I've noticed that there are tons of threads about which is better, manual or auto. But this question isn't quite about that (although its close).

 

The general consensus seems to be that the auto has problems above 400-450 bhp. So what's the weak point? Is it just the torque converter or is there more to it?

 

What needs upgrading to handle more power with the auto box?

 

Oh - and should this be in help and advice or general discussion? :D

Top (third) gear clutch too small for the job really.

 

Many people feel that an extra/bigger cooler saves the box, but I think that in many cases their boxes were on the way out anyway, IMHO.

Heres a bit I posted on a thread a while ago, basically its an engineers report from when the box on mine blew before I owned it:

 

The auto box oil cooler on the jap cars cools the oil by putting the oil through a section of the radiator, which doesnt really do alot in terms of cooling the autobox oil.

 

An aftermarket one takes the oil into a seperate rad where it gets much better cooling.

 

Im probably a bit biased becouse first zed i had was a freshly imported one had no cooler, within 6 weeks the box blew.

 

Second one i bought had been fine for alll the time ive owned it (over a year now)It had beeen in uk for 3 years but had an oil cooler fitted, this was done by the first uk owner becouse sure enough after a couple of months in the uk the autobox fried same as my old one, the recipts in my history for the new box in Jan 2000 totaled £1400.

 

Ive typed this out from a document in my service history from a company called Automatic Transmission Service Group

 

Technical ServiceInformation

RE4R01A

REPEATED PLANETARY FALIURE

 

COMPLAINT; RE4R01A transmissions found in Nissan Pathfinders, 200sx and 300zx vehicles may experience repeated planitary faliure.

 

CAUSE; Most Nissan vehicles which have what is known as a fin type cooler. This type of cooler becomes easily restricted causing poor cooler flow resulting in repeated planitary faliure. Cooler line flushing machines cannot flush clear this type of cooler.

 

CORRECTION; in times past the radiator would need to be replaced to update the cooling system. Nissan has now made available a spiral cooler replacement kit so the entire radiator does not need to be replaced. The part number for this kit is 21606-15V25.

 

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I dont think by the picture that I have that particular cooler stated above on mine, but i do have one of some description!!

 

Cant recomend them enough!!

I am not saying an extra cooler does not help. it does. But, your fault, ie REPEATED PLANETARY FALIURE, is I feel not caused by the box getting a bit hot.

The planet gears, or epicyclic gearbox is a mechanical means of changing the ratios in the box. And this could be boiled for weeks and not suffer any undue wear as it is a hardened part.

 

The more likely cause of this failure, IMHO, is abuse/neglect/too much hard use. Of course failure of another component, torque converter/needle roller races etc, can contaminate the box and so damage the planet gears.

 

Please do not think I am saying dont fit an extra cooler, what I am saying is I dont feel that the failure of the box is down to the lack of cooler and the failure is just coincidence...........