[xj] Overdrive Failing to Engage

XJ
1

For a while now my overdrive has been inop. When I turn the switch
on I get the familiar solenoid click, but no drop in revs.

If I lift off then the revs drop, but rise back up to the direct
4th speed as soon as I reapply some throttle.

I’ll be checking it out this weekend with a bit of luck, but I seem
to recall someone else (Arnoud perhaps?) having the same problem at
a similar time (i.e. a month or two back). Anyone had a similar
failure and tracked down the cause?

Cheers,–
Rob Hod '73 Daimler Sovereign MOD
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2

For a while now my overdrive has been inop. When I turn the switch
on I get the familiar solenoid click, but no drop in revs.

If I lift off then the revs drop, but rise back up to the direct
4th speed as soon as I reapply some throttle.

Hi Rob,

I talked to an OD specialist about this. The cause is either low
pressure or worn friction pads. You could start by checking the
accumulator piston for scoring (big brass plug at the bottom). He
also said that you could raise the pressure a bit by putting some
rings between the piston spring and the plug. A fluid change may
improve things as well. On the LH side of the unit there’s a plate
that covers a lever. That may require adjustment. If none of that
works (as was my case) you’re in for a rebuild, which he claims isn’t
all that difficult…–
Arnoud

iMac, therefore I am

http://www.se7en.nl

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3

Peter

Sounds like the linings are not engaging properly, which might be lack of
pressure or lack of lining.

The latter would certainly require removal and dismantling. That’s what
happened to me. As soon as the linings slip, the Spragg clutch takes over.
In the early stages it’s just like kicking down an automatic. Then over
time you gradually lose O/D until eventually it goes altogether.

If it’s lack of pressure, it might be worthwhile to try a heavier oil
(depending on what you’re currently using). I’ve used 85/140 without ill
effect. Does it slip when the oil is still cold?

I think it may also be possible to adjust the plunger which rides the cam.
Haven’t tried it myself but I think I have some notes somewhere on how to
remove it

Good luck

George

You wrote
"…When I turn the switch
on I get the familiar solenoid click, but no drop in revs.

If I lift off then the revs drop, but rise back up to the direct
4th speed as soon as I reapply some throttle.

I’ll be checking it out this weekend with a bit of luck, but I seem
to recall someone else (Arnoud perhaps?) having the same problem at
a similar time (i.e. a month or two back). Anyone had a similar
failure and tracked down the cause?"===================================================
The archives and FAQ will answer many queries on the XJ series…
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4

Rob,

I’m coming at this from a Saloon perspective, so my recommended sites
may not be spot-on…but a month ago or so we had quite a discussion
over on Saloons about overdrives.

There is a strong contingent that says test your unit with a special
pressure gauge…and you’ll be able to diagnose it yourself.

In any event, my Mark 2 shifts into overdrive just fine for the first
20 miles or so, then needs careful throttle feathering to coax it in up
to about 40 or 50 miles…then, if I were to keep driving (in Juneau,
I’m home by that time!), I suppose to would continue to get worse.

Anyway, I’ve come to the conclusion that I need to have a few O-rings
renewed in my overdrive (leakage past the hardened O-ring (s) make it
impossible for the unit to maintain pressure). I have identified the
man I will send my unit to when the time comes, again thanks to the
Saloon list. His name is Duane Hoberg, in Kansas City, MO.

OK, here’s some overdrive reading for you:


http://www.buckeyetriumphs.org/technical/AOD/AOD1/AOD1.htm
http://www.ntahc.org/techtips/OVERDRIVE1.html
http://www.geocities.com/jholekamp/index

I have copies of a series of emails to and from Hoberg back in 2002
(from a Saloon Lister in BC) that convinced me.

Regards,

Tom Carson
1954 XK 120SE OTS S674946
1962 3.8 Mark 2 MOD, chrome wires
1970 XJ6 1L55441BW
Juneau, AlaskaOn Nov 17, 2004, at 1:46 PM, Rob Hod wrote:

For a while now my overdrive has been inop. When I turn the switch
on I get the familiar solenoid click, but no drop in revs.

If I lift off then the revs drop, but rise back up to the direct
4th speed as soon as I reapply some throttle.
…
Rob Hod '73 Daimler Sovereign MOD

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5

Rob

Factory spec for a 4.2 is 490-510psi; 2.8 400-420.

My favourite specialist says you should get by with 250-300 at a pinch. I
suspect the different pressures arise from the stronger springs used in the
4.2 OD. So if your OD came from a 2.8, you should not need so much pressure
but may have greater risk of slippage in reverse as the reverse lining
wears.

My good OD gives about 450

cheers

George

Tom wrote
There is a strong contingent that says test your unit with a special
pressure gauge…and you’ll be able to diagnose it yourself.===================================================
The archives and FAQ will answer many queries on the XJ series…
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6

In reply to a message from Tom Carson sent Thu 18 Nov 2004:

That’s very interesting My overdrive drops out occasionally when
travelling at speed on a motorway so far it has re-engaged when I
operate the switch. trouble ahead maybe?–
Keith Turner '79 XJ6 based Aristocat, , '81 3.4 XJ6
Swansea, United Kingdom
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7

In reply to a message from Keith Turner sent Thu 18 Nov 2004:

Thanks for everyone’s comments. Should make me better prepared
for a spot of diagnostics at the weekend. The funny thing is that
it was as good as gold for 17 years, no dropping in or out or
slipping and then one day, during a run, packed up. I’m hoping it’s
something twixt solenoid and operating valve.

I’ll let you all know how it goes, though it maybe a while till I
report…

Cheers,–
Rob Hod '73 Daimler Sovereign MOD
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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8

In reply to a message from Rob Hod sent Wed 17 Nov 2004:

My two-bobs worth - check the things you can externally
first, like the hyraulic accumulator which can lose
pressure. Look at the ‘‘rings’’ to the piston as well as the
O-rings around the piston housing. Yes you could pack the
big spring but that shouldn’t have lost too much tension.
Check the setting of the operating lever by all means -
don’t think trying to alter the stroke of the pump would
help. The friction surfaces on the sliding member would
only wear if you’d been particularly brutal with the way you
engaged the o’drive - the throttle should always be
‘‘feathered’’ - it makes for a smoother change.
Good luck.–
The original message included these comments:

If I lift off then the revs drop, but rise back up to the direct
4th speed as soon as I reapply some throttle.

–
Barry Woolcott
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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