The only time I've ever had anything to do with a car with straight cut gear boxes, its been on a no nonse race mini, with all other straight cut gears (drop gears, diff etc)...

So I've just always known them to be way to noisy for any sane person to use on the road...

But... I've hear a feel times now,, from a few different people, that

Quote

"all the noise comes from the drop gears. Straight cut gear boxes are a tiny bit noisier, but if you have helical drop gears you hardly notice it above the engine"

Now, I've always thought

"yeah but 1st is straight cut, and you hear that"...

But it only just occured to me that its not often that your sitting at 4500rpm in 1st for any length of time long enough to really notice the noise...

So whats the verdict?

Bullsh1t or Bloody oath?

Cheers

i'm running a SC/CR set from minispares, with helical drop gear.
you clearly hear it and sometimes you are happy to reach 4th gear as it gets silent with giving the power directly to the final drive

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Rover 214 atm ....

yes,,, "All" Sc gears are noisy

you may hear people say that they have had the tips "nipped off" or trimmed off to help "lessen the noise,,, But they`re still noisy

"You cannot change the laws of Physics"

There`s Klingons on the starboard bow, starboard bow, sta,,,,

ah whatever

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

KLAS and TheMiniMan,

Thanks guys, thats what I thought

Even my drill presses straight cut gears are noisy, I couldn't for the life of me figure out why on earth anyone would think that they wouldn't be noisy.

And as for topping, yeah I've heard of that. I figured it would be crap.

The way I figure, if there was a way of making straight cut gears quite, then all the major manufactures would be doing it because straight cut gears are cheaper to make than helical..... infact, that logic kinda negates the need to even post this question huh?

Unless... maybe... just maybe... I wanted to hear it from someone else other than the voice in my head


Cheers guys,

I have a helical gearbox and straight cut drop gears, and blimey the drop gears are noisy! A bit overkill for a road car, but hey, it's hardly a 'road' engine

I haven't heard a straight cut box with a helical drop gear set, so I can't really compare.

Tell me about it. One of my old mans mates has a 4WD moke, and it has straight cut drop gears.... damn they are noisy!!! its bad enough in a moke, let alone like that

maybe its a different topic, but theres a lot of banter about whether sc gears are any stronger, after all the contact area is smaller. Comments?

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--Insert legal disclaimer here--

Straight cut gears are definitely not stronger than helical, they are however easier and cheaper to manufacture for small production runs and reduce side loadings in the box so absorb a little less HP for competition purposes.

I'm sure if you spent the time to optimise the SC teeth profiles and gear diameters to tighter tolerances, you could quiet them down (topping the teeth to stop the tips bottoming out in the root of its partner) Oh and it would also be dependent on the tolerances of the gear case but then it would still be noisier than a helical box and its all wasted for a competition box.

cheers

Kevin

Also on the side loading topic: Straight (compared to helical) cut gears would considerably reduce the axial forces on the bearings and gearbox casing flex in high powered applications. (IE no force trying to axially separate the mating gears)
This would mean that the distance between the centre lines of the gears / shafts would stay consistent thus keeping gear tooth interaction consistent also.

I'd imagine this would limit the chance of stripping teeth in a box with a flimsy casing such as Suzuki swift GTI, Subi WRX.... etc.

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-James.

Toyota 4EFTE Powered Minivan.
102 Kw @ The Front Wheels....Oh What a Feeling!

Is noise really that much of a turn off ?

All the minis I've had you generally need to yell at the passenger to have a converstation with them anyways.

How much noise do they make ?

As said it's the drop gears that are noisiest.
Your 1st gear in any Mini is straight cut anyway, but they are properly made.
2nd and 3rd SC will be a bit noisier because the tooth speeds are higher.

They don't last as long as helicals- look at a high mileage set of SCCR ones and I bet they are through the hardening on the teeth.
There is more shock load `tooth to tooth' with SC gears.
Fine for the track though, you aren't doing many miles.

As for the so-called power gains from no side loading on the bearings- has anybody measured it?
It's a bit hard to do on an engine dyno as the power there is taken from the flywheel, not the output shafts.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

why do so many people use them if they're a waste of time?

or is it like all the other stuff which is hyped up by everyone so people think it must be good.

Try buying helical close ratio dog box

People use them on the track because they want the close gear ratios they provide. Not necessarily a good thing on the street, where we do have some steep hills and driveways..
Dog boxes are just a further development of the SCCR gearset, the face dogs give faster engagement and you don't need to use the (now mostly crappy) baulk rings. They also take up less room so you can have more gears or wider ones.
Again, a dog box probably would be a PITA on the street, in traffic.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Not a turn off at all , but it would get wearing day in and day out on the road or a long trip.
If you listen carefully you can hear the high pitched whine above the induction and engine noise here:
http://www.youtube.com/user/Curly948#p/u/7/lMGMrqiLNlw

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Curly
'64 Cooper 'S' (Group Nb spec)
'67 Mini Marcos GT www.mm7056.wordpress.com