Gearbox Noise

[rcharman]

I have this strange noise coming from the gearbox. It started when I tried to reverse, selected the gear, released the clutch then it sounded like a chattering sound with no vibration underneath the front floor. Then 15 minutes later it stopped doing it reverse and started in first, now 2 hours later it's doing it occasionally when changing down from fourth to third.

A new cluch kit was installed 2 months ago and is working perfectly while driving, changing gears up and down very smoothly apart from this chattering sound that started today. Engine is great with no difference in power, there are no oil leaks anywhere as the whole engine and gearbox had all the seals and gaskets replaced when the clutch kit went in. A total new clutch linkage kit was also installed as it seemed to be a waste of time to put the old worn out one back in.

Could anyone help me to determine if the gearbox is stuffed or near to it.

The engine is a 948cc.

[Kevin]

Well as you have replaced the complete clutch and linkage that should eliminate that area, I assume both your engine steady is in good order and the gearbox steady cable is correctly tensioned and not over tight as this causes strange noises when too tight. I would check the propshaft UJ`s as they can make some noise if anything has become worn or even loose, but if there is no vibration its unlikely, its not something like the front pulley starting to break up as these have been known to go occasionally.

[bmcecosse]

Better take the gearbox side cover off (watch for two wee springs) and have a look inside. Perhaps a selector fork has come loose - and you can try lifting the shafts to see if the bearings have collapsed. If it is bearings , and caught quickly enough you should get away with just new bearings. But if run like that then obviously the gears will quickly deteriorate.

[MoggyTech]

I had the very same thing a few months back, and it turned out ot be the NEW clutch relay lever, the bit that fits between the gearbox side cover and the RH chassis leg. Refitted the old one problem gone.

Also worth checking before doing anything to the gearbox, Clutch return spring, and that the wave washers are fitted correctly to the clutch lever linkage pivot pins. Speedometer cable screwed fully into the box, and clipped to chassis leg.

[rcharman]

Thanks for the responses.

Kevin: The universal joints are okay, a new complete engine steady bar kit went in when the clutch kit was installed and the gearbox steady cable is firm but not tight. The front pulley will be checked for anything out of the norm.

Bmcecosse: I went to my mechanic today (use to race Morries and MGs) and he took the car for a drive, said the gearbox was great (geez that was a relief to hear that). Isn't it typical when you take a strange noise to a mechanic to find what is wrong, the little Morrie was quiet and well behaved.

MoggyTech: Unable to put the old clutch relay lever back on as the holes are not round, they had become oval from the previous owner who had the car for 47 years, so I don't have an option there. I took your advice and removed the speedo cable and reinserted it into the gearbox, even though it was screwed in fully the first time I didn't want to leave a stone unturned.

[bmcecosse]

So - the noise has now disappeared ? Is it possible the noise was something like the bonnet release mechanism resonating at certain revs ?

[rcharman]

The noise is still there but very occasionally, it is definately coming from the gearbox area, when it happens there is no vibration through the gear stick. It is such a mystery as I have been underneath the car for hours checking everything that could have or might have come loose, even replaced all the split pins on the linkages (nothing wrong with them as they were new).

Checked bonnet stay, hinges, brackets, wiring loom, under the dash, suspension mounts, engine and gearbox mounts, seats (even underneath rear seat, no money to be found), doors, pipes, tubes, etc. etc.

But I won't give up until it's resolved.

[MoggyTech]

When it happens gently press the clutch pedal, just enough to take up the free play. If the noise stops it's the new relay shaft or tuffnel bush. Other than that, anything from an old bolt lying in the gearbox cross member to gearbox getting ready to exlode (Only kidding about the exploding bit)

[Kevin]

Dont suppose you have a pal who works at a test centre who could put the rear wheels on the brake tester while you put it in reverse to see if a helper can narrow it down or perhaps see something astray under the cars (I know this sounds like clutching at straws but you never know) the last poster on here with a strange noise found it to be the link arm between the chassis and damper at the rear so anything is possible.

[Orkney]

When's the last time you changed the gearbox oil?
My gearbox is doomed, changed the oil last week and it quietened it down something amazing, own blend of oil
The remaining noise is now the prop UJ which is probably also kanckered as keep it well greased.

[bmcecosse]

Should be engine oil in that gearbox! 20W50 probably best.

[rcharman]

Hi from Australia

MoggyTech: The noise is there when changing from fourth to third, it starts when the clutch pedal is up and lasts for 1-2 seconds. Then on the other occasion it has happened with the clutch depressed and lasts for 1-2 seconds (the noise doesn't happen all the time, one in every eight times when changing down to third). You might be right about the tuffnel bush, I will check that also. I checked the gearbox mounting bracket, thought that I might have picked up a stone and it was causing the problem (nothing was there). Geez, I am glad you were joking about the exploding gearbox.

Kevin: Wouldn't it be an advantage to have a friend with that sort of equipment.

Orkney: The gearbox oil is brand new (20W50 as bmcecosse suggested), replaced it when the clutch kit was installed. I even strained the old oil to see if there was metal particles in the oil, to my surprise it was clean with the normal sediment you'd expect from any gearbox. Universal joints are in very good condition with no sloppiness in the drivetrain.

I also checked the exhaust fittings (brand new complete system fitted), gear selector fittings on the top of the gearbox, hand brake mountings and cables.

[Peetee]

It won't be easy to check but perhaps a fracture on the gearbox mounting plate is the problem. Like this:

[rcharman]

Hi Peetee

The gearbox and engine mounting plates were glass bead blasted when the engine /gearbox were removed for the clutch kit. The drivers side engine plate had cracks like the one you described, so both engine plates were reinforced and welded. The gearbox mount had no signs of fatigue in any of the welds (had all suspect parts tested at the welding trade school where I work as a teacher). Your suggestion sounds plausible, that's roughly where the noise seems to be coming from (when your inside the car driving it) and even though I had it tested that doesn't mean it is still perfect.

Your right, it's not easy to check it, but if the noise continues to annoy the crap out of me then what's time worth if the problem gets fixed.

[Peetee]

It seems odd to me that the welds stop so low down. Presumably the digonal support plate is left unwelded to allow a degree of spring in it to reduce vibrations?

[rcharman]

Certainly odd alright, you can clearly see that fatigue eventually does happen. Why would it need to be like that as it has two rubber mounts to eliminate the vibration.

[Peetee]

I had the crack repaired and a weld added further up. With new rubber mounts fitted the transmition vibration was dreadful. I know that new mounts are know for this so it is bit difficult to advise for or against this sort of 'fix'.