26 replies to this topic

[Bam]

Absolutely, I ran a sunchro box in mine for over a year as I couldn't afford a dog box, I was forever breaking baulk rings and even teeth off the gears so I had to bite the bullet in the end. It was the best move I ever made with my car.

You're right though, they are prohibitively expensive for most.

Thats anoying about the bulk rings. Im not going to bother with a dog box in the rally car, because if I broke it I would proberly have a break down!!!

[mini93]

or u could think that its going to be alot harder to break a dog box in the 1st place having less parts to go wrong

[danwebster]

You'd do well to break one, you'd need a lot of power and to drive like a gorilla hehe

Thats not to say its impossible though!

[Bam]

On one of the straights at Down Ampney I was up to 110MPH, and I think evan a dog box would get broken if I came off at that speed!!!

Also, I could never afford one in the first place.

Edited by Bam, 15 June 2007 - 02:59 PM.

[Mini Mad James]

Sorry to jump the thread but I need a strong gearbox as im expecting 180bhp from my turbo lump...

would a s/c box with s/c transfer gears cope? or would i need a dog box?
have compared prices the dog boxes are almost an extra £1000 each!

Those swift shift boxes from swifttune look the dogs bolloks tho

[Jammy]

Straight cut gears are no stronger than helical gears.

[danwebster]

Not that old chesnut

[mini13]

straight cut gears may not be any stronger, but you need to consider the side loadings on the case and bearings.

The only person I can think of that has had a problem with a non dog sc gear set is Miniwilliams, It apears he may have found the limit of the minispares gearkits he runs, and he puts a fair bit more than 180 bhp through his.

[danwebster]

He's not the only one.....I snapped a tooth of 3rd gear on my old tran x synchro straight cut gearset just like he did.....and I only have 160hp....

Edited by danwebster, 15 June 2007 - 05:39 PM.

[mini13]

ahh, i think he's broke more than one now though!

nothings unbreakeable of course...

[danwebster]

True, but the point you're making is absolutely right.

The fact that a helical gear by design is able to transmit more load than a straight cut one is not relevant to 99% of mini owners. Its the lateral thrust that helicals produce that destroys bearings very quickly in big torque motors.

[Dan]

Surely the major problem is that all the helical kts available for the Mini use the problematic original Mini shallow baulk ring design and still crash the second gear slightly every time you select reverse too quick. If there were a helical kit available with dog engagement or even a newer design of synchro it would be a different matter. The main side loading problem happens in the drop gear chain rather than the box itself doesn't it? I don't know of any side loading problems in the main box that show up before the baulks wear out but maybe I'm wrong. I know that you get main shafts snapping but that's due to wind up rather than end thrust on the shaft, or due to the speedo gears jamming in the slot instead of sliding (and being Nylon rather than something brittle which would be a much better idea).