How to Drive Your Laycock Overdrive Equipped Car « Britsport of Seattle


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How to Drive Your Laycock Overdrive Equipped Car

It is a mystery to many British car enthusiasts driving their Laycock equipped overdrive cars, how to properly engage and disengage the overdrive function with the least trauma to the car. A rule of thumb that I subscribe to, is to treat the overdrive function as an additional gear when upshifting. That means when accelerating up to freeway speeds and you are in fourth gear direct drive, depress the clutch prior to engaging overdrive for cruise, treating it as an additional normal gear, much like the gearchange from third to fourth. That eliminates the “kick in the butt” feeling experienced when engaging 450 PSI of operating pressure without clutch engagement and your foot on the throttle. You need to lower your engine revs by 400-500 RPM’s for smooth engagement. A depressed clutch and minimal to no throttle will accomplish this. Conversely, when downshifting from fourth gear overdrive to fourth gear direct, it is necessary to increase your engine revs approximately 400-500 RPM’s to match engine revs with road speed. The Austin Healey cars accomplished this through the kick-down switch located on the bulkhead that made it necessary to “blip” the throttle for electric disengagement of the overdrive to occur, thereby increasing engine revs to match road speed. Triumph and Jaguar overdrive equipped cars do not have this function, but disengagement of overdrive with the electric switch, coupled with a manual throttle blip with your foot and a depressed clutch, will increase the engine rev’s sufficiently to allow a smooth transition to direct drive to match road speed.  This habit of overdrive engagement/disengagement will extend the life of your OD clutch linings, as well as allowing the use of your overdrive to cause the least amount of stress to your British (or other Laycock equipped) car. Smooth is good. If you are using your British car in a competitive environment in full anger, forget I said anything. Thrash it until it breaks.

11 Responses to “How to Drive Your Laycock Overdrive Equipped Car”

  1. WC Spencer says:

    Thanks for confirming my suspicions about engaging the Laycock O/D on my ’61 Volvo P1800. Now if I could only get it to stop slipping when warm. WC

  2. markjones says:

    I would try a full service including cleaning the filters, fluid change, etc. I would also check your solenoid operation/o-ring condition. It may be weak on the hold-in winding when warm. A pressure tester/circuit test lamp during a test drive would tell you alot.

  3. Dallas Johnson says:

    I recently pruchased a 63 BJ& in generally good condition . This is my 5th 3000 .My first was a 60 3000 in 63 wtih 20K on it. The over drive kickdown worked great. All BJ 7s and 8 since would only engage or disengage from the dash switch. This car does noeven have the relay and or any accel. linkage to the bulk head area.
    There is only a silver relay or sel. ???? Removed ?


  4. Steve Campbell says:

    Good article, well written so thanks. I wonder can you help? I am in process of removing the engine and transmission from my 3.8 Mark2. It has a Laycock DeNormanville electric overdrive from an XJ6 fitted. I cannot remove the gearknob!! I’ve loosened the collar below the knob and the knob can be unscrewed about 4mm but that’s it. I have only used my hands and don’t want to start applying monkey grips .. yet! Any advice appreciated

  5. Mark says:

    Sounds like time for something soft jawed alright. Maybe try a oil filter style rubber strap wrench? Good Luck!

  6. drew aitchison says:

    I keep hearing and reading conflicting advice on how best to use a Laycock overdrive. Mine is in an FD Series Vauxhall VX 4/90.
    I get the `kick in the butt` effect if I don`t clutch it during switch over, but have been told that`s the wrong way to engage it?

  7. Mark says:

    That “kick in the butt” feeling is the cone clutch slamming into the brake ring for engagement of the OD function. With clutches now selling in excess of $300 to replace, I would want to prolong the life of the linings as long as possible. Cheers, Mark

  8. George Galbraith says:

    Hi, I live in South Africa and am trying to obtain an A type L de Normanville for my Healey 3000 BT7, as the unit currently fitted also slips and disengages when hot. It does however, work great on starting off and in cold weather. I am also thinking of changing the SAE 30 Castrol g/box oil for a specialist oil, perhaps 40 grade. Any thoughts on this?
    So, looking for guaranteed rebuilt or used unit as a final solution – thanks George

  9. markjones says:

    The Austin Healey has a kick down switch on the bulkhead, and when working properly requires a throttle blip to activate and disengage the electrical feed to the OD solenoid. The throttle blip raises engine RPM to match road speed. I feel the transition is less abrupt with a clutch depression. Jaguars and Triumphs do not have a throttle switch but ease into direct drive smoother with a throttle blip during disengagement.

  10. Joe Guagliardo says:

    Mark , do you need to flip the toggle switch to normal to disengage overdrive while blipping the gas pedal on my Healey 100-6 ?

  11. markjones says: disengage the OD in your Healey, assuming the kick down switch is working correctly, is to flip the switch to Normal position, then a throttle blip will operate your kickdown switch and electrically isolate the operating solenoid.

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