Strongest Gearbox Possible

[mmoe]

I think you could have a fairly easy shifting syncho-less box.. not sure though. I really think it depends on the # of dogs and the rest of the design. With such a small case to work with you need every mm of gear face (in my totally uneducated opinion) and synchros take up a lot of width...

The gearboxes in most offroad motorcycles are straight cut dog boxes. Of course the power, weight, and load ratios are completely different....but its very easy to shift them up or down without using the clutch and without grinding gears. Probably a lot more challenging in a car version. The big drawback to keep in mind with the straight cut gears is going to be the meshing noise. Probably fine for a race car but not something I'd want to listen to if I had it in a road car. I think the Mitsubishi Evo's run a Gemini gearbox that uses straight cut gears and they howl a bit.

The main concern I have about a synchroless c900/99 box is that the rotating mass of steel in these transmissions seems excessively high as compared to most transmissions and I just can't see even reasonably functional shifting happening that would work for a road vehicle. I suspect that's why the synchro rings are so large when compared to other transmissions such as a VW. Even the smaller 5th gear synchro would be a large synchro in other manufacturer's gearboxes. After giving thought to the need for such large synchros, my conclusion (right or wrong) is that they are necessary due to the massive cluster gear and relatively massive pinion/ring/differential combination to combat the kinetic energy present. It's really a wonder to me why these transmissions aren't stronger given that they seen to have twice as much steel as other transmissions designed for similar horsepower.

[Geoff]

I'd be in for a reasonably priced (as in, not $10K) gearset.

My requirements:
Rally gear ratios - the S&R gearset ratio should work
Fit into earlier boxes (a 4spd gearset would be just fine)
Easy to source replacement parts (bearings etc.)
Non-synchro would be preferred as to maximize gearbox strength and minimize excess (breakable) parts
Straight cut or helical, whichever works
Strong
Complete set with all components would be best (gears, muffs). Could do our own bearing sourcing if necessary.

FYI, the S&R gearsets are synchroless (dog engagement)

What part of the country are you/the gear shop located in?

The Gemini boxes in the Evos give mad street cred

[Luke]

[quote="mmoe] After giving thought to the need for such large synchros, my conclusion (right or wrong) is that they are necessary due to the massive cluster gear and relatively massive pinion/ring/differential combination to combat the kinetic energy present. It's really a wonder to me why these transmissions aren't stronger given that they seen to have twice as much steel as other transmissions designed for similar horsepower.[/quote]

I think you're on the right track here, but the ring gear/pinion weight and other weight down downstream of the gears in is constant mesh with the wheels. Its the upstream weight to be concerned about. I was advised when setting up my factory rally gearset to use the lightest clutch disk possible and avoid 4 chain primaries unless I was having a problem specifically breaking the chains to try to reduce the rotating weight on the input side of the gearbox, as thats the mass the needs to be syncronized to the wheel speed.

[mmoe]

I'd be in for a reasonably priced (as in, not $10K) gearset.

My requirements:
Rally gear ratios - the S&R gearset ratio should work
Fit into earlier boxes (a 4spd gearset would be just fine)
Easy to source replacement parts (bearings etc.)
Non-synchro would be preferred as to maximize gearbox strength and minimize excess (breakable) parts
Straight cut or helical, whichever works
Strong
Complete set with all components would be best (gears, muffs). Could do our own bearing sourcing if necessary.

FYI, the S&R gearsets are synchroless (dog engagement)

What part of the country are you/the gear shop located in?

The Gemini boxes in the Evos give mad street cred

I'm located in Seattle as is the gear shop. I originally went to The Gear Works in hopes that they did small jobs looking for someone to make type 8 primaries. As amazing as their shop is, they did not have the tools to properly cut a triple chain primary and they consider chain sprockets to be a different field than gears. They then recommended the shop I went to, which is called Custom Gear, Inc. My conversation with them was mostly centered around pricing for the primaries, but we did talk a bit about the gearset as well. I'm going to be dropping by with a full gearset so he can see all the parts that would be necessary, while keeping in mind the general changes. From that, I'll at least be able to get a ballpark number. Then more specifics would be necessary to get a more accurate number, but at least I'll know if I'm barking up the right tree.

Can you elaborate on the specific ratios on the S&R set? I've not been able to find that documented using Google.

[Jordan]

I think there were a couple of S&R factory ratios, but I'm not positive. I do happen to have some ratio # on my computer. Maybe it was the multiple R&P's they had.

1st: 2.2:1
2nd: 1.53:1
3rd: 1.22:1
4th: 1:1
Rev.: 4.3

[Rallyho]

Not sure what the ratios are, but I'm sure someone will chime in.

I will remind folks that the right ring & pinion ratio are critical to getting out what you put into any sort of "close" gear ratio. Those looking for a stronger gearset so the big horsepower turbo motors don't eat them so quick, this may be less of an issue. Use the ratios Saab came up with for the turbo. But, for NA motors or race/rally, the R&P gets you in the right place so the close ratios can work.

Don't know what a proper rally R&P would cost.

[Geoff]

True. Add to my list a proper R&P :-)

The same could be achieved with custom primaries but as Luke has pointed out, make the overall final drive changes at the R&P to keep the stresses off the rest of the box.

[Crazyswede]

My conversation with the local gear shop from a few years ago:

Seth,

The item pictured is a helical, cluster gear shaft. The two inner gears must be cut by gear shaping. Each has a unique "lead". Lead is a function of, number of teeth, and helix angle. To generate a specific lead, require both, matching guide and cutter. Guides are about $7500, and cutters are about $1200.
Alternatively, we can redesign and manufacture as spur. Although, does require all mating gears be replaced with spur also.
Still interested?


gear in question:

[Crazyswede]

Now...Luke and I discussed the possibility of making a custom gearset that would work off of a big splined shaft and have slip on gears. This was talking off hand without any measurements or calculations but it would simplify the build on the cluster gear.


But see what your gear friend thinks...maybe the guy I talked to was way overpriced or just not used to making these kinds of gears. It is definitely worth pursuing other venues.

[Jordan]

It sounds to me like we're talking about two slightly different, but important, things. Seth's estimate was based on reproducing said gears which would require special tooling to match the original, while now we are talking about getting similar results, but using already manufactured shaping equipment to make a whole new matched set. Yes, no?

[mmoe]

It sounds to me like we're talking about two slightly different, but important, things. Seth's estimate was based on reproducing said gears which would require special tooling to match the original, while now we are talking about getting similar results, but using already manufactured shaping equipment to make a whole new matched set. Yes, no?

Correct. The additional reverse/reverse idler gears that would not be necessary with teeth that match the original will probably cost considerably less than the tooling to produce a perfect match when spread over 10 sets. Plus you have a new reverse idler and reverse gear, which is value added instead of just upping the cost of the rest of the gears. If the tooling is $10k, then you have $1k per set to cover the tooling where as I suspect 10 reverse/reverse idler gear sets will run closer to $500/set as a best guess (they are no more complicated and possibly even less complicated than the primary set he quoted at $600 going by number of separate operations to run). There is also the possibility that he already has the tooling to match the gears, in which case the reverse/reverse idler set becomes unnecessary and the cost to produce the sets doesn't require the initial investment in tooling. He's got a pretty large selection of tooling, so that would not shock me.

[mmoe]

Now...Luke and I discussed the possibility of making a custom gearset that would work off of a big splined shaft and have slip on gears. This was talking off hand without any measurements or calculations but it would simplify the build on the cluster gear.


But see what your gear friend thinks...maybe the guy I talked to was way overpriced or just not used to making these kinds of gears. It is definitely worth pursuing other venues.

I had considered this as well, but I suspect it's a double edged sword. You make the parts easier to produce, but increase the number of parts needed to be produced, so the net result may be the same price.

Another issue would be the bearings. The front bearings (or bearing surface in the 5 speed) would be fine, but the rear cluster bearing may be difficult to accommodate. It's hard enough to get enough room machined out of the stock cluster gear, but if you had to leave enough structural steel for the splined shaft AND the gear on top of it, there may not be enough to even get the insufficient factory caged bearing from pre-'89 in there. Ideally, I'd like to see a significant upgrade to this bearing if we're going through the trouble. I place it second behind the pinion bearings in terms of weaknesses in the transmission, personally (well, technically not the bearing, but the shaft and cluster gear race)

[DrewP]

Now...Luke and I discussed the possibility of making a custom gearset that would work off of a big splined shaft and have slip on gears. This was talking off hand without any measurements or calculations but it would simplify the build on the cluster gear.

Ideally to do it this way you just need to find gearsets with the same center-to-center separation so you could spline on available parts from the Hewland or similar catalog, rather than have to muck with producing the gears.

I had always hoped to find something off-the-shelf that could be either modified to fit, or the case modified to accept it, rather than completely custom making everything.

Even if you could just make the gear clusters aren't the syncro cups different?


Drew

[nkro]

The probelm whit the gearset Is the angle.

Here in sweden they talked about Us, or GB angles. But in GB they don´t have the tools to make that angle. So they have to make a new tool for 2500 £.

Niklas

[mmoe]

The probelm whit the gearset Is the angle.

Here in sweden they talked about Us, or GB angles. But in GB they don´t have the tools to make that angle. So they have to make a new tool for 2500 £.

Niklas

Could you elaborate a little please? Is there a problem with using a different angle? Or are you saying the problem with the angle is matching the angle? If it's the latter, there would be no problem since the meshing gears would all be made to work together rather than with what is already there. It would be a complete change out.