This is all true, but has no effect on the mechanism that causes the transmission to shift from one gear to another, which seems to be the focus of the OP.

 

I don't see how you read his OP only that way. His follow-up postings provide more detail and questions, too.

 

The OP (original poster) seems to be concerned about the "tranny pumps and valves" and is asking if it makes any difference if the transmission is shifted semi-automatically (J-gated) or allowed to do it's thing in fully automatic mode.

I think.

 

Well my comments seem to be relevant then.

 

A little background...

I once owned an automatic '96 Saab 9000 Aero, a heavy car with 200HP that had a ZF tranny but couldn't pull the skin off a rice pudding. Fitted a performance chip from Sweden, a big turbo, 3" down-pipe, race cat, etc., got it to 360HP, car became a monster but still had a ZF tranny rated for 200HP.

Everyone predicted instant tranny destruction but Abbott Racing in England said that if I "nursed" the tranny all should be OK. From then on, I only used "D" in traffic, and always pre-selected lower gears before accelerating. Blew gaskets, but never had a tranny failure in 4 years. Sold in early-2012, car still going strong.

Now I have this gorgeous STR, and a 200HP twin-screw S/C upgrade is in the works from forum member Avos. But, just like the Saab, no mention of how to upgrade the tranny.

Hence the question about J-gate use.

 

An extra 200HP is too much for the box but maybe it'll cope. It has more sensors so maybe it will at least throw codes rather than just breaking.

I don't know any car with this box that has put so much power through it but I haven't looked hard - try the BMW (possibly Audi) forums as they also use the 6HP26.

But... adding 200HP is likely to cause some grief, it comes with the territory!

I don't think babying it makes sense if adding 200HP as what are you adding the 200HP for?

 

Nothing wrong with J-gate use. I use the J-gate and D setting about equally. I find through J-gate use, the TCM has made some adaptions to my driving style and improved shifting/holding strategies when in regular D modes,

If you're worried about transmission life, most significant difference might be with sport mode on/off.

The less a transmission slips between shifts, and the harder/quicker the servo bangs each gear will supposedly wear the transmission less.

So if you're concerned about durability, consider driving with sport mode on. I prefer to keep Sport mode off and leave the sport mode adaptions mostly in tune with the aggressive driving sessions.

 

I think we're both saying the same thing but with an emphasis on different parts of the discussion. The OP has now clarified that he is worried about destroying 'the gears part' of the transmission through excessive use of the J gate function. The gears part is completely separate and unrelated to the "tranny pumps and valves".

 

I did not mean to give the impression that I was worried about the gears themselves. My concern was the wear and tear of the pumps and valves involved as the tranny makes the decision to change down when the accelerator is floored, versus the absence of wear and tear if I change down myself prior to accelerating. May not matter at 400 HP, but at 550 HP?

 

This goes back to my posts way above- makes no difference. I'm thinking you're possibly not familiar with how an auto box works. The pumps and valves are simply servos or actuators (ie 'the controls') and have no idea how much power there might be going through the box.

Possibly using the analogy of a gas pedal not wearing any faster on a stock 3.0 S type than on a highly modified 4.2L type R might help.

 

Mikey, point taken.

Here's something I read about the ZF6P26:
The other shift elements in addition to the torque converter lock-up clutch are:
a) Three rotating multi-plate clutches.
b) Two fixed multi-disc brakes.
All gear shifts from 1st to 6th or from 6th to 1st are power-on overlapping
shifts, that is to say during the shift one of the clutches must continue to
transmit the drive at lower main pressure until the other clutch is able to
accept the input torque.
Multi-plate clutches supply power from the engine to the planetary gear train; multi-disc brakes bear against the transmission housing in order to achieve a torque reaction effect.

Hard to believe that, with the increasing torque as the revs rise, there's no significant stress wear at that time among all these components or the torque converter clutch. Unless, as JagV8 says, the engineering is so good that it's not a matter of real concern.

So, like a few others have noted here, the J-gate may be used for braking, convenience or fun without any extra long-term risk whatsoever to the tranny, as long the car is at a stop before moving from forward to reverse and vice versa.

 

I think it will suffer with so much extra power & torque. I suspect it will not literally break (fracture) anything, let alone immediately, but rather will wear something or overheat. Now, the TFT (aka TOT) - the trans fluid/oil temp - is available via OBD so it may be worth monitoring under harsh testing.

Identifying the harshest tests is beyond me, though off-the-line and the 1/4 mile spring to mind. Max power with no let up sounds plausibly the worst case.

I suspect the worst possible in terms of fracturing anything would be standing start except that the wheels will spin as they already do with 400HP. With 600HP launching is gonna be a challenge.

At a guess, constantly forcing gear changes with lots of power on won't be good but to do many changes also means lots of hard braking. Sounds like track use. Another good time to check TFT?

Surely 600HP is gonna cause things to get damaged, trans included - is it a surprise? Generally people don't soup up cars to that extent without expecting some pain...

As I recall, avos's XK gradually gets through the ZF trans which I think will be the "ZF little brother" 5HP24.

 

The 6HP26 is rated for a maximum input torque of 600 Nm (440 lb-ft).
I believe the standard STR produced 400 lb-ft.
I'd think it would be torque rather than transmitted power that would pull a gearbox apart.
I don't know what Avos's kit does to torque but a 10% increase puts you at the design limit.
Robin (the OP) did mention this in another thread
https://www.jaguarforums.com/forum/s...e2/#post500345
- the same thread also suggested getting in a spare 6HP26 box and accepting that breaking them was part of the 'fun'.

 

Which brings us back to 'the gears part' of the auto box going bang. If it were not the tranny, it might be the diff, if it's not that, then possibly rear wheel spindles and half shafts, etc. etc., without ancillary systems like fuel delivery, cooling, crankcase ventilation etc getting in the way.

Adding 50% to the standard power output of a car- or any machine- will surely find the weakest spots in short order.

 

Avos, Avos, are you there?

I saw somewhere that the Maserati Quattroporte uses a ZF 6HP26, and the Bentley uses a ZF 6HP26A. Sounds hopeful for a not-too-costly tranny upgrade for a beefed-up STR.

 

The gearbox is designed for a max sustained (so constant usage) of 600nm, and for this to happen (for its service life) it’s of course slightly overdesigned to handle more than that. Am not sure what power levels you can achieve on a STR with the twin-screw kit, but in torque I would guess you could go close/around to 700nm, which is only 16% more. So far people have only used the kit for street driving, where power usage is actually only occasional. For sustained high power driving (ie track) I always recommend to change the upper pulley to lower the output somewhat.

There are already a couple 6HP26 cars running with these power levels but of course that isn’t any guarantee! Tuning isn’t going to prolong longevity, so there is always a risk for a weak link somewhere, heck even stock cars have failures. But so far the 6HP26 is holding up pretty well on 2 XKR’s and also 1 STR (iirc already for about 50Kmiles).

 

I know for sure the Bentley box is non-standard to take the extra torque.
The problem is that we don't know what Factor of Safety (FoS) ZF designed into their box. The designers will have been under the usual pressures to keep things light (cost of materials, inertia of moving parts, fuel economy etc.)
The 'overall' FoS of a car is quoted as 3 but that simply means the bodywork/chassis/suspension won't disintegrate until 3x the maximum expected loading is applied.
If I were designing a powertrain I'd probably be happy with a FoS of 1.5 (aircraft landing gear Fos = 1.25) which suggests it could cope with 50% increased torque but life isn't that simple.
Long before catastrophic failure due to a single overload event occurs components will begin to fatigue if subjected to stresses above a certain limit.
The higher the stress the faster failure by fatigue cracking will occur so even though a component may not immediately break when pushed outside its design limit its lifetime may be (drastically) reduced.
Here endeth the lesson.......

 

And they don't fail faster by a straight-line amount...