When I took a tooth off a pinion it was because the locating bracket for the centre oil pick up decided to break and fall into the diff gears.

it wasnt how it was driven.
But gears are expensive so i didnt replace them when the box was rebuilt.
the problem might be 30+ year old gears, the fact that they're stock gears or who knows what the PO's did to it?

i am not really upset, because its an old crappy design and i am running significantly more torque than it was designed for.

i have thrashed the &%$ out of stocko smallblock engines and boxes and never had any problems.
i reckon problems come when you modify for more power.

problem was, that i was still running low boost to test its reliability.
Now i can see i am going to need some serious kit to get that power down reliably.
and nah i havent had it dynoed.

My idler gear bearing died in my supercharged motor, also the diff pin was 'rooted' but not dead. I treated my car with tons of repect, no clutch dropping or silly gear changes. But I was not afraid to floor it while moving. Also, being a blown motor it makes tons of low end torque, which was, after looking through the dismantled motor and 'box, the most probable reason for gearbox failure.

It's all been rebuilt with some better bits here and there, but the first rebuild (done professionally by a reputable Mini mechanic) was cheap, this newly rebuilt box is the real test. It will be driven with care, but the power and torque will be used when appropriate.

Due to all this stuff I'm moving away from A-series, great motor not-so-great 'box. Hopefully Toyota will be better, at least it has 135hp stock, as oppossed to my ~120hp S motor.

PS Ryan, when the money slowly appears, I'm probably going to be building a proper Mini gearbox, using a rod change box as I have some spares. Most likely S/C gears, S/C drop gears and a tapered-roller, idler gear bearing conversion.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

So doz, which manufacturer did you get your straight cuts from?
I guess a close ratio box is good for a turbo or NA but what about a supercharged?
you would want to make the most of the flatish torque curve wouldn't you, but the only straight cuts around, assuming there stronger, are close ratio

My gears were purchased from Minispares in 96, they may have changed supplier by now. I thought they had an 'S' ratio SC set as well?

Close ratio is for circuit work, no one else can drive my car without stalling it from the tall first gear (I think its 11:1 overall, standard S is about 13.5:1?). I wouldn't recommend it for a street car, its a biatch to drive off the lights...

Straight Cut is not stronger than helical (I've posted this before) but the material of aftermarket gears are usually better to make them stronger.

Have a search for using 'helical gears' author 'DOZ'...I reckon the main problem causing gearbox failures is the gearbox casing allowing the gears to separate.

If I were building a street car, turbo or supercharged, I personally would go for an S gear set with a 3.1:1 diff ratio (if i could find one) for the highway cruising and torque. This would be cheap enough and won't cause the same tears should it go bang as a SC box!

Daniel

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Videos - Turbocharged A-Series on Dyno & at Wakefield
Mafs waz not my strong subgeckt at skkol

Good point, in the next gearbox rebuild, I will look for a 3.1 diff for better highway cruising.

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Lillee - 1969 Morris Mini K

Pfft, 3.765 for me

Pete

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Click here for the Turbo Conversion Thread!

agreed, 3.1

I run 3.647 diffs in both the 1293 and the 1360, but the 1412 stroker in the van is getting a 3.44.

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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.

my turbo has 3.2, soon to become 2.76

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Rover 214 atm ....

You don't have a 110KMH blanket speed limit there...

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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.

Ill eventually put in something closer to 3.44 or even 3.1... but for now, its keeping the diff thats in there for some fun

Peter

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Click here for the Turbo Conversion Thread!

A while back Minisport had a 3.2 diff sitting on the desk, I was there today, it wasn't. They might still have it though....

I would go 3.2 next time. 3.44 is good too, but nothing shorter, afterall it's only a street car - with s**tloads of torque.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

So from all this would it be right to assume that a very good box for a supercharged big power motor would be;
A well built box by a competent person, straight cuts in S ratio from a good manufacture (maybe quaife?), straight cut drop gears and a cross pin diff, oh and a 3.1:1 dif to take advantage of the extra torque

And more questions
How well do the inner joints, CV's and drive shafts cope with large power?
I'm guessing a bonded clutch plate and orange clutch diaphragm are a must?

Whoa tiger!

How's about a new, specific thread. "Gearbox for blown beast" or similiar?

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T