Autoboxes - robust?

[flamingm0]

There seems to be an abundance of motors these day with fairly responsive tiptronic type autoboxes. Autoboxes in general have been round for ages and my question is how relible/robust are they for more "spirited" driving. There are some fairly pokey cars that can come with them which suggests the torque converter design in principal can take significant power. I appreciate they're not typically the choice for a drivers car and fair enough they do absorb some power but in terms of taking abuse how do they compare with a manual gearbox/clutch? In theory there is no clutch to wear? What is a typical failure for example?

[eliot]

They still have clutches.. lots of them in fact, but they are wet motorbike type clutches that are used to hold/release planetry gearsets.
If you stuff too much power through the box, these clutches will slip as they engage, burning them out.

So you put better clutch packs and raise the clamping force, then other parts starts breaking then - upgrade those parts - rinse and repeat.

I need a box that can take 600bhp/600ft-lb torque, I think a manual box that can take that will be a pig to live with. Auto's are a pain, but they are easier on the rest of the driveline- I think a manual would of chewed the rest of my driveline along time ago.

(not busted any diffs or half shafts since going Auto on a 5.7 from manual on a 3.9)

[chuntington101]

if you want really beefy auto boxes take a look at some of the US corvette site! there are guys running a hell of a lot of power through stock transmition that are just beefed up a bit!

thanks Chris.

[eliot]

I'm running 700r4, just spent lots of $$ on more HD parts for it (Torque drive package, 5 pinion GM planetries, Carbon bands etc) which is supposed to take 600-700. But I suspect it will break again, the internals are just not up to the job, its really only a medium duty box.
It needs a 4L80e in it (still with upgrades, but not as much) - thats what they fit to all the really big heavy stuff in the US - but I dont want to spend 2k only to find out I cant make it fit. (its a BIG box)

[eliot]

chuntington101 said:

if you want really beefy auto boxes take a look at some of the US corvette site! there are guys running a hell of a lot of power through stock transmition that are just beefed up a bit! thanks Chris.

The boxes last a bit better because they break traction in 1st and 2nd - wheras mine grips (just) because its 4wd.

[FlamingM0]

Ok so at the heavyweight end the design principal can take a punishing but what about your typical modern tiptro saloon car? How do these compare to a manual in terms of toughness when driven hard? As an example a friend of mine had a Scooby auto which packed up. Are they perhaps more fragile than a manual and not ideally suited to taking abuse?

[eliot]

Ive not really heard of people using modern auto's (read European) as a performance part. The main auto's that are used in high performance cars are powerglides, torqueflytes, TH350, TH400, 700r4 and 4l60e/4l80e (essentially all the yank boxes) - the latter "e" ones being electronic control, requiring a standalone ecu costing around $700. Rebuild parts and upgraded internals on the yank boxes is plentiful.

Ive got a bmw540i with a tiptronic, I noted that when LSV supercharged the 540 they stopped at 400bhp on the autos but went to 450bhp on the manual, presumably because the box couldn't take it. Its a great box, but its too slushy to be considered a performance box. The yank boxes can be made to have very snappy shifts, you can even fit full manual valve bodies on them (ive had one) but there really focussed for drag use.

[flamingm0]

Eliot, do you know much about the Mitsu INVECS II autobox as used in the Galant etc? Does this class as a yank or jap box? All interesting insight!