overdrive not working

#1
fuse Ok wiring seems good. new really fitted . No 'clicking' when activated on lever and ignition on with gearbox in 4th gear. ( or any other gear) was working but just stopped .any advise ? no idea where to start checking. theres a very small 'micro' with on throttle body actuator . no clicking or voltage noted when closing /opening throttle. any suggestions other than sell it? this is a mates car and gentleman is suffering ill health hence my trying to assist in any way.
 

roverp480

Active Member
#3
Do you have a wiring diagram? I think the throttle needs to be partly open for the O/D to work , not closed . The solenoid is fairly temperamental. I would look to that first. It has two coils , one to actuate it and one to hold & there is a set of contacts inside, working the actuating coil, give that a clean. Which model of P4 and year will help. You should get the 12V at the solenoid , in 4th gear and throttle at partly open
 
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jp928

Well-Known Member
#6
Rover Laycocks that I drove were manually activated, but the 105R unit might have been governor activated. Dont recall if there was a relay involved. As above , apply +12v directly to the solenoid and it should pull the lever. The 2 windings are know as pick and hold, used to reduce current drawn once pulled in.
jp P2,P3,P4,P6x3,RR,Disco x2
 

Huo

New Member
#7
The overdrive on my old p4 100 has also stopped working, checked circuit all seems ok power to switch on top of gearbox when 4th gear is selected, solenoid switch on back of gearbox, i took it off and connect 12v it operates. all this since i replaced servo, but forgot to disconnect battery although all fuses intact occasionally overdrive fuse blows, any suggestions.
 

jp928

Well-Known Member
#8
You need to test that it pulls the lever fully while fitted in place, and that it switches from 'pick' current to 'hold' current (lower) at full stroke. You could test the switching from pick to hold off the car, but should also do it on the gearbox. Its possible that long periods on pick current could pop the fuse. Check and clean all the contacts in the related wiring.
 

Huo

New Member
#9
No luck with my overdrive problem there seems to be power to relay except nothing on c2 terminal, changed solenoid today on gearbox must be wiring issue.
 

Huo

New Member
#11
Thank you for the very clear wiring diagram, had another look at it today seems to be power to all the terminals on the relay except C1, so no feed to solenoid on back of gearbox, could it be a relay fault? C4 has power, thought about putting a bridging wire from C4 to C1, but don't want to fry the relay. any ideas?
 
#13
Check the earth lead to the relay is actually still earthed, they can lose connectivity over the years.
The connections on some relays are riveted on and the rivet also carries the current. sometimes the connection breaks down. soldering the rivet to the tab works (after cleaning).
 

Huo

New Member
#14
Yes that's a good idea, all the 5 tabs are riveted, and C1, which is the ground to the solenoid might be the problem as there is a bit of movement there, thanks for all advice will give an update in few days.
 

Huo

New Member
#15
Tested solenoid and all working on gearbox, also put current on C1 on relay and that operates solenoid as well, so i guess the prob is between switch and supply, anyone know which wire on the spaghetti wiring panel in engine compartment it is? otherwise need to do a new feed to switch.
lot of head scratching''''''going on.
 

colnerov

Well-Known Member
#16
Hi, On the wiring diagram up there /\/\ the letters beside the connecting wires are the colours. So perhaps @roverp480 could post up the colour legend from the wiring diagram.

Colin
 

roverp480

Active Member
#17
B= BLACK, R = RED, O = ORANGE, P = PURPLE, Y = YELLOW,G= GREEN, W = WHITE, U = BLUE, S = SLATE ( Light Grey) , N = BROWN
The SG wire going into the fuse 75 connects to a terminal A3 at the fuse box , which will have white wires to it.
 

Huo

New Member
#18
Finally solved my overdrive problem, after replacing various parts it became clear that the fault was with the relay, very difficult to find a replacement and costly. I put in a bridging wire from C4 to C1, this allows all switches to work, enclose a photo...hey!!
 

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roverp480

Active Member
#19
Glad you got it sorted . I think the relay is a standard Lucas 6RA changeover relay but finding one with screw connectors is difficult and expensive . Ones with Lucar connectors are readily available, but again not cheap. A modern cube relay to do the same job is probably about £10. As you said you can hear the relay working , if you are confident enough, it may be worth taking off the cover & cleaning the contacts inside, as the edge is just crimped over
 
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Huo

New Member
#20
Thanks it has taken some time to sort this out although I will find an alternative one. I have opened it up and cleaned it but didn't work will have another look later. Regards
 
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