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Gearbox dilema

Hrvoje Kraljev

Hrvoje Kraljev

Just got it firing!
Joined
Jan 24, 2020
Messages
17
Location
Croatia, Europe
Gearbox on my Breva 750 ie 2004 is almost gone...
I have opportunity to buy V65 5 speed gearbox that (seller told me) will be straight forward fit ...

But...


Primary gearing on Breva is 16/21 and on a V65 is 15/22...
Everything else is the same...

So...
How big would be the difference??

Thanks
 
Bit shorter gearing, but nothing major. You can compensate it, but it won't be cheap, by installing early(carb) Nevada bevel box, which is higher ratio than IE Nevadas and Brevas. A big positive change will be, you'll get a small block trademark: a neutral between every gear!, as these boxes have still old style shifting mechs. So, if you're hungry for a ride, buy it, fit it, and you won't loose a penny, as such a box has its price. And, I bet your original box is fully restorable, whatever happens inside - if only you kept oil level right! The other solution is, just swap primary gearing, this is an hour job with 36 and 22 spanners to hand and couple of other simple tools. See
https://photos.app.goo.gl/S7uZ5BaFz3LEM8jMA
The primary cogs are helical ones, you just need to undo a bell-housing on both gearboxes, without getting into a "real" gearbox, which will stay untouched.
 
Adamigo said:
Bit shorter gearing, but nothing major. You can compensate it, but it won't be cheap, by installing early(carb) Nevada bevel box, which is higher ratio than IE Nevadas and Brevas. A big positive change will be, you'll get a small block trademark: a neutral between every gear!, as these boxes have still old style shifting mechs. So, if you're hungry for a ride, buy it, fit it, and you won't loose a penny, as such a box has its price. And, I bet your original box is fully restorable, whatever happens inside - if only you kept oil level right! The other solution is, just swap primary gearing, this is an hour job with 36 and 22 spanners to hand and couple of other simple tools. See
https://photos.app.goo.gl/S7uZ5BaFz3LEM8jMA
The primary cogs are helical ones, you just need to undo a bell-housing on both gearboxes, without getting into a "real" gearbox, which will stay untouched.
Click to expand...
Thank you very much for the answer/help...
The photos will help a lot...
Do you maybe know what would be the difference in rpms?
Or in top speed?
 
You can work it out from primary ratios given. It'll be in the region of 10%, so, at the same speed, what used to be say 4000 rpm, it'll be 4400. In practice, you will feel like you have lost top gear, having revs from 4th, when using 5th. I got no idea about top speed in Brevas, but I dare to say, top speed may even increase...
 
I was doing a little research on Internet...and I found that v65 and Breva 750 both have almost the same bhp and almost identical top speed...106/108 mph
The biggest difference is (as I can see) in wheel diameter
V65 has 18 and Breva 17 inch wheel...
But total difference in wheels is about 2.4%...
If all that data is correct...than I think it will not be a problem...
I was just hoping that someone has already done this kind of conversion...
 
I did! I got well butchered Nevada with long bevel box and Breva wheel - you can't go any further with gearing. The difference between 18" wheel in V65 and 17" in Breva won't be a lot, as Breva's tyre is wider, so even if smaller diameter, it won't be THAT small. The other conversions I made and rode was V35III with V50 gearbox, and V50 with Imola 16" wheel - for sidecar duties. Going down in wheel diameter in this case did same job as fitting V35 gearbox: 10% down in gearing. But I don't need to explain, wheel is much easier to swap:)
 
Well...
When I consider all together... I think that I will just swap gearboxes like they are now...
Without changing anything...except oil and good cleaning of course...and just keep driving...

Adamigo...thanks for your help
 
If you will not be happy with higher revs, Breva shares long ratios with all the bikes on 16 in wheel: Nevada, Lario, Targa - but not Florida. Try to be patient and keep an eye - you'll get right one sooner or later.
 
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