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Overdrive stops working after about 20 minutes


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Hi all

 

 

TR3A 1959

 

My overdrive stopped working and discovered it to be a faulty solenoid. It has been replaced as has the relay which burnt out during the fault finding exercise! All appeared good but after running for 20 minutes or so it stopped engaging. The ammeter still shows a surge although I couldn't hear any clicking. But this is what's weird.. I left the car overnight and went out the next day and once again all worked from form the start for 20/25 mins and then stopped... same again the next day. The one constant is that on each occasion I have been in 4th gear around 2000rpm, clicked the overdrive OFF coming into a corner which worked but then clicking back ON once the revs climb and the overdrive fails to engage.

 

Has anyone come across this before... is it possible something is heating up and warping the housing preventing the operation?

 

Thanks, Archie

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Hi Archie,

it does sound like a heat issue.

Next time it happens have a feel around the wiring loom near the relay for hot connectors.

 

Any high resistance connection will generate heat and then develope more resistance. This will stop things in their tracks.

 

Roger

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Thanks Clive and Roger for your input so far. First thing was I took the car out this morning and the overdrive failed to engage at all. So using that excellent Buckeye guide (thanks Clive) and multi meter I proved the relay is working. There is power right the way to the solenoid. So I tried tapping the outside of the solenoid with switch engaged and lo and behold it started working. So bearing in mind this is a new solenoid is it likely that something is misaligned where it engages with the overdrive? Any thoughts on how to proceed?

 

 

One other thing not sure if it is important. On the feed i.e. where the bullet terminal from the solenoid plugs in there is a bit over 12V but at the solenoid terminal itself it is only 9.6V... as a test I used some crocodile clips to make that last connection to rule out the last bit of wire but still only got 9.6V does that indicate a problem with the solenoid after all or is that normal?

 

Thanks Archie

Edited by AtLast
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Hi again...I'll check the electrics again tomorrow but the feed from battery to the solenoid terminal was reading 12v all the way, it's only at the actual solenoid terminal did it appear to be 9.6V, that being said, it's working since I gave it a tap albeit not road tested yet. I was looking through the service manual re checking gaps and the hole alignment that goes through the shaft that runs from one side of overdrive to the other... wondered if it could be a very minor misalignment? Can I just remove the solenoid (two screws?) to have a look and then pop it back on or will anything need resetting? The rubber washer at the bottom doesn't seem to be very uniform in it's fitment so want to have look at that... is it possible that could prevent the solenoid working?

 

Thanks Archie

Edited by AtLast
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9.6V may well be not enough to operate the solenoid reliably. you should have the same volts (give or take half a volt) at both ends of the wire.

 

Bob.

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I have a similar situation as commented at http://www.tr-register.co.uk/forums/index.php?/topic/32434-overdrive-relay-switch/ I did a long run last weekend and after 120 miles or so it started dropping out and did so regularly. I've tried wiggling the column switch to see if it had anything to do with it and there was no change. This week it's started dropping out after even a short run.

 

Paul.

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Did you reset the solinoid operating shaft after fiting the new solinoid,could be out of adjustment. Also the dust boot may be restricting the piston, there is nothing inside the box that can get stuck or stop the shaft from moving.

Edited by Graham Harris
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And remember that the old adage about aligning the two holes using the drill bit method, doesn't always apply.

After ORS sold me a new solenoid at IWE in 2011, I tested the car and found o/d still wasn't engaging consistently.

The ORS chap was prepared for this and advanced the clamp positioning (so that the holes were no longer aligned).

Result: everything was OK - and has been since.

He said sthg to the effect that 'you sometimes have to assist the voltage'... : )

 

Just a thought...

Tim.

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All back together and working so far, albeit only a short test... to be honest there was nothing 100% obvious after tapping with the hammer got it going again although the dust boot (I think I called it a rubber washer earlier) as suggested by Graham was certainly only half in place with the rest sort of squeezed out so maybe that was just enough to jam it. Pretty sure the electrics are ok despite that odd reading on the solenoid terminal itself. I didn't try adjusting the clamp Tim but interesting to know that tip about not always aligning the holes. If it sticks again I may try a tiny adjustment before getting the hammer out. Thanks for all the help to all that replied. I'll feed back into later in the week after I've been out for a longer run.

 

Archie

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I would want to re-check the voltages at the relay, & the solenoid, if there is still a difference of 12 - 9.6 = 2.4V then there is something amis with that wire & or connections to it. A low voltage could easily explain your problem.

 

Bob.

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Hi Bob and thanks for your persistence! :) I completely understand what you are saying and can understand exactly where you are coming from....so I've just taken it all apart again this morning and re-tested. The reading is now a touch under 12v at all points including the solenoid terminal. I've wiggled the solenoid feed wire just to check there are no breaks and it looks good. So I can't explain why I got that 9.6v reading. That reading only happened BEFORE I tapped the solenoid with the hammer and got it working so my question to you is... Is it possible it would read 9.6v just because it was stuck? Electrics aren't my strong point so don't know if this question even makes sense. Or is it possible it read 9.6v because I hadn't got the multi-meter black lead earthed properly when I took the reading?

 

Thanks Archie

PS. It's a brand new solenoid & relay and the wiring loom was replaced during a full nuts & bolts restoration only 18 months ago.

Edited by AtLast
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Hi Archie.

If your low volts reading was when the solenoid was energised, but had not engaged, then it would have been drawing a lot of current, as the holding current (much lower) only comes into play when the solenoid has pulled fully in. A large current would induce a correspondingly larger volts drop across the wire.

Even so, it does seem a large drop in voltage over a fairly short wire, & I would not rule it out as a contributing factor.

 

Cheers

Bob.

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Cheers... that does seem to be what happened then if I've understood you correctly i.e. I switched on overdrive switch hence the solenoid 'energised' but it was stuck so it never physically moved and thus remained on the higher drawingcurrent hence the voltage drop. I think I'll change the last wire just to be sure. As you said it may be a combination of little things.

 

Thanks again for help, Archie

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Hello again... put case back on etc after re-doing the readings (haven't changed the wire) and now it works in 3rd but not 2nd or 4th! This is with the car stationery not road tested again. Power (12v) reaches the solenoid in 3rd but nothing in 2nd or 4th. Using the buckeye guide I do get a ground on positive terminal on 3/4 switch when in 3rd but not in 4th. So to my mind it can't be the wiring because it is the same wire. So can it be that the 3rd/4th switch is faulty/intermittent that would perhaps explain 3rd working and 4th not however I don't think it explains why 2nd isn't working...

 

EDIT: Forgive me if this is a daft question but could the physical movement of the gear stick not be getting recognised by the switches.... is there any electrical connection between the gear stick mechanism and the switches?

 

Stumped any ideas?

Edited by AtLast
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Sorry to bounce but just in case anyone has any more input. The issue is sort of mechanical after all. I loosened of the bolt and nut that retains the gearstick. Then I found that overdrive worked in 2nd, 3rd and 4th.. in fact 2nd and 4th worked well but now 3rd needed a bit of a push of the gear stick to engage. So it looks as if the issue is that the movement of the gearstick isn't always enough for the 'rods' to engage the switches... at least this makes sense and also explains why it started as an intermittent issue.

 

Do you think that this is likely to need a gearbox overall or is it something adjustable from the gearstick itself?

 

Thanks

PS. Is the little bolt on the gearstick cap supposed to the the anti rattle bolt. It won't do up tightly.. perhaps related? Is the spring inside the cap I can't tell from the drawings?

Edited by AtLast
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Hi Archie,

it sounds like the inhibit switches need adjustment - the pics below show the 2 inhibit switches and the reverse light switch.

The switch is activated when a ramp on the selector fork lifts the ball in the switch.

The ramp may be a little worn.

 

Remove the switch and either remove a fibre washer or if only one fitted then sand it down to 1/2 its thickness.

 

Roger

 

 

 

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Roger where do I send the beer!!! That sorted it....fantastic! I removed the washer completely just to test and sure enough 3rd now engages; It is still a little bit temperamental and only needs a slight knock to disengage even without a washer so I haven't got any more room for adjustment. Are the switches for 3rd/4th and 2nd identical? Because if so I'll swap to see if 2nd is any better as perhaps it may be a fraction longer and I really never use overdrive in 2nd.

 

Thanks again, Archie

PS. Niall - thanks I'll make sure I keep an eye on the gaiter when I put it all back together.

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Cheers Clive that's very helpful. I see if I can get the exact depth as indicated and perhaps that will fine tune it enough. I've got that manual but didn't actually see this... got side tracked thinking it was electrics I think. Maybe a job for the weekend as I really must do some work!

 

Archie

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