dodgeman- my understanding (misunderstanding?) was that the helical gears had a smaller contact area rather than a larger one, and the straight cut allows for a greater width to the gearset, especially if it is a full dog box with no sinchro's.... as this appears to be.

They are noisy buggers tho- definatley not for road use.

I'm led to believe, for racing instances straight cut are stronger and allow for quicker shifting between gears, but god damn it they are loud. Maybe its a match made in heaven you also have the little noisy A-series reving in the 8's.

Benny

Yes, its the guts out of a dog box.
Yes they are very noisy.
Yes they are heaps stronger.
The other, often unspoken, advantage of straight cut gearsets is that they dont apply the loads the same as a normal gear arrangement, therefore there is less chance of the loads wanting to spread the shafts apart and destroy the gearbox.
An A series at 8 1/2 grand with straight cut gears has a very unique sound. I can hear my coupe from miles away whenever my son is behind the wheel in a rally. They sound awesome.
Dog boxes do allow for quicker changes partly because the dog engagement faces are usually machined with a slight reverse taper on the dog edges, this allows the dogs to fully engage quickly and avoids the problems of the dogs not grabbing properly and therefore missing a gear. For those that have not driven dog boxes you have to be very firm when selecting gears, none of this drive by feel stuff, just quickly and firmly select the gear you want. Most of the dog boxes in Possum Bourne's cars are much more efficient when driven without using the clutch. All that is necessary for a quick positive gearchange is to quickly unload off the throttle and drive the lever into the next gear via the dogs. The true term "muscle car" comes to mind whenever I drive said cars for tuning purposes.

Ewwww they look nice! Must be clsoe ratio too....

You are right Dodgeman, the helical teeth are stronger for the reason you gave. The advantage with the straight teeth is a slight imporvement in efficiency and there is no side load.

But more important to this is the contact ratio. Imagine two gears mating (not in the reproductive sense dummy)...if one tooth comes into contact with the gear just as the previous tooth leaves contact, then the contact ratio is said to be 1.0. That means, on average there is exactly 1 tooth in contact at any time to absorb the torque. A contact ratio of 2.5 means that, on average, there is 2.5 teeth in contact to absorb the torque. So, 50% 2 teeth in contact, 50% 3 teeth in contact - you get the idea!

I think you'll find helical gears have a higher contact ratio for a given number of teeth that staight spur gears, and its this load sharing across the teeth which makes them notably stronger.

Shifting shouldn't matter, since either way the shifter engages the synchros, not the gears (these transmissions use constant-mesh gears).

I heard there was a big improvement in efficiency. The helical gears put a lot of heat and torque lost in sideways motion. They say up to 30% is lost through helical gears (gearbox and diff). F1 cars use straight-cut gears.Quote:

So are straight cut gears stronger, or are helical gears stronger? It seems for every one that says "helical" someone else says "straight".

There does seem to be concensus that straight gears wear faster, so ultimately don't last as long.

Quote:

I couldn't find any manufacturer saying one way or the other, but race sets (Quaife, for example) all use straight gears.

dd,
You can generally assume that most straight cut manufactured gears will be stronger simply because the materials they use usually have a higher yield stress, therefore making them stronger than standard gearsets. The water becomes a little murky if you compare the different designs using the same materials. Its hard to answer such a general question because there are so many variables in design and materials used in their manufacture. Application can also make a difference.
I have raced with a straight cut gearsets for many years and in my opinion I would never go back to a standard form cut gearset.
As you say most if not all the top aftermarket manufacturers only sell straight cut versions. Obviously there are good reasons for this and I believe strength to be one of them.

Paul.

I know from playing with Subaru's (weak gearboxes) that straight cuts are stronger. When buying from PPG or similar you can usually buy 3 types of upgraded gearsets all made from the same strength material.
The weakest is the helical cut with synchros (which were 15% stronger than the standard subaru).
Then the straight cuts with synchros which is what I got.
The strongest are the straight cuts with dog engagement which I've seen take maximum rev launches in sub 10 second 4WD cars time and time again.

So, straight cuts are always stronger - why I don't know for sure, but I've been told its that the shock is more evenly distributed in a straight cut gear, where as in a helical gear it concentrates the shock more in one point.....which kinda makes sense i guess

So, what gearbox are these cogs out of?

Quote:

what he said

I made these gears to suit the 4spd A-series gearbox...

Quote:

For what its worth - shifting will matter in this case because the above pic shows no synchros and only dog engagement. This makes a big difference to the operation of the gearbox and the way the driver treats it. Driving technique must be modified to successfully use any dog box.
I have included a "how to shift guide" for others to read as it directly relates to how driving technique must be modified to get the best out of any dogbox. This basic guide comes from Hewland Engineering.

N.B. For succesful gear shifting, remember that it is critical to ensure that all mechanical elements between the drivers hand and the dog faces are in good order and properly set. This includes the gear linkage in the chassis!

Successful up-shifting, (defined as fast and non dog-damaging) will be achieved by fully moving the dog ring as rapidly as possible from one gear to the next, preferably with the engine's driving load removed until the shift is completed. (The opposite is true of a synchromesh gearbox as used in passenger cars, where slow movement helps). It should be remembered that it is not possible to damage the dogs when fully engaged (in gear). The damage can only take place when initiating contact during a shift, (the `danger zone`) therefore this element must be made as short as possible. If a driver moves the gear lever slowly, or if the linkage is not rigid and effective, dog wear will occur. We always recommend lightweight yet solid rod linkage, not cables ideally.

I list below the different methods of up-shifting that are used in racing most commonly. The best at the top, the worst at the bottom:

Automated (semi automated). The movement of the dog ring is powered and the engine is cut / re-instated in a co-ordinated manner. Gear-shifts take milliseconds. This system produces zero dog wear when set up well. It is not applicable to most cars, but it illustrates that speed of shift is a good thing.

Manual with engine cut. This system is almost as good as an automated one as long as the driver pulls the lever very quickly. Again it is not applicable to many cars, but it illustrates that speed of shift is a good thing. A `cheat` version of this is to shift on the engine rev limiter, which can work well. With this system it is especially important to move the lever ultra fast, otherwise the engine will be reinstated during partial dog engagement, causing damage. The damage can usually be felt by the driver.

Manual.
Best method: With no assistance from the engine management, the driver must lift off the throttle sufficiently to allow the dog ring to be pulled out of engagement. He should then stay off the throttle long enough to allow the dog ring to engage with the next gear. In practice, the driver can move the gear lever faster than he can move his foot off and back on to the throttle. Therefore the effective method is to apply load to the gear lever with your hand and then lift the throttle foot off and back on to the pedal as fast as physically possible. In lifting your foot, the loaded gear lever will almost involuntarily flick to the next gear before the foot is re-applied to the throttle.
Another method is to load the gear lever with your hand, stay flat on the throttle and dab the clutch to release the dog ring. The overall effect on the gear shift is similar to the above method, but clutch wear may become a big issue.
The worst method (most destructive and definitely slowest) is to attempt to change gear in a `passenger car / synchromesh` way, i.e. lifting off the throttle, dipping the clutch, moving the gear lever, letting the clutch up and re-instating the throttle. The method causes unnecessary clutch wear, does absolutely nothing to help come out of gear and usually causes dog wear whilst engaging the next gear. This wear is due to several reasons. Firstly, it is impossible for a driver to co-ordinate the complicated sequence of all five physical movements accurately. Consequently the engagement dogs often find themselves engaging whilst the throttle is applied. The lever is usually pulled more slowly as it was not pre-loaded, lengthening the `danger zone`.

Successful down-shifting, has similar rules applied regarding speed of shift. Unloading the dogs is done in the opposite manner obviously. Whilst braking, the dogs must be unloaded by either touching the throttle pedal or- my preferred method- by dipping the clutch. However, one sharp dab of clutch or throttle is appropriate per shift. Continued pressure on either will cause dog damage for different reasons. `Blipping the throttle` just before engagement is advisable if the rev drops between gears are over 1300 rpm, as this will aid engagement and stabilise the car.

TOP TIP for ease of downshifting: Make the downshifts as late as possible in your braking zone (i.e. at lower road speed), because the rev drops between each gear are then lower. So many drivers make the mistake of downshifting as soon as they begin braking, causing gearbox wear, engine damage and `disruption` to the driving wheels.

This is a subject which can be much expanded on, but I feel that these are the basics, which I hope are of use.

William Hewland

Will you be making these and have you thought through a price?

Does this mean that you can't flat shift with a set up like this?

Nice looking gears. Also interested in more info about it.
Nice article about using a dog box Paul. I know people who have changed over and love them, and others who just couldn't adapt to them and got rid of them. I'm sure the advantages are worth re-learning how to drive!

I like how the cluster gears are all made separately & mounted to the cluster shaft on a spline.
I guess that this was done for ease of manufacture, but the upside is that it looks to be possible to replace only the damaged gear whenever a replacement is needed, or to change just one gear ratio without changing the whole cluster gear assembly.This would allow a degree of flexibility without the higher expense of a conventional construction.

Certainly not a gearbox for everyday driving, but just the ticket for those with a need for this sort of thing.

Quote:

I know of plenty of Subaru drivers who would disagree. There's quite a few who have dog boxes in daily driven cars. I find that once you get used to rev-matching it takes less effort then putting your foot on the clutch. The only reason I put synchros in mine is because other people drive it too.

I was thinking of the noise factor, which can be a bit wearisome after a while, & the 'learned' driving technique, which would be a problem for most average everyday drivers who see the car as nothing more than a transportation device.

Nooo, the noise is the best bit
Although you can also get helical cut dog gears.
This is the 2nd gear out of my box....straight cut with synchros. They're nice and strong and can handle big launches but can still be driven inexperienced drivers.

Just for interests sake. Do ya reckon a 56 series box with a set of straight cut gears on 1,2,3, helical on 4th would handle a tough A15 at the strip?

Helical on 4 for a quiet cruise, thinking for a streetcar. I have issues with the lifespan of 56 and 60 series boxes.

Also wanting to keep the weight down by leaving the 63 out.

The next question is cost?

Quote:If you are talking of a four speed, then there no gears driving in the gearbox when in fourth. The input shaft is locked to the main shaft in the gearbox & the power flows straight through.

The cluster remains driven by the input shaft gear & all of the other foward gears are driven by the cluster, but since these gears are not locked to the mainshaft when in fourth, they just revolve around the mainshaft for the fun of it.

The hub of the 3-4 synchro is always locked to the mainshaft & the outer synchro ring simply moves foward to allow its dog clutch to engage the input shaft, locking the two together, a 1 to 1 ratio is achieved, & no gears involved.

Have a look at the photo.
The gear on the cluster at right of picture receives the drive from the input shaft & makes the whole cluster assembly go round, then, starting from the left, the gears are 1st, 2nd, & 3rd.
Easy peasy.

Im toying with th idea of selling these gears assembled in a gearbox...
They are in a 56a 4spd case suit 1200...

Cant remember the exact ratios but I "think" they are-

1- 2.4
2- 1.6
3- 1.25
4- 1.0

Im not desperate to sell it, but if i was offered enough id let it go...

Hi Topgear,
Would you mind sending me a p.m with price idea that would tempt you to part with these please.
Also is the assembly in a 4 speed box something that you would need to do yourself or is it something that a competent mechanic could do? ( thinking of minimising freight costs to NZ )
Cheers
Dave

Id love

2:6
1:6
1:1
0.8

On a normal 60 series cluster to suit turbo A15