Section : Overdrive

GT6 Mk1 --J Type overdrive

Posted By : Geoffrey Griffiths, 12-Jul-2006, 09:12pm

I have a problem with my overdrive. It engages and disengages OK when I operate the column switch but when driving at speed it sometimes disengages and re-engages in quick sucession. Sometimes only twice or 3 times and then settles down. Sometimes up to 10 times before settling down. I have not checked the oil level but there is no evidence of leaking (how critical is the level?)

There is no relay; just wired into the solenoid which when stopped can be heard clicking in and out when operating the switch and gear lever. It all seems fine but there is this intermittent fault when driving. My next step is to check the wiring isn't earthing (would this cause the solenoid to disengage ?) How about the inhibiter on the gearbox. These are supposed to be reliable.

I do not want to take the gearbox cover off yet - that's a last resort. Has anybody experienced something similar?

Geoff

Followups :

GT6 Mk1 --J Type overdrive

Posted By : Jonathan Binnington, 12-Jul-2006, 09:44pm

Geoff, it's an electrical fault, anywhere between the fuse and the earth including the inhibitor switch and the actuator switch

can't pin it down any more accurately from here, you need to apply the good ole... from here on in

j
- GT6 Mk1 --J Type overdrive
  
  Posted By : Chris Taylor, 13-Jul-2006, 11:44pm
  
  It could also be a lack of hydraulic pressure, especially of the problem is worse when the gearbox is nice and hot after a long run. This could be down to low oil level, a defective pump, or leaking operating or pressure relieve valve (or just possibly a worn cone clutch, but that is unlikely). A dcent manual will tell you how to inspect and reseat these valves if needed. Also suggest you have a look at the techical stuff on overdrives on the Canley Classics website.
  Coul also be anywhere in the electrical circuit. I'd check the oil level and then thoroughly check the wiring first.
  - GT6 Mk1 --J Type overdrive
    
    Posted By : Jonathan Reed, 13-Jul-2006, 11:56pm
    
    Where are you powering it from ?
    
    Switched mine from ignition switch to coil and it fixed my intermit problem probably a coincidence.
    
    My self loosening column switch does the same thing.
    
    Intermit o/d problems are a nightmare to pin down.
    
    Fiddle and hope for the best.
    - GT6 Mk1 --J Type overdrive
      
      Posted By : Colin Lindsay, 14-Jul-2006, 09:02am
      
      My own conversion was using the J type O/D powered from the reversing light assembly on the gearbox. I'd suspect this fault is electrical; the wires are shorting or breaking as the car drives. It's amazing how brittle these wires get after years of use. Are you using the gearknob switch or the column mounted version? The gearstick wires have a habit of shorting out or geting caught in the mechanism. You could turn the ignition on and then put the car into third or fourth; listen for the solenoid clicking as you wiggle or gently pull the O/D wiring or wiggle the gear stick if that's where the switch is. I'd have to recommend taking the gearbox cover off and tracing the cables; replace any dodgy looking ones or buy the complete loom assembly for the J type O/D; it's not expensive and should stop the problem recurring for the next twenty years or so. Replace both the reversing and O/D inhibitor switches while you're at it and you can be sure it'll all work properly.
      Colin
      - GT6 Mk1 --J Type overdrive
        
        Posted By : Geoffrey Griffiths, 17-Jul-2006, 09:57am
        
        Thanks for the replies. The supply for the O/D, as colin's own conversion, is from the reversing light switch and the control is on the column. I have had a look underneath but never realised you cannot see a thing regarding the O/D controls. I'll just have to remove the G/Box cover. I know the solenoid works when stationary because I can hear it clicking in and out.
        The Overdrive repair website www.overdrive-repairs.co.uk does not give much info on possible hydraulic causes and Canley's talks about solenoid problems so it's still unresolved. I think the only way to eliminate electrical problems from the list is to wire an indicator light into the circuit at the solenoid. If the jumping out of O/D occurs then I can perhaps watch for some indication of solenoid failure at that instance.
        Anyway I'll post the outcome
        
        Geoff
        
        GT6 Mk1 --J Type overdrive
        
        Posted By : John Davies, 17-Jul-2006, 10:06am
        
        Geof,
        Chris mentioned low oil pressure, but not that this could be due to a blocked filter. It is possible to remove this and clean it in situ, and it's simpler tahn valve renewal etc, so worth a try, especaily if the electrical system is OK. I won't describe how to - it's in the manuals.
        
        John
        
        GT6 Mk1 --J Type overdrive
        
        Posted By : Colin Lindsay, 18-Jul-2006, 11:19pm
        
        Oil level is important, I love my gears to be soaked in the stuff... love the smell of EP90....
        If the oil level is good, you could find the O/D clicking in and out because a) wind resistance at speed is stretching or waving the wires causing an intermittent electrical fault or b) heat from the engine / exhaust is softening the wires again causing an intermittent fault. This could be why it clicks ok when stationary but plays about at speed...
        Well it's worth a try....
        Colin