Overdrive not working although solenoid is activated.

[Jean-Marie Raedts]

Last year, my overdrive (J-type in a TR4A car) stopped working. I topped up the oil level and it worked again. Now it stopped again with working and my TR guru tested it and found out that the inhibit switch failed. The previous solution by topping up the oil was maybe a coincidence for the inhibitor switch which failed from time to time. He made a temporary wiring (eliminating the inhibitor switch) allowing me the drive home and use te overdrive. The idea was that I removed the gearbox tunnel at home and went back to him. Everything worked fine and, of course I took care to always switch off the overdrive stalk at the steering wheel when stopping the car and took care that the overdrive was not activated when using reverse gear.

I toke away the gearbox tunnel at home and went back to the specialist where the inhibitor switch was replaced and the wiring was changed back to the situation how it should be. There was also an oil change in the gearbox and cleaning the filter in the overdrive. 

But during driving home, the overdrive didn't work anymore. While the tunnel is not put back, it is easy to test everything. In 3th and 4th gear I hear the relay clicking by operating the overdrive and I measure on the input of the solenoid 11,89 Volt; measuring the current during the activation of the solenoid gives me 4,42 A for this J-type overdrive.

Is the solenoid defect? How can I test it?

[RobH]

If the solenoid is clicking in OK and it wasn't disturbed in any way it doesn't sound as though the fault is an electrical one, particularly since it was working OK when you drove home the first time.  Perhaps something wasn't put back properly when the overdrive filter was cleaned?  (Having said that, 4.4Amps sounds a bit high - a J solenoid is usually reckoned to draw around 2 Amps but it may just be there is a wide range).   It might to useful to re-rig the wiring to the temporary setup and see if it works again then. 

I don't think there is any way of testing the solenoid other than by swapping it for another, though this forum describes a repair:

https://forum.tssc.org.uk/topic/6540-repairing-j-type-solenoid/

(unfortunately the chap doing the repair writes in a local slang dialect which can be difficult to interpret -   "solly wer,nt wuk,n" for "solenoid wasn't working" for example)

Edited April 22, 2023 by RobH

[RogerH]

Hi Jean-Marie,

Ooooops!!

Roger

Edited April 22, 2023 by RogerH

[RobH]

1 minute ago, RogerH said:

You should see the alignment lever move on the right hand side of the GB.

It may be that the lever attached to the solenoid has slipped and thus the OD internals are not moving enough.

Reset the OD solenoid and lever.  If the problem persists  Then re-adjust the OD again but move it a little further than optimum.

 

Its a J type Roger so no lever and no adjustment. 

 

 

Edited April 22, 2023 by RobH

[RogerH]

Ooops!!!

[Motorsport Mickey]

1 hour ago, RobH said:

If the solenoid is clicking in OK and it wasn't disturbed in any way it doesn't sound as though the fault is an electrical one, particularly since it was working OK when you drove home the first time.  Perhaps something wasn't put back properly when the overdrive filter was cleaned?  

I don't think there is any way of testing the solenoid other than by swapping it for another, though this forum describes a repair:

https://forum.tssc.org.uk/topic/6540-repairing-j-type-solenoid/

(unfortunately the chap doing the repair writes in a Scottish slang dialect which can be difficult to interpret -   "solly wer,nt wuk,n" for "solenoid wasn't working" for example)

Yeah, that's Marcus, he's posted on here a good few times. Nice chap and has some interesting (and good) ideas and practices to follow. From Scaryport (Maryport in Cumbria) as I remember.

Mick Richards

[Z320]

Oooops, Roger!

Edited April 22, 2023 by Z320

[Mastaphixa]

You could remove the solenoid, apply 12 volts to it and make sure the plunger strokes properly.  Doesn't it take a while sometimes for the trans oil to fill the overdrive after its been drained? 

[Jean-Marie Raedts]

I did some measurements in the meantime:

1. Resistance old inhibitor switch: depending on how far the activating knob is pushed: ranging from 4,1 ohm to 10 ohm.

2. Resistance new inhibitor switch: ranging from 0,5 ohm to 1 ohm.

3. Resistance of the solenoid (of course this must be an impedance while it is a coil but I measured it as it was an ohms resistance): 6 ohm.

4. Current during activating the solenoid: 4,16 A.

5. Current if the solenoid is bypassed, it means the only remaining resistance is then the contact in the relais: 4,42 A. This means that the resistance of the contact in the relais is 12V divided by 4,42 A = 2,71 ohm. Is that not too high?

6. If I combine item 4 and 5, I conclude that the current is limited by the high resistance in the contact of the relais. It is the very old big classic relais which was delivered with the car. Is the relais the culprit?

I appreciate your comments.

Jean-Marie

 

[RobH]

Something doesn't add up then Jean-Marie. By Ohm's law, if the solenoid resistance is 6 Ohms then it can only draw 2Amps from a 12 V supply. 

A standard J type setup does not use a relay because the current is too low to need it;  the switch acts directly ( the green wire is 12V from the fuse box) :

 

I suggest you re-arrange the wiring like this to eliminate the relay and then see what happens. 

 

[Jean-Marie Raedts]

Thank you for your reply Rob. This afternoon I was out with the car and the overdrive was working, but also failed once. Seen the huge voltage drop over the Relay and associated wiring (due to its high resistance), the solonoïd get not 12V and is sometimes working and sometimes not. The better thing is follow your proposal, change the wiring to act the switch directly. Especially in this case, ones the cover of the gearbox with the H-frame is mounted again, there is hardly no access to the inhibitor switch and the solenoïd.

 

[Waldi]

Jean-Marie,

I cleaned my inhibitor switches (and all other switches) with contact spray, and had “close to zero” resistance readings on all switches finally.

Maybe you can check the circuit?

I have an A-type, so not a straight comparison on the OD.

Waldi