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hxk494

Member Since: 29 Apr 2013
Location: Edinburgh
Posts: 239

GKN OVerdrive

Managed a half day under the new landy earlier in the week and got started on my first job - the non-functioning overdrive.

First off I removed the cubby box to get access to the panel in the seat box (was planning to remove it anyway and replace with a centre seat that I was given years ago and has been waiting in the loft for just this time).

Overdrive was filthy and doesn't have the breather arrangement I've seen in most of the pics online, instead there is a metal "button" loosely in the same position (I've seen one shot of this type of thing on a German forum). I'm thinking mine is an early one perhaps?

Click image to enlarge

Anyway, outside cleaned off then onto the oil change. There is zero clearance between the exhaust box and base of OD so had to remove two exhaust brackets and lever it down to get bolts out and plate off. So far so good but oil did look pretty manky. Refilled with ATF then onto the control mechanisms.

Click image to enlarge

Click image to enlarge

I had read a lot about the speed sensor causing problems (this already had a RS Components part in place of the original) so wired 12v directly to the solenoid through a switch and took it out for a test run. Flicked switch at 40mph in 4th and it worked! Have been using it this way for a bit and no strange noises so next job is to try and test speed sensor, check wiring out properly and the poss source a new sensor.

Click image to enlarge

Don't suppose anyone has a spare speed sensor (GKN Original) that they could measure up for me - want to know the distance from the shoulder down to the end of the sensor as the RS part has a threaded body and lock nut so may have been set too far away to work properly - but don't want to screw it in and find it destroys itself on the OD internals.

Cheers,
Martin. 1996 300Tdi Defender 110

9th May 2013 3:16pm

ashtrans
Site Sponsor

Member Since: 08 Nov 2008
Location: Harpenden
Posts: 257

It's the speed sensor and the ecu that causes all the problems, my advice would be to use it manually, just remember to disengage under about 40,

Dave Dave

9th May 2013 5:55pm

appaloosadude

Member Since: 17 Oct 2012
Location: Buckinghamshire
Posts: 630

Sorry to hijack, but here goes anyway

- my overdrive sometimes drops out when not under load, is there anything I can do to stop it doing it, or is it rebuild time? Dave, as your username is AshTrans, I'm hoping you're from Ashcrofts!?

9th May 2013 6:21pm

hxk494

Member Since: 29 Apr 2013
Location: Edinburgh
Posts: 239

I'm used to manually disengaging the OD in my Series 3 so would probably manage that OK.

Would it be as simple as wiring the switch/light on the gearknob up to a relay to switch the solenoid in and out? I've read about the sensor being there to prevent use below say 30mph - is this just because the torque is too high for the unit to handle in the lower gears? What about reverse - torque again or is it something more sinister?

Oh - no probs with the thread hijack, interested to find out all I can about these units.

Cheers,
Martin. 1996 300Tdi Defender 110

9th May 2013 7:17pm

appaloosadude

Member Since: 17 Oct 2012
Location: Buckinghamshire
Posts: 630

The reverse thing is to do with a one-way bearing. It works on a series of little ramps set around rollers - can't really explain it well with words, but trust me, it only works in one direction. I think my clutch pack is failing...

9th May 2013 7:35pm

ashtrans
Site Sponsor

Member Since: 08 Nov 2008
Location: Harpenden
Posts: 257

appaloosadude wrote:
Sorry to hijack, but here goes anyway
- my overdrive sometimes drops out when not under load, is there anything I can do to stop it doing it, or is it rebuild time? Dave, as your username is AshTrans, I'm hoping you're from Ashcrofts!?

Yes but I am no expert on these units !

I am familier with some of their faults but I am not sure why it would drop out when not under load, Dave

9th May 2013 9:09pm

ashtrans
Site Sponsor

Member Since: 08 Nov 2008
Location: Harpenden
Posts: 257

hxk494 wrote:
I'm used to manually disengaging the OD in my Series 3 so would probably manage that OK.

Would it be as simple as wiring the switch/light on the gearknob up to a relay to switch the solenoid in and out? I've read about the sensor being there to prevent use below say 30mph - is this just because the torque is too high for the unit to handle in the lower gears? What about reverse - torque again or is it something more sinister?

Oh - no probs with the thread hijack, interested to find out all I can about these units.

Cheers,
Martin.

Yes wire it up like that,

I think the torque is just too high at lower speeds,

I know they can loose drive in reverse but I have not had one apart to see why or if its fixable,

Dave Dave

9th May 2013 9:12pm

big steve

Member Since: 24 Dec 2009
Location: hertfordshire
Posts: 2456

2015 Defender 90 Puma 2.2 HT Montalcino Red

i had one on my td5 which straight after a replacemnt gearbox was fitted for some reason decided to loose drive in reverse it was deemed not fixable after that either

steve 2015 2.2 tdci hardtop xs
3.2 conversion DONE 238bhp and 707nm torque and thats just the start ;-P
hybrid turbo in build -done ready to fit
ashcroft atb in transfer box
6 speed auto in build

10th May 2013 5:30am

yobbie

Member Since: 15 Nov 2010
Location: Isle of Wight
Posts: 712

1999 Defender 90 Td5 Heritage LE Bronze Green

I think Devon 4x4 bought all the spares and do rebuilds.

10th May 2013 5:46am

hxk494

Member Since: 29 Apr 2013
Location: Edinburgh
Posts: 239

Steve,

don't suppose you held onto your knackered unit and would like to sell it for spares?

M. 1996 300Tdi Defender 110

10th May 2013 9:11am

hxk494

Member Since: 29 Apr 2013
Location: Edinburgh
Posts: 239

an update on this at last.

Checked out all the wiring for continuity and no problems found.

Pulled the speed sensor out to find that the seal around the metal tip was missing and the tip was loose - looked like it had rubbed on something at some point previously. Old sensor had RS part number on it under the heat shrink and I thought at that point it had been spliced in by previous owner but pic on Devon site looks exactly like mine so I now think the original (old style) sensor was made up with a RS sensor in it.

Ordered new sensor from RS - (RS285-756) (£36+VAT) (compared to £160 odd from Devon). Soldered it in to the fitting plug, screwed it in all the way, backed it out half a turn, tightened lock nut. Success - it now works as it should through the switch on the gear knob.

Happy days - next on the list is the leak from one of the oil cooler pipes.

Cheers,
Martin. 1996 300Tdi Defender 110

4th Jun 2013 4:02pm

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