3rd and 4th gear grinding

[Spitfiredriver71]

I was driving my Spitfire yesterday when half way home I had a problem changing from 2nd to 3rd, the gears grinded as if i had not used the clutch. The same then happened from 3rd to 4th.

I stopped at the side of the road and can select all gears stationary with no problem and 1st 2nd work fine when moving. There is no strange sounds coming from the gearbox and once in gear it drives fine with no movement from the gear stick. I had the cir clip go that effects 3rd gear about 10 years ago so know it is not the same. When that happened the gear stick would move forward and backward with throttle input.

I tried 3rd and 4th at a slow roll less than 10 miles an hour and goes in fine it just does not want to go smoothly at higher speed. I assume the syncro has failed but both 3rd and 4th within a couple of seconds and no noticeable wear before that moment seems unlikely.

The ball and spring below the selector are fine as that was my first check. I guess it is going to be a gearbox out job.

Any ideas? I have not worked on the gearbox for a long time so could be a steep learning curve.

Alan

[Pete Lewis]

whilst the synchro design inside is somewhat similar is this 3 rail or single rail ,

this does have  the hall marks of mainshaft circlip adrift or the mainshaft spigot bearing has give up

1st job is check the oil level. !!!

but a clearing clutch is a must for synchro to work

Pete

 

[Spitfiredriver71]

Hello Pete

It is a 3 rail gearbox with J type overdrive. I did not check the oil but the overdrive normally drops out when the fluid is a bit on the low side so I have assumed there was plenty in there.

The clutch seems to be disengaging fine as i can select any gear with the engine running and the car is stationary. When I had a weeping slave cylinder in the past reverse and first were difficult to engage but they seem fine at the moment.

[Pete Lewis]

if you try to engage at idle , no clutch , just a firm attempt to engage does the stick get baulked or does it try to crash through and make a clatter 

its pretty endemic when 3rd 4th misbehave  that the spigot has a lack of needles etc.

Pete

[hugh]

Broken spring 104445 on 3rd 4th syncro assembly, had these break in the past causes no syncro, only got to get one of the three to break to cause it

[Spitfiredriver71]

I took the remote selector off tonight and there was a black sticky mess at this joint. Not sure what it is called. Is there supposed to be a rubber or nylon bush here as the hole is huge? There is a small metal bush that I am holding in the photo but it is tiny compared to the hole below it. 

[thescrapman]

Yes, the bush has self destructed.

[Pete Lewis]

Its the insert from the rubber bush  you need a repair kit

This obviously gives uncontrolled selection you may not be aligned to push the fork your think you are.

Well worth correcting before you dive in any further. 

Most kits cover a range of evolved changes , so you get a variety of bushes and spacers  there will, be some 0 rings for the front shaft

I would leave that alone the square headed dowelis a pig to undo amd you chop the new rings on refitting if its not pouring oil leave that end alone

Pete

 

Pete

 

 

[Spitfiredriver71]

I tried a new bush and it made no difference to 3rd and 4th. With the gear box removed and the top cover off I can apply force to the 1st or 2nd synchro and get them to start to engage. The synchro hub for 3rd and 4th does not move at all. I looked in a spare non overdrive gear box I have and the hub moves fine in that box so the problem is definitely the 3rd and 4th synchro hub.

How do I remove the constant pinion shaft?  Also will I be able to get the synchro hub off without removing the main shaft as I only have a problem with one bit?

[yorkshire_spam]

First step is to drop the lay gear set into the bottom of the box, if you want to avoid a full strip down you'll need to push the shaft out with a shorter "dummy" shaft, otherwise the needle rollers will drop out all over the place.

Once that's dropped 1st motion (aka input) shaft can come out

[Spitfiredriver71]

I have made a shorter dummy shaft and dropped the lay gear but can not see a way to remove the large input shaft bearing. It looks Like  a special tool is required.

[yorkshire_spam]

There's a "by the book" method and a less gentle method. (Input shaft and bearing together....)

By the book, you attach the "special tool" to the input shaft and use a slide hammer to pull it out of the case.

The risky potentially damaging method is to get a circular drift onto the back of the bearing and tap it out from the back.

 

[thescrapman]

I have tapped them out successfully on a few occassions

[Pete Lewis]

its it quite normal and easy to  punch with a drift the input shaft out, just take care not to damage the thin chip shield 

Th cluster must have dropped fully into the bottom of the case,  you will have to remove the mainshaft to change or check the baulk rings on 3 4th as the sliding hub will not come off the main shaft in situ,

Again its knock the shaft thro the bearing  , knock bearing out of case with a drift

Sugest you change the hub springs while its in bits, dont mix 3/4 are diferent to 1/2 

Make sure the dog teeth  have a well defined chamfer  /\  not chimbled by crashed changes 

 

Where are you,  ???

Pete

 

[Spitfiredriver71]

Hello Peter

I am in Basingstoke, Hampshire.

I got the input shaft out by making a tool to press it out from the inside. The next problem is the bearing on the main shaft. I got it to move about 2mm by hitting the shaft with a large rubber mallet but 1st gear is now up against the gearbox casing. I assume the Haynes manual is talking rubbish about hitting the shaft though. I can not see how the gears can move up the shaft without taking the circlip off 3rd gear first. Feeling like a bit of an idiot over this. 3 days and only slightly further. I built the last engine and fitted it back in the car in less time than this.

[Pete Lewis]

With the main shaft rear bearing circlip removed you should be able to whack the shaft through the bearing

Then knock the bearing out the case with a drift reawards, this gives enough room tpmremove at an angle the assembled main shaft

When refitting sleeve balls and springs its best done in clear poly bag so if you dont get them popped in you catch the blighters as they escape

You can remove the bearing clip and push the whole lot into the case but im sure there is not enough case length to get the shaft assy  out 

Some thin wire to hold the 3rd 4th sleeve in place whilst refitting saves it all popping apart

If you get into trouble do you fancy a trip up to Luton   ?..

Soon get this sorted  over a cuppa

Pete

 

[Spitfiredriver71]

Thank you Pete.

I will try again later this week but if I still can not sort It, I might just take you up on your offer.

Alan

[Spitfiredriver71]

I finally got it to pieces and the main shaft has a crack in it. You can just about see it between the splines. That was why the synchro hub would not slide.

[Pete Lewis]

And the tip spigot looks pretty shot

Might be worth considering a 18mm spigot shaft but  needs a new input shaft , and possibly the clutch disc to suit rolled spline 

Pete