Halfway Between A Dog Box And A Syncromesh Box.

[Rolls]

Background for people that don't know, dog boxes have no syncromesh and hence engage by the dogs only, eg notches that latch and fully engage the gear instantly. On a dog box these are spaced further apart to allow for some rpm mis match, if you get it wrong the dogs bash against each other and make a mess. A syncromesh still has these dogs however they are very closely spaced together to allow for essentially zero mismatch in speed, the syncromesh then forces them to the correct speed to guarantee they mate properly.

My question is I always wondered if there existed a design that was sort of half half, eg a smaller syncro (less weight to spin up, but not as good at matching gear speeds) and big spacing between the dogs to allow clutchless shifting.

So if I did this would I get the best of both worlds? Eg I can do fast clutchless shifting due to large dog spacing however if I do slow shifts I can still utilise the syncromesh? Or does the syncro itself always slow the shift down (due to the force required to spin them up) and hence mean you can't shift fast enough to do a clutchless shift in this hypothetical design?

Curious what peoples thoughts are, I'm not actually considering this, just curious if it would work.

[NYTSKY]

There is no need really, you can still drive a dog set normally on the street.

[Rolls]

I saw that video but I wasn't convinced that he didn't do like 20 takes to get it that nice. I mean can you really drive it like that without ever crunching it? He says 9/10 times putting it into first, that means 10% of the time you crunch it.. if you know how to drive it.

I guess the alternative is to put a syncro mesh on 1st gear I mean you never used 1st on the track/when racing.

Regardless though would my idea work or would the syncromesh slow the shifting down too much? I get the impression that it is the dog spacing that makes a dog box work.

Edited June 29, 2013 by Rolls

[GTSBoy]

It's not the spacing of the dogs that makes it work. You couldn't get away with your idea. A box either has proper synchro, or it has none. If you want to find out what your idea would feel like to drive, go borrow a 105 or 116 ALFA that hasn't had new synchros in 50000 kays and that'll be pretty much it.

By the way, in the video he said "9 times out of 10 you won't hear a noise". Not a crunch, a noise. The noise you did hear when he did it was the thump of dogs hitting each other. They can and do engage without much noise. But you can't always get it just right.

[NYTSKY]

It will go into first everytime, what he is saying is there will be a louder clunk if you dont wait those few seconds, which is nothing to worry about as it is only the dog gears engaging each other at a faster speed.

As in this vid with PJ, listen as he engages 3rd (1st at 1.37sec) without waiting those few seconds:

[NYTSKY]

Also it isnt the dog spacing that makes them work it is simply the dog gears slotting into each other.

[Rolls]

Anyone seen this before?

http://www.gizmag.com/zeroshift-instant-transmission-for-trucks/8418/

http://www.zeroshift.com/

[GTSBoy]

Really old and never went anywhere IIRC.

[Rolls]

After a good look it looks like maintenance would be increased with the only benefit being slightly more power transmitted during shifts. Down shifts are essentially the same with upshifts still needing ignition cut or you spin the wheels upsetting traction so you don't end up getting that extra power anyway.

[Bennis]

Dont have much to add technical wise, but I saw you mention that hte ppg guy might have taken several takes to get that vid.

Heres an AWD rb26 cefiro with a quaife dogbox, street driving it. Just incase you were wanting to see some other AWD nissan dogbox street work.

Seems to drive nicely.

http://www.youtube.com/watch?v=M37PnaLbOJs

and

http://www.youtube.com/watch?feature=player_detailpage&v=D1yFXlJYtI0#t=86s

[Duncan]

BTW on the other hand, you don't need a clutch to change gears, you just need the right revs. unfortunately the window is much smaller with a synchro box and there is often only a small gap in required revs due to slow speeds which makes it very hard on the street (I can only get it right 80-90% of the time).

Fundamentally the synchros slow down gear changes, that's the bottom line.

[abr33]

It's not the spacing of the dogs that makes it work. You couldn't get away with your idea. A box either has proper synchro, or it has none. If you want to find out what your idea would feel like to drive, go borrow a 105 or 116 ALFA that hasn't had new synchros in 50000 kays and that'll be pretty much it. By the way, in the video he said "9 times out of 10 you won't hear a noise". Not a crunch, a noise. The noise you did hear when he did it was the thump of dogs hitting each other. They can and do engage without much noise. But you can't always get it just right.

I guess the alfa syncros are kinda what rolls is on about, I had a 80' gtv alfa and the syncros are very odd, like bigger spaced dogs and the slip ring thing only lets it do half a turn ish before engaging, hence lots of crunching. That said I could smash it through gears like it was a dog box. But it never works well as a syncro box or a dog box lol

[GTSBoy]

ALFA boxes had Porsche style synchros. They are completely unbeatable......right up until they are 50% worn, at which point they are rooted and don't work at all. The engagement dogs on them are otherwise no different from any other synchro box however. Little pointy teeth.

[Rolls]

GTSBoy I see you deleted your reply but this was a reply someone on OCAU wrote regarding removing half the syncro

"I have done it in a Toyota 5 Speed... Actually took two out of every three synchro teeth.. also cut a heap more oil slots into the friction face of the synchro where it mates to the cone on the gear set.

Along with a lot of other small modifications it makes shifting faster if you have your speeds about matched... also increases the odds of breaking syncro rings and suffering premature wear.
Takes a bit of experimentation to get the right balance and it ain't a 'quick job' to do..

Unless you are chasing the bleeding edge of performance, it is a waste of time. And if you are chasing the bleeding edge... there are probably better ways of doing it.

Again... it falls into the category of "most people only do it so they can brag about the fact they did it"

[GTSBoy]

I didn't delete anything.

Cutting teeth right out of a synchro set is an incredibly rough mod. Proper dog boxes have big square edged dogs that just grab hold of each other and go. Synchro engagement teeth have nice little sharp points on them that ease the engagement of the square part of tooth. If you drive a box that has all the tips of the teeth knocked off you'll know what I meant about driving a worn out ALFA box. The pointy bits are necessary. The grinding noise you hear when you miss a shift is those teeth being damaged. If you do what the OCAU guy did, you're essentially just ruining it for little good reason, as per the last line of your post.

[Rolls]

For some reason your post didn't show up until after I posted. I'm not going to do anything to my box, this was just for my curiosity.

Cheers