The GKN Overdrive

[Little mule]

11 hours ago, vulcan bomber said:

A sump is something I have a lot of ideas on, as soon as I can get the one Richard (Reb78) is sending my way fitted I'll be able to make a start on it. 

 

Speed sensors seem to be a major problem, I know several ways of sorting this one. It appears there are 2 types used, does any one know for sure what threads were used? 

I could take mine out of the box and snap some pics and put a thread gauge on it to find out would that help ? 
 

[Little mule]

I also forgot to mention I would be interested in some of the gaskets kits as well . This way I’ll have some in stock for my own over drive and not have to part with an arm or a leg or two lol . 
 

let me know and I’ll get the money transfer out and ready 

Tony 

[Troll Hunter]

23 hours ago, vulcan bomber said:

I hope the mods are ok with this but I can now sell people a set of gaskets for the GKN unit. £15 a set including postage and with a couple of extra gaskets for the inspection cover to allow you to remove the cover for servicing. And significantlu cheaper than Devon who sell 1 gasket for £12!!

 

How many people here are actually running a GKN?

I am definitely up for a set.  Please let me know the postage to BC, Canada.  I don't expect UK postage to apply internationally.  PM me for my address.

Mike

[vulcan bomber]

7 hours ago, Little mule said:

I could take mine out of the box and snap some pics and put a thread gauge on it to find out would that help ? 
 

Yes please, knowing my luck it will be the same as the very dead overdrive I've already got. 

[vulcan bomber]

On 8/20/2023 at 12:05 PM, Oakmaster said:

I have 2 - one in my 110 V8 - Not in use due to a lack of the speed sensor, and another "Sulking on a shelf" 

Could I borrow the Speed Sensor from the unit you have fitted but not working?

[FridgeFreezer]

What does this speed sensor look like? I'm betting it can be replaced with a cheap standard sensor from something else.

[Bowie69]

https://forums.lr4x4.com/topic/92725-gkn-overdrive-speed-sensor/

[vulcan bomber]

1 hour ago, FridgeFreezer said:

What does this speed sensor look like? I'm betting it can be replaced with a cheap standard sensor from something else.

It's just a Hall sensor.

[FridgeFreezer]

A hall sensor would give a low-voltage digital signal (typically 0-5v square wave) while a standard magnetic variable reluctance (VR) sensor gives an analogue signal that is very small at low speeds and gets quite large at higher speeds.

The two would not be interchangeable without a bit of extra circuitry, but both types are common enough on engines and ABS systems.

[vulcan bomber]

They also have nothing inside them that will fail, I have a feeling there not failing. Hence wanting to borrow one that's believed to have failed.

[reb78]

I have one that definitely failed. Replaced just the sensor and it works again. 

[reb78]

Its just a magnet to detect one dip (from memory) in a hunk of spinning metal. So its one pulse per revolution I guess. I dont know how it generates its voltage or what voltage that is though. 

Edited August 23, 2023 by reb78

[FridgeFreezer]

If it's a 2-wire sensor it's almost certainly VR which means tonnes of crank/cam/ABS sensors would potentially work in its place.

The Ford Vr sensors we use on Megasquirt are about £10 and seem very bulletproof.

[JeffR]

On 8/20/2023 at 8:10 AM, vulcan bomber said:

I hope the mods are ok with this but I can now sell people a set of gaskets for the GKN unit. £15 a set including postage and with a couple of extra gaskets for the inspection cover to allow you to remove the cover for servicing. And significantlu cheaper than Devon who sell 1 gasket for £12!!

 

How many people here are actually running a GKN?

I have a couple, but both vehicles not roadworthy, does that count

[Oakmaster]

21 hours ago, vulcan bomber said:

Could I borrow the Speed Sensor from the unit you have fitted but not working?

Sorry missed this - Yes be happy to lend you it - But I'll need a bung to stop the ATF draining out - maybe the sensor from the 'shelf' one? 

 

[vulcan bomber]

3 minutes ago, Oakmaster said:

Sorry missed this - Yes be happy to lend you it - But I'll need a bung to stop the ATF draining out - maybe the sensor from the 'shelf' one? 

 

I want one that is definitely believed to have failed. I can make you a bung for the hole or if your happy to swap sensors over temporarily that would be great.

[Oakmaster]

I'll modify an oak peg to make a bung.

I had severe memory loss after Sepsis during lockdown, resulting a a new heart valve - so I cant remember which has the faulty sensor 

But - I previously had issues that were caused by the flimsy wiring loom that went up the gear stick, so I'm wondering whether to look at those too?  

Triggered by your comment about there being nothing in them to fail - I'm wondering whether we are heading in the wrong direction 

Has anyone got a wiring diagram?

Maybe a simple jig could be made to test the sensors - Somebody could chuck-up a (Blunt) Sawbalde in a lathe or mill or drill and introduce a sensor (carefully) to see if pulses are generated? 

 

I'll get my coat!

 

 

 

[Bowie69]

Are they definitely 2 wire? 

 

[Ibex94]

3 hours ago, Oakmaster said:

I'll modify an oak peg to make a bung.

I had severe memory loss after Sepsis during lockdown, resulting a a new heart valve - so I cant remember which has the faulty sensor 

But - I previously had issues that were caused by the flimsy wiring loom that went up the gear stick, so I'm wondering whether to look at those too?  

Triggered by your comment about there being nothing in them to fail - I'm wondering whether we are heading in the wrong direction 

Has anyone got a wiring diagram?

Maybe a simple jig could be made to test the sensors - Somebody could chuck-up a (Blunt) Sawbalde in a lathe or mill or drill and introduce a sensor (carefully) to see if pulses are generated? 

 

I'll get my coat!

 

 

 

The manual is in the tech archive just search for Overdrive

[FridgeFreezer]

4 hours ago, Oakmaster said:

Triggered by your comment about there being nothing in them to fail - I'm wondering whether we are heading in the wrong direction 

Any sensor can fail no matter how simple it is - although generally VR sensors are very robust things.

An easy check with a multimeter would prove it free of major problems - should have some continuity across the pins, probably nothing to ground (infinite resistance) from either pin, and across the pins you should get a little voltage if you wave it near something ferrous.

[Little mule]

I have a long time rover friend and he has been running Volvo cares for years .

he has had the over drive systems in his Volvos as well. 
I’ll be headed his way this week and we are going to be looking at the ins and outs of the over drives and see how close they are to the GKN .

he told me on the phone that they did use some sort of speed control on them . 
If the over drive was left on and you down shifted the over drive switched off . When you were back into forth gear it automatically came back on.

the Volvo cars used two types of engagement button . One of them was on the shifter like the GKN and the other type was a switch on the dash like a signal light switch.

the hydraulic shift unit mounted on the side to shift it in and out could be connected directly and would work with out any problems.

he also stated when the over drive was on and you shifted into reverse nothing happened you just backed up.

I’ll have more info and pics as well.

Tony 

[reb78]

1 hour ago, Little mule said:

I have a long time rover friend and he has been running Volvo cares for years .

he has had the over drive systems in his Volvos as well. 
I’ll be headed his way this week and we are going to be looking at the ins and outs of the over drives and see how close they are to the GKN .

he told me on the phone that they did use some sort of speed control on them . 
If the over drive was left on and you down shifted the over drive switched off . When you were back into forth gear it automatically came back on.

the Volvo cars used two types of engagement button . One of them was on the shifter like the GKN and the other type was a switch on the dash like a signal light switch.

the hydraulic shift unit mounted on the side to shift it in and out could be connected directly and would work with out any problems.

he also stated when the over drive was on and you shifted into reverse nothing happened you just backed up.

I’ll have more info and pics as well.

Tony 

The volvo units were GKN - I think they used D and J types. Pretty sure our defender ones are modified J types. The big difference is the drive on ours comes in and out the same end. On the volvo/triumph versions drive goes in the front and out the back. 

[reb78]

3 hours ago, Bowie69 said:

Are they definitely 2 wire? 

 

Only two wires connect to it. 

[Bowie69]

Can only really be a VR sensor then. 

[Little mule]

My friend mentioned this as well . They are either in and out the same end or a through and through. I’m thinking the shifting piston might be the same thread and some parts might fit.

he also mentioned that he had one that was shifting in and out on its own . He took it apart and found the “O” rings were worn out on the internal pistons . He replaced them and it worked very well.

we might find or be able to find parts this way rather than paying the arm and leg price from known dealers. 
 

I’ll take a look at one or two of them this week when I have some time . 
the shift button on the shifter and wiring might be a little more robust than the GKN version 

Tony