Differences between dogbox, dog teeth, syncho, 915, G50, modern gearboxes - Page 2

sc_rufctr · 05-14-2016, 07:01 PM

Quote:

Originally Posted by Matt Monson

Is this a dog box?

Yes... Second shift fork from the top. You can see the dog teeth.

They clunk when you shift them. Great design but a PITA on the street.

Quote:

Originally Posted by cstreit

Some of you probably winced every time I posted here about another blown gearbox. I think that's over.

I've been racing 8 years now and for 6 had maybe one DNF... Then in the last 1.5 I accumulated over 6 all due to gearbox failure. Most were related to failures of the 3rd gear dog-teeth pulling off the gear and/or other components being damaged as a result. This included 3 blown syncro assemblies, 2 blown guide-forks, several damaged gears, etc... Needless to say the cost of my 915 was well exceeding what is reasonable even for my heavily modified GT car.

At some point you come to the realization that doing the same thing (rebuilding with new gears/syncros) over and over and expecting a different result is a bit silly.

I've thrown my hands up several times and asked someone else to help make it right several times without success. The last time I wrote a substantial check the place assembled it improperly TWICE (giving them one more chance to do the right thing before I post who). Okay it's time to take matters back into my own greasy hands.

I turned to WEVO and Guard Trans for help and got what I was looking for. Hayden@Wevo helped me assemble a package for my 3/4 shift plane to address the issues I've been having, mainly weak dog teeth and pulling off dogs. He guided the modification of the Guard Transmission pro-shift syncros to fit my 915 3/4 gears and had them peened on to the gear itself. We had some initial challenges but Hayden stuck with me thru the whole thing, unlike any of the other vendors. Literally spent a massive amount of time on the phone with me making sure we got everything setup and running properly. THANKS Hayden.

I've got one event on the gearbox now, shifting was weird at first with 1, 2, and 5 being syncros and 3/4 being dogs but you get used to it quickly. The shifting into these is VERY fast and VERY positive. The collars you see on the shift-rail are WEVO's locking shim kit to ensure the shock-load from the new engagement style do not move the fork.

masraum · 05-14-2016, 07:09 PM

Quote:

Originally Posted by Matt Monson

Some in this cesspool lack a sense of humour.

That's what the various smileys are for buttface.

(or green font if you're a regular)

See how that works?

masraum · 05-14-2016, 07:10 PM

Quote:

Originally Posted by red-beard

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.

I thought I had read that all Porsche trannies should be fully synced, but wasn't 100% certain. I guess I should have trusted my gut.

Shaun @ Tru6 · 05-15-2016, 03:42 AM

Quote:

Originally Posted by Matt Monson

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

That is of course one of your pieces of limited slip jewelry Matt. It's a little breathtaking in person, shame to hide it inside the box. The Ferrari shop owner who stopped by yesterday was suitably impressed.

Getting some shims and should be all set with the rebuild. Thanks again for your help, you are a real asset to the community.

javadog · 05-15-2016, 05:01 AM

Quote:

Originally Posted by sc_rufctr

Yes... Second shift fork from the top. You can see the dog teeth.

They clunk when you shift them. Great design but a PITA on the street.

Of course, most motorcycles have this style of gearbox and they usually shift pretty well...

JR

Matt Monson · 05-15-2016, 06:15 AM

Quote:

Originally Posted by sc_rufctr

Yes... Second shift fork from the top. You can see the dog teeth.

They clunk when you shift them. Great design but a PITA on the street.

Peter,
If you look closely you will see that not only is it a dog box but as Javadog suggests a proper sequential. The dog box conversion we designed and manufactured for Wevo continues to use an h-pattern, detents, and neutral between each gear.

The sequential box pictured, which we designed for the GT3 and Cup Car, doesn't have neutral between gears. Instead of flopping the pairs of idler gears back and forth across the shafts, all fixed gears are aligned on a single shaft. The shift drum rotates and actuates two shift forks simultaneously and they slide up and down the single shift rod. They aren't attached to the rod, it just aligns them. It also is hollow and serves as a spray bar for lubrication of the gears.

Matt Monson · 05-15-2016, 06:16 AM

Quote:

Originally Posted by masraum

That's what the various smileys are for buttface.

(or green font if you're a regular)

See how that works?

Buttface? Are you 12?

Geary · 05-15-2016, 06:20 AM

Oh, man .. this question is asked on possibly my busiest weekend of the year, when my wife & I are moving up to Bend, Oregon. So two cents worth is all ya get ..

The Guard GT3 dog box shown below (some OE parts purposely omitted) is what changed Porsche's direction in race transaxles. Up until this point, the pinnacle of Porsche race box shift performance had been the steel synchronizer ring.

The dogs in this H-pattern box utilized the "pent roof" design, which resisted rapid wear found in prior dog box designs. Within 5 years, the sequential dog box was developed, which unfortunately must use flat roof dogs.

The 915 synchronizing system was a joke for the era in which it was still utilized. (Thanks for the explanation of "why", Matt.) In truth, VW was decades ahead of Porsche in adapting the Borg Warner synchro system.

masraum · 05-15-2016, 06:22 AM

Quote:

Originally Posted by Matt Monson

Buttface? Are you 12?

Demonstrating a point. Name calling/insults/whatever followed by smileys is often used to indicate that the insults were in jest.

Tone and intent is generally impossible to convey via text alone. If we'd all been face to face, we would have been able to pick up on subtle clues of tone and body language, but since this is all via text....

Matt Monson · 05-15-2016, 06:27 AM

Quote:

Originally Posted by masraum

Demonstrating a point. Name calling/insults/whatever followed by smileys is often used to indicate that the insults were in jest.

Tone and intent is generally impossible to convey via text alone. If we'd all been face to face, we would have been able to pick up on subtle clues of tone and body language, but since this is all via text....

I think you got punk'd.

You were pretty much the only one in the conversation who didn't know who I was.

Regards,

Matt Monson
Guard Transmission LLC.

manbridge 74 · 05-15-2016, 06:34 AM

I think motorcycles get away with dog box sequential due to low weight, small engines and little need for noise concerns. They can be balky/clunky at low speeds. At least the street bikes I rode 20 years back.

Matt Monson · 05-15-2016, 06:42 AM

Quote:

Originally Posted by manbridge 74

I think motorcycles get away with dog box sequential due to low weight, small engines and little need for noise concerns. They can be balky/clunky at low speeds. At least the street bikes I rode 20 years back.

It's also a "logistic" issue. With the foot shifting and hands braking and clutching and throttle, it is far easier to choreograph the shifting than in a car where the functions are reversed. It's totally possible to drive a modern sequential gearbox in a car on the street, but it is way easier to ride a bike.

sugarwood · sugarwood's Garage

Ok, so the 915 is synch'ed just like a modern tranny. My 915 works great, but just has an occasional delay, usually when cold.
With a modern car, once the synchros have some comparable age, you may also also get that slight delay resistance when shifting into a gear?
ie: Modern gearboxes are not immune to this, by some other design. They are similar.

Matt Monson · 05-15-2016, 07:23 AM

That's correct. Your 915 will never shift as quickly as a modern gearbox but the triple ring synchross on something like a Gt3 in 1 and 2 are balky when cold.

masraum · 05-15-2016, 07:34 AM

Quote:

Originally Posted by Matt Monson

I think you got punk'd.

You were pretty much the only one in the conversation who didn't know who I was.

Regards,

Matt Monson
Guard Transmission LLC.

Absolutely true. It's been years since I spent much time on the 911 Tech board. I think my first 10-15k posts were over there, but after I sold my 911, I eventually migrated to this side.

Matt Monson · 05-15-2016, 08:07 AM

Quote:

Originally Posted by masraum

Absolutely true. It's been years since I spent much time on the 911 Tech board. I think my first 10-15k posts were over there, but after I sold my 911, I eventually migrated to this side.

No worries. I'm playful.

Jon B · 05-15-2016, 08:08 AM

Quote:

Originally Posted by sugarwood

What about "dogbox" ? Is dogbox even more primitive than the 915 ? Or is the 915 a dogbox style gearbox?

A "dogbox" is a constant-mesh transmission without synchromesh.
I would not consider it a "primitive" design, just a simpler design.
Gears of a constant-mesh transmission, whether synchronized or not, are usually engaged by means of a dog clutch.

A "crashbox" or sliding-mesh transmission, where the gears themselves are moved into engagement, is considered a primitive design.