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Rev light switch problem


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Hi Guy’s

I really can’t fathom this one out.

And I’ve have had a classic gearbox specialist have a look and no joy.

My reverse lights are on all of the time. So I’ve gone back to basics. Not the switch(es), tried 3. Then bench checked them, they all work, spot on. Then checked the wiring is ok. Rev lights work fine when switch connected up but out of GBox and operated by hand. So thought I would try the switch screwed in varying amounts.

With the GBox in reverse I’ve screwed the switch in until it just turns the lights on then took it out of reverse. Lights stay on. Then started with it in neutral and screwed the switch in until the lights just come on and then back ¼ of a turn so the light go off. Then put it in reverse and …nothing no lights.

So if the switches ae fine and the electrics are fine it must be the GBox not operating the switch correctly.

And if I look down the switch hole when in and out of reverse the “high” part which tell the switch to turn on the reverse light is always there.

Now the GBox guys says ther is no adjustment in this. But something must be wrong has anyone got any ideas?

My radical approach is to get the reverse selector fork, make sure I know which bit is in the way of the switch operating correctly when out of reverse and errr attack it with an Angle Grinder. If I take just the right amount away I think (hope) I can get the light working.

But before I take that quite radical action of angle grinding bits inside the gearbox and one got any suggestions what might be wrong cuz it can’t always have been like this surely.

Cheers  Keith

 

 

Rev switch 1.jpg

 

 

Rev Switch2.jpg

Edited by Keith66
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I would remove the cover and then probably see what is the issue. But not grind.

Waldi

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Hi Keith,

1 - has this problem always been there in your ownership or has it suddenly started

2 - have ever had the top cover of the gear box removed for any work.

From your pics the switch would always be set one way.

The reversing light switch can be fitted in at least two positions depending on the age of the GB and the top cover - on top or on the side.

 

Roger

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2 hours ago, Drewmotty said:

My reversing light switch goes on the rear left hand side of the selector casting. Are you using the correct position?

29201CC8-17BD-4499-88D0-15442BA1DEA1.jpeg

Thats the later alternative position for the switch and often used on saloons.

Stuart.

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Is the position you are using for the Seat belt warning buzzer put on for USA models??

do you have an switch or empty position on the side as seen on Drewmotty’s post. Seems like the solution.

David B

Switch referred to as Safety switch on wiring diagrams goes to seat belt module. Check wire colour codes as on www.advanceautowire.com on TR6 ‘73 onwards.

Edited by David B2
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Hi All

Now all of my comments assume i know what i'm on about, which is debatable at the best of times. So the reason for posting was to find out if anyone had any ideas or could tell me what a plonker i was for getting XXX wrong.:D But i'm kind of stumped.

As Stuart says that is a late top cover with the diff rev light switch position. Mine is def right for the age of car, build late 71 reg very early 72, so no worries there.

It def not a switch issue as i've tried 3 diff switches, that have all been bench tested and work as they should. Its not a switch position issue as in in or out of the hole far enough as i tried with no shim and tried with it out over 1/4 of and inch. I can get the lights on all of the time or off all of the time just not on when in rev and off when out of rev.

I've got the top off and stripped down and can now see its actually the reverse selector (129780) that operates the switch and its either in the wrong position on the selector rod or its just not quiet the right dimensions.

So i've tried two sets of selector rods and no joy and how can it be incorrect dimensions? I mean 1970's Leyland products were made to the best quality but making internal gearbox bits the wrong size? That would amaze even me.

But surprisingly a new one is cheap at under a tenner so i've ordered one. I can then compare it to my existing one, test if the new one is any better and experiment with my angle grinder if needs be.

Still curious on the cause but in 48years a lot could have happened.

Cheers    Keith

 

 

Edited by Keith66
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16 minutes ago, David B2 said:

Is the position you are using for the Seat belt warning buzzer put on for USA models??

do you have an switch or empty position on the side as seen on Drewmotty’s post. Seems like the solution.

David B

Switch referred to as Safety switch on wiring diagrams goes to seat belt module. Check wire colour codes as on www.advanceautowire.com on TR6 ‘73 onwards.

Seat belt warning is via a pad under the seat. His switch is in the right position, its the position of the cut out in the selector rod thats the problem.

Stuart.

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I think its a drilling problem, Ive noticed on quite a few boxes the hole for the switch isnt always in the middle of the plinth and are quite often slightly offset and its seems like this is why the switch doesnt line up especially as Keith says he`s tried several different selector rods and they all have the same problem.

Stuart.

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Hi All

Stuart my thoughts were kind of on similar lines.

Trouble is re-drilling or slight modificatiom of the rev selector fork is difficult, well for me with a hand drill it is.

So I'll see how the new cast selector fork works, if it does great if its the same it might be something else so then its out with the angle grinder and at least i will have a spare fork if i fork it all up. :D

Well my motto is find out as much as you can then errrr drive right in, how wrong can it go.

Cheers   Keith

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As your going to fit another rod I would just see how it lines up and if needed go for it with the grinder to get it lined up, bear in mind it only needs the ball to go down the ramp just enough.

Stuart.

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Hi All

Stuart, fortunate now to have two sets of rods and when the selector for arrives tow of those so i'll try each combo before grinding anything. Also good point that the ball just needs to fall off the ramp a little bit so it'll be tiny bits at a time.

Mark cheers for that, hopefully all will be ok because as it was an OD GBox i wasn't confident in my abilities to do both, i got them checked and rebuilt professionally as needed.

All the GBox bits seem to work ok, its just that part of a GBox rebuild obvs isnt to check if the Rev lights work exactly as they should. And i wouldn't necessarily expect it to be. 

I'm sure Stuarts come across similar before as when he installs a GBox he has to make sure it works Rev lights switch on and off and OD switches work as well. The GBox guy just does the GBox and doesn't necessarily check the GBox ancillaries as well.

Esp for something very uncommon (it seems) like mine prob.

Anyway I'll await my Rev selector and see if i can get it working ok.

Cheers    Keith

 

Edited by Keith66
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Just to add my penny worth, I worked in the microswitch biz for a number of years and there is a parameter called movement differential, which essentially is the difference between the operating point and the reset point of the switch. If this is large - and it could well be with replacement/remanufactured parts ex China, then the movement created by the operating mechanism i.e. the rod, may not be enough to operate and reset the switch. Movement will be within the differential and will either stay off or stay on. The smaller the movement differential the more accuracy you have in controlling the function of the switch. This may explain why you can’t get the thing to work even when setting the switch up to just turn on when the reverse position is selected, or just turn off when it is deselected. Might be nice to beg, steal or borrow an original switch that works and try it on your gb before committing to surgery.

Hope it helps.

TonyC

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Hi Tony

I have two new switchs and one old original that came with the car.

With the known history of my car and its errr, extended time off the road i'm pretty sure that is either original or early 80 replacement not a modern one in todays money.

and all three switch perform the same.

just waiting for my new reverse slector fork so i can try it all agian amd modify if i need to.

Cheers   Keith

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Hi All

Thought I would update everyone with the latest developments on my dodgy reverse lights.

So I was convinced that either the switch actuator section of the reverse gear selector wasn’t moving far enough out of the way or was just too big. Hence my threat to the gearbox to get my angle grinder out.

But I decided on caution and ordered a new bit as it was surprisingly cheap and better to have a spare if I ruin one with my angle grinder skills or lack of.

Well my new bit arrived today and sorted all of my problems. As you can see from the pic the high part of the step that actuates the switch is just shorter (top one), so the switch works perfectly. I bench tested it, its fine, I dry fitted and tested it, its fine so now fitted with new gaskets etc and its all fine. Lights on when in rev and off when out. Yeah:D

And from the pic of the switch hole you can immediately see why. In my original pics the switch actuator part was in the centre of the switch hole, in the new ones it’s there in one but in the other its far enough out of the way.

I also tested the OD switches and can hear the satifying clunk as the solenoid operates so everything in that bit looks like it works as it should.

Just got to get on and finish the rest now, before my possible new charge arrives

Cheers   Keith

 

 

Switch Actuator 2.jpg

Switch Actuator1.jpg

Rev Selector.jpg

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