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Synchro vs. Dog Box

PostPosted: Mon Oct 24, 2005 12:34 pm
by jkolb
Could someone tell me what the difference is in shifting a dog engagement transmission as opposed to a conventional synchromesh transmission? I know they are noisier, but want to understand the difference in the way they are shifted.



Re: Synchro vs. Dog Box

PostPosted: Tue Oct 25, 2005 9:33 am
by Dag-Henning
Jerry, - the gears in a dog-box have a positive and absolute locking between them ( - does my English reach far enough here...?? ) that consists of "dogs" that fit into equally shaped holes in the opposite part. Shifting gears require a fast, accurate and determined move. If you hesitate, the gears will not enter. ( - the dogs will not enter the holes ).
Yes, they are noicier than a syncro box, as you get a very hearable "clonck" when you enter 1st. from neutral. Driving hard and shifting up and down, you wil not notice this, and the gears can be shiften much faster than with a conventional box. A dog-box is very usefull in a rally-car, but is a total vaste in your road car.


Re: Synchro vs. Dog Box

PostPosted: Tue Oct 25, 2005 10:29 am
by rgh0

Dog boxes, apart from the gear selection mode, all use straight cut gears rather than helical gears found in stanard oxes thus they make more noise in the indirect gears. Helical cut gears are quieter but not as strong thus they are used in road boxes where noise rather than strength is a prime requirement. Straight cut gears are also cheaper to make in small runs thus also preferred for race boxes in addition to their greater strength.

Your can get straight cut synchro gears for your ford box from Quaiffe. You can also get the same straight cut gears with a dog change rather than synchro change. The dog change relies on the driver to synchronise the speed of the input and output of the gear box for the dogs to smoothly engage. In a synchro box this synchronisation is done for you by the synchro ring and blocker bars which dont allow the gears to be engage until the speed is near synconised.

For a skilled race driver the dog box is quicker but for an unskilled driver the life of a dog box can be measured in 1 race. Unless you are a serious racer with a sponsor paying for gear box repairs or are extremely skilled I suggest sticking to a synchrobox and use straight cut gears if racing and normal helical gears if using on the road.


Re: Synchro vs. Dog Box

PostPosted: Tue Oct 25, 2005 2:06 pm
by type26owner
Surprising I find many folks that have a dogring box and have no clue how to actually actuate it correctly. If the mechanical preparation is done correctly, the shifting should be done with just two fingers as a very GENTLE flicking motion. The low inertia shifter must have a throw of only several inches at most to facilitate the speed required to complete the motion. You can tell how good you really are by pulling the magnetic drainplug.

If you have no prior expereince it's well worth the expense to attend a driver's school that utilize a dogring gearbox. Even if you suck at it you'll find there a lot of folks that are much worse. :lol:

Re: Synchro vs. Dog Box

PostPosted: Fri Dec 02, 2005 6:12 pm
by cabc26b
One last thing - with a dog box the clutch is optional, in fact, some people claim its worth measurable time on a lap to for go the clutch ( at least with a Hewland)

Re: Synchro vs. Dog Box

PostPosted: Sat Dec 03, 2005 7:44 pm
by type26owner
How do you do it by left foot braking? IIRC, regardless a blip of the throttle is required to catch the next lower gear whether or not the clutch is dabbed if grinding is wanted.

I discovered some tweaks to do to the Hewland Mk5 to make it shift sweet. I have a technical article I wrote on this subject if you're interested. The changes are easy to do and the results are amazing. Never miss a shift again from a balky gearbox! Your standard excuse for abusing the gearbox will be nullified.

Re: Synchro vs. Dog Box

PostPosted: Mon Dec 05, 2005 5:47 pm
by cabc26b
Upshifts are super easy, Downs required a little blip in neutral to be effective and kind to the box . I had a baptism of fire on this cause I lost the clutch pedel one weekend . Currently I only use clutchless on the upshifts. I feel the clutch blip , on the downs preserves the drivetrain.

Re: Synchro vs. Dog Box

PostPosted: Mon Dec 05, 2005 6:23 pm
by type26owner
Oops, that should be 'NOT wanted'. Yup, rubber donuts are an asset to cushion the driveline too.

Put my son through Skip Barber just so he learn the feel on a Webster gearbox first. :lol: Awful noises are heard when the class goes for it the first day. :cry: Never knew a full sized dodge van piloted by an instructor and full of students could go that fast with four wheel drifts around Laguna Seca Racetrack. :shock:

Dog Box

PostPosted: Thu Dec 15, 2005 2:36 pm
by S. Kuwatch
As one poster has said, cluth is opitional. Takes some guts to try this, but worth the effort. Know your shift point RPM's and start slowly till you get the feel. After a few laps you'll forget about the tach and trust your ears. Build feel and speed from there. Driving using only 2 pedals (brake/gas) frees up your mind for many racing needs.
I lost my cluth master cyl. on a race weekend and had no replacement, so options were: 1) Trailor up and drive 450 miles home, or 2) learn and worry about a trans rebuild after the weekend. I sure didn't win, but still had a fun and productive weekend, and didn't need the rebuild. Dog boxes are strong.
BTW: This occurred in a Lola 598 S2 with Hewland box and Hewland gears, but I have to believe the same strength is there in a Richmond or Webster box.
Racers go in deep and come out fast, lap after lap