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MG Midget and Sprite Technical - Gearbox noise - soon after clutch job

Regular readers may remember my "tinkly clutch" thread, which resulted in me getting a garage to fit a new clutch to my 1275 midget. They also refitted the gearbox mount, which they had told me on a previous occasion was wrongly fitted.

I've done about 200 miles in the ensuing month. Last weekend, I noticed a slight new noise from the gearbox and today it was louder, such that my wife noticed it too, though it's still not really loud.

The noise is kindof a grinding or grumbling. It initially happened when engine-braking. It's now happening a far amount of the time, though louder during acceleration or deceleration in the top two gears. Gearchange is unaffected, by which I mean that 2nd through 4th are easy and smooth, while non-synchro 1st is its usual recalcitrant self.

I'm no expert on gearbox internals, but I imagine that each of the shafts runs in some bearings and the noise is the sort that a failing bearing might make. But that's absolutely just a wild guess.

The gearbox is one of the few remaining old parts of the car. I don't have enough history to know if it's the 1970 original, but I'm sure it wasn't replaced or rebuilt in the 2000's restoration of the car. It's got 20/50 oil in it, less than 2 years old. Level was last checked a few months ago, but it required a noticeable top-up today (not overly low, though).

Would anyone like to take a stab at possible causes of such a noise? Am I likely to be correct to correlate the clutch work with the noise? Or is it more likely to be just bad luck?

Any diagnostics that I can do without major dismantling? If it is related to the clutch work, any suggestions on proving it? I don't fancy relying totally on the honesty of the garage, even though they've been OK in the past.
Pete AC

Diagnostics can be difficult. If the box has never been overhauled then the most likely problem is worn layshaft bearings. They are needle roller bearings that take a fair bit of stick when accelerating/decelerating. The main bearings on the input and output shafts do wear but are quite robust.
The problem with Midget gearboxes is that they are relatively weak. They were originally designed for the A30 producing 30 odd BHP. Whilst the Midget box is stronger it still based on the A30, (for example the layshaft bearings are the same) but the box has to handle 65 BHP.

If its not been overhauled then a rebuild with all new bearings may be needed.
Bob Beaumont

Pete

If your having to rely on a shop to do the work, id recommend upgrading to a 5 speed ford type 9

Im sure its not cheap to have a shop pull the engine out each time

Prop
Prop and the Blackhole Midget

This thread was discussed between 22/08/2015 and 23/08/2015

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