TurboIIGuy

Hey what's up everybody.
I've got my experience with racing and modding cars and such but obviously there's always something new to learn.
What is all this stuff about dog cut gears, dog box transmissions and stuff like that. I basically want to know what is the purpose of such equipment, what is the advantage, and how do these trannys drive?
Thanx in advance for any and all info.

rx7f4n4tic

as far as i know the dog boxes dont use synchros and you dont need to use the clutch to shift. If something blows up all you have to do is replace the gear, something about it being independant from anything else. Only time i read about these is from an eclipse site about a GSX dogmission box. So thats all I know. Anyone else feel free to add/correct me if im wrong.

peejay

It's still a very good idea to use the clutch to shift a dogbox.

Instead of a splined collar mating with splines on the side of a gear, with a brass clutch (synchro) to equalize the speeds of the two before the splines mate, a dogbox just has four or six or so big huge freaking dogs, or lugs, on the collar and on the side of the gear. No synchronizer to block a fast shift. Just CLACK and you are in gear.

if you shift quickly.

If you shift slowly... GROOOOOOOOOOONNKKKKKTHUNK.

The slower you shift, the more the setup wears. No matter how quickly you shift, it still wears much much faster than a normal synchronized transmission.

Whether all of the gears are independently replaceable depends on the transmission. Since most dogboxes are dedicated race transmissions, and serviceability is important in a race transmission, MOST dogboxes have individually replaceable gears. But not all, there are gearsets available for many transmissions that maintain a one piece countershaft with no individually replaceable gears.

Likewise the cut of the gear doesn't have anything to do with it. MOST dogboxes have straight cut gears, because again these are generally race only transmissions and straight cut gears are stronger, load the bearings less, and heat up the oil less. They are also cheaper to machine. However they are loud. Very loud. (Which is why you don't see straight cut gears in OEM trannies except for Reverse gear, which is why many cars whine in Reverse. That's straight cut gear talking) You can get dogboxes with helical-cut teeth, and you can get synchro boxes with straight cut teeth.

Kenku

Welp, peejay said it already. Just thought I'd chip in with the anecdote that the 787B was actually running a synchro box at LeMans instead of a dogbox, for reliability reasons. Though nowadays everyone's running dogboxes, they're also hydraulicially actuating the shifts (usually) so it's all as quick as possible, and the gears are now made out of forged unobtanium or somesuch.

peejay

I remember watching a WRC rally on the evil tube, and Markko Martin's Focus's electronic gearchange failed, so he had to convert to manual (unhook handbrake lever, attach to transmission linkage). The commentator noted that not only would he not hindered by not having a handbrake, but he would have to shift very carefully in order to keep from breaking the transmission.

Flash forward to a couple months ago, watching our new CNC equipment making metal shavings in the process of converting a 2 bolt main Chevy block into a splayed 4 bolt main. First it milled the registers wider, then it changed tools and drilled the new holes, then it changed tools and countersunk, then it changed tools and tapped the holes. Very impressive to watch, especially when it ran full bore with the tap and did all ten caps faster than you could watch. I told my boss how impressed I was, then he smiled and told me I haven't seen anything yet. He fiddled with the controller and started the program at the point where it tapped the holes. It retapped all of the holes, threading the tap PRECISELY where it had run the first time, into the existing threads, running full bore! No chips! He said that because the computer knows the distances to an exact degree, and it knows the exact rotational position of the head, the mill not only can accurately reproduce, but it does it precisely the same way right down to the tool's position rotationally, every time.

Then I thought about that commentators' comment. What if the gearbox were fitted with rotational sensors? If it were, a computer could KNOW the position of each slider in relation to its gear, and it could time each shift so that there was no dog/dog contact at all until the slider was fully slid home. End result, greatly increased transmission life.

Note that I don't know if they are actually doing this, it's just a neat idea I had.

Kenku

Hmmm. Makes me wonder how many dog teeth they're running in F1 transmissions. The parts diagrams for one of the fairly recent model Hewland boxes is online, and IIRC, there's only like, 6 teeth on the gear faces. It was intended as primarily a manual sequential box though.

Interesting thought indeed about keeping track of all the gear positions but it's not really necessecary. If you think about it, what kills the dog teeth is them being partially engaged while there's a great deal of differential speed and inertia (used genericially to mean anything resisting change in rotational speed, IE the engine, and not just the inertia of the flywheel) on the input shaft side. There's three ways around this. First is, obviously, lift the throttle (to reduce the engine's resistance to slowing down) and shift quickly enough that the teeth are fully engaged ASAP. Second is to press in the clutch so that the only inertia resisting the input shaft changing speed is that of the flywheel/clutch, which the teeth damn well should be able to handle though if there's enough of them or you shift too damn slowly it might make some noise.

The third is to make the engine lose enough RPM fast enough that there is no speed differential by the time the slider's reengaging... which is done by cutting fuel and/or spark. And having a light enough rotating mass that the engine can lose enough speed in the very brief (how brief exactly being computer controlled) instant it's in neutral. Which on F1 cars anyway, isn't *too* difficult as most only lose 1-2k RPM per shift.

The 3rd is the fastest and easiest on the teeth, but... not really doable without electronics.

88GT

Interesting thread..
At one point I considered going to a Dog Box in my TII circuit project but this thread is exactly why I just didn't dive in. I didn't have enough personal info to justify the work. I tell ya.. the more you know.. Anyone here actually using one in a 2nd gen?

KevinK2

Not sure about the new bikes, but based on a rebuld I did, my 75 Trident 750 triple uses dog gears. Also has a dry clutch. I often didn't use the clutch for easy upshifts. Very smooth shifter.

The audi electronic manual is brilliant, using dual lay shafts, dual clutches, so the next gear can be preselected during acceleration.

http://www.vwvortex.com/artman/publi...nter_317.shtml

peejay

Most (all?) bikes have dog trannies.

I used to know a 'Stang-banger who used a pro-shifted (dogbox) transmission in a semi-daily driver. He said it's fine if you know what you're doing, but you can't shift casually. He also said that at the dragstrip he didn't use the clutch, he'd just yank the lever as the engine hit the rev limiter (it was either 8800 or 9800, he revved the snot out of his engine), and the unloading from the limiter was enough to let him out of gear and slammed into the next one.

speedturn

iTrader: (1)

I run a dog ring G-Force GF-5R box in my road racing peripheral port 13B RX-7. Pretty much everything peejay said is right about dog ring boxes. You must shift them as fast as you can or else they will grind.

Here is some more info: they are a major pain to downshift smoothly. If you don't match revs absolutely perfectly, they are going to grind.

They cost a LOT of money. The cheapest rotary box is the Saenz gearbox, and they start at $4500. My G-Force, by the time you get the adapter spool, and the RX-4 bell housing, and the special clutch setup with Chevy splines, and the special driveshaft made with a hardened front yoke, and the Long Machine Tool company shifter, all total cost about $7000. Plus a couple of weeks labor cutting up the floor, reinforcing the floor, fabricating new tunnels, fabricating new cross member, getting everything lined up perfectly to get rid of the vibration (at least another 20 hours in my case.)

Was it worth it? I am not sure if the cost was justified, but I do have big positive: no more DNF from transmission failures. The G-Force race box has not failed since it has been in the car. I was getting lots of DNFs with the old Mazda race tranny.
+) Another good thing is that race boxes can be ordered with the exact ratios you want; very close ratios to keep your race engine in the power band at all times.
+)Most modern race boxes have 1:1 fifth gears; no power losses going thru overdrive gears; maximum power delivered to rear wheels when in top gear.
+) The slickest, absolute fastest upshifts that can be made. The G-Force box is very popular among drag racers as well as road racers.

Crusader_9x

What about the dogbox tha guru makes? i mean as far as speedturns last post goes. with the guru box you shouldnt have to get all those adapters and what not. what does it come out to cost wise after everything is said and done?

peejay

It's still going to be weaker because the gears have to fit in the Mazda case, so they're going to be narrower. The shafts are only going to be so large, as well.

Crusader_9x

https://www.rx7club.com/showthread.p...highlight=guru
well its suppose to hold up to 650 lbs of torque.

Red-Rx7

I am still waiting on my Guru. Millions of things have prevented me from getting it, nothing at fault to Rohan, but just seems that way with my luck.

speedturn

iTrader: (1)

The guru website said 650 hp, not 650 ft-lbf of engine torque. There is a huge difference.

Most transmission manufacturers rate their gear boxes in how much engine torque can be applied to the input shaft. Gear boxes are rated by torque because torque is what stresses the gear teeth.
Horsepower is a function of torque x rpm, and the stress in the gear teeth is not a function of rpm; that is why most gear makers rate their gear boxes by how much torque you can put into the box.

If you live in America, it is not easy to buy very expensive things from Austrailia. At that level of money, I prefer to deal directly with someone here in America, or at least someone wtih a distributor here in America. I don't want to have to spend another $1000 on a plane ticket to Austraila to go and find out why my expensive tranny has not made it to me in time for my next race.

Maxthe7man

I see Quaife is making a dog box kit for the rx-7, its also sold as the Greddy/trust kit..
Other options are Jericho and Liberty, apparently Liberty can do a dog gear modification to any box for a reasonable cost. I sent them an email, waiting for reply..
Hks has a full transmission kit for the Rx7, but $$$$$$$$$....
Max