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MattR

Member Since: 30 Dec 2021
Location: Normandy
Posts: 4

Strange behaviour of a GKN Overdrive - HELP!

Hi,
Apologies if GKN issues are anodyne here, but I have trouble finding anyone local willing to touch the drive system of my 300TDI (1996).
In 1997 a GKN overdrive was fitted and worked perfectly until around 2007 when the speed required to engage it increased and it became unusable. No speed sensor could be bought here so a garage bypassed the control box and put a switch on the dash. I had to manually remember to switch it off when slowing.
This worked fine for a while, but then in 2017, after a long motorway journey with it engaged, I switched it off slowing for the toll. It went off, then on, then off and seemed to have a mind of its own. I stopped and let it cool and all was well. So I replaced the oil in the Tx box and overdrive but this had no effect.
Then, I noticed that the bypass wiring under the seat was a mess so tied it up. This seemed to cure the on, off, on, off issue so I thought it electrical, not heat.
But now, if I drive 30 mins or more with it off, it switches on automatically with the switch in the off position.

So is it heat?
If I switch the switch to on, it stays on and i can turn it off when slowing (clutch down as I arrive home so it doesn't go back on).
Is it heat? Is it electrical? ... any ideas. I'm not good with electrics but would love to hear opinions.

30th Dec 2021 10:43am

geobloke

Member Since: 06 Nov 2012
Location: Nottinghamshire
Posts: 4410

The GKN overdrives are well known for having problems with their control boxes. Sounds like the control module is playing up. At the end of the day the OD is actuated by a solenoid, so it would be possible to remove the control box altogether and just manually activate the OD when needed.

30th Dec 2021 11:34am

MattR

Member Since: 30 Dec 2021
Location: Normandy
Posts: 4

Thanks for the reply.
That sounds logical.
The speed sensor was supposedly bypassed using a kit from Devon 4x4. I didn't do it as i'm a numpty with wiring. It was done by ACC16 who built a dashboard for her.
Is the soleniod in the control box?
Can I get a similar one and put it (get it fitted) in the circuit?
Having just moved, I need to find an auto-electrician who isn't afraid if 4x4s.
Thanks again
M

30th Dec 2021 3:58pm

geobloke

Member Since: 06 Nov 2012
Location: Nottinghamshire
Posts: 4410

The solenoid will be on the OD, but energised from the control module. I am afraid my knowledge of the GKN unit begins to run out at that point

But... I did find this old post on another forum that may help you https://forums.lr4x4.com/topic/103207-odd-...behaviour/

30th Dec 2021 4:48pm

htb2

Member Since: 02 Nov 2018
Location: Carmarthenshire
Posts: 527

I would assume solenoid on or near the overdrive as thats what s being controlled.

30th Dec 2021 4:50pm

Linds Hanson

Member Since: 16 Jan 2021
Location: Cornwall
Posts: 484

The solenoid is on the overdrive unit it just has a single switched live feed to it. The overdrive musnt be left engaged in reverse as this will permently damage the epicyclic gear train inside the unit. If you disconnect the single wire on the overdrive unit and drive the car the unit shoudnt engage at all.

30th Dec 2021 6:41pm

MattR

Member Since: 30 Dec 2021
Location: Normandy
Posts: 4

Thank you.

31st Dec 2021 6:56am

MattR

Member Since: 30 Dec 2021
Location: Normandy
Posts: 4

Well, I disconnected the solenoid and took her for a spin.
Sure enough, the switch on the dashboard no longer had any effect ........ but after 20mins, she dropped into OD, then out again and it seemed to want to be half in, half out like a slipping clutch.
If I can find the original box, I'll ditch the OD unit as local duties don't require it.

1st Jan 2022 7:41pm

ickle

Member Since: 22 Jul 2010
Location: South Vendee
Posts: 1777

2008 Defender 110 Puma 2.4 CSW Alpine White

I had a GKN OD on my 200tdi 100" for several years, swapped in the end for a Disco transfer box with the higher 1.2 ratio, did masses of heavy towing both locally and long trips from Broadway to here in France with the 1.2 and never had a problem. If there was ever a heavily loaded hill start to do, there is always low ratio.

Keith

1st Jan 2022 9:03pm

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 8006

2011 Defender 110 Puma 2.4 USW Stornoway Grey

i had a gkn overdrive on my td5, 105k miles with it fitted.

remove the solenoid actuation completely and fit a manual selection. Cheers

James
110 2012 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

6th Jan 2022 5:26pm

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