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MG Midget and Sprite Technical - Gear box 'whirring' noise

Recently, I've noticed a "whirring" noise, coming from the gearbox when in neutral, clutch pedal out. The noise disappears when the clutch pedal is depressed and I can't notice in when in gear (perhaps due to engine and road noise however its loud enough at idle that I would expect to hear it anyway).
I have had other issues with the clutch, occasionally slips when in higher gears under load/heavy acceleration, although infrequent. The only issue noticeable with the gearbox is a "clunk"/grinding noise when down-changing to second gear. Moving up through the gears is good and down is as expected (except 2nd).
I've read that the clutch bearing could cause this and that changing my clutch should solve the issue however I've also read that it may be the gearbox input shaft bearing that is at fault.
Do I just replace all those parts or is there a test to confirm where the fault lies? Is it 'easy' to fix the 2nd gear issue at the same time?
Thanks,
Steve
MG midget 1500, 1979 UK build
S Travis

When you remove the engine/gearbox you will be able to tell by feel/sound if the throw-out bearing is bad.
Trevor Jessie

Steve, nice looking car.

Is it a high mileage gearbox?

From my research (albeit quite a few years ago when I refurbed my box) I remember the input shaft bearing being noted as a common wear item on the Triumph box. This might be the whirring sound. Pushing down clutch decouples gearbox, stops load and sound goes away.

The other normal wear point is the layshaft and its associated needle rollers. This requires a full strip down to replace.

Maybe 2nd gear problem is unrelated, worn synchro maybe?

Useful diagrams of your 'box if you haven't found any yet...

http://www.rimmerbros.co.uk/ItemList--Triumph-Spitfire-Gearbox-Single-Rail--m-3166

Cheers,
Malcolm
M Le Chevalier

Thread with lots of internal pictures to help you out...

http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1357476767/

M Le Chevalier

Generally, a release bearing makes more noise when engaged (clutch pedal on) than not. The box bearings make the most noise when clutch is engaged (clutch pedal off). YMMV of course. Disengaging the clutch removes the drive to the gearbox and stops the bearings making noise, as said above.

A drop and change of the oil will help see what's occuring inside by how many metal fragments you find.

I'd guess some or all of your gearbox bearings were on the way out and also the synch on 2nd gear as it has the hardest work going from 3rd to 2nd, up from 1st to 2nd isn't much of a hike.

How long will it last? I did over 10k miles on a gearbox with similar problems and it was still working when the car was parked up. Admittedly it's now on its last legs but it's one of those things you could ignore for a while if you want to. The longer you ignore it though the more likely long term damage occurs. Eventually my box was jumping out of certain gears and others became very problematic to engage. Opening the box revealed the layshaft to be toast as well as the other bearings, syncros and the reverse idler (another common problem with these boxes).

If the clutch is slipping, have the engine and box removed and sort the clutch and the box out at the same time. Should last years then and you'll have some peace of mind. Heck, while you're at it, put in the overdrive box from a Spitfire 1500.
Roadwarrior

Thanks guys.
I'll book the car in to have the clutch replaced and examine the gearbox then, hopefully it's just the clutch and throw-out bearing. In the meantime, I'll check/fill the gearbox oil.
My issue is that I have no garage (nor engine hoist etc) to do the work myself. I use this car as my daily driver and parts are hard to source (and/or ridiculous prices) locally in Australia, so was hoping to have everything ready to delay off road downtime.
From what I can ascertain from the manual (Bentley's), changing the input shaft bearing is fairly straight forward whilst the gearbox is out and shouldn't take long but the manual does not indicate time-frames for jobs. Should I just get that changed anyway? How much extra time should that take (for an experienced mechanic)?
I'd love an overdrive or 5-speed box but don't even have funds to recondition the current box, so that's out of the question.
S Travis

I'd ignore it completely while you save for a full rebuild of the gearbox. Just do the clutch for now, it's a simple day job.
You could spend $$$ on the 1st motion bearing and fix nothing at all if you ignore other issues. Despite how simple it seems (just pulls out the front, right?), you'll be pulling a lot of the box apart just for access reasons and to enable the gear to slip out past the laygear set. Once the rear housing, layshaft, etc is removed, you'd be mad to put old needle rollers back in and might as well put on rear bearings and seals while you're there. Then you'll be thinking about that synch...
Roadwarrior

Good points, sounds good to me.
Oh, forgot to say - car has 125000 miles on it, to the best of my knowledge the gearbox hasn't been touched in that time. I've had it for the last 40000.
S Travis

Road warriors advice is good.

If you can find the parts a home refurb isn't all that tricky (I managed!). The only special tools you need are a bearing press (aka big hammer!) And circlip pliers.

A spitty overdrive gearbox won't fit without chassis chopping, so if you are happy living with a 4 speed discount the OD option.

Cheers
Malc.

P.S. good on you for covering so many miles in your MG
M Le Chevalier

This thread was discussed between 20/02/2015 and 21/02/2015

MG Midget and Sprite Technical index

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