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TwinCamJohn

Overdrive problem

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My TR3A is 1960 so I assume has the A type overdrive.

Anyway, today on the way to a wedding the overdrive dropped out a couple of times. Once when I was at I think about 40 mph and another time whilst accelerating lightly in 4th at about 55mph.

I can't add anymore as I left the O/D off so as not to, perhaps, make the problem worse and I was needed at the wedding !

Will have a look tomorrow but wondered if anyone had some pointers. My first line of attack is to check the gearbox oil level.

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Definitely check the oil level. Then work on the electrical connections.

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...and solenoid actuator arm position

Edited by ijonsson

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Most likely an A type, although if your TR did not come

fitted with overdrive from new, someone may have converted

using a J type.

 

Oil level then electrical connections (solenoid AND earth).

 

The overdrive switch earths through the selectors fitted in

the top cover. You can check if these are working by taking

earthing wire directly to earth but DO NOT leave it like that

as the overdrive will then operate on ALL gears, including

reverse. If you forget, and reverse with overdrive engaged,

say goodbye to your overdrive.

 

AlanR

Edited by TR 2100

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Thanks for the replies.

Today I topped up the oil, but the problem is still there. So, oil level now discounted.

Had a run tonight and it dropped out several times and then wouldn't work at all. Then came back again.

I noticed an electrical buzzing as I changed to O/D which was coming from under the car on the left side. Car is LHD so easy to hear.

Car back in workshop. Will continue during the week.

Not sure if the above gives any more pointers ?

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Sounds like the noise you are hearing is coming from the solenoid. Check the bullet connection near the sol. for looseness or corrosion. If no joy, remove the rubber boot on the sol. and run a ign. point file or emery cloth across the contacts.

Berry

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If the connections and interlock switches are OK and the operating lever is correctly adjusted you might have a problem with the solenoid. It has two stages of engagement. A high current pull in phase then a lower current holding phase. If the pull in winding is faulty you could get your symptoms.

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Buzzing suggests that the hold-in coil of the solenoid is not doing its job. It has a very fine wire and this can fracture, usually adjacent to the contact on the top of the solenoid (under the rubber gaiter). The wire can be re-soldered if you are careful.

 

 

Pete (Post #7): if the pull-in (high current) coil is open-circuit, you won't get a buzzing, but the overdrive can take a very long time to engage as the poor little hold-in coil (low current) struggles to lift the armature. And it may not succeed, in which case, the overdrive won't engage.

 

For a detailed explanation, see my article in Section D8, page D49, of the Technicalities CD (written in about 1973, at a guess!).

 

Ian Cornish

Edited by ianc

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+1 for Ian's explanation.

 

Bob.

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Got sidetracked this morning, so haven't started. In case anyone is looking at this over lunchtime, another question.

Is it better to take out the tunnel to start with rather than grovelling around underneath with the car on stands ?

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Hi John,

it's a lot of work but it is often better to remove the tunnel - it's surprising what you find that needs TLC.

 

Roger

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Also I forgot to ask..................I couldn't find the O/D relay ! It is not on the rear of the battery box on the left of the heater. I can't see it anywher in the cabin or under the bonnet..

Any tips on getting the tunnel out.

Is it just all the fixings to take out ? Car has been all apart and repâinted in the last 8 years so shouldn't be anything never moved since 1960 !

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John ~

 

+1 with Roger.

 

If you remove the tunnel modify it as I did with mine by providing inspection panels which will make it

far easier in future to service the gearbox/overdrive without having to remove the cover.

 

Tom.

 

Edited by Fireman049

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OK, I can see that there is much less faffing about if the tunnel comes off ! Anyway with the car on the stands there was nothing obvious.

However , I did the first tests that are in the overdrive workshop manual. That is testing the wires on the relay.

The relay is not original and I at last found it hidden behind the heater support strut. A positive thing was that the terminals had been marked by hand.

First test ignition on and W1 was live. OK

Second C1 was NOT live all the time.

Third C2 was live when O/D switched on and in neutral OK

According to my diagram C1 should go to "Generator control box-A (or ammeter)". But C1 appears to go out of the cabin and back under to the top of the gearbox.

 

That's all I can say for now. I don't know if that is enough for any conclusions ?

I shall have the tunnel off next week after the weekend run.

 

Thanks for your replies and patience.

Edited by TwinCamJohn

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Thanks for that Tom.

In advance of taking the tunnel out does the fact that C1 is not live all the time as it should be according to the manual, give any clues ?

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OK, I can see that there is much less faffing about if the tunnel comes off ! Anyway with the car on the stands there was nothing obvious.

However , I did the first tests that are in the overdrive workshop manual. That is testing the wires on the relay.

The relay is not original and I at last found it hidden behind the heater support strut. A positive thing was that the terminals had been marked by hand.

First test ignition on and W1 was live. OK

Second C1 was NOT live all the time. C1 and C2 may be swapped around. Ideally C1 should be live all the time and C2 only live when in 2/3/4th gear and OD switched on.

Third C2 was live when O/D switched on and in neutral OK

According to my diagram C1 should go to "Generator control box-A (or ammeter)". But C1 appears to go out of the cabin and back under to the top of the gearbox.

 

That's all I can say for now. I don't know if that is enough for any conclusions ?

I shall have the tunnel off next week after the weekend run.

 

Thanks for your replies and patience.

 

 

Roger

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OK Roger

Following your comment here are the latest tests !

W1 live with ignition

C2 live all the time

C1 live if in gear with O/D on (buzzing loudly for a moment and then stops)

W2 live with ignition on and O/D selected and car in neutral

W2 not live with ignition,O/D selected and in gear.

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OK Roger

Following your comment here are the latest tests !

W1 live with ignition correct

C2 live all the time Should be C1 but OK

C1 live if in gear with O/D on (buzzing loudly for a moment and then stops) Correct but shouldn't really be buzzing. This suggests that the solenoid change over from pull in to hold in is sluggish

W2 live with ignition on and O/D selected and car in neutral Correct. W2 is live because the volts have nowhere to go

W2 not live with ignition,O/D selected and in gear. Correct if in 2/3/4th gear. The volts drain to earth through the inhibit switches.

 

 

Hi John,

have a look at this wiring diagram

http://www.advanceautowire.com/tr24a.pdf

 

Roger

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I have that TR3A wiring diagram. But not too brilliant with electrics !

C1 So if the solenoid changeover from pull to hold in is sluggish where would that suggest the cause is ?

And presumably that would be why it drops out ?

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Not boasting, but please read my Post #8 and then look at the Technicalities CD.

 

Ian Cornish

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Hi John,

not sure if the solenoid relays (within the solenoid) can be got at and cleaned.

It would probably be easier to just fit a new one.

 

Before doing that you could run a 12V lead from the battery and try powering the solenoid direct. That would remove all the other components.

If it is the same then it is the solenoid. If it improves then perhaps the wiring loom needs looking at.

Dirty/ corroded electrical joints can cause volts to disappear. Clean or replace.

 

Roger

Edited by RogerH

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Not boasting, but please read my Post #8 and then look at the Technicalities CD.

 

Ian Cornish

hello Ian,

I haven't ignored your post (very grateful for all help) but I didn't know what the " Technicalities CD" was. Presumably a CD that one could have bought ?

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