The GKN Overdrive

[Oakmaster]

I suppose its time to raise the hoary old GKN Overdrive issues.  This was precipitated by the return of my old 110 CSW 300 Tdi  M Reg having spent the last 11 years being trashed on my sisters little farm.  I had this from 1999 to 2010  put 100K on it with no real issues  did a lot of towing and the GKN was an absolute god send - you can select exactly the right gear for every situation - and being able to change on the fly was a real bonus.  Needless to say - the GKN no longer works, the speed sensor being the likly suspect. 

So now I have 2 110s with GKNs that dont work siting outside.

I haven't approached Devon 4X4 since they sold out of sensors years ago, and wondering whether anybody on here had come up with a solution?

Thanks 

 

B

[western]

You can delete the control unit & speed sensor, I did on mine by fitting Devon4x4's relay

https://www.devon4x4.com/overdrive-speed-sensor-control-box-over-ride-kit.html

Then it can be selected as required without the 30mph lower limit, 

There is plenty of info on here about speed sensor & the GKN Overdrive. 

[hxk494]

When I had a GKN on my 90 I got a replacement sensor (early smaller diameter type with wires rather than the type that has a connector plug directly on the back of it) from RS Components, wired it up and it worked perfectly. I'll have the details of the RS part number somewhere.

I've also got a second hand later type sensor squireled away somewhere which I bough in error second hand and have never done anything about moving on yet, I can take a look for it if you like?

[reb78]

The RS part would be interesting to see. I looked at this for mine a while back but the only RS offering I could find at the time was the wrong thread for the hole on the OD so if you have something that fits and works that would be really handy to know. When D44 were selling the original ones they were extortionate... but then their usual markup is kind of along those lines on most stuff!

The other option is to remove the speed sensor and control box completely. I would favour a relay triggered by the button on the gearlever that wont engage if the vehicle is in reverse (use the reverse light feed). I think speed sensors are about the only spares I dont have for a GKN OD!

[Oakmaster]

Thanks for the info Gents.

I can remember looking through the RS Catalogue at the time (early 2004/5 maybe) and having the same problem with the thread and diameter, it would be a benefit for all the GKN owners if you had a tried and tested solution?

Thanks 

Bill

[reb78]

2 hours ago, Oakmaster said:

Thanks for the info Gents.

I can remember looking through the RS Catalogue at the time (early 2004/5 maybe) and having the same problem with the thread and diameter, it would be a benefit for all the GKN owners if you had a tried and tested solution?

Thanks 

Bill

We had a big long chat about them in 2015 apparently. I dont think we found a resolution though...

 

 

[western]

I was looking for that thread earlier but couldn't find it. 

[Sigi_H]

Since my GKN OD passed away I decided to take the 1.1 ratio for the LT230 from Ashcroft on my slightly tuned 200Tdi as an alternative. Works way better than with the GKN, ist a lot easier and lighter and the 200Tdi pulls it easily.

The car works up to 80 km/h like a 4 gear car. From 80 km/h I can use 5th, which makes the old OneTen a lot mor silent when traveling with 100 to 110 km/h.

For me a perfect situation.

Config is 200Tdi slightly tunded, LT77 gearbox, LT230 Transferbox with ratio 1.1, wheels are 265/75R16

 

Edited June 20, 2022 by Sigi_H

[Oakmaster]

4 hours ago, reb78 said:

We had a big long chat about them in 2015 apparently. I dont think we found a resolution though...

 

 

We did have a long chat about it in 2015 - (probably triggered by me - I think of these GKN gatherings as the school reunions I never went to) 

[reb78]

Haha. Well, theres only a few of us that still run them successfully so it feels like a club I can contribute something useful to! I seem to have a sad hobby and have collected two others as spares for mine. 
 

@vulcan bomber has been able to repair some broken ones. 
 

Ralph - is yours all fitted and working now?

Edited June 21, 2022 by reb78

[Snagger]

It’s probably worth a forum of its own, such is the frequency of issues!

[Nonimouse]

I'd love a GKN in the Disco. Been after one for years, but the money is never there when I find one

[western]

1 hour ago, reb78 said:

Haha. Well, theres only a few of us that still run them successfully so it feels like a club I can contribute something useful to! I seem to have a sad hobby and have collected two others as spares for mine. 
 

@vulcan bomber has been able to repair some broken ones. 
 

Ralph - is yours all fitted and working now?

It's sat on bench in my garage waiting for some time off so I can refit & test it before doing any long drives, it maybe October before it gets fitted. 

[reb78]

2 hours ago, Nonimouse said:

I'd love a GKN in the Disco. Been after one for years, but the money is never there when I find one

I've said the same about our TD5 disco - it revs quite high and I reckon putting a 1.4 transfer box in with a GKN OD would be ideal. Input gear teeth are different for the 1.2 boxes arent they so much harder to find??

[reb78]

2 hours ago, Snagger said:

It’s probably worth a forum of its own, such is the frequency of issues!

I dont think GKN got it right with maintenance intervals at all on these and thats a big part of the issues. They recommend a 50,000 km oil change interval I think (so about 31k miles)? The thing takes about 750ml of ATF and has very very very poor ability to disperse heat but gets very hot in use. I change my OD oil at every engine service (every 6k miles). It comes out a little dark but not the burnt colour you get if you leave it much longer. I'm convinced this is a big cause of issues seen.

Its interesting though as the Roamerdrive was seen as more robust but now they have been around a bit we are seeing failures on them too - although some of that appears to be down to very cheap parts used.

[Snagger]

1 hour ago, reb78 said:

I've said the same about our TD5 disco - it revs quite high and I reckon putting a 1.4 transfer box in with a GKN OD would be ideal. Input gear teeth are different for the 1.2 boxes arent they so much harder to find??

Don’t exist to my knowledge, must for the 1.4.  Same as the Roverdrive.

As for failures, yes, we are seeing a fair few on Roverdrive,  lastly Defender versions, but mySeries version failed because of bearing failure and Mark Saville allegedly had his rebuilt three times in 15,000 miles.  They have poor quality unbranded Chinese bearings.  I think the later versions have weaker cases too, where they made the extra oil slots in the front cover (at least on the Series model).  That’s one extra (tenuous) reason I’m using to justify an over-expensive Fairey rebuild if I can source the parts.

I was joking about the GKNs needing their own forum, but we could perhaps have a forum for all overdrives, or transmission assemblies as a whole.  Maybe it’d save Nige and Dave a lot of wading through the other forums? 😉  Lots of forums does clutter the home page though, I suppose.

[FridgeFreezer]

If we know the specs of the RS sensor & we know the thread it should be easy enough to source & adapt a replacement.

[Nonimouse]

4 hours ago, reb78 said:

I've said the same about our TD5 disco - it revs quite high and I reckon putting a 1.4 transfer box in with a GKN OD would be ideal. Input gear teeth are different for the 1.2 boxes arent they so much harder to find??

My dream vehicle, a 460 G wagen, would be fitted with the military spec 5 speed box, this has a low first and overdrive fifth. As I'm never going to be able to afford my dream, I would like to get as close to that option as possible in the Disco. So a 1.44 T box, OD and 235/85's is about perfect. Maybe one day

[FridgeFreezer]

4 hours ago, Nonimouse said:

a 1.44 T box, OD and 235/85's is about perfect.

That's the exact combo we've got on the 127 and I can confirm it's lovely, cruises at 75-80 all day long but you have lower gearing for easy setting-off when loaded up or any twisty/hilly bits.

[Nonimouse]

4 minutes ago, FridgeFreezer said:

That's the exact combo we've got on the 127 and I can confirm it's lovely, cruises at 75-80 all day long but you have lower gearing for easy setting-off when loaded up or any twisty/hilly bits.

Nice to know it works. I regularly have an all up gross train weight of a snadge over 6 tonnes, and although this isn't a big issue, first is a tadge too tall with the 235/86x16 tyres, so I generally work with all ten gears. I'd like to not have to do that

[Retroanaconda]

Same setup on my 90 too. I never use the OD on normal roads, but it allows me to cruise as fast as I want on the motorway. The only limiting factor becomes fuel consumption, which gets silly over 75mph.

[western]

My 110 has 255/85 tyres & the 1.4 Transfer box, it goes along quite well, likes to sit around 60 to 65 on Dual carriageways & motorways, once the OD is back in will sit a 70 with 2400 to 2500rpm on rev counter. 

[Nonimouse]

5 minutes ago, western said:

My 110 has 255/85 tyres & the 1.4 Transfer box, it goes along quite well, likes to sit around 60 to 65 on Dual carriageways & motorways, once the OD is back in will sit a 70 with 2400 to 2500rpm on rev counter. 

At 2500rpm, I'm hitting 75mph. 3000rpm is 85mph, after that it's not comfy. I like about 2,200rpm as a nice safe, frugal place. If I was to keep the 1.22 box and fit a GKN, I could be sitting at a tadge over 2k rpm and doing 80! Drop[ in a 1.44 T box and that's 2.3k rpm. So 70 would be lovely

[FridgeFreezer]

2 hours ago, Nonimouse said:

I regularly have an all up gross train weight of a snadge over 6 tonnes

Can confirm that a similar snadge works nicely - although the 4.6 helps make life easier especially on the hills. General unladen cruising is very nice, Ashcroft's ratio calculator puts 70mph at a smidge over 2000rpm in 5th and 2300rpm at 80.

[robperrie]

good morning, ive had my gkn for about 100k so far, yes , had to totally strip it down a few times and clean it and replace some bits, now also looking for a speed sensor and maybe a clutch, it had a hard drive to malaga with 4.5 ton on the back, been ok though the last 18 months and then it started to slip the other day, but when i carried on using it, it stopped slipping, weird, but my lights flashing like a good un, if i go below 50 it cuts off, so im guessing now the speed sensor has given up, i also looked at the roamer drive a few years back and read that the use of inferior parts they have been unreliable too...why change something when it works.