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jumping out of first gear


colin smith
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Finally got round to removing the gearbox from my spitfire Mk2 which has been off the road for several years. It was jumping out of first gear which was a bit dodgy turning out onto a main road. I started taking the gearbox out a few years ago but never got round to doing it. Finally got it out today! But I have no idea where to start on the gearbox. Does anybody have any experience of this fault and what might be the cause/ remedy. Thanks

 

Colin

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How longs a piece of string??

I would start with agood look at the  bushes and swivels on the remote to ensure you are getting full engagement

Do you have a workshop manual ???

You dont need any special tools to strip a box but start with the easy external first and let us know what  you find 

Then Come back for more clues

Pete

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Yes it jumps out under power. At first it only happened occasionally, then I had to hold it in to move on. The last time i drove the car it was every timeI engaged 1st and seemed to push my hand back when I held it in gear (which is why i decided then to stop driving the car until I sorted it) - 

 

Colin

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as said previously sounds very much like theres excessive play in the linkage so although youre pushing the lever into position that movement isnt being completely transferred into the engaging the gear. This means that when the power is applied the mechanism is free to jump out and the solution is to ensure all the linkage bushes plus lever pivot are in good condition.

If the problem isnt here then the next possibility is that one of the spring loaded detents that positively locate the '3 rails' during their movements isnt working correctly (for example if its spring has broken) so that the first gear selector fork is freer to move.....  

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good point so heres a few easy but useful things you could check/do while its out:

tighten all casing joint bolts, replace front and rear oil seals, replace bronze spigot bush (slides in end of crank to support the tip of the gearbox input shaft) and

check clutch friction plate wear (if removing it you will have to realign it on reassembly though)....

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26 minutes ago, johny said:

good point so heres a few easy but useful things you could check/do while its out:

tighten all casing joint bolts, replace front and rear oil seals, replace bronze spigot bush (slides in end of crank to support the tip of the gearbox input shaft) and

check clutch friction plate wear (if removing it you will have to realign it on reassembly though)....

Also replace thrust bearing?, though if it's running an older one, that may well last longer than a modern new one?.

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hmmm in my opinion the thrust bearing does so little (depends on your use of the clutch of course) it should last the life of the car. But what about improving the sound deadening of the gearbox cover while its off as that helps with all sorts of bearing wear🤣

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Probably find the bush at the base of the gear lever in a similar state..... The replacements usually come as a kit so you replace everything at the same time then when its all back in place the action should feel much more positive. Will you be taking off the gearbox top cover or just the gear lever casing shown in the photo?

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agree its certainly needs replacing   if you order a remote kit it comes with a variety of bushes and washers to cover small evolutions in the remote over the years  

if you do get a kit the metal spherical cup can have sharp cropped edges these need a file or use your old one

PETE

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My gear lever was very loose and I ordered a refurb kit. When I got the gear lever out, it had been put together (not by me!!) with a single undersized nut and bolt. This means that, with wear, the hole at the base of the gear stick is now oval and the metal very thin. It either needs the metal building up and re-drilling or a replacement gear stick, if I can get one. I put it back together with the new bushes etc, but how long it will last, who knows. I don't think overdrive gear sticks come up for sale very often and, with the 'hybrid' nature of the car I'm not even sure its the original one.

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Inside the box you can try sliding the selector rings forward and backwards as happens when changing gear. Its takes a bit of force with your fingers to slide but the ring should click off neutral to positively engage with each gear and by turning the input shaft you can confirm that when the output starts to turn....

Also check the state of the selector fingers on the '3 rails' under the top cover - if any is bent or severely worn it could also produce reduced movement of the selector rings so that they dont engage completely and can jump out of gear.

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Thanks johny,

really impressed with the details and usefulness of everyone's replies. I'll do what you suggest above. I've ordered bits for the linkage mechanism which should improve things a lot, but it would be good to know I've checked the selectors before going through the pain of replacing the assembly. A few years ago I had to replace the clutch twice in a year (because the back plate on the engine was warped the first time), so I have some experience of refitting the gear box etc. At least I know it goes in eventually!

I'll report back when its all back together but it might take me some time to get the rest of the car working again after its long rest!

 

Thanks again

 

Colin 

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Yes I dont know how many miles the box has done but its always difficult to judge whether to go further with overhauling while its out. The main causes of problems are the needle bearing between the input and mainshafts you can see in the top of the case and the needle bearings either end of the layshaft at the bottom of the case. To get an indication of the first you can try rocking the external end of the input shaft to check the amount of relative movement between it and the mainshaft. For the layshaft, without dismantling it, I cant think of any test other than using the gearbox but of course by then its a bit late to find out its bearings are shot!   

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Hello again.

Had a go at changing the gears by moving the selector rings. Succeeded in getting 2nd 3rd 4th and reverse with a bit of force, but 1st wouldnt go. Perhaps its more difficult to push on  but when I fiddled with the alignment of the bronze coloured cog next to the selector ring (on the drive shaft side) I was able to get it to engage. This cog seems very loose on its shaft so suspect this might have a problem? There's also a little play in the drive shaft. Colin

 

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