Manual control of auto box.
06-26-2010, 12:25 PM
#1
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Thread Starter
Manual control of auto box.
I've raised this topic in a couple of previous threads and got some
good information about how to increase control of the auto box
by disabling the kickdown and loosening the Bowden cable but
this is all a "work-around". I would like full manual control of the
auto with an electro-mechanical device worked by paddles that would
lock the box in each ratio being my ideal solution.
In the thread about big H.P boxes for racing there was a link to a
company that makes a kit for converting Chevy autos.
http://www.superchevy.com/technical/...ers/index.html
Since older auto boxes are essentially similar in operation
could this control device be applied or adapted to the
Porsche/ Mercedes auto.
Apologies if this is a dumb question but the 928 is the
first auto I have ever had and since autos in general were,
and still are, unusual in the UK I have never needed to know
much about them.
good information about how to increase control of the auto box
by disabling the kickdown and loosening the Bowden cable but
this is all a "work-around". I would like full manual control of the
auto with an electro-mechanical device worked by paddles that would
lock the box in each ratio being my ideal solution.
In the thread about big H.P boxes for racing there was a link to a
company that makes a kit for converting Chevy autos.
http://www.superchevy.com/technical/...ers/index.html
Since older auto boxes are essentially similar in operation
could this control device be applied or adapted to the
Porsche/ Mercedes auto.
Apologies if this is a dumb question but the 928 is the
first auto I have ever had and since autos in general were,
and still are, unusual in the UK I have never needed to know
much about them.
06-26-2010, 02:01 PM
#3
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You get used to it. The box itself, when properly adjusted etc., is nice and predictable i.e. I know what it's going to do for given inputs, no unexpected downshifts or upshifts.
When I took my 928 to the nurburgring to earn its wings (my first laps in an automatic) I was using the gearlever to shift gears manually and was absolutely fine. About the only problem I had was in the wet, downshifting to 2nd gear from highish revs the engine braking was enough to momentarily lock/break traction on the rear wheels and try to tip me sideways :S because it's an old school auto box and doesn't "blip"/rev match on downshifts. Which is where I miss being able to heel & toe like in a manual. I don't think any aftermarket shift conversion would be able to help with that, though.
However 99% of the time, in its character as a GT, the auto box suits it perfectly imho.
When I took my 928 to the nurburgring to earn its wings (my first laps in an automatic) I was using the gearlever to shift gears manually and was absolutely fine. About the only problem I had was in the wet, downshifting to 2nd gear from highish revs the engine braking was enough to momentarily lock/break traction on the rear wheels and try to tip me sideways :S because it's an old school auto box and doesn't "blip"/rev match on downshifts. Which is where I miss being able to heel & toe like in a manual. I don't think any aftermarket shift conversion would be able to help with that, though.
However 99% of the time, in its character as a GT, the auto box suits it perfectly imho.
06-26-2010, 03:54 PM
#4
Rennlist Member
Thread Starter
Ken,
I wasn't referring to 928s but to UK cars in general
and that over the fifty odd years I have been driving.
In that time have only had one auto, a Daf 44 which
had the quirky Variomatic system.
I have always done a lot of my own work on cars
but I have never needed to learn about autos and how
they work. I was hoping some of our US friends could
bring their knowledge to bear on the subject, autos
being the norm over there.
C-span,
I don't find the auto box a BIG problem. Like you I think it
suits the torquey nature of the car and I don't think I
would want a 928 manual but I do have a worry that under
heavy throttle it might change down mid corner and kick the
tail out especially on a wet, greasy road. I would like to be
able to apply full throttle in say third without the risk of a change
down to second. It hasn't happened yet but it concerns me.
Also on twisty hilly roads the auto just can't settle on a ratio and
constantly hunts up and down wereas I want it to stay in one
gear and just drive on the throttle.
As far as your problem goes I have learned to left foot brake
in the 928 and so can still blip the throttle on intended manual
downshifts. I do this even without braking, say getting
ready to overtake rather than waiting for kickdown
which always feels a bit frantic and jerky.
It makes the whole process much more smooth.
I guess a kickdown bypass switch would let you do the same,
i.e. change down with less than full throttle applied.
I wasn't referring to 928s but to UK cars in general
and that over the fifty odd years I have been driving.
In that time have only had one auto, a Daf 44 which
had the quirky Variomatic system.
I have always done a lot of my own work on cars
but I have never needed to learn about autos and how
they work. I was hoping some of our US friends could
bring their knowledge to bear on the subject, autos
being the norm over there.
C-span,
I don't find the auto box a BIG problem. Like you I think it
suits the torquey nature of the car and I don't think I
would want a 928 manual but I do have a worry that under
heavy throttle it might change down mid corner and kick the
tail out especially on a wet, greasy road. I would like to be
able to apply full throttle in say third without the risk of a change
down to second. It hasn't happened yet but it concerns me.
Also on twisty hilly roads the auto just can't settle on a ratio and
constantly hunts up and down wereas I want it to stay in one
gear and just drive on the throttle.
As far as your problem goes I have learned to left foot brake
in the 928 and so can still blip the throttle on intended manual
downshifts. I do this even without braking, say getting
ready to overtake rather than waiting for kickdown
which always feels a bit frantic and jerky.
It makes the whole process much more smooth.
I guess a kickdown bypass switch would let you do the same,
i.e. change down with less than full throttle applied.
06-26-2010, 10:09 PM
#7
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You may want to look-up Steve Cattaneo - he is an expert on automatic transmissions and posts here occasionally. His company is on the East Coast - website is http://mastertechtrans.com
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06-26-2010, 10:29 PM
#8
Race Director
the easiest way to manually control the autobox is to disconnect the bowden cable at the TB......we did this on the 928 Estate and it was the single best mod we ever did!!!!
06-27-2010, 02:54 AM
#12
Rennlist Member
About the only problem I had was in the wet, downshifting to 2nd gear from highish revs the engine braking was enough to momentarily lock/break traction on the rear wheels and try to tip me sideways :S because it's an old school auto box and doesn't "blip"/rev match on downshifts. Which is where I miss being able to heel & toe like in a manual.
I think a lot of A/T owner's that track their cars get sloppy with their downshifting and the first time they find themselves on a wet track are going to be in for a real surprise.
06-27-2010, 05:46 PM
#13
Race Director
It was SO easy.....heres what it was doing when the bowden was hooked up
It would hold 2nd gear (the lowest we used racing) to silly high RPM...well north of redline...6200 to 6500rpm was normal!!!!
It also kicked down itself with the lever in 3 in not ideal times, like say when you are in the middle of a corner!!!
So all we did was disconnect the bowden cable (kickdown switch is broken) and now it does this:
It will shift ONLY when you tell it....the only gear it can shift itself is 1-2m, since there is no way to manually control 1-2 in the 4 speed....
When 1st gear was working (it stopped recently) it would hold 1st gear until you selected 3..then it would instantly double upshift into 3rd, so if you wanted 2 you just pull back to 2.......then whenever you move the lever it goes to that gear......2-3-4 are all driver controlled....be cautious....because if you downshift too hot into 2 it will lock the rear wheels!!!
In summary with the kickdown switch (or solenoid) and bowden cable disconnected the automatic always wants to select a higher gear....so the instant you choose one it does it.....choose 3 at once...it will do it.....
I also was able to adjust shift firmness by the vac modulator on the trans too...it was a bit lazy in its shifts....so I cranked it up a bit!!
06-27-2010, 07:56 PM
#14
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