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Gearbox Strength
Just can't stay away
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2002/11/18 21:48
From Birchip, VIc , Australia
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Guys,
What's the best way to strengthen a 60A speed Dogleg gearbox. I've heard a little about Straight Cut Gearsets but not much. I don't know exactly what they do, being that I am new to the mechanical world. If someone could draw from there vast knowledge and help me out I would be most appreciative.
I want to keep my 1200 ute Datsun throughout so don't want to change the gearbox. I've got a blown A14 in it and the box needs to handle about 300hp. Can anyone help?

Posted on: 2004/2/27 0:46
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Re: Gearbox Strength
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Well, this is a big subject but I will do my best to try and help.
In short, your best bet would be to replace your existing box with something stronger because it is a very time consuming and expensive exercise to strenghten your current box. You can expect to pay around $1000 for a straight cut gearset and idlers, then extra for any other necessary mods to make it all work and handle the power output of your engine.There is a fair amount of machining and TIG welding required to get it all to work.
I know you want to keep things "datsun" but replacing your existing box with something else "bigger datsun/nissan" would be by far the cheapest and simplest option, especially if it has to cope with 300 Hp.
Normal gearsets inside your gearbox are helical, that means when they are cut they are cut on a sloping angle to the gear shaft axis. The gears when in operation sort of slide over each other and the loads are distributed over a smaller area than a straight cut gear ie:not as strong, they also apply more side load to the operating shaft. Straight cut gears are just that, gears that are cut straight in relationship to their axis. they dont have the gear teeth engage on a sliding angle. The load that a straight cut gear can handle is far greater than a helical gear because the surface area to which the load is applied is greater therefore distributing the load over a larger tooth area, they also apply less side load to the operating shaft.
I tend to wear syncro's at a far greater rate and the steel ones are getting hard to find - Usually ex works stuff.
If you still want to modify your box after everyone's had their say on the subject and you want it done properly then you should budget at least $2000 - $2500. What you could end up with is a strong gearbox with a straight cut gearset, stronger/larger front shaft, Alluminuim oxide bushes and thrust washers and quick shift with modified detents.
It's an aweful lot of work and a lot of developement time, that's why I suggest you look at other options for a streetcar.

Hope this helps

Posted on: 2004/2/27 1:35
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Re: Gearbox Strength
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From Millgrove Vic OZ
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Its not hp that kills boxes but torque.

Datsun boxes are numbered by the distance between the centres of the countershaft and the main shaft. 56 series 56 mm, 60 series 60 mm, 63 series 63mm, 71 series 71 mm.

The larger the distance between shafts the larger the shaft diameters and gear sizes that can be used. With helical spiral gears, rotation of the gears under load tends to make the gears try and spread away from the other gear. The shaft must be strong enough to with stand this load without distortion.

A smaller shaft will distort more for a given load than a larger shaft.

My tip is that the A15 will produce about 150 - 160 ft/lb torque and about 230-240 hp @ 14 psi boost.

As a guide the maximum continuous torque limits of the various boxes can be determined by the ratings of the bearings or the torque the smallest diameter of countershaft or mainshaft will take without approaching plastic limits

Approximate guides are 50 % up on the stock engine torque : -

56A 4 speeds 105 ft/lbs
56A option boxes 120 ft/lb
60 series boxes 135 ft/lb
63 series boxes 175 ft/lb
71B series boxes 240 ft/lb
71C series boxes 300 ft/lb

Posted on: 2004/2/27 2:29
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Re: Gearbox Strength
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Hay feral,
Thanks for the info on the relationship between the two shafts, their centres, and the series numbering. I never put 2 and 2 together like that but it makes perfect sense. This has to be one of the best websites in the world, knowledge base is huge.
Good stuff.

Posted on: 2004/2/27 4:14
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Re: Gearbox Strength
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2002/11/26 22:13
From Wellington New Zealand
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I learned something too. I always assumed that the straight cut boxes weren't as strong, as there was less contact patch between two straight teeth than between two angle cut teeth.
The transmission losses in a straight cut box are significantly less however....

For a replacement box for an A series, it'd be hard to beat the Dellow kit to fit a (i'll say it) Toyota box...

Posted on: 2004/2/27 6:12
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Re: Gearbox Strength
No life (a.k.a. DattoMaster)
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2003/6/27 14:53
From Southern Tablelands N.S.W. Australia
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The Dellow kit is not cheap, as it is more than an adapter plate. It actually incorporates the front part of the gearbox. The upside is that the gearboxes are cheap. They are cheap because they are good.

Huh? Good boxes dont break much in normal service, & they have a long service life, & demand at the wreckers is low, so they are priced to sell.
Those who remember the rubbish 4 speeds first used behind Holden 6's will also remember that wreckers wanted a lot for them. They broke a lot, & demand was high.

Much as i hate to say it, the Toyota boxes are a bloody good trans & are a good choice behind a hot A series.

Posted on: 2004/2/27 14:26
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Re: Gearbox Strength
No life (a.k.a. DattoMaster)
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From campbelltown (sydney) australia
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a bit off topic, but can anyone tell me what gearbox i have i replaced the clutch yesterday and it has castings 60, and #2 on the r/h side.
thanks.

Posted on: 2004/2/28 9:38
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Re: Gearbox Strength
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from this informative discussion it seems that straight cut gears r all winning then why not most OEM GB comes with them?
there must b a catch.

Posted on: 2004/2/28 11:40
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Re: Gearbox Strength
No life (a.k.a. DattoMaster)
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From campbelltown (sydney) australia
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straight cut gears make alot of noise and wer out quicker

Posted on: 2004/2/28 12:50
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Re: Gearbox Strength
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Quote:
me what gearbox i have ... it has castings 60, and #2 on the r/h side
That is a 60-series gearbox! The question is, is it a 60L or 60A? You can tell: The 60L has reverse above first. The 60A has reverse below fifth.

Posted on: 2004/2/28 18:17
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