Wear with dog engagement gearboxes.

[love machine]

I was looking at a dog engagement kit earlier and then a thought struck me.

There is a fair bit of play between power on and power off, this must cause them to chatter at idle as well as wear quicker. I thought since no-one seems to answer the question anywhere, what is the life expectancy of a dogbox relative to a synchro kit?

[Martin_S]

Life expectancy of a dog box vs. synchro = bugger all.

Dog boxes are only really suitable for race use on cars, where you can expect to rebuild them regularly.

Bikes are not so bad due to the lack of weight and relative lack of torque, and while you might get away with reasonable mileage out of a Bike Engined Car gearbox, I can't see you getting anywhere close to the 200K+ miles which has come to be seen as commonplace for a synchro road car gearbox these days.

Actual life expectancy will vary according to use and driver as well as the type of box and the engine it is connected to, but a particularly brutal driver can knock the dogs off in a single, long race.

edited to add: ...and yes, they do chatter at idle!

>> Edited by Martin_S on Tuesday 29th March 23:11

[matt_fp]

Rought Guesstimate between 100 and 10,000 miles.

Matt

[love machine]

I thought old cars before synchros had a choice, either sliding mesh (sliding gears) or constant mesh (dog engagement) I assume that the design must have been different. Some look very flimsy indeed. I would have thought that dogboxes were pretty strong if used properly.

Lorry boxes? I suppose the designs will differ. The ones I was looking at had big trapaezoidal teeth with the widest lengths facing. I believe that the jelly bean dog which Quaife do looks quite flimsy.

I like the simplicity of it as well as "good use produces better results".

Cheers Chaps.

Stu

[Trooper2]

It's a matter of surface area, dog gears don't have as much area as Helical or especially spiral cut gears, thus they wear much sooner. I'm just finishing the Manual trans course at school.

[love machine]

Trooper2 said:

It's a matter of surface area, dog gears don't have as much area as Helical or especially spiral cut gears, thus they wear much sooner. I'm just finishing the Manual trans course at school.

Good point about the tooth area, I suppose that the oil would sort that out to an extent.

If I remember rightly, the shear loads imposed on oil are directly proportional to the helix angle of the gears. Hence hypoid oil is hardcore stuff.

I'm not sure that with a set of strong, big dogs that the crash loads would chip the teeth up that badly, I have no idea. It's one of those areas where no-one can give a definitive answer.

I think there are no problems with straight cut (spur) gears as generally aftermarket sets are ground to closer tolerances/finer finish/better material spec.

Dog ratios available for my application are not favourable with my desired, I was just curious about whether they were OK for a road car.

[FrenchTVR]

Why not give Bernie Braden at Competition Transmissions a bell? What he doesn't know about transmission systems probably isn't worth knowing.

01582 840008
www.gearboxman.freeserve.co.uk/content/home.html

[dannylt]

What do you mean chatter at idle? Do you drive along at idle? Yes it will shunt in this case, but usually you're in neutral or have clutch in at idle.

I have a straight-cut dog box in my Caterham, and it's managed over 1000 miles so far .