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MG MGA - Knocking in first and second gear...

I am experiencing knocking while accelerating hard in first and second gears. The knocking does not occur in third or fourth gear. I do not feel any vibration through the shifter but I do "feel" as well as hear the knocking under the car. The speed of the knocking also seems to correspond with the RPM's. I have inspected the drive shaft and see nothing hanging off that would cause the knocking. Is this a transmission problem? Please Help!!
gerard hutchinson

Have you had a good look at the universal joints Gerard?

Or it could be the engine or gearbox mountings that are coming adrift.

If it was the mountings, the knocking would be even worse in reverse gear.

Colyn
Colyn Firth

Colyn,
The sound seems to come from the vicinity of the universal joints. Do they need tightening? Or grease?

Also, the sound doesn't occur when I take it easy.
gerard hutchinson

I think replacement is the only option in both cases Gerard, Im sure that you cant adjust universal joints, you just have to replace them.

The same with engine and gearbox mountings, if the rubber on them has failed, then the engine or gearbox will move too far under hard acceleration and the mountings would similarly need replacing.

I meant to explain in my first post that there is even more torque being applied through the drive train in reverse gear than in 1st and 2nd gear which is why the knocking can be even worse when reversing.

Colyn
Colyn Firth

Worn universal joints will vibrate at road speed long before they otherwise make noise. You have to drive with a vibrating U-joint for a long time before it is worn enough to make noise. Then it will make noise all the time. So this is probably not a bad U-joint.

Loud knocking noise in 1st gear is (in every case I've known) is a broken gear tooth. This would be either on the 1st gear ring or the small pinion of the laygear. Broken tooth on the laygear pinion should also make knocking noise in reverse, while a single broken tooth on the bull gear may not knock in reverse.

Loud knocking noise in 2nd gear (or 3rd gear) would also be a broken gear tooth. One broken tooth for 2nd or 3rd may not make noise at all, so many cases go undetected until it breaks another tooth. Two adjacent broke teeth will make the knocking noise, Three adjacent broken teeth will make evil screaming noise when you try to engage the gear, and it won't go into gear while the vehicle is in motion. You might guess I have personally encountered all of these conditions.

The condition of knocking noise in 1st and 2nd gears implies broken teeth on two gears. That would be unusual but could happen if one was cause and the other was effect. That is, if a broken tooth fragment got caught in another gear it might break the other gear as well.

If you need gearbox parts, I have some spares.
Barney Gaylord

And if 1st and 2nd gear both have broken teeth, you will need a laygear as well
dominic clancy

Was kind of being optimistic on your behalf Gerard, would be much easier to fix a universal joint or an engine mounting than a gearbox!

Colyn
Colyn Firth

Clattering 1st gear is most likely a broken tooth on the laygear, but it might be a spalling "divot" out of the face of a tooth on the bull gear. For 2nd and 3rd gears, I have seen more broken teeth on the driven gears than on the lay gear.
Barney Gaylord

So... What is the best way to pull the transmission? Do I have to remove the engine as well?
gerard hutchinson

In a word - yes, either as a unit with transmission or engine first then transmission many advocates on both ways. Chuck
Charles O'Brien

Hi Gerard,

Don't panic! I ran an A35 for 3 years and 15,000 miles with that problem. It was noisy but you only need those gears for a short while. I just changed the gearbox oil regularly (with the engine at 4000 miles) and checked carefully for bits of tooth.

Eventually a gearbox turned up at a price I was willing to pay and I swapped it out.

Paddy
P Reardon

This thread was discussed between 21/04/2012 and 23/04/2012

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