After a decade, I’m returning to the call of the big cat. I
used to have a 73 XJS I loved, but other projects took over
and I sold it. Now I’m looking at XJS’.
I searched the threads and saw no mention of possible 5 or 6
speed automatic transmission conversions? The last I knew,
John’s Cars was offering 4-speed 700R4 swaps, but does
anyone have any information about the GM Hydramatic 5L40-E,
6L50, 6L80 or 6L90 transmission swaps?
I know some people are really purists and love the 3-speed,
but I’m all about making mechanical changes to improve the
original vehicle (not so fond of engine swaps - it’s just
not a jag anymore).
Thoughts? Anyone know of any links or people who have done
the tranny swap? I know there are 6-speed manual swaps, but
I’m thinking automatic may be easier.–
linesplice
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In reply to a message from linesplice sent Thu 16 Apr 2009:
You might want to consider a ZF 5HP30 transmission. It’s a
5-speed auto gearbox. The gear ratios are 3.55, 2.24, 1.54,
1.00 and 0.79.
This is speculation on my part. I don’t know how difficult
it would be to fit it, if the ZF can be done at all. I
don’t know of anyone who has fitted one in an XJ-S.
However, they were used in Aston Martin DB7s with V12s (as
well as Bentley, RR, and BMW). There’s some (and I
emphasize the word some) connection between the DB7 and the
XJ-S. ZF tech support will provide info on dimensions,
mounting, bolt pattern and the like, if you ask. One
definite drawback: a rebuilt ZF 5HP30 looks to be pricey.
If (when?) my GM TH400 (1991 XJ-S; 125,000 miles) goes, I
might try the ZF. I have some graphs prepared by someone on
the list. I’ll send these if you contact me off-line.–
The original message included these comments:
Thoughts? Anyone know of any links or people who have done
the tranny swap? I know there are 6-speed manual swaps, but
I’m thinking automatic may be easier.
In reply to a message from BWP sent Fri 17 Apr 2009:
The ZF is a great auto trans, the best and smartest IMHO.
However, based on my understanding of the unit, I think
there would be a challenge using it on an older vehicle.
My understanding is that the ZF relies on the ability to
communicate with the engine and back off the throttle during
upshifts, in order to not slip the clutches and bands, as it
is not designed to operate that way… The 5HP30 TCU
expects to be able to command a particular torque or rpm
from the engine ECU, and for the engine ECU to respond that
the specified torque has been reached and then to go ahead
with the gear change. So, I’m not sure it can be used,
unless they have a special version that works with ‘‘dumb’’
throttle, or you built some custom gadgets to fake all the
communications and retard timing or whatnot. I’ve played
with these, and if you ‘‘lie’’ to the trans, the gear changes
are instantaneous… meaning it feels like you were hit
from behind by a train. Not good for the car’s driveline of
course, and I’m sure the trans wouldn’t last. Now, this is
just based on my experience, but I just don’t think the
5HP30 is designed for the old way of doing things -
overlapping/slipping the clutches - like the old GM400 and
other old transmissions were designed to do. Perhaps
there’s a version of it that can work without all the
interaction? I would think that’s unlikely, since I’d wager
they usee smaller wear surfaces since it does not expect to
ever slip them.
Having said all this, I’d love the challenge of interfacing
it all with an electric throttle-back-off-override to make
it work.
The way a ZF orchestrates gear changes, particularly in the
german cars where it’s used very often, is an art form, at
least to me. And yes they are pricey.–
87 XJ-S V12, vin 135xxx ---- PICS: www.myrq.com/jag
Evington, VA, United States
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