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MG MGA - Tyre screech

I had a strange thing happen with my car today. I reversed out of my drive onto the road on right hand lock and noticed a screech from my right rear tyre (right hand drive 1500 roadster with top down), exactly the same sound you would get if you really hustled round a sharp bend, except I was doing less than 1MPH in reverse! I drove 100 yards down the road and everything seemed fine until I took a right turn and got tyre screech again. The tyre sounded like we ought to be cornering on two wheels, but the car was planted firmly on all four wheels as we took the turn at quite a sedate pace with not the slightest hint of slide. I stopped and checked all the tyres, thinking I might have a flat, but everything was in order. We continued our journey of about 40 miles, with plenty of turns, some taken at speed, but no more tyre screeching. The car had unusually, not moved for two weeks or more (it usually gets driven at least twice a week), so I wonder if that could have anything to do with it. Tyres are Firestone 560s with pressures 25lb front and 27lb rear. It definitely sounded like a rubber on road sound, any ideas?
Lindsay Sampford

A locked differential perhaps. Jack up the rear and see if one rear wheel will turn without the other turning.
Barney Gaylord

Could be the brake shoe sticking on the drum as it had been standing for a couple of weeks.
Cam Cunningham

It was a real rubbery squeak Cam, not a scraping sound. I think Barney could be right, it sounded like the tyre was being forced to do something it didn't want to. When I first got the car it would squeal the tyres on corners, but I put that down to the ancient Pirelli Cints and the fact that it had hardly turned a wheel in three years. The problem all but disappeared once I started using it, and it never happened at all once I got rid of those old tyres; until yesterday. Like I said, it only did it on those two occasions, could a diff lock up and then free itself? I'm taking the car for its MOT this morning, so I will see what the diff does while the tester has it jacked up.
Lindsay Sampford

Has it been dampish there? Old VW were famous for making all sorts of odd graunching from the brakes, even to locking up as you stopped. I've had other cars do it on occasion, but on VW it was a sure thing. It all had something to do with the combo of lining and drum material, and was much worse in cold or damp weather and after sitting for days or weeks. The cure was to remove the drums and blow the dust out. I breathed a lot of asbestos!

FRM
FR Millmore

Does it have a limited slip diff? Sometimes my limited slip diff tends to grab a wheel when backing out of the gargage after a long lay up.
Mike
Mike Ellsmore

Mike, not as far as I know. Everything else about the car is bog standard, I can't think that anyone would have intentionally fitted a LSD.
Lindsay Sampford

If the car has been involved in an accident in the past resulting in a slight bend of the rear axle it can act as a limite slip differential.

JB
John Bray

Just returned from MOT (passed). The mechanic could find nothing wrong with the diff and the brakes went on and off perfectly, nothing sticking, curious!
Lindsay Sampford

Lindsay

Probably a mouse had made its nest on the back axle while you were away.

Steve
Steve Gyles

Lindsay, you may find that pressure is a bit lower on that tyre than the others
dominic clancy

Were you driving over any painted road lines? It doesn't take too much to get tires chirping at low sppeds on those guys. Especially with the top down and if it wasn't too windy (noisey) you might be hearing it when otherwise it would be muffled by engine or road noise. Just a thought...
J DeRienzo

Could the U bolts for the rear axle be not tight enough and allow one side of the axle to shift on occasion and possibly re-locating itself after a bit of forward driving? This can cause the car to "dog track" as a friend of mine found out on an MGB.

Ralph
L Poupard

Dominic, I checked the tyre pressures and the rear ones are today reading 29lb, so nothing untoward there.
JDR, no painted lines where it happened, but I know what you mean. Painted white lines are to be avoided when riding a motorcycle in the wet!
Ralph, your comment had me reaching for the spanner! I replaced the pads and bushes on the rear springs last year so I wondered if the pads may have compressed, making the U bolt nuts loose.... No, as tight as the day I fitted them.
Thanks for your comments. The noise hasn't happened since, but I think Barney's comment about the diff is the most likely cause. I think something must have happened in there which has cleared itself for now. Maybe a broken tooth or a siezure of some kind. It'll probably fail completely one day....then I'll know!
Lindsay Sampford

Lindsay, did you check for rodents?



Art Pearse

Art, that could be a new 'carbon-neutral' form of propulsion, a chipmunk running round inside each wheel!
Lindsay Sampford

Lindsay,
It may have just been the type of tarmac, the type of rubber and the temperature on that day.

My wife Chris has a Toyota Rav 4 fitted with mud and snow tyres. They dont have particularly deep tread on them but in summer on warm days they tend to squeal when we apply lots of lock ( in car parks etc )but not on cooler days.

If there was some oil on the road this can have a similar effect too.

Maybe you should discontinue the handbrake turns too Lindsay!

Colyn
Colyn Firth

Colin has a point there. The Ackerman steering geometry on most cars is not perfectly aligned with large steering angles. The inside front wheel needs to steer farther than the outside one to track (orbit) around the same center of rotation in the turn. Ideally the axis of the front wheel spindles should intersect on the rear axle line. Quite often with a tight turn the outside front tire will turn too far, or the inside front tire does not turn enough (all relative). Then one of the front tires has to skid sideways a bit during a tight turn. This is equivalent to having toe-in severely misaligned when driving in a straight line.

Older tires are more likely to squeal than new ones. Brand new tires may squeal during the first five minutes of use until the mold release compound is worn away. Freshly sealed asphalt pavement has poor grip and is likely to make tires squeal. Lots of cars will make front tires squeal on full steering lock, perhaps more likely when backing up.


Barney Gaylord

This thread was discussed between 29/08/2011 and 03/09/2011

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