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Overdrive fail = no drive?

L90TD5

L90TD5

In Fourth Gear
I recall reading on a forum someone saying that if your GKN OD failed you could be left with no drive at all.

Is this true?

Cheers,

James:rolleyes:
 
Can't see how. As I understand it, the O/D is either engaged or not. Failure of the O/D unit would result in normal gearing.

AJ
 
Erm it can happen, dont ask me how. We've had a defender in that couldn't select reverse so we fitted a gearbox and still couldn't select reverse turned out it was the O/D not sure if you could select forward but definatly not reverse.
 
Cocky Lil Guy said:
Erm it can happen, dont ask me how. We've had a defender in that couldn't select reverse so we fitted a gearbox and still couldn't select reverse turned out it was the O/D not sure if you could select forward but definatly not reverse.
Click to expand...

Is that how main dealers deal with fault finding then?.....replace the most awkward and expensive item first, then when it still doesn't work, try and find out why????????

Jeez.........
 
It depends on the type of failure, doesn't it?

If the solenoid or selector system fails, the OD will be stuck in one position or the other, engaged or disengaged, so you'd still have drive either way, unless you're really unlucky and in fails in transition.

If it's down to a bearing, gear or shaft failure it could loose drive and, in the worst case, lock the transmission causing other damage elsewhere.
 
If it's an electric solenoid engaged Overdrive, then they aren't designed work in reverse.

They lock the cluster, or lock the outer track for overdrive, the pressure from the drive keeps the track on the clutch face of the casing. In reverse, it tries to pull the track away, so no drive. That is why you have an inhibiter switch and can only engage them in forward gears.

Chris
 
Is that not basically the same unit as was in my old PI Triumph ie a Laycock ?
If so it was silent.
Alex
 
Lacy said:
Is that how main dealers deal with fault finding then?.....replace the most awkward and expensive item first, then when it still doesn't work, try and find out why????????

Jeez.........
Click to expand...

Expensive for who?? When the vehicle is under warrenty and they pay for the gearbox.
 
The GKN OD has a speed sensor. If you go near about 25 mph it knocks off. Never happened though, I flick it off before it does it.

Maybe its revs though? The person who recommended it to me said he was off roading, accidentaly flicked to OD on in Low range diff lock giving it some stick...it came on, his revs dropped but he wasnt happy! :) Ran fine after though.

T
 
no idea im afraid, my series o/d would work in reverse and hit some daft speeds while at it.

when it failed however there was no drive at all.
 
The Series type use mechanical action to engage the parts. The Electro hydraulic ones use helical cut gears to help with the pressure. They use springs to hold the clutch together, hydraulic pressure to part them and lock the cluster for straight through drive..

Similar principal to 4wd and pto clutch engagement on Tractors.

Chris
 
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