[xj] No Kick down reaction BW 12

My XJC with V12 and BW 12 automatic does not give any kick down
reaction if the accelerator is pressed to the bottom. Given the
enormeos power of the engine it picks up the acceleration easily,
but I would expect that at certain speed levels the automatic would
go back from 3rd gear to the 2nd gear in case of kick down.

Is my observation correct? and what could be the cause / what do I
need to check.

thanks!

Peter–
''76 Jaguar XJ12C 5.3 litre RHD
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In reply to a message from phros sent Wed 24 Jun 2009:

The BW12 uses an electric kickdown, peter. Check the switch on the
throttle cable where it attaches to the throttle capstan. Make
sure that full throttle movement closes the switch.

The ROM outlines some checks you can perform on the trans kickdown.–
The original message included these comments:

My XJC with V12 and BW 12 automatic does not give any kick down
reaction if the accelerator is pressed to the bottom. Given the
enormeos power of the engine it picks up the acceleration easily,
but I would expect that at certain speed levels the automatic would
go back from 3rd gear to the 2nd gear in case of kick down.
Is my observation correct? and what could be the cause / what do I
need to check.


John Testrake 74XJ12L rhd, 84 XJ6 700R4
St.Louis, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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phros wrote:

My XJC with V12 and BW 12 automatic does not give any kick down
reaction if the accelerator is pressed to the bottom. Given the
enormeos power of the engine it picks up the acceleration easily,
but I would expect that at certain speed levels the automatic would
go back from 3rd gear to the 2nd gear in case of kick down.

Is my observation correct? and what could be the cause / what do I
need to check.

As John says, Peter - the full throttle kickdown is activated
electrically, to be checked and adjusted…

However, during normal driving the up and downshifts are regulated by a
vacuum control unit outside ‘full throttle’ downshift. I trust this is
working normally…?

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Frank Andersen sent Wed 24 Jun 2009:

There is also the little screw inside the modulator valve vacuum
unit that will assist kickdown on partial throttle and also holding
lower gears before upshift.
This can be adjusted by lying on road removing hose and turn with
small flat blade screwdriver don’t turn more than 1/4 turn before
trying again.(I used to be able to do it when I wasn’t as
adequately proportioned!!-been a few years all my cars have
different trans now)
You will know you’ve over done it when the trans won’t shift to 2nd
from first.
Have fun–
The original message included these comments:

However, during normal driving the up and downshifts are regulated by a
vacuum control unit outside ‘full throttle’ downshift. I trust this is


AndrewB
Aberfoyle Park/South Australia, Australia
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AndrewB wrote:

In reply to a message from Frank Andersen sent Wed 24 Jun 2009:

There is also the little screw inside the modulator valve vacuum
unit that will assist kickdown on partial throttle and also holding
lower gears before upshift.
This can be adjusted by lying on road removing hose and turn with
small flat blade screwdriver don’t turn more than 1/4 turn before
trying again.(I used to be able to do it when I wasn’t as
adequately proportioned!!-been a few years all my cars have
different trans now)
You will know you’ve over done it when the trans won’t shift to 2nd
from first.

This is actually the same adjustment as done on the 65/66 downshift
cable, Andrew - but on the BW12 both a vacuum gauge and a pressure gauge
is used for a ‘proper’ adjustment…:slight_smile:

The box should certainly downshift as required without the specific
kick-down circuit, as you say - but the vacuum control unit may also be
leaking/inoperative. But as he didn’t comment on any other shift
anomalies we may assume that everything else is hunky-dory…?

Frank
xj6 85 Sov Europe (UK/NZ)>The original message included these comments:

However, during normal driving the up and downshifts are regulated by a
vacuum control unit outside ‘full throttle’ downshift. I trust this is

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The archives and FAQ will answer many queries on the XJ series…
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