3-Speed Gearbox Overhaul

This thread is for discussing technical topics.

Moderators: Ian Grace, Will Grace

john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

3-Speed Gearbox Overhaul

Post by john haine »

Can anyone please advise how to strip the 3-speed gearbox for my M-Type. Neither Blower nor Malcolm Green's book cover this box. I have removed the selector mechanism and rear cover but it is not obvious how to proceed. Many Thanks John
garagiste
Posts: 93
Joined: Wed Jun 15, 2011 8:22 pm

Re: 3-Speed Gearbox Overhaul

Post by garagiste »

John,

Several points.

Why do you wish to overhaul the box? Was it running ok, or are there faults when driving?

If you have the top off, have you stripped the lever from its ball socket? What is the condition of the selector end of the lever, ball, socket, pin and groove? Problems start with wear on any/all of these.

With the top off & oil drained is there obviously wrong inside the box? Is there muck/metal in the oil?

Has anyone worked on the box recently - had problems with my box where a spacer had been wrongly placed on a selector rail.

From memory, starting from the back remove the body holding the speedo drive, this exposes a cir-clip which holds the rear bearing in position. Remove this and it comes apart in a fairly obvious way. Cir-clip on front bearing somewhat of a pain to release.

Take lots of photos as you strip it down - will aid reassembly. Post them on the site to get a second opinion on wear/defects etc.

Where are you located geographically?

I am a great believer in "if it ain't busted don't fix it!". But have rebuilt boxes in the past.

Come back if you get stuck.
john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

Re: 3-Speed Gearbox Overhaul

Post by john haine »

Hello Garagiste,

Thank you for replying.

First of all I usually run a 4-speed box but acquired this one in order to run in VSCC events as a standard car, rather than modified, according to their rules. It only cost £50 as no-one else bid for it, possibly because it was advertised without the change mechanism, but the owner found this a week later and agreed to let me have it for £5. Possibly a bargain!

Last year I used the box for 10 minutes only. It works OK but is really noisy. When I cleaned it I found some bits of broken glass inside but the gears and change mechanism look OK to my layman's eye, so I think I really need to check the bearings, especially the one at the front end of the main shaft.

This morning I removed the speedo drive body as you suggest, but found no circlip on the outside. There is one on the inside of the box against the rear main bearing but its purpose is not clear as it looks as if the bearing is removed rearwards. Removing the circlip with my circlip pliers will not be easy. I tried to drive the bearing out by giving it a few (gentle) taps using a brass drift but it does not budge so I am coming back to you for more advice if possible.

I live near Haslemere in Surrey

Regards

John
garagiste
Posts: 93
Joined: Wed Jun 15, 2011 8:22 pm

Re: 3-Speed Gearbox Overhaul

Post by garagiste »

Hi John,

Sorry that you are too far away to be able to visit you. I'm in the Presteigne area.

Understand your reason for wanting a 3 speed box.

Will take a look at a complete box that lurks in the back of my spares and refresh my memory of how the thing goes together, or more to the point comes apart!

Will come back in a day or two
john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

Re: 3-Speed Gearbox Overhaul

Post by john haine »

Hello Garagiste,

Soon after I wrote my previous post I got a bit braver and managed to drive the rear bearing and main shaft out of the box successfully and then found it easy to drive out the input shaft and front bearing, meaning that neither of the circlips need to be removed prior to doing this. I cleaned the bearings and found them pretty worn so have ordered replacements. The cage bearing at the front of the main shaft seems OK and probably would be difficult to replace. Does anyone know of a supplier for this bearing?

Many thanks for your support

Regards

John
Ronald
Posts: 327
Joined: Sun Nov 26, 2006 10:05 pm
Location: Dorset.........

Re: 3-Speed Gearbox Overhaul

Post by Ronald »

You should be able to take it to any bearing specialist and they could measure it and most likely find a replacement..... i would be very interested in seeing pictures.... are you going to remove the layshaft..?? as in my box it seems to be 2nd that makes most noise, ie using the layshaft... third is direct drive and the layshaft then just idles.... so its quieter....
john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

Re: 3-Speed Gearbox Overhaul

Post by john haine »

Hello Ronald,

Yes, I have removed the layshaft and the reverse gear shaft. There is some wear in the bushes so I need to find someone local to rebush the gears. I also need a local bearing supplier for the cage bearing. Otherwise the gears themselves and the two shafts are in good condition. I have taken several photos - are there any views in which you are particularly interested? Regards John
Ronald
Posts: 327
Joined: Sun Nov 26, 2006 10:05 pm
Location: Dorset.........

Re: 3-Speed Gearbox Overhaul

Post by Ronald »

HI John, well, all pictures would be interesting, if you can't work out how to post them on here, if you want to email them to me i can post them.....
ronnie_hogg@yahoo.co.uk
Ian Grace
Site Admin
Posts: 5035
Joined: Sun Nov 19, 2006 12:55 am
Location: USA

Re: 3-Speed Gearbox Overhaul

Post by Ian Grace »

I can feel a Tech Topics article for the Magazine coming on here! All submissions gratefully received!
john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

Re: 3-Speed Gearbox Overhaul

Post by john haine »

I went to see a local engineering workshop yesterday and the outcome is that to grind the worn part of the layshaft (or make a new one) and replace the bushes is going to be expensive. As the wear is not excessive and I would probably only use the 3-speed box for one event a year (VSCC) I have decided to put everything back together (using the new main bearings) and see how it goes.

I will email some photos after the box is back together, but I am not the person to write a technical article - my engineering is civil, not mechanical. What is needed is a 3-Speed version of Barry Foster's article on 4-Speed boxes in the 2005 Triple-M Yearbook. John
Simon
Posts: 275
Joined: Sat Dec 09, 2006 4:56 pm
Location: Surrey UK

Re: 3-Speed Gearbox Overhaul

Post by Simon »

If you have not yet got the bearings go to Marksman in Aldershot. Their prices are good but they can be a little difficult to find . Phone 01252 345455 . I also live not far fro Haslemere.
john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

Re: 3-Speed Gearbox Overhaul

Post by john haine »

Simon, Thank you for the advice of a local bearing supplier

The gearbox is now installed in the car and the noise in second gear is now reasonable. However I am finding it harder to make quiet gear changes than with the 4-Speed box. One problem is that It is more difficult to find the gear lever, which seems to flap about all over the place. Does anyone know of a remote for sale for a 3-Speed box? Regards John
garagiste
Posts: 93
Joined: Wed Jun 15, 2011 8:22 pm

Re: 3-Speed Gearbox Overhaul

Post by garagiste »

John,

See my earlier posting regarding the condition of the ball, peg, etc. where these enter the box. Also the condition of the end of the rod where it meets the selector mechanism.

I have fitted a remote which makes the gear changing a lot easier, however it rattles badly due to the warn bushes both ends of the shaft between the top of the box and the lever, so if you find one be prepared to have to rebush it! Oilite bushes have a good range of suitable sized ones for my remote.
john haine
Posts: 11
Joined: Wed Jan 04, 2012 4:54 pm

Re: 3-Speed Gearbox Overhaul

Post by john haine »

Hello Garagiste, I think the ball on the gear lever is OK but no doubt there must be too much wear on the end of the lever. My next job is to check. Any suggestions for remedial work welcomed. John
garagiste
Posts: 93
Joined: Wed Jun 15, 2011 8:22 pm

Re: 3-Speed Gearbox Overhaul

Post by garagiste »

John,

There must be a drawing about somewhere, have the end built up with "stelite" (spelling)? and reground to the spec. on the drawing.

Who can help with a drawing? Wouldn't mind a copy.
Post Reply