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MG MGB Technical - Constant clonking from back end

Hi all. Greetings from a very windy and wet Nottinghamshire! My B has just started to make a really loud clonking sound from under the back end - a constant clonking which speeds up and slows down with the speed of the car. It almost disappears on acceleration but on the overrun or when declutching is awful! Could the diff be causing this or is it more likely to be the prop? A collapsed wheel bearing? Hopefully not the gearbox. I've never heard such a loud banging! Any ideas, folks? Cheers, Rich
r j symons

Hopefully the propshaft UJs, but could be diff, less likely gearbox/OD. Wheel bearings usually growl, but with each raised in turn with the front wheels chocked and the handbrake off turn the road wheel while listening and pull it up and down looking for vertical and lateral movement that isn't the suspension.

Then it's a case of getting underneath and turning the propshaft back and fore with the rear wheels locked looking for play in the UJs, or loose flanges.

Then raising a rear wheel slightly and turning it with the propshaft. You may have to support and chock the car very carefully like that and run the engine in gear and using a long listening stick (so you aren't under the car!) to try and locate it.
paulh4

Hi Paul. Thanks for your most comprehensive answer! No idea why it has suddenly started to do this though. It's been out of action for about six months due to a mini resto. and when I took it out for its first run - all of a sudden, bang bang bang! No warning, no quiet clonking at first. Looks like I need to save some pennies up...will keep you posted. Cheers, Rich
r j symons

My guess is that the needle rollers have fallen out of the rear universal joint on the propshaft leaving the spider to clunk about.

I'd not drive it till it is fixed!
Chris at Octarine Services

Hi Chris. Thanks for your reply. It certainly did clonk loudly! Loud enough for people walking to turn around and stare! It's now off until I've raised the pennies to have it trailored away to go up on a lift and be fixed. Cheers, Rich
r j symons

If you own a couple of 1/2 AF spanners and can get underneath safely then you can check and if broken, remove the propshaft for repair off the car.
Chris at Octarine Services

Hi Chris and Hi Paul. Panic over, problem solved. You'll never guess what was wrong...and it embarrasses me greatly to tell you...all 4 N/S rear wheel nuts weren't even finger tight, 2 O/S rear wheel nuts wereloose and a couple at the front were also loose. All 16 nuts now torqued up properly to 88Nm and they will be retorqued in a few days' time. Car runs absolutely fine. No damage to wheel holes nor studs either. The bodyshop which has had my car for over 5 months has had a phone call today...
r j symons

They need a visit-------
William Revit

Professionals!

Mind you, I've done the same myself in the past ...
paulh4

Me too, to my shame. The rear wheel coming adrift and tucking up underneath the wheel arch. I had to pay to pay the price by walking up and down the road trying to find the lost wheel nuts on a torrential day in my work suit.

I should have learnt the lesson my dad once told me of always completing a safety related job before stopping work. He'd not tightened a knock-off wheel nut on his jalopy when called in for lunch by his mother and had subsequently out on the road seen the wheel overtake him......
Peter Allen

There's no excuse for negligence--
no second chances, whoever left it loose needs sacking and think him/her self lucky noone got hurt
This is the difference between a professional automotive repairer ------ and not
William Revit

The lad next door to my in-laws got a job at the local garage. One night he was told to put the wheels back on a car before he went home, but rather than do a bit of unpaid overtime decided to leave the wheel nuts inside the hub cap intending to fit them properly next morning in paid time. Of course the customer picked up the car early. He did get the sack.
paulh4

Incompetence is rife and not new. Decades ago a work colleague bought a brand new Hillman Hunter. It went in for its first service and the proud owner picked it up. After driving for a day or so the gearbox felt stiff to use, so it went back to the agent who discovered there was no gearbox drain plug, and obviously no oil. They just wanted to fill it up - "It will be fine madam." Sensibly she insisted on a replacement gearbox which came from the car in the showroom. I would bet a pound to a penny that her gearbox went back in the showroom car.
Mike Howlett

Unbelievable---no due diligence or ethics there then

It's got me intrigued, so doesn't anyone over there do wheelnuts up with a tension wrench to spec.
William Revit

It's the human element. Even top class surgeons drop the ball (or scalpel) occasionally.

I've noticed they use a torque wrench at the tyre fitters, but as to what torque setting I'm not sure. Now I tend to take wheels to get tyres fitted in the back of the good lady's hatchback.
Peter Allen

I've had front tyres fitted to the V8 at National Tyre and Autowreck and they did the nuts up with an air gun. Sure enough he checked with a torque wrench that they had reached the minimum torque, but he had no idea how much they actually were. On my return I used a bendy-bar torque wrench and got that up to 120 ft lb before it snapped. Those nuts were all loose on the studs after getting them off with a breaker-bar, which could have been studs, nuts or both. But swapping nuts front and rear it turned out to be the nuts so less of a problem. Wrote to the regional manager explaining what they were doing wrong and got a very snotty letter back in which he either couldn't or wouldn't understand the concept of doing the final tightening with a torque wrench, and not just a check, or accept they had damaged the nuts. My regular places now may use an air-gun to take them off but a spider to put them back, then a torque wrench for final tightening - I watch them!

The nuts were another saga - they were fairly ratty so wan't that bothered and bought a set of stainless. Which started showing signs of rust and peeling after just one year. Testing with a magnet showed half of them were magnetic i.e. steel and the other half not i.e. stainless, although some grades of stainless ARE magnetic like both my exhaust systems. More letters to the supplier, who again wouldn't do anything about it, until I invoked the relevant consumer protection act. After multiple problems with that supplier I won't use them any more, even though they come out top or near in the MGOC poll.

Someone bought a hood/top from that supplier and the fastenings were different side to side. "Must be your car, sir" even though the old one fitted perfectly. So he drove several hundred miles and waited while they looked one out that did fit, and called that good service!
paulh4

I disagree with the human element view Peter
If a mechanic can't do his job properly he shouldn't be doing it at all----and neither should a surgeon-
William Revit

I always undo any garage tightened wheel nuts and re-tighten using the car's wheel nut spanner, by standing on the end of it.

I reason that if I have to change the wheel out on the road I want to be able to undo the nuts...
Chris at Octarine Services

There is no excuse for not doing your job properly---specially safety items--
The tyre service should be using colour coded sockets if they're using airtools for refitting wheels and then checking with a tension wrench
If your studs have been wound up to 120 ft/lb Paul, they need replacing -their strength has been compromised and failure is imminent, when you don't expect it, after all it is twice the 60-65 lb spec---------------
William Revit

Reminds me of an incident that I experienced during my Kart racing days back in the 90s.

We were driving to a kart race meeting when we noticed that a small mini sized wheel was overtaking us on the hard shoulder of the motorway we were driving on.
I coasted the car and kart trailer to a stop on the hard shoulder and had a look at the trailer to find that the left hand wheel was missing. Fortunately, the hub on the trailer had a flange on it that was much wider than the wheel studs and the studs were unaffected.

So we ran up the hard shoulder and found the wheel in a ditch about 300 yards ahead of the car.

The next problem was that we had no spare wheel nuts!

I then had a brainwave and looked at the mounting nuts on the Villiers Kart engine, they turned out to be exactly the same thread as the Mini wheel stud threads on the trailer hubs and so we cannibalised them to get the trailer wheel back onto the hub.

So, of course we had to put them back on to the kart engine to get us through the racing day and then transfer them again to the trailer wheel to get us home later.

It turned out that the wheel nuts were aluminium and just not strong enough to do the job and I naturally swapped them for the proper steel ones once I got home.

Colyn
Colyn Firth

Rich - before your original thread grew legs (a favourite topic!), I was going to add an angle: I hopped in my work car in Melbourne early one morning, drove down the sloping driveway onto the road - to be greeted by rattling all round. Upon examination, all four sets of wheelnuts had been almost-but-not-quite removed during the night by some ar$ehole. Thank goodness my wife, who is deaf, didn’t use that car that day - the 3 boys were 2,3 and 4 at the time. Doesn’t bear thinking about.
Since then, I can’t help checking the nuts on every car, regularly!
Oh - and I concur with all the comments on so-called professional tyre fitters. My local guys would happily use a rattle gun for speed, no follow-up check at all. So I take the rims in and fit ‘em myself. John.
J P Hall

Roger Parker said how each time a patrol took a car out they had to check the wheel nuts were tight, but they did so by tightening them a bit more. So quite a few patrols later - snapped wheel studs.

I'm sure I remember from way back that if you lost all the nuts from one wheel while changing it by the roadside you could take one nut from each of the other wheels and proceed with caution. Not any more though.
paulh4

I feel I may have started something here! Needless to say, I'll be checking me nuts regularly from now on...
r j symons

This thread was discussed between 20/02/2020 and 24/02/2020

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