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MG MG Y Type - Running rumble

Up until today the YA used to simply purr at 40mph but once above 50mph there was a beating effect not unlike two fans slightly out of sync. The beat rate increases with road speed.

Since the car had been driven very few miles in the 5 years before I bought it I wondered if there were flats spots on the tyres from prolonged parking. Since the age and provenance of the tyres was unknown and I had different sizes on the front and rear, I took the forum advice and shouted the old girl 5 new tubes and tyres, all balanced. Unfortunately, this expenditure did nothing for the drumming over 50. (Under load or coasting downhill, it is the same.)

On the way to a Naviscat today we commented on how pleasant travelling at 40 was but on the way home even 40 is now becoming unpleasant due to the drumming noise.

What is next on the expense list? Any ideas? Propshaft? Universals?

Thanks, in advance, for your input.
Murray
MG

Check for free play on the Universal joints on the prop shaft. Excessive free play due to worn or broken bearings will give you this result and may eventually tear the yoke apart on either the gear box or axle or either end of the prop shaft if left unattended.

Paul
Paul Barrow

Also check that your rims do not suffer from "run out". As I understand that means the rims are bent. They can be made straight,where in the UK I do not know.The rims are of soft steel and were usualy bent out of round by tyre shops using presses which attached to the rims. Terry
Terry O'Brien

"Since the age and provenance of the tyres was unknown"

I would seriously recommend that you get new tyres (even if the rumble is coming from somewhere else). The rubber in tyres over about 7 years old is getting hard and brittle and can be hazardous. Cheers - Dave
David DuBois

Dave, if you reread Murray's message, you'll conclude he already "shouted the old girl 5 new tubes and tyres"?
Willem van der Veer

I had a terrible "rumble" after I replaced the gearbox mountings. The new ones were far too hard, I put the old ones back (looked a bit oily but were still useable) and no more rumbles. Other friends here have had similar experiences. It is noticeable even if the car is stationary, I found out by placing a bottle jack under the drain plug with just enough lift to take the load off the mounts and revving the engine.
Barry Bahnisch

Murray

Do you get any similar 'thrumming' at high revs in lower gears, or only at 50/40 mph?

Universal jounts ar enot too expensive - I actually gave one away to an MGA which had lost its drive during one rally, and found it reasonable to replace.

As well as the tyres, is there any XS play on the wheels, (in any direction, including end float) slight play may produce resonance on flat surfaces at certain speeds of revolution.

(Arlene was reminded by your problem of our first car at College nealry 40 years ago - a Morris 1000 traveller. At 40 the glove box popped open due to 'resonance'; at 50 the gear box chattered incessantly and at higher speeds you developed a synchronised pain just behind both eyes - and we never found out what was causing it! But the glove box event was a superb way of ensuring you kept within speed limits!)

Cheers, Andrew
Andrew Coulson

Andrew raises a good point there - check your wheel lug nuts - if they are loose you could be getting a rumble from them too.

Paul
Paul Barrow

Took 'Clara' out for a run on Saturday to nail down the conditions under which the noise/vibration occurs. The speed is getting lower all the time, 35 is now unpleasant in 4th.

It is rev related as it can be produced in 2nd or 3rd at lower speeds.

Contrary to what I said originally, coasting downhill in neutral at 45-50 is blissfully quiet, so that ruled out tyres/wheels/UJs/Prop shaft etc.

It turns out that it may be a badly worn water pump. I noticed the pulley was running out of true the other day and now it is really bad.

So, maybe a new water pump will fix the vibration problem and my persistant water loss issue???

I'll let you know, and thanks for all the helpful suggestions.

Murray
MG

MG... Take off the belt and give it a short run to check and see if it isthe pump.It will not overheat in a 1/4 mile run.
Sandy
conrad sanders

"Dave, if you reread Murray's message, you'll conclude he already "shouted the old girl 5 new tubes and tyres"?"
Oops, missed that. - Belay my last Murray :) Cheers - Dave
David DuBois

Murray,
"coasting downhill in neutral at 45-50 is blissfully quiet, so that ruled out tyres/wheels/UJs/Prop shaft etc"
Coasting downhill in neutral is not putting any load on the UJs on the prop so I am sorry - it wont rule that one out, only maybe confirm it. I would definitely check them out. If they havent been lubed in many a year, they may well be shot!

Paul
Paul Barrow

This thread was discussed between 29/06/2008 and 09/07/2008

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