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Sodo
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Joined: July 06, 2007
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Location: Western WA
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 Posted: Mon Sep 04, 2023 10:28 am Post subject: Big engine + NOT downshifting.... damages 4th gear |
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The purpose of this post is a PSA about the importance of "downshifting" an over-engined Vanagon (T25, T3 091 or 094) gearbox. I'll try to edit this "top post" as errors/omissions appear in the replies.
If you have a genuine, on-topic question or observation, others members do too..... and it helps understanding.
I'm in so deep I can't possibly know what others DON'T understand.
And I want to know the details that I'm missing too.
Quotes excerpted from another thread Honda K24 Swapped 87 Syncro Camper Build
I pick on Pchill2 because I enjoy his approach to attacking problems and bringing new energy to the conversion subject.
I hope this is an opportunity to get more articulate perspectives on what we are studying (in what kinda feels like a vacuum of just a few co-conspirators).
| Pchill2 wrote: |
| DIYCarLab wrote: |
| I think these engines have more of a building torque curve from low RPMs which shouldn't hit the trans as hard while driving. |
I get a lot of satisfaction from not needing to down shift when climbing steep mountain roads. My theory is the lack of torque on WBX probably leads to premature gearbox failures due to the constant rowing of gears necessary to maintain speeds on roads of any incline. Banging a 4-3 or 3-2 downshift puts a massive peak torque load on the gear sets. |
Here's a video where I try to explain it so you don't have to read the TL;DR below
Sorry I'm not a pro filmmaker, I did the best I could, solo, and no re-makes.
Link
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TL;DR below
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========= In case of TL;DR skip to the BOLDS =========
My opinion from studying this hard since 2016 with the help of Grand Master Tom Lengyel (Syncroshop).
These gearboxes have a 'funny arrangement' of one shaft vertically above the other. The upper shaft (input shaft) has the 3rd and 4th gear idler gears. 4th gear, which sees the highest "duty", suffers from lack of oil, especially when a bigger engine is added, such as VW South Africa's 2.5L 5-cyl. VW SA engineered the "Oiling plates" to help throw oil up to the starving 4th gear.
"Oil climb plates" are a well-known "splash lubrication" method that works well at a specific RPM range and oil temperature/viscosity. The ideal RPM & temperature in a VW gearbox would be 'highway speed'. IMHO..... the temperature gets 'too high' and viscosity 'too low' when over-engined.
I have never seen even one tiny shred of evidence that the oiling plates work for our usage. But they are not expensive and probably better than nothing, and work 'sometimes'. But Oiling plate gearboxes roast their 4th gears just line non-plate gearboxes do. I suppose.... ----->Often the oiling plates coincide with over-engining. There are lots of variables.
The OEM gears are high quality. Gear size is determined by the shaft-to-shaft distance, which originated at ~60hp. Consequently, shaft-to-shaft distance determines the power-handling capability. VW "over-engined" the gearbox to ~90hp then discontinued the model.
Then our gears "got old" ~ 35 years old. The surface hardening is wearing away, to the butter below. Gears are softer inside, for resistance to cracking. It did not help us antiquers that VW said that the oil need not be changed. VW omitted the second part of that sentence. I will write the complete sentence.
"The oil need not be changed to last the 90,000 miles that VW feels responsibility for".
You may notice 90k is the highest miles listed in the service intervals. If the gearbox is ruined and eating iteslf at 90,001 miles due to lack of maintenance, that's OK with VW. The original purchaser has been satisfied.
And what's hard to notice (as null-data) is there is not a single mention of 'how to replace gear oil' in the Bentley manual. That is intentional omission, , perhaps forced upon Mr. Bentley, not an oversight.
OK on to shifting.
Never 'shock-loading' your drivetrain gears ------> is beneficial too.
But 4th gear has some "details". I don't know enough about other gearboxes and how their 4th gears are lubricated, and I wish I did.
But I'll try to explain our Vanagon 4th.
4th gear has a "helical cut", meaning the teeth are angled. This allows quiet running because each successive tooth is 'handed off' gently after other teeth have already engaged. Smooth running is long-running.
This angle-cut gear causes an 'axial thrust' along the shaft, which presses 4th gear against it's stop, which is the mainshaft bearing. Constant pressure 'seals' this area from lubrication. The centrifugal force throws the oil OUT but there's no way for more to get back in.
The oil depletes.
There is a thrust surface and a needle bearing that starve of oil, even in the STORM of oil that must be inside that case.
VW South Africa engineers tried to solve it by throwing more oil on the outside, (with oil-climb plates) but the oil cannot get inside the 4th gear (in long periods holding 4th gear). That's IF it actually climbs the plates at freeway speeds.
In the past we attributed the erosion to '4th gear cocking' but have mostly abandoned that concern because there was no angled wear observed.
Some 4th gears do not erode at all. Here's a pic..
Is it a 'driving style'? Did this van only drive in the city (no long trips)? Did some anal van owner actually "change his gear oil"? Did the the transaxle live its life in a dry climate and it's electrical ground path remain 100%? It's unknown why these 4th gear thrust surfaces did not erode.
Then there's the "GT straight cut gears" solution.
Straight cut gears eliminate the helical gear-thrust, and consequently 4th gear remains lubricated.
Logically.....we think. Straight cut gears are are 'too new' to really know - but it's 100% logical that 4th gear lubrication problem will disappear with straight cut gears.
Downshifting periodically will certainly increase lubrication of 4th but it may be unnecessary with straight cut.
At the cost of gear noise.
That's for you to decide. Some people think of straight-cut as "the sound of freedom".
"Corrosion Fretting". <-----Google it.
Our recent discovery of corrosion fretting has advanced understanding of this problem. It's an erosion phenomenon under micro-motions that can ONLY occur 'when dry'. We are about 100% positive the erosion is "corrosion fretting". And secondly; positive that the gear is "dry" inside.
Think of an orbital sander, or perhaps a vibrational cutter such as a "multi-tool". The erosion is exacerbated when the lubricant is contaminated with steel (micro-particles, steel dust). And oxidized oil provides more oxygen to create Fe2O3, a wicked, non-magnetic grinding compound otherwise know as 'jeweler's rouge' in-site at the erosion location. The erosion is exacerbated by electricity (so isolate your gearbox!! Delete that front gearbox ground.
The two places this erosion appears is "the mainshaft bearing thrust surface" and "false brinelling" lines from the non-rotating needle bearing in the 4th gear idler bore. When the brinelling gets 'too deep,' bearing precession cannot roll the needles up out of their 'slots' and then it just gets worse and worse.
When the gears & shafts (or both) are "NEW" this is the highest danger. So if you put in a rebuilt gearbox, a big engine, then go right to a 75mph cross-country drive, not changing the glittery break-in oil, you're checking all the boxes for "please Brinnell my 4th gear". This happens in 4th gear because 4th gear sees the most miles while at the top of the (big?) engine's torque curve. The other gears are much lesser concern.
A new gearbox should be broken in, with gentle driving and lots of shifting between 3rd & 4th gear to burnish the needle bearing races on the shaft and on 4th gear. Every time you take the gearbox OUT of 4th gear you spin the needle bearing and it stops in a different, random location.
A stock WBX is likely considered a gentle engine. An EJ25 or 1.8T, capable of sustained high torque, and sustained 4th gear, is not gentle.
The WBX doesn't push as hard, and needs periodic downshifts, but I suppose it's still some risk if your break-in is on a long highway trip.
How many miles to break-in? I don't know.... I observed elevated swarf for 5,000 miles on my recent rebuild, so minimum 5,000mi is my best number.
I'm not an "OEM". Understood 5k miles is a long time. (8k km)
You gearbox fellers should google 'corrosion fretting' and learn it too, dig up more details. I can't be the only conduit to this info, I'll inevitably miss some important detail.
OK so onward..... (whew......(sorry ))
I said it myself so many times after over-engining.... "Its so satisfying to NOT have to downshift". Everybody gets tired of downshifting an 'under-engined' vehicle.
But everyone should take this to heart. We know this as fact now.
Holding 4th gear starves it of lubrication.
Thge needle bearing in 4th gear does not spin when you're in 4th. It just sits there "like a spacer" its needles each sitting on one "line".
I've held 4th gear "for hours" at 80mph crossing Utah.
My cruise control doesn't work but it too would mash 4th against the mainshaft bearing, sealing the internal bearing "for hours".
Downshifting lubricates 4th gear. It's good to downshift.. Even just shift to neutral for a moment if 3rd is too slow. That lubricates 4th gear AND spins the needle bearing then it stops in a different, random location on the shaft.
And every time you decel in 4th, you allow oil into the 'dry area'. Not ad good as a downshift, but better than not doing it. When we discovered this 'proof of dry 4th', I then tried to develop a driving style that "periodically decels' every few minutes.
It was not possible to 'remember' to do this.
Here's a driving style change "that works".
Use 65mph as your max speed. 65mph is "perhaps" within VW's design parameters ---> which we'll never know.
The over-engined van wants to go 70, 75 mph.
So every time speed hits 70, DON"T EASE OFF ----> lift your foot OFF the pedal, cause a "decel" that backs 4th gear away from where it seals against the mainshaft bearing and lets oil into the 'dry area'.
And be happy with downshifting.
While in 3rd, your 4th gear idler is FLOODED with oil.
Also note that sustained 75mph can overheat your gearbox, which causes other problems. (bearing movement wears out the mainshaft bearing bore in the gear carrier)
65 is a good max sustained speed for a Vanagon gearbox.
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb
Last edited by Sodo on Wed Sep 06, 2023 8:25 pm; edited 5 times in total |
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E1
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| Posted: Mon Sep 04, 2023 10:47 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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What a freaking EPIC post!
The bigger engine phenomenon is also putting a *huge* strain on rebuilders who can’t possibly afford warranty work for users who want to constantly go 80, and using full-throttle up every hill they find whether paved or dirt. Vanagons were built for neither!
For one, I had no idea that Paul Guard’s 4th was a different cut. It runs dead quiet for us although 3rd makes a little whine. This made me nervous at first in sounding like a quieter version of the panic- and rebuild-inducing 3rd gear slider whine — partly since the mechanic who swapped the tranny put MT90 in as “break-in oil!” — but after about 15k if anything it’s quieting down. Lest you ask, the break-in oil was changed for dino after a thousand miles or a bit more.
People like Paul Guard are very welcome in our community. Builds great stuff and was educated from decades of endurance racing Porsche gearboxes — and maybe of equal importance is a nice guy who respects his customers, too.
Again, AWESOME JOB on the post.
_________________
1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere." — Colin Chapman |
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elizer
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| Posted: Mon Sep 04, 2023 10:58 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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I have one of Paul guards first batch of straight cut gears. 4th gear whine is very noticeable in mine. It is probably loud enough to put off some people. I do think he made semi straight cut gear that cut down on the noise.
Great post Sodo. The video was very well explained.
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91 syncro westy fas tdi |
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Pchill2
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| Posted: Mon Sep 04, 2023 11:08 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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Somewhat of a coincidence but I was thinking of posting a debate thread on this exact topic. Obviously I my opinion is somewhat contradictory to this.
Why would the 4th gear needle roller need lubrication while in 4th gear? There’s no relative motion.
The square notched 3-4 slider hub is a design used in most MT vehicles without issue.
The wear on the main housing is likely due to massive thrust loads during some peak torque event such as an aggressive downshift.
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87 Syncro Westy
Honda K24 swap |
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ScottShelley
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| Posted: Mon Sep 04, 2023 11:11 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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| Great Post and Great video too. |
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AndyBees
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Joined: January 31, 2008
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| Posted: Mon Sep 04, 2023 11:24 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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Wow!
I cannot wait to tear down my DK that I built back in 2010 which has almost 88k miles on it with a TDI.
Subscribed ...
_________________
'84 Vanagon Tin-top, ALH TDI, two trips to Alaska, 2014 & 16. 1989 Tin-top unmolested.
1983 Air-cool, 225k miles, 180k miles mine, seven trips to Alaska from 1986 thru 2003. 1975 Bay hopeful.
Last edited by AndyBees on Tue Sep 05, 2023 6:21 am; edited 1 time in total |
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Sodo
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| Posted: Mon Sep 04, 2023 11:28 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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| Pchill2 wrote: |
| Why would the 4th gear needle roller need lubrication while in 4th gear? There’s no relative motion. |
We said that too, for years and years.
And yet, the erosion is real.
There is (almost) no rotation, but there is micro-motion. It's smalll motion to you and I but it's a miles "to a molecule" or even to an asperity.
A needle bearing MUST have slop or the rollers opposite the load will "scrub".
The amplitude of the micro-motion is equal to 'the slop' of the needle bearing.
It goes a full-cycle with every rotation. 3600RPM is 60 times per second (=60Hz).
The needle bearing does "precess" within the locked gears due to this difference in diameters, which is a blessing actually. Bearing precession stops when the brinnelling gets too deep and the riollers cannot climb out (to precess).
Pchill2 I'd like you to read about corrosion fretting and give your take on it WRT to our problem. I can feed you some links..... but I'd much rather see the results of your independent research first. In case my understanding is becoming 'in-bred'. Howesight's is another POV I'd like to hear WRT corrosion fretting. And others. How can we get 10cent to get in on this? There are many others too. I always write a book and others can't get a word in edgewise. This is good and bad.
I will help however I can (hoping for your reply) but with caution  . Too much of "popular science" these days is parroting some single point of view, more like religion than science.
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb |
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MarkWard
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| Posted: Mon Sep 04, 2023 11:41 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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I like the theory, but the wear is similar to what I recorded on a stock powered Syncro.
This photo shows the mainshaft inner race bearing pretty well.
This photo includes the 4th gear idler.
On my second rebuild of my 091/1 4 speed mated to a TDI. The extra power seemed to actually damage the synchronizer ring the most. Transmission was actually sticking in 4th gear. You can see how the dogs were climbing the syncro over time.
Here are the backsides of the dogs. You can see they are deformed from the slider ring which wasn't helping.
My mainshaft bearing had similar wear and 4th gear teeth were failing. Mainshaft bearing was hammering the stock retainer as well.
I have since added a GT square cut 4th. I can hear it if I listen, but the Weddle 4th gear made noise too and wore out too soon in my opinion. I am using the Weddle heavy duty main bearing retainer as a compromise to the 4 bolt retainer. Gear carriers were not available during my build, and the end case was already distorted from the stock retainer plate. I also installed a Dual Mass Flywheel. Plan is to hopefuly make another 60,000 miles and do a premptive tear down. I am not running any pumps or coolers. I will run 65 to 70 all day long except for fuel stops etc. I like simple. The less points of failure the better for me. |
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Sodo
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| Posted: Mon Sep 04, 2023 12:00 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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| MarkWard wrote: |
| I like the theory, but the wear is similar to what I recorded on a stock powered Syncro.. |
There are a lot of factors.
Here are some Qs (for perspective).
How many miles on this WBX Syncro? 60,000 from new?
Or something like 180,000mi? Big engine will inevitably wear the gearbox faster because the composite speed/duty is higher.
And what about the gear oil.
Always fresh? Bedding-in oil replaced early like 1st 200 milesn then successively until clean?
Or original factory oil with all the bedding in trash from mile zero to ~100k mi? (Or 150k)
And the full 25 year dose of oxidation too?
What about electrical? Gearbox case bolts along the ground path to the forward strap periodically removed, maintained, cleaned, shined, replaced? (very unlikely)
Did the bolts have the telltale white oxide of 25 years undisturbed, dissimilar metals outdoors? Series resistance-additive?
Did this van have cruise control?
Anyway...... danged "previous owners".
Can't live with'em, can't live without'em.
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb |
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MarkWard
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| Posted: Mon Sep 04, 2023 12:27 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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| No cruise control, no idea on the miles or care. How long did it usually take for the 3/4 hub to break? Found it in pieces, but all in place and shifting well. |
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E1
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| Posted: Mon Sep 04, 2023 12:47 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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We bought our first van showing 239,000 on it. Two owners prior said the odo never worked while he had it and he estimated doing “at least 50K.” We added about 40K more in our ownership.
So that original box had about 329,000 miles on it.
Slider started to *shriek* soon after seeing you at Mid-Ohio, on Blue Ridge. Had no choice but to sympathetically nurse the box, it wasn’t getting hot, so we limped it 7,000 more miles to the awaiting rebuilt in Santa Cruz. God I miss those guys.
_________________
1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere." — Colin Chapman |
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dkoesyncro
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| Posted: Mon Sep 04, 2023 6:18 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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Excellent write up Tom, I have always appreciated you “diving in” and finding truth.
I don’t have a lot to add but my own experience and discipline. My break in procedure was 5K miles of Town/City and Highway/Rural landscapes. The first of the two allowed for plenty of shifting 1-3 gears and the ladder allowed for 4th gear encounters, usually no more than .5 an hour in 4th between a stop sign or entering into a town. My Top speeds would hit 60 mph.
Since the rebuild of the trans and the 1.8T, I’ve adopted the old school driving characteristics of the decade the Syncro was new.
When road tripping, going the distance I stick to the highway or leave super early and stay in the slow lane of the interstate. My 4th gear speed is +\-60 mph, I take time off the beaten path every two hours to paddle through the gears etc. This has been beneficial in keeping temps down, personal blood pressure down and has allowed for seeing small town America along with great conversations. |
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Pchill2
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| Posted: Mon Sep 04, 2023 7:43 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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All those pictures show fretting on the thrust face and bore. It just tells me that 4th gear is moving in a way it shouldn’t.you said this is from the gear moving in an orbital motion radially? Makes sense. What doesn’t make sense to me is why.
Does anyone have the supplier part number of the needle bearing?
4th gear should have lubrication grooves cut into the trust face. Better yet it would be easy enough to turn the face down to work with a grooved bronze washer.
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87 Syncro Westy
Honda K24 swap |
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charleslabri
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AndyBees
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| Posted: Tue Sep 05, 2023 8:38 am Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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| Pchill2 wrote: |
Does anyone have the supplier part number of the needle bearing?
4th gear should have lubrication grooves cut into the trust face. Better yet it would be easy enough to turn the face down to work with a grooved bronze washer. |
4-323826 <<< At Weddle Industries, that is the part number for the updated/graded stock/OE bearing for 4th gear.. Metal Cage vs Plastic.
There is a 4th Gear Thrust Washer with Oiling Grooves for the 002 Transporter/Bus Transmission. The OE is NLA but Weddle has made a replacement. Of course, it will not fit with in the 091, 091/1 or the 094 as is.
_________________
'84 Vanagon Tin-top, ALH TDI, two trips to Alaska, 2014 & 16. 1989 Tin-top unmolested.
1983 Air-cool, 225k miles, 180k miles mine, seven trips to Alaska from 1986 thru 2003. 1975 Bay hopeful. |
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Pchill2
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Howesight
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| Posted: Tue Sep 05, 2023 1:37 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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| Pchill2 wrote: |
All those pictures show fretting on the thrust face and bore. It just tells me that 4th gear is moving in a way it shouldn’t.you said this is from the gear moving in an orbital motion radially? Makes sense. What doesn’t make sense to me is why.
Does anyone have the supplier part number of the needle bearing?
4th gear should have lubrication grooves cut into the trust face. Better yet it would be easy enough to turn the face down to work with a grooved bronze washer. |
Hi Sodo:
Excellent and thoughtful posts and great videos!
My thoughts on the question that Pchill2 asks are simple:
1. The axial forces on the 4th gear idler are high;
2. There are also unequal forces on the 4th gear idler (Paul Guard referred to this as "gear cocking";
3. Due to the bearing clearance between the mainshaft, rollers and inside diameter (ID) of the 4th gear idler, the idler gear itself can move in an oscillating manner best envisioned by thinking about a hulu hoop in action on somebody's waist;
4. By comparison, the inner race of the mainshaft bearing, as a light press-fit, has none of these motions (relative to the mainshaft) and can be thought of a stationary element against which the oscillating idler gear presses axially.
5. If you think of the idler gear as cocked (not running perfectly vertical) while the thrust surface of the mainshaft bearing remains truly vertical (or very close to vertical), then you can visualize the contact between those surfaces is not constant. Instead, the location of the actual contact between these surfaces is constantly changing and as such, there is localized contact followed by localized separation. These repeated compression and separation events are, I theorize, what causes or at least contributes to the metal erosion.
6. This is why, with the greatest respect, I don't think that Sodo's suggestion of disengaging 4th gear from time to time will eliminate or substantially reduce this kind of wear. My thinking is that the compression and separation which leads to this erosion is already happening at a tremendous frequency. But the main contribution, I think, is excess torque which increases the amount of axial thrust loading and the amount of gear cocking.
7. However, if the gear oil, or its properties when new (referring to the various additives that oil companies use which are consumed over time), can reduce or eliminate the erosion at a molecular level, that might help reduce this type of erosion wear significantly. I don't profess to know this chemistry at all, but think that there may well be additives of some kind which might help with this metal erosion and/or the oxidation component. It may be that gear oils like the Swepco products (I use Swepco 210) already contain some such chemicals.
8. To illustrate this concept (of the cocking gear and the interface between the 4th idler gear and the mainshaft bearing interface) to yourself graphically, think of a bowl with a small base on a hard surface that you have caused to wobble. That is another exaggerated version of the relative movement I am thinking of.
My other theories on Syncro transaxle issues:
1. Simply put, the forces generated by re-powering the 094 arise in part from the small distance between the gearshafts which do not permit larger diameter gears. Small diameter gears mean applying larger forces to each tooth due to smaller lever-arm effect. Each tooth has greater force applied to it, with potential for greater wear and even case-hardening erosion - -plus all those other wear and failure modes that Paul Guard knows far better than the rest of us.
2. The excess forces (excess over the design limits) also apply to the ring and pinion set.
3. The aluminum castings in the gearbox expand more, and more quickly, than the steel components. This causes a variety of excess clearance issues (including, I theorize, pinion bearing retention, and even the orientations of ring gear and pinion gear due to uneven thermal expansion) all of which affects the gear mesh in the helical gears and in the hypoid gears.
4. All of these forces also cause earlier bearing wear and failures.
I have never built an 094. I have built several Type 1 IRS boxes in the distant past both for trhe street and for my 12 second hobby drag bug (in the '80's). We were concerned about overall strength in that application, not wear over time, so very few lessons translate to this discussion from that experience. I have also rebuilt several motorcycle gearboxes, which is a comparatively simple endeavour with no syncros, no hypoid gears, and no helical-cut gears. Therefore, there were no axial thrust forces.
But on my 750 SS Ducati, which was heavily modified with higher compression and racing cams, I did experience gear failure that essentially was the case hardening simply popping off some of the gear teeth. Notably, the firing dynamics of these v-twins caused, in hindsight, damage similar to what 094 users with TDi engines are seeing. The cause in both instances might well be the very high momentary power pulses that these engines can see at the flywheel. (I should say, however, that Ducati's gear metallurgy in their 1970's models might have been poor  ).
There are good reasons that both automotive racing gearboxes and heavy trucks use straight-cut gears: They do away with axial thrust and are stronger and more resistant to wear. In trucks, racing cars and even motorcycles, gear-whine is not a big deal. In our Vanagons - - well, we shall see. In our rig, Mrs. Howesight is apt to point out, I am the biggest source of whining.
In the Syncro, we are still rocking the 2012 transaxle rebuild that Darryl Christiansen did. I have never done a burnout nor even a hard-accelerating start with this SVX-powered rig. Even off-road, I drive this rig like it has glass gears - - gently. On the highway, Mrs. Howesight and I did abuse the gearbox a bit with some high speeds (over 90 mph at one point, for shiggles), and held 80 mph for hours at a time. When this gearbox is disassembled in due course, we will have to see what mayhem (if any) these abuses caused. The box was broken in with Swepco 201 and then changed over to Swepco 210 after a few hundred miles. This box has Weddle "coarse pitch" 3rd and 4th gears which whine as Weddle and Darryl said they would.
On a rebuild (hopefully a preventive version, not catastophic failure), we will be using Paul Guard's excellent products, including, particulary, his straight-cut 4th gear, drilled mainshaft, new R&P, etc etc. The hope is that we can, again, do high-speed driving when necessary. Straight-cut gears, I think, are the only real solution to the wear at the 4th gear/mainshaft bearing interface. I also think, however, that eliminating this single largest source,(in terms of long term axial thrust forces, not all thrust forces) will have knock-on benefits for the rest of the gearbox components because, as Sodo has rightly preached from his Seattle soapbox for a long time now, the swarf in the gear oil has to be controlled and, if possible, eliminated. The reduction in axial forces on the mainshaft likely will result in longer bearing life.
On driving technique, all I ever wanted was to keep up with traffic when I chose the SVX platform to re-power. So, I am content to downshift to 3rd gear on steep mountain passes. It is possible, on the less steep passes, to stay in 4th gear, but my 4th gear ratio (very high) and large tires give an overall ratio that requires even the SVX to be floored if I stay in 4th. In this scenario, I am not so concerned about the gearbox as I am about straining the SVX needlessly (it has no oil cooler) and burning a LOT of gas with the full-throttle enrichment. I chose a very high 3rd gear also, and can run 62mph at 3,900-4,000 rpm (IIRC) in 3rd gear. So, that's what I actually do on those long passes.
By the same token, I avoid flooring it in 3rd gear up hills, even though my road rage sometimes begs me to do so. The SVX has max torque of 228 ft/lb at 4,400 rpm. I try to not run at full throttle at 4,400 rpm. Backing off the throttle at the re-powered engine's peak torque rpm is, I think, a good way to minimize damage to the Syncro gearbox. For the TDi folks, the peak torque engine speed is much lower, and they have to be a bit more careful.
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'86 Syncro Westy SVX |
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Pchill2
Samba Member
Joined: November 19, 2021
Posts: 410
Location: Georgia
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| Posted: Tue Sep 05, 2023 1:55 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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Good post Howesight but I'm not on board with "cocking" of the gear. The axial force relatively uniform across the mesh. It would be visibly evident if the contact mesh was skewed towards one side of the gear and the bore would be tapered.
I do agree with the loose fit of the gear and bearing to the shaft. The false Brinelling on the inside of the gear bore shows a stationary vibration. The 4th gear is always spinning when the vehicle is in motion. Couple this with a ton of folks reporting noises when idling in neutral and it makes me lean towards some harmonic vibration.
If the false Brinell marks were actually Brinell damage it would have been due to shock loading. Until they are measured I assume they are from stationary micro movements from vibration. As could be the wear on the thrust face.
I do agree with Sodo on the lack of lubrication on the trust face but don't think that is correlated big engines due to the nature of the failure.
Many Vanagons fail with stock engines.
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87 Syncro Westy
Honda K24 swap |
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AndyBees
Samba Member
Joined: January 31, 2008
Posts: 2623
Location: Southeast Kentucky
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| Posted: Tue Sep 05, 2023 5:24 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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Maybe I am missing something in this discussion.
As I understand, once the slider engages the dog teeth on the cone (shifting into 4th), let out the clutch pedal, then the torque/thrust of 4th gear pushing off it’s counter part on the Pinion Shaft pushes it up against the thrust surface of the Main Shaft Bearing. The Thrust Surface of the bearing is an extension of the center race. Thus, it seems to me that the Hub, Slider, Gear and Bearing Race (and 8 ball bearings) are all aligned perpendicular with the Main Shaft and will spin in unison. If so, then the only time the face of the gear is “grinding” against the Thrust Face of the Bearing is during that instant Torque takes up the slack or during deceleration. So, in reference to brinelling, if torque is reduced, does the “bowl” begin the wobble such as in slow speeds with little torque being applied and/or during complete deceleration? If so, does accelerating stop the wobble.
For what it is worth, the years/miles of pounding by engaging into 4th gear and/or letting up on the throttle to decelerate causes the transmission end cap/shifter housing to becomes wallered, especially if/when the bearing becomes loose in the case. This phenomenon is common from the first Beetle transmission to the last Vanagon transmission and everything in between. An aftermarket Thrust Plate is offered for each model.
I recently rebuilt an 091/1 transmission out of an 85 Westy with original 2.1 WBXer (a first for me). It had over 200k miles on it and likely the OE oil. I did not see any 4th gear and Main Shaft Bearing Thrust wear (nothing that stuck out like a sore thumb). The MS bearing was worn out. The 3rd/4th Hub was broken and the end cap was hammered badly (wallered). After the break-in oil, the guy drove it to Bar Harbor Maine and returned with no issues. So, yes, maybe the low torque engines don’t do the damage that is likely to happen with high torque engines.
Anyway, this is a great discussion.
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'84 Vanagon Tin-top, ALH TDI, two trips to Alaska, 2014 & 16. 1989 Tin-top unmolested.
1983 Air-cool, 225k miles, 180k miles mine, seven trips to Alaska from 1986 thru 2003. 1975 Bay hopeful. |
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Howesight
Samba Member
Joined: July 02, 2008
Posts: 3402
Location: Vancouver, B.C.
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| Posted: Tue Sep 05, 2023 6:04 pm Post subject: Re: Big engine + NOT downshifting.... damages 4th gear |
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Hi Pchill:
I think that the cocking of the gear occurs not due to tapering wear (hence little or no evidence of gear bore wear), but due to the designed-in clearance, plus, when gearboxes accrue miles, the additional clearance caused by wear on all surfaces and on the needle rollers too.
Since the ID of the mainshaft bearing and the thrust surface of 4th gear turn at the same nominal rotational speed, there really is no other available explanation. (I say nominal because there may be some harmonics in the gear mesh and/or arising from the engine.) The open question is really how much of that erosion is due to cocking and how much is due to pure axial thrust forces. I don't think it matters since straight-cut gears will eliminate both forces. With both axial and cocking forces eliminated, oil can occupy the space between the mainshaft bearing ID and 4th gear, instead of being squeezed out. Then, the erosion should not occur.
My thought is that the brinelling and false brinnelling are likely not a serious concern for most of us because most of the transaxle's life occurs in 4th gear, where the condition of the gear bore and needle rollers are not so critical. If the brinelling were to be found on 3rd gear, for example, which is spinning on the mainshaft most of its life, brinelling of either flavour would be rather critical.
Rather, the brinnelling and false brinelling are mainly some evidence of the beyond-design-parameter forces involved when re-powering. Even with straight-cut gears of the same material, we might very well see these brinelling clues. But the GT gears are made of better alloy and hopefully will not experience any brinelling.
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'86 Syncro Westy SVX |
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