewheeling, but rather ONLY while 4th gear is engaged (and theoretically stationary against the thrust surface). Again, proof of this is that the wear pattern is splotchy-weld in appearance, rather than the expected circular wear pattern. This splotchy copper-colored pattern is literally minor friction welding occurring, the result of an odd oscillating friction between the two surfaces.

One can see that any efforts to "get oil between the two surfaces" by adding oiling grooves to the gear merely reduces thrust surface area, while doing nothing to solve the real issue.

This photo shows the second major issue caused by a cocking gear .. severe wear to one side of the gear teeth.

SOLUTIONS:
Rancho is experimenting with adding a thrust washer back into the design. They highly modify (grind in 3 areas) the steel caged bearing and washer on the left, with the finished parts on the right:

I think this is a great idea (and Mike @ Rancho reports good results so far), but I also believe that since orbiting will still occur, the wear will eventually show up elsewhere .. perhaps the inside diameter of the thrust washer rubbing a wear groove into the mainshaft. (Regardless of the washer's fit on the shaft, a helical gear is still going to cock.) But .. the washer undeniably adds about 30% more surface area against the bearing inner race, which is a tremendous help.


The ULTIMATE solution IMO is to use a straight-cut 4th gear. This eliminates any cocking of the gear, thus any erosion of ball bearing thrust surface and any lopsided wear to one end of the gear teeth.

Even tooth wear:

Zero wear on the thrust surface

While most straight-cut gears are rather noisy, GT 4th (and 3rd) gears now use a street-friendly tooth profile that's rather quiet. We now have about 30 of these straight-cut 4th gears of various ratios out there, and all reports so far are favorable. There's slightly more noise than an OEM helical gear, but not an objectionable noise level at all. In fact, we've recently received a special order request for multiple sets of 1st-4th straight-cut gears.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[ALIKA T3]

Hi Paul!

Nice documentation, as we needed clarification after Simmo`s misfortune

Aloha!
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget

[gears]

Simmo's misfortune was due to a radial bearing that had been preloaded .. nothing to do with any of the above. However, we will be updating him with a straight-cut gear.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Sodo]

All very interesting, thanks gears for your thoughtful and educational post.
_________________


'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

[MarkWard]

This has been bothering me since I went through my syncro transaxle. Currently it is mated to a stock WBX and if I keep this van, will likely have the transaxle apart for a "look see" but to probably add a taller 4th gear for TDI power.

In my spare time, I've been thinking about this problem. Paul, have you considered a more robust needle bearing arrangement? Seems with better support, that might also help cocking. The gear, mainshaft, or both would need machining some. Your drilled mainshaft might also help if you could get oil pressure in between those surfaces too.

Daryl did my 4 speed for me some years ago. Once I got the van quieted up, I did start to notice 4th gear makes some noise. Most noticeable is the sound change off and on loads. It hasn't been a problem for me. I think at the time Daryl was getting gears from Weddle.

I would be willing if try your 4th gear in either van at some point. Thanks for sharing. Mark
_________________
☮️

[Silentbay]

[gears]

Ah, Simmo .. I was wondering if you were here with us on Samba. Maybe leave that radial bearing out altogether this time ;^ )

Mark, I've been through all the attempts to cure cocking through loose needles and the lot .. It does not work. Straight-cut gears are the FINAL solution to cocking caused by powerful conversion engines (when that extra power is actually used).
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Silentbay]

[gears]

Perhaps better in direct email, rather than sidetrack this thread.
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Jake de Villiers]

Thanks Paul, for the continuing education!
_________________
'84 Vanagon GL 1.9 WBX
'86 Westy Weekender Poptop/2.5 Subaru/5 Speed Posi/Audi Front Brakes/16 x 7 Mercedes Wheels - answers to 'Dixie'
@jakedevilliersmusic1
http://sites.google.com/site/subyjake/mydixiedarlin%27
www.crescentbeachguitar.com
www.thebassspa.com

[Sodo]

I'm pretty sure this erosion is "fretting corrosion".
When I think of corrosion there's always an electrolyte,,,,
but apparently there's other kinds of corrosion.

This type under the category of "frictional corrosion" requires very small movements between two steel items (the asperities, or 'peaks'), that dislodges very tiny particles.
It's like the peaks 'weld' together then the (tiny) movement rips them apart, and results in a tiny particle loosed into the oil.
Very tiny, but this can happen many times in an ultrasonic environment.
The movements are small, (vibrational) but "large" to a molecule.
The particles can be "magnetite" which is magnetic black dust.

Keep in mind that 4th gear is not spinning against the bearing race,
it's pressing on the race motionless, but vibrating due to the gearteeth
and the orbital motion from the slop in the needle bearing.
The motion resembles “precession" but not actually rotating because it's locked to the shaft by the dogs.
The motion is more radial, but it 'looks' axial, as if it happens while in 3rd gear. Strange stuff.
You would expect that it erodes the engagement dogs rather than the thrust surface. But the dogs apparently have lubrication.

I recall member 'gears' explaining this ~5 years ago, on a stormy night at Descend on Bend, as we cowered from the storm in our cozy vans.
I didn't really comprehend what he was describing or accept it, as I thought he was referring to separation when you shift away from 4th to 3rd.
But upon reading more on the subject, have come to agree this IS what's happening, but the 'separation' is the tiny orbital motion (slop) of the gear relative to the bearing race.

Here is a pic of a couple mainshaft bearings with NO step erosion, but on the left has the beginning of fretting corrosion, and the red "hematite" that looks like rust.

What can be done about this?

First and foremost is lack of a lubricant film separating the steel parts.
Constant pressure, requires metal-to-metal and small movements, such as
the orbital motion of the gear mesh trying to push apart but constrained on the bearing axis.
This is the problem with having the mainshaft above the oil level.

I think drivers need to let off the gas pedal from time to time and back 4th gear off it's thrust surface, periodically introducing the oil fog into this interface.
That's one problem about modern engines, they have a little 'run-on" to reduce pollution.
So even if you do let off the gas, the engine waits a second or two to 'decel' consequently the thrust on the gear never actually lets up.
So in normal driving, the engine control never lets 4th gear back away from the mainshaft bearing race.

You could push the clutch for a moment to back off.
Or actually "let up" long enough for 'decel' to occur.
"Gear protection" is kind of hard to incorporate into your driving habits.
People will think you’re insane if you explain “why”.
Driving 'the brick' into the wind, there's ALWAYS gonna be forward pressure.
And harder with a bigger engine.

Well anyway this is where I'm at, thinking about this problem.
The way some people drive, they let up, and re-lubricate this thrust surface.
I recall watching someone drive, the RPM needle rising, falling all the time.
I thought "this lady's gas mileage must be a couple miles lower than if I was driving....."
But I bet she wouldn't erode a 4th gear....

Now I'm thinking of pumping oil into the GT gears gun-drilled mainshaft,
with a speed sensor control that runs the pump anytime > 65mph.

But other than that....if you develop an ethic to drive no faster than "65 sustained" then with a big engine you're periodically letting off the gas at 70 to get back down to 65.
And during the decel, the thrust reverses, and 4th gear lifts off the mainshaft bearing which may allow oil vapor into the thrust area.

“Proposition 65” ^^above^^ could also prevent brinelling in the 4th gear idler and shaft.
Two solid reasons to use 65 as your max cruise speed.

Page 53 describing "frictional corrosion" or "fretting corrosion"
from: SKF publication: Bearing damage and failure analysis p53
_________________


'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

[11BC2]

^^^^^
And use better lubricants that get changed regularly.

I can't imagine the whine from that straight cut 4th gear set up.

[Sodo]

[dobryan]

I had a weddle straight cut 0.77 4th gear back in 2009-2014. It whined but not horribly. I got used to it.

I am getting the Western Syncro trans rebuilt and likely using a stock gear ratio but straight cut 4th. I'll report back on how 'whiny' it is. Please remind me in about 6 months....
_________________
Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794

[elizer]

I believe I got some of Paul's earlier straight cut 4th back in 2018/2019. It is definitely noticeable. It was pretty harsh but I've gotten used to it. Some sound proofing should help but it's been to cold out. I think Paul's new ones are more quiet than mine. I have bad hearing anyways so it's not horrible for me.

[Sodo]

[ALIKA T3]

I have to say, my Syncro transmission never saw any temperatures higher than 68°C with the 1.9 M-Tdi at 2770 Kilos loaded during my trip down Central America. Top speed of 110km/h, cruising at 103-105 km/h when I could.
Mountain trips at 2500m altitude. Coupled or decoupled ( I was hearing noises under load in 3rd that bothered me, like a fork rubbing in 2WD so going uphill and most times I was in 4WD).
7x34 R&P, 0.77 4th I recall. 215/70 R16 tires. Swepco 210 oil. Full lubrication and filtration system.
In Hawai'i the transmission doesn't even get to 60°C, mostly 45-52°C, short trips, lighter van now obvioulsy.

I want to re-open the transmission to be installing straight cut gears, 3rd and 4th one of these days and inspect parts. I just past 15k miles, haven't inspected the oil once, nor replaced filters yet, such a PITA.... It's due anyway bc the transmission is starting to leak from the side cover and some of my lubrication pipes.
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget

[AndyBees]

The DK transmission I built for my ALH TDI has a smidge over 85k miles on it. Weddle 3rd and 4th gears (non-straight) have always had a whine, especially 3rd when letting up on the go pedal. I've not driven the Van much over the last 3 years, primarily due to a worn spot on one Pinion Tooth.

Anyway, over the last year and a half, I've been building another DK with an oiling and cooling system.

This Thread is quite interesting and brings interesting info to the table, to say the least.

After seeing this info, I may drop my transmission and disassemble it before doing the final assemble of the new build. Although, I did several fluid changes up front and continued to change it quite often, the amount of swarf never really tapered off.
_________________
'84 Vanagon Tin-top, ALH TDI. 1989 Tin-top
1983 Air-cool, 225k miles, 180k miles mine. Seven trips to Alaska from 1986 thru 2003.

[Sodo]

(translate French to English) 68°C=154°F & 110kph= 68mph
Central America would be an ideal place to break in a new trans. Slower speeds, lots of shifting between 3rd&4th.
Driving across the USA on the freeway in 4th gear for hours (days) with a big new engine....being about the worst.

I cringe when I see a story about some person who gets a big engine, then destroys the old trans,
and then has to break in the new trans with the big engine.
Sometimes the 'maiden voyage' being

- a heavy, hot freeway slog for hours.
- 4th gear needle bearing motionless, for hours
- with soft new shafts and gear bores
- lots of bedding-in trash in the 'early oil'.
- big engine pounding hard at the top of its power curve (double) on this stationary needle bearing =“spacer”.

Bad scenario for brinelling the new parts.
And not false brinelling, real brinelling.

Far better to break in a new trans on the last legs of the old WBX.
-----> But life just doesn't work that way.

-------------------------

But break-in is not the subject of this thread on 4th gear erosion and would likely drive this specific topic off into the loony bin.

Alika sorry you have to open your trans but I think many of us like to see inside a 15,000 mile. AndyBees too.

The 4th gear erosion is a strange phenomenon that does NOT happen to all gearboxes.
Nobody seems to know what causes it. And we're not OEMs, we cannot study this except by 'observation'
and come up with clumsy (....in comparison) conclusions.

I kinda think we have identified the mode of "metal removal" but not really "the cause".
Lack of lubrication is a feasible contributor - but why does thrust surface erosion occur on some vans and not others?
It could be a "resonance" condition where all vans are 'on the edge', where some resonate and some do not.
Resonance is a "violent condition" and would certainly cause extreme pressures and shortened life.

My van had a vibration at 70-72mph that I thought was the driveshaft.
It was a faint vibration that nobody else could hear unless I specifically pointed it out and demonstrated it coming and going (speed up& slow down, around 70-72mph =3770 rpm.
Was that the cause of the early bearing failure?
Or was that the symptom of the failing bearing becoming audible?

A couple weeks ago I changed to a different transaxle (same driveshaft, same decoupler) and the vibration is gone (silent) at 72mph.

This condition causing puzzlement for so many years heralds the emergence of straight-cut gears,
which eliminate the 'thrust' load of 4th gear against the mainshaft bearing.
Which would eliminate the possibility of erosion ----> at the cost of 'gear whine'.
But how bad is this whine? Probably not as bad as what you hear from me WRT my 4th gear erosion (at 40,000 miles).
I'd like to listen to a straight-cut van someday (soon).
_________________


'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

[ALIKA T3]

2nd and 3rd were the most used gears honestly

I don't have to re-open the transmission to re-seal things but I want to do it all at once pro actively, might as well install straight cut gears and inspect parts for science.

I do have a dual mass flywheel. I had to install it before leaving on my trip, the single mass flywheel was causing the clutch disc springs to rattle ( they were VR6 parts, not Tdi), and also the low gear housing cluster of gears was rattling at idle. Shows there's harmonic or impulse going through the transmission.

My seat of the pants analysis would be that all the dead rotating weight is an opposite force applied on the transmission part upon acceleration, kinda like a twisting axle, and that's what happens between parts with trust. If you would make the shafts out of rubber they would twist and bent out of straight line, come into vibration from being out of balance as a result. All this causes wear. That's how I make that little movie in my head from all these moving and suffering parts
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget