Pelican Parts Forums - Differences between dogbox, dog teeth, syncho, 915, G50, modern gearboxes

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Differences between dogbox, dog teeth, syncho, 915, G50, modern gearboxes

Does the 915 fundamentally differ from modern gearboxes? Or does it have more in common with a modern gearbox than you'd think? More specifically, synchros.

Is the 915 meant to be operated in a fundamentally different way than a G50 or a Sentra gearbox? When I shift my 915 gearbox, I don't force it. Sometimes, if I feel a resistance, I lightly maintain pressure on it, and then it slides into gear. I understand this to be normal. Would this also be the case in a G50 or Sentra? Or are they totally different?

Is this attributed to the synchro? Does the synchro (or something else) need to speed up to match or something? Does this not apply to modern gearboxes? Is the 915 part of the "Syncromesh" paradigm? What about "dogbox" ? Is dogbox even more primitive than the 915 ? Or is the 915 a dogbox style gearbox? Where does the G50 and a 2005 Sentra gearbox fit into all this?

kevin we are waiting for your informed treatise.. thanks in advance! matt.. how about you!

Quote:

Originally Posted by sugarwood (Post 9120771)

Manual transmissions since the 50s have had syncros on most gears (sometimes not on #1).. My old 901 was syncromesh.

I suspect the syncros on your 915 are a bit worn, but are still doing their job.

Dogboxes are not necessarily more primitive, there are no syncros. Here's a pretty good explanation from superstreet dot com.
"Dog engagement is normally used in racing applications where fast, precise shifting is needed. Dog gear engagement is facilitated by numerous large teeth (dogs) that mate into matching openings machined into the opposite surface of the drive gear. Unlike the synchro engagement, there is no synchronizing mechanism to assist in equalizing speed. Ideal gear selection—e.g. minimal clashing and wear of the dog rings—is achieved by quick shifts; the motto here is “the quicker the better”, so bang away."

Best
Les

Quote:

Originally Posted by Geneman (Post 9120776)

kevin we are waiting for your informed treatise.. thanks in advance! matt.. how about you!

This is OT and not the Tech forum. My only input is that if you aren't careful with a dog box it will bite you in the arse.

If my replica thread hadn't been moved here I wouldnt even be checking in to this shyte hole.

Quote:

Originally Posted by Matt Monson (Post 9120822)

HEY! Some of us live here! SmileWavy

Here

Let me google that for you

Synchromesh vs. Dog Box - Gearbox Beatdown - Import Tuner Magazine

Synchromesh Transmissions vs Dog engagement

Synchro vs. Dog Box : Racing by LotusElan.net

<iframe width="853" height="480" src="https://www.youtube.com/embed/n_1jO64tuQA" frameborder="0" allowfullscreen></iframe>

Dog engaged transmissions aka the “Dog Box” | Automotive Thinker - Discussing the finer points of automobiles

Dog engaged transmissions aka the “Dog Box” | Automotive Thinker - Discussing the finer points of automobiles

Ask the Best and Brightest: Dog Engagement vs. Synchromesh - The Truth About Cars

Quote:

Originally Posted by sugarwood (Post 9120771)

Does the 915 fundamentally differ from modern gearboxes? Or does it have more in common with a modern gearbox than you'd think? More specifically, synchros.

The 915 is a full synchro box. It's "modern".

Quote:

Is the 915 meant to be operated in a fundamentally different way than a G50 or a Sentra gearbox? When I shift my 915 gearbox, I don't force it. Sometimes, if I feel a resistance, I lightly maintain pressure on it, and then it slides into gear. I understand this to be normal. Would this also be the case in a G50 or Sentra? Or are they totally different?

Your 915 is probably worn, and would do with a refreshing. I once drove an '84 or '86 911 with a 915 that shifted up and down like butter.

Quote:

Is this attributed to the synchro? Does the synchro (or something else) need to speed up to match or something?

Yes, it does, that's how they work.

Quote:

Does this not apply to modern gearboxes?

Nope, that's how they work too.

Quote:

Is the 915 part of the "Syncromesh" paradigm?

Yes it is

Quote:

What about "dogbox" ? Is dogbox even more primitive than the 915 ?

They are often used for racing and can be faster than a synchro box. I guess they could be called more primitive, but I'm not sure if that's actually accurate or not.

Quote:

Or is the 915 a dogbox style gearbox?

Absolutely not, unless it's been modified which I believe is possible, but I'm pretty sure you'd know.

Quote:

Where does the G50 and a 2005 Sentra gearbox fit into all this?

There are multiple ways to synchromesh a trans. The G50 uses a different type. I believe it's quite a bit more robust than the system in the 915. I have no idea what style is used in the Sentra, but the 915, G50 and Sentra manual trans are all fully syncro.

It's my understanding that Porsche invented a syncro system for transmissions, and therefore pretty much all of their stuff has been synchronized. I guess it's possible that some of the early stuff wasn't.

I had a guy try to sell me an SC once who tried to tell me that 1st wasn't synchronized. He was either a scheister or horribly misinformed.

Porsche Split-Ring Synchromesh

Quote:

Porsche Split-Ring Synchromesh

The Porsche system was patented in 1947 by Dr Ferdinand Porsche, a German engineer renowned for his own high-performance cars as well as for having designed the original Volkswagen car. Dr Porsche produced the design specifically for the Cisitalia racing car of that era but the principle has since been applied, with amendments, by numerous other car manufacturers.

Apart from its undoubted efficiency, the Porsche layout has the advantage of compactness, allowing the gearbox to be relatively short and the three shafts to be correspondingly shorter and stiffer than those on other gearboxes.

It is simplest to describe the layout of Porsche synchromesh if it is applied to the third and fourth gears of a four-speed gearbox. Between the input shaft pinion and the third-gear pinion on the mainshaft a "spider" is solidly mounted on the mainshaft. The spider has three equally-spaced radial projections.

These projections have feet which are a sliding fit in slots cut into an internally toothed ring. Both ends of the teeth have a shallow taper, thus forming two outward-facing cones. On the outside of the ring are ribs that carry the gear selector fork.

The two gear pinions have the usual externally toothed dog clutch member, the teeth of which correspond to those within the sliding ring. Each of the pinions also has an extended hub which carries a gapped or split ring known as the "Porsche ring" and this resembles a large-section piston ring.

The Porsche rings have conical outer surfaces which, in turn, correspond to the cones within the sliding ring. Since the rings taper slightly in thickness round their circumference, from the middle to the ends, they cannot be carried directly on the hubs of the dog clutch members since that would make their outer surfaces eccentric. Between the ring and the member is another ring with the appropriate eccentricity between its inner and outer surfaces, thus making the outside diameter of the Porsche ring coaxial with the shaft assembly. A key prevents the intermediate ring from rotating on the hub.

Diametrically opposite this key, on the outside of the intermediate ring, is a projection that fits into the gap of the Porsche ring. The latter is thus compelled to revolve with its pinion and dog clutch member but, however, the gap is significantly wider than the projection, allowing the Porsche ring some rotational freedom on the intermediate ring.

Thus, when the gear lever is moved from neutral towards one of the gear positions, the selector fork takes the sliding ring in the appropriate direction, bringing one of its internal cones into contact with the facing cone on the Porsche ring. The first effect of the friction between the cones is to rotate the Porsche ring by the amount necessary to take up the clearance between its gap and the projection on the intermediate ring.

Once one end of the Porsche ring has butted up against the projection, the rotational drag on the ring causes it to expand. Expansion of the ring in this manner has two results; it increases the pressure between the cone faces of the Porsche ring and the sliding ring and it prevents the latter from moving any further towards the dog clutch teeth.

The tapering thickness of the Porsche ring makes it exert an equal outward thrust all round its circumference when it is expanded. Increasing the force applied to the gear lever merely raises the pressure between the cones, thus helping synchronization of the speeds. When synchronization is achieved, the frictional drag on the Porsche ring disappears, so that the ring is no longer expanded. The effort on the lever then causes the sliding ring's cone to exert a wedging action on the Porsche ring, thereby forcing down the intermediate ring and reducing the Porsche ring's diameter enough for the sliding ring to pass outside it and engage the teeth of the dog clutch member.

Quote:

Originally Posted by Matt Monson (Post 9120822)

Thanks for the info. You're welcome to not let the door hit you in the arse on the way out, ya wanker.

Have a nice day!

SmileWavy

As I understand it, Porsche finally gave up on its own method of shifting gears and went to the BorgWarner syncro set up.......I think that was when they came out with the G-50 trans.......a much better arrangement.

Quote:

Originally Posted by J P Stein (Post 9120957)

That's my understanding as well.

Quote:

Originally Posted by masraum (Post 9120953)

Thanks for the info. You're welcome to not let the door hit you in the arse on the way out, ya wanker.

Have a nice day!

SmileWavy

Some in this cesspool lack a sense of humour. :)

Quote:

Originally Posted by masraum (Post 9120952)

I've rebuilt early 901s, 914-901s, late 911-901, early 915s and late 915s. They are all basically the same sync system and 1st gear is synced on all of them.

Quote:

Originally Posted by Matt Monson (Post 9121001)

Some in this cesspool lack a sense of humour. :)

Then you should have used GREEN FONT SmileWavy

Quote:

Originally Posted by red-beard (Post 9121009)

Then you should have used GREEN FONT SmileWavy

Sorry. Call me noob. I live in a world where nothing in an OT forum is taken seriously.

Quote:

Originally Posted by Shaun @ Tru6 (Post 9120933)

http://forums.pelicanparts.com/uploa...1463269803.jpg

Shaun,
What's that silly looking silver thing in the middle of this picture? Does that go inside of a transmission?

Quote:

Originally Posted by Matt Monson (Post 9121001)

Some in this cesspool lack a sense of humour. :)

When did 90% become known as "some"? :)

Quote:

Originally Posted by J P Stein (Post 9120957)

I don't know when they changed, but the compressed ring system used on my 519s are very slow. From 1 to 2 you need to shift fast and hard and not worry about the noise. The 741s were a little better. I understand the 901 was a 741 with more gears.

Quote:

Originally Posted by wdfifteen (Post 9121096)

The 519 and 644 are a weird design, but technially synchronized. It doesn't have traditional dog teeth in the way we usually see them. You are correct that the 741 is when they "modernized" the design. Porsche was stubborn and refused to abandon the split ring design for more than a decade after the Borg Warner design had proven itself better. But then they were also financially on the ropes and considering killing the 911 model line compltely.

The 924, 928 and 944 we're the first to get Borg Warner style Getrag gearboxes. The 911 kept using the 915 for another ten years because the whole car was on the chopping block and they weren't going to invest in a new gearbox for it. Only once it got a stay of execution did they commission the G50 Getrag gearbox and out Borg Warner syptyle syncrhos in the "flagship" as well.