Gearbox overdrive

[Clive Brown]

Just when I was enjoying a problem free time. The overdrive did not operate when selected, tried to select in both 3rd and 4th several times, to no avail. Next time I started the car and went from 1st to 2nd the overdrive kicked out. Car is L reg.

What should I start looking at?

Clive

[Mike C]

Most overdrive problems are caused by the electrics. I've installed a light in mine to confirm the solenoid is energized.

The electrical interlocks on the gear selectors should ensure that no  overdrive is engaged in first and only A type overdrives are engaged in second- although some have had this feature disabled to protect the O/D.

If your gearbox is leaking oil it would be worth confirming that its oil level is correct. 

[PodOne]

Just now, Mike C said:

The electrical interlocks on the gear selectors should ensure that no  overdrive is engaged in first and only A type overdrives are engaged in second- although some have had this feature disabled to protect the O/D.

Hi Mike why does disabling it protect the OD?

Andy 

[Mike C]

The gearbox output torque is huge in first and second due to the torque multiplying effect of the gear reduction. This torque  is above the design limit of the J type O/D in first and second and borderline in A type O/Ds in the same gears. Hence the electrical interlocks prevent the O/D engagement in these gears- the  drive goes straight through the O/D bypassing its gears.

Edited August 5 by Mike C

[John Morrison]

Use my A type overdrive on second  'Occasionally' third and fourth ALL the time, 

never an issue in 30 + years

John.

[Clive Brown]

9 hours ago, Mike C said:

Most overdrive problems are caused by the electrics. I've installed a light in mine to confirm the solenoid is energized.

The electrical interlocks on the gear selectors should ensure that no  overdrive is engaged in first and only A type overdrives are engaged in second- although some have had this feature disabled to protect the O/D.

If your gearbox is leaking oil it would be worth confirming that its oil level is correct. 

The gearbox is not leaking.

[Richard65]

Had a similar issue with my A type overdrive recently, in that I lost overdrive mid journey. After checking the inner wing relay by substitution to eliminate a simple cause, it turned out it was a loose bolt holding an electrical connection on to the top of the gearbox. Unfortunately this is a transmission tunnel out job to access the top of the gearbox. The gearbox to chassis mount was changed at the same time as it was disintegrating.

[Steve-B]

Could this be as simple as the OD switch has failed? My reservse light failed and I decided to replace both it and the OD switch to avoid future disassembly and reassembly of the transmission tunnel, etc...

 

[Casar66]

My J-OD worked flawlessly for over 20 years before it suddenly stopped working altogether. I feared the worst but hoped for the best. So I checked the steering column lever first. That wasn’t the problem. Then I checked the relay (which was always connected in series). There was no negative battery/ground connection there. I was already worried I’d have to open up the entire wiring harness to look for a break. Fortunately, I remembered that I’d replaced the tachometer cable, which didn’t go quite as smoothly. 

And that was it—the cable or better my somewhat rough approach had dislodged the connector from the relay. It was a bit of a hassle to fix it. But now I have new ventilation hoses and a new glove compartment.😇

[RogerH]

11 hours ago, John Morrison said:

Use my A type overdrive on second  'Occasionally' third and fourth ALL the time, 

never an issue in 30 + years

John.

Hi John

compared to the TR6 the TR4 has a lot less torque so 2nd is not a problem.

Roger