Testing a Laycock Overdrive

[Peter Wells]

Can anyone advise please on the possibility of testing a Laycock overdrive installed in my TR4a, with the car stationary.? It worked fine until a few days before I took the car off the road to replace the interior trim. Then it ceased working. With the overdrive now exposed and electrical connections checked and tightened I hope to confirm that all now works well before I cover everything up again. Grateful for any advice.

Cheers

Pete

[openroad]

Hi Pete,

With the ignition on, putting it in gears and flicking the overdrive switch, you should hear the solenoid clicking in and out.

 

I jacked the back end up then and ran it in gear, flicking the overdrive switch.

That worked.

Conrad.

[ianc]

When you jack the rear end of the ground, make sure that the front wheels have substantial chocks to prevent rotation in either direction.

With the engine on tick-over, car in top gear, release the clutch slowly then increase engine speed to about 1500 rpm, wait about 30 seconds, then operate the overdrive switch. See whether the speedo reflects the overdrive having operated (speedometer reading increased by about 24%).

 

If seems OK, disengage overdrive, then repeat the procedure.

 

Ian Cornish

[Charlie D]

Sorry if this sounds obvious, but use axle stands, don’t just rely on the jack.

 

Charlie.

[Peter Wells]

Thanks Guys, Testing with the back wheels of the ground was to be my last option. I have the engine partly stripped at present and was hoping that testing of the solenoid could be done without the engine running. The relay clicks in and out but no activity yet at the solenoid. I will refit the carbs and run the engine on axle stands.

Cheers Pete

[RogerH]

Hi Peter,

before running the engine you need to get that solenoid working.

 

Have you got a decent wiring diagram. http://www.advanceautowire.com/tr24a.pdf

With ignition on, in 4th gear and the column switch ON to select OD did the solenoid clunk

If yes then it's working.

If no - then have you got 12V at the solenoid. Disconnect the closest connector and check there.

If YES then suspect the solenoid.

If no then check the output of the relay, tag C2. Check relay tag C1 to make sure 12V is going in.

 

If the relay is giving 12V then try the above in 2nd gear. If this works then suspect the 3/4th gear Inhibit switch.

If the relay is not giving 12V then check relay tag W1 for 12V - this should always be live with the Ignition ON.

With the OD column switch OFF there should also be 12V at relay tag C2.

 

With the OD column switch ON there should be 0 volts on C2. If not check the wiring through to the inhibit switches.

 

Roger

[Peter Wells]

Thanks Roger, that's just the type of advice I was hoping for.

I will check it out.

Regards

Pete

[harrytr5]

All with the gearbox cover off, of course. As with the above and axle stands a must. Check the pressure relief valve is working and there is no dirt blocking the tiny hole in the stem. Hexagon head drivers side,undo that and withdraw the spring, ball bearing and shaft/stem clean out and refit.

Look in the brown bible how to adjust the solenoid settings.

The filters may be blocked. You can get at these by undoing that big brass nut underneath.Look in the brown bible how to do it.

Relays can give trouble but Rogers excellent advise should find it if it is.

Check wiring as that can break up inside the insulation.

Good luck you will find it.

Regards Harry

[ianc]

Pete - If the relay clicks as you say, then your first priority is the electrics, and Roger's guide should pinpoint the problem.

However, the clicking of the relay does not necessarily mean that it's doing its job properly as the relay contact can wear such that it fails to make proper contact. The solenoid demands some 15-17 amps to pull-in and if the relay contact has deteriorated, the solenoid will be starved of power and won't operate.

After 25 years since the re-build, I am on my 3rd or 4th overdrive relay and each has exhibited this failure - clicked, but failed to energise the solenoid.

Ian Cornish

[Peter Wells]

Hello Ian,

I think you may have put your finger on the problem and it must be the relay.

I have 12V at the connector just prior to the solenoid.

I took the solenoid of and tried it across the battery. It works well.

So, power is there but the solenoid doesn't activate.

I will go looking for the 15 to 17 amps but if I need to replace the relay, where do I find it.?

The click comes from somewhere behind the dash, but where precisely.?

Pete

[RogerH]

Hi Peter,

the OD relay should be under the dash just forward of your left knee on the edge of the battery tray.

 

With Ignition ON there should be 12V at the W1 tag.

W2 may also be 12V as the OD switch will be open circuit.

 

Whilst in 2/3 or 4th gear and Ign ON pull the OD switch ON. W2 should now read 0V

C1 and C2 should now read 12V on both tags.

 

The OD solenoid should now have energised and pulled in the plunger.

 

Roger

[Peter Wells]

Thanks Roger, I have now found it where you said it should be. Needed to be a bit of a gymnast to see it. !!

Have now ordered a replacement from Rimmers.

What would we do without the technical knowledge of guys like you.? Rimmers tell me that their tech guy Carl has left the Company.

Cheers

Pete

[Peter Wells]

Well, all now works as it should. When I replaced the relay the solenoid worked and with the rear wheels off the ground I have overdrive.

Thanks again .

Pete

[BlueTR3A-5EKT]

Well, all now works as it should. When I replaced the relay the solenoid worked and with the rear wheels off the ground I have overdrive.

Thanks again .

Pete

If it is a metal box 6RA type relay you can take it to bits and clean the contacts. I came across same fault recently and refurbished the existing relay after establishing fault by replacing with a known good relay.

Peter W