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Rebuilding 091 DM transmission (early diesel)
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DanHoug
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PostPosted: Fri Nov 17, 2017 4:11 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

thanks for correcting the information regarding the slider hub, Pablo! didn't realize the trans had those differences. i guess i'll just read and learn on this thread!

-dan
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Waldi
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PostPosted: Fri Nov 17, 2017 4:19 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

epowell wrote:
MarkWard wrote:

Yes, all gears sets are always meshed.

It is always best to replace gears in sets even though the wear is on the floating gear engagement teeth. The reason is over time, they wear into each other.


Wow they must be made so incredibly precisely to all 4 be emeshed... but that is clearly why the gears over time get worn in to eachother (as pairs) because of the microscopic inaccuracies in the sizes of the gears would force that.

MarkWard wrote:

edit: the slider has several other pieces. The hub it slides on is splined to the shaft. Look at the inside of the slider and you can see the splines it moves on. There are also 3 metal lugs around the center of the slider, that are spring loaded and are forced against the brass syncro ring when the slider is moved forward. These are what fix the brass syncro ring to the slider assembly and keep it from spinning.


Yes yes! It is all finally clear now... I found the OTHER part of the slider hub, and can clearly see now how it both affixes to the outer part of the slider and to the shaft via these splines... mine is missing the lugs.
Image may have been reduced in size. Click image to view fullscreen.


Original gears can be mixed.
Ofc if you have them paired, you use them paired.
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PostPosted: Fri Nov 17, 2017 4:26 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

gears wrote:
Edward, that is a 1st/2nd slider hub, which doesn't have a full compliment of teeth like the 3rd/4th hub has.

Dan, that is a cracked 091/1 slider hub. The 091 hubs don't readily crack like the 091/1 (094) hubs. That doesn't mean they've never cracked or that they can't wear out .. just that cracking isn't a common problem with those.


Hmm, i think they just did not crack as the engines on those old boxes had less power.
Arent they the same as in the newer boxes ?
The old boxes were never used with JX.
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PostPosted: Fri Nov 17, 2017 5:06 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Waldi wrote:
gears wrote:


Dan, that is a cracked 091/1 slider hub. The 091 hubs don't readily crack like the 091/1 (094) hubs. That doesn't mean they've never cracked or that they can't wear out .. just that cracking isn't a common problem with those.


Hmm, i think they just did not crack as the engines on those old boxes had less power.
Arent they the same as in the newer boxes ?
The old boxes were never used with JX.


That is some interesting info for me also... when I came to Vanagons I came with the assumption that VW BUSES have basically indestructable gearboxes, because years ago I drove BayBuses forever and never had any problems at all with the boxes >>> but to my dismay, after getting a Vanagon and researching, I find out about this hidden 3/4 slider horror and began to feel afraid - this fear is largely what motivates me currently to learn about gearboxes.

But what I am finding out is that my 091's, as gearboxes, seem to have more in common with the BayBus boxes than the later Vanagon boxes - therefore I am intregued by Gear's comment that the 091's don't have the 3/4 slider issue. Can it be stated that a 091 DM is as strong and reliable as an 002 from a 70's bus?



gears wrote:
Edward, that is a 1st/2nd slider hub, which doesn't have a full compliment of teeth like the 3rd/4th hub has.


I'm not sure what "a full compliment of teeth" is but I guess I will see that when I dismantle this shaft.

- - -

I am now looking at my DK 3/4 slider, and can't see any cracks.
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

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gears
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PostPosted: Fri Nov 17, 2017 5:17 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

The later hubs splines have larger ID. That's PART of the reason they break. I feel the other contributing factor is the later shift rail style, which doesn't have defined "stops" (detent positions) like the earlier boxes.

We've thrashed the early 091 transaxles in off-road race cars for years, so the hubs are known to hold up to horsepower & shock loading pretty well.

What we normally did was to go through all the 002 & 091 hubs and sort them into groups: soft, medium, and hard (Rc). Soft for dragrace or shorter off-road races, medium for recreational off-road cars, and the hardest we put in 100K miles street cars.

The softer (more ductile ones) were least likely to crack, but were the first to show excessive wear. (I took all of this into account when we had our own waterboxer hubs made recently.)

Edward .. that photo does not constitute a close-up, parts apart and cleaned, inspection.
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PostPosted: Fri Nov 17, 2017 5:31 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Thinking more about how the actual 'shift' and 'engagement' happens... so, the pinion shaft is always and directly 'fixed' to the wheels (via CVs) - so as long as the wheels are turning the pinion shaft is also turning.

The main shaft however :
1) will not spin at all when in neutral with clutch disengaged (pedal down)
2) but will spin in unison with the pinion shaft (according to wheel speed) when in gear and clutch disengaged (pedal down)
3) when rolling down a hill in neutral (not touching clutch pedal) then the main and pinion shafts are spinning at different speeds: the pinion shaft speed determined by the speed of the wheels, and the main shaft speed determined by the engine revs. This means that the idler gears will be spinning at different speeds than the shafts that support them. Can I now correctly say that unless the idler gear's speed is brought in synch with it's supporting shaft that gear can not be engaged? Therefore the job of the synchro ring is to get the idler gear to spin at the same speed as the slider hub (which is fixed to a shaft).
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Last edited by epowell on Fri Nov 17, 2017 5:40 pm; edited 1 time in total
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Waldi
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PostPosted: Fri Nov 17, 2017 5:36 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Oh yeah thin inner diametr is smaler same like the gears.
But i think the cracks going on from the edges has nothing to do with the id.
Different hardening maybe.
Anyway the edged holes are bad ingineering like square windows on old plaines.
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epowell
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PostPosted: Fri Nov 17, 2017 5:46 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

gears wrote:

Edward .. that photo does not constitute a close-up, parts apart and cleaned, inspection.


No doubt!
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PostPosted: Sat Nov 18, 2017 3:15 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Sorry to bore you all with my thinking aloud, but I finally see it clearly how shifting works. It's actually very simple
1) slider hub and idler gear must be spinning at close to the same speed before engagement can occur
2) before a shift, when the clutch pedal goes down, the hub and idler will most likely not be spinning at equal speeds.
3) as we push the gearshift "into" gear the slider forces the synchro gradually onto the idler's tapered cone thereby (via friction) FORCING the idler's speed to become similar to the slider's speed. [this can happen, meaning that the slider's speed can 'over-rule' the idler's speed, simply because the slider is fixed to the shaft and the idler is freely floating]
4) because of the somewhat long taper of the idler's cone, the speed of the idler will match the slider's speed slightly before the 2 become engaged.
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PostPosted: Sat Nov 18, 2017 5:58 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Ed,
Youtube is full with educational videos about transmission basics like:


Link


Link


The difference between a standard transmission and the Vanagons transaxle is the differential is built into the same housing and the pinion shaft of the differential is the output shaft of the transmission

edit: and the Vanagon transaxle has only two shafts so there is no separate countershaft.
Two gears are running freely on the input shaft and two gears are running freely on the output shaft. With this design there is no need for a third shaft so the gearbox is shorter and narrower.


Link

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PostPosted: Sat Nov 18, 2017 4:27 pm    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Thanks Zoltan.... phew! I got it now! Those vids helped to confirm what I've been figuring out. It's totally ingenious!
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PostPosted: Sun Nov 19, 2017 5:33 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Now I will throw a wrench in your thoughts. My racing transmission has 1:1 5th gear. Instead of a 2 gear set, 5th does not have a set. When you shift to 5th, it locks the input shaft to the output shaft. A 1:1 5th would not be practical for a hwy box.
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PostPosted: Sun Nov 19, 2017 6:41 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

And, the 5-speed tranny (Vanagon) has very little advantage over a 4-speed, factory or aftermarket conversion, and no difference in the two top gears.

Explanation: Factory, going backward from top gear, the 5-speed 5th gear and 4-speed 4th gear are in the same location on the shafts and so on until 1st gear of the 5-speed. There is a difference in ratio of the lower gears and the extra gear in the 5-speed is actually 1st gear. So, in the end upgrading either transmission to taller top end gears (5-speed [4th & 5th] and 4-speed [3rd & 4th]) you can end up with the same ratios.

As for the Weddle 5-speed conversion, I'm not sure, but if I remember correctly, it's the same as described above.

The YouTubes do put it all into prospective. Thanks for sharing ZsZ. I've seen a lot of them. I really like the one on the DSG tranny.
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PostPosted: Sun Nov 19, 2017 9:20 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

MarkWard wrote:
A 1:1 5th would not be practical for a hwy box.

why not?

In the above vid it shows 4th as 1:1.
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PostPosted: Sun Nov 19, 2017 9:23 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Our VW manual trannys are all overdrive type, including the 4 speeds.

Mark



epowell wrote:


In the above vid it shows 4th as 1:1.
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PostPosted: Sun Nov 19, 2017 9:26 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Did not watch the videos, but a 1:1 final gear would be very short for hwy cruising unless paired to a tall final drive. The vanagon final gear in all the versions had an overdrive final gear.
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PostPosted: Sun Nov 19, 2017 9:32 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

AndyBees wrote:
And, the 5-speed tranny (Vanagon) has very little advantage over a 4-speed, factory or aftermarket conversion, and no difference in the two top gears.

...I feel OK about sticking with 4 speeds - I love the "H" pattern.
What I am wondering about is why were the 70's 002's having such a longer pinion then the early diesel vanagon 091's! Is it true that the 70's buses' engines were more powerful than a CS (50HP) early vanagon engine?? [I should look that up]

AndyBees wrote:

Explanation: Factory, going backward from top gear, the 5-speed 5th gear and 4-speed 4th gear are in the same location on the shafts and so on until 1st gear of the 5-speed. There is a difference in ratio of the lower gears and the extra gear in the 5-speed is actually 1st gear.


Ah, that explains a lot.... so I can see that might be more accuratly described not as having 1st - 2nd - 3rd - 4th - 5th.... but rather, having 0 -1 -2 -3 -4th ...the "0" gear being the added gear rather than the 5th. Smile clever, but that also means you need the "non-H" pattern. - - - - is it true then that 5 speeds that have the H+ pattern have 5th as the added gear? I'd assume so.
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PostPosted: Sun Nov 19, 2017 9:44 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

That is baloney. The 2wd 5 speeds are closer spaced throughout and generally had a 5th ratio taller than 4th in a 4 speed and a 4th that was a taller ratio than 3rd in a 4 speed. The overall gearing depends in both models on the r&p ratio.

Syncro 5 speeds are in fact what you describe as they have a special G gear for very low speed driving and a matching special low R gear.

Mark

epowell wrote:
...... so I can see that might be more accuratly described not as having 1st - 2nd - 3rd - 4th - 5th.... but rather, having 0 -1 -2 -3 -4th ...the "0" gear being the added gear rather than the 5th. Smile clever, but that also means you need the "non-H" pattern. - - - - is it true then that 5 speeds that have the H+ pattern have 5th as the added gear? I'd assume so.
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PostPosted: Sun Nov 19, 2017 9:48 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

OVERDRIVE: I get it... so "overdrive" means the highest gear causes the output shaft to spin fast then the input shaft. Cool, I've listened to BTO my whole life and never known exactly what that word meant Very Happy
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PostPosted: Sun Nov 19, 2017 10:18 am    Post subject: Re: Rebuilding 091 DM transmission (early diesel) Reply with quote

Like Mark said, the 094 5-spd is great for engines with narrow power band or low horsepower, because 4th gear is 20% taller than 3rd in a 4-spd. This allows one to maintain reasonable uphill highway speeds when running a stock 1.9 / 2.1, or especially an underpowered 1.6 diesel (or overloaded expedition Westy).
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