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Gear stick moving in 3rd


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The last few times I have taken my TR out for a drive, I have noticed some movement of the gear stick back and forwards whilst in third gear.  It’s not that much, but enough to give a bit of a click.

It usually happens when I let the power off; this is when the gear stick moves backwards a little, it usually moves forward again when I re apply the power.  Any idea what the cause of this could be?

 

As a bit of background, the box was rebuilt just over a year ago, following the collapse of the counter shaft bearings.  The Counter shaft, Laygear and constant gear were replaced along with main bearings etc.

Since I have noticed the problem with the box, I have drained the oil to check for any debris, and was relived to find not obvious metallic parts, other than the usual brassy tinge you typically find in the oil.

 

I can’t detect any noise from the box over the sound of the exhausts, and there doesn’t appear to be any vibration through the stick.

 

I would appreciate any advice on what could be causing the problem and if I should be concerned about it or not?

 

Thanks,

 

Tony

 

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I'd be tempted to monitor but otherwise leave alone. Other options would probably involve removal of the gearbox which is a difficult job. 

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It’s probably worth checking the remote selector assembly first as it’s possible a selector fork screw is loose or broken,  but more ominously is the possibility of the circlip on the main shaft not in place properly or maybe top hat bush broken so the hub is moving? Does it jump out of gear at all?

These are only ideas based on my own recent rebuild, but a chat with Pete Cox might be the best bet. If it is different than it was I’d suggest diagnosing sooner rather than later to prevent any damage.

Kevin

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Hi Tony,

3rd and 4th use the same shaft. Does this movement happen in 4th gear. If it does then perhaps something is happening in detent ball/spring in the top cover.

As Kevin mentions above maybe the 3rd/4th fork wedgelok screw has worked loose.  if this has happened then it need immediate inspection as if the screw drops out completely and jams in a gear then iot could cause a lot of damage.

The top cover comes off easily (once the seats/H dash support/carpets and tunnel are removed.

With the top cover in your hand you can check the detent and the fork wedgelok.

 

Roger 

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Gents,

 

Thank you for your replies;  I think I will take your advice and remove the gear box top cover and check out the selector mechanism.  This part of the box did not get any significant work done to it when it was repaired apart from a new inhibitor switch and bit of a clean-up.

So far there has been no occurrences of it jumping out of gear, and I have not noticed any movement in 4th gear.  I would hope it’s not the top hat bush that has broken as this was replaced with one of the uprated steel one piece units, similarly a new circlip was fitted to the shaft to hold things in place.

However nothing would surprise me with this gearbox!

I will let you know what I find.

Thanks again,

Tony

 

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Update on gearbox investigation:

 

I have now removed the gearbox top cover and not found very much in the way of a smoking gun.

The selector mechanism appears to be all nice and tight.  Wedge lock screws are tight, and selector forks seem to be held firmly in place.  The ball detents also seem to be strong and firm and hold the selectors in place with a nice firm click.

 

Looking inside the box, there is no apparent debris.  The gears look clean an bright just as they were when they went back last year.

 

Pulling and prodding the 2nd and 3rd gear cluster only results in a small amount of end float, so I don’t think the top hat bush has broken?  (10 thou ish)

 

The only thing that seems a bit off, is the amount of back lash in the third gear train when it is engaged.  I can detect a bit more slack when turning the prop shaft compared to the other gears.  I would say this was about a degree or two when looking at the prop shaft.

This does not seem to transfer back into the synchro selector with the cover off though.  I guess this could be a bit different with the top cover bolted back down and the selector butted against it though?

 

Does anyone have any other suggestions on what I could check before I put the top cover back on?

 

I was thinking of a test drive with the gear box exposed next to see if I can see any other movement in the mechanism.

 

Thanks,

 

Tony

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Hi Roger,

 

Yes, the ball and spring are in place at the bottom of the gearstick and seem to be working fine.  It takes up all the slack in the stick as it should.

 

I have also tried to re-create the movement of the stick by holding the gearbox top cover upside down in the vice and trying to waggle the selector yoke back and forth, and nothing much happens, so I am a bit baffled at the moment.

Maybe it’s something to do with the gearbox mountings causing movement, that is why I was thinking of driving it with the tunnel off, so I can see if anything odd is going on.  That will have to wait for the rain to stop though J

 

Tony

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Thanks Harold,

That is an interesting idea, I will give it a try when I put the top cover back on.

Since my last post, I have managed to recreate a bit of movement through the top cover.  I needed to clamp it a bit tighter in the vice and waggle a bit harder, and the stick did move in a similar way to when it drives.

Though I find it a bit hard to see how this would come back up from the gearbox through the selector yoke and then into the leaver based on the amount of float there is in the gear synchro?

Maybe I am worrying about this a bit too much, but after the devastation the counter shaft failure caused last time, and the amount of expensive parts required to rebuilt it, I am a bit risk averse!

 

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One thing I had with my 6 when I first had it was the lever moving back off the power. In extreme cases (particularly one corner on the spa gp circuit) it would pop out of 3rd. In the end i put it down to chassis flex and/or soft transmission  mounts.  New mountings and a new chassis  and all was fine. I am not saying you should get a new chassis however  ;)

Tim

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"I was thinking of a test drive with the gear box exposed next to see if I can see any other movement in the mechanism."- I did this when I had problems jumping out of 2nd. I wanted to check that I wasn't getting interference at the ball on the base of the selector lever. Things wobble around a bit with no H frame but it's worth it to get a good look.

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Well, I have just taken the car out for a drive with the gearbox tunnel removed, What fun that was watching the road zip past, with the prop shaft buzzing around by side and the heat of the exhaust wafting up against my legs.  It felt like a big go-cart!

So what did I learn from this, apart from it being fun?

 

First off the movement on the gear stick dose seem to come from the selector mechanism, though it must be amplified a lot by the length of the gearstick since the movement at the bottom of the rod is quite small.  My conclusion is that this is probably nothing much to worry about at the moment, and is probably due to the backlash in the gear train I observed yesterday, perhaps also a bit more float on the gears/bush that is ideal, but that is very hard to say without taking the box out and measuring it all.

 

Secondly, I tried out Haralds tip about bushing the bottom of the gear stick, there was definitely some excess clearance between the stick and the cup that the spring seats in.  This worked a treat, and has reduced the movement and eliminated the annoying click from the stick.  So thank you for a top tip!

 

I think that I have probably spent too much time driving modern German cars recently, and have forgotten that this is 50+ year old technology, that is a bit worn and has its own personality, so I am going to refit the covers and leave it be for now.

 

Thanks to all for your help and suggestions.

 

Tony

 

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Yes, thank you AndyR100 for your original post.

One thing I forgot to say was that I used two layers of electrical heat shrink tubing to take up the gap as I did not have a bit of silicone tube the right size.  This seemed to have done the trick and was quite neat.

Tony

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