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MG MGB Technical - Clonk when braking

For a while now both cars have exhibited a bit of a clonk from the front when applying the brakes after travelling forwards anything more than a short distance. Pondering the forces involved, I applied the handbrake with all four wheels on the ground, then grasped the front wheel firmly trying to rotate it back and fore against the braking effect of the handbrake, and a definite clonk in each direction. However I couldn't do that and see what was happening round the back at the same time, so arranged for a pal to come over.

While waiting I pondered some more, looking at the drawings of the front suspension assembly to see if I could work out what the source might be, and the main contender was the lower king-pin trunnion sliding back and fore on the distance tube. Pal duly arrived, did the rotating, and that's exactly what was happening. The distance tube itself is tightly clamped between the A-arms and thrust washers, the king-pin bush pivots round that, is fractionally shorter than the distance tube, and rubs against the inner faces of the thrust washers as the suspension moves up and down.

Potentially £ to £££ depending on what is replaced, so have a look first. Supported the front of the car on axle stands under the rear edge of the cross-member, and jacked up the spring-pan until the damper arms were just clear of the rebound rubbers. Removed the nut, and tapped the bolt out. Removing the thrust washers with seals and seal supports there are clear wear grooves on the inner faces of the washers. Hadn't laid any parts in, but as the outer faces of the thrust washers are unworn I simply turned them round - clonk gone. If planning to do the same then lay in two washers AAA1390 (per side) at 50p each.



paulh4

Both of my cars have the same "clonk". I always thought that it was the coil spring shifting that made the noise.

Now added to my to-do list.

(When you said you said "jacked up the spring-pan until the damper arms were just clear of the rebound rubbers", did you mean the a-arms to be clear of the rebound rubbers?)
Steven Rechter

I have noticed a bit of a clonk from mine, but fitted new kingpins during the rebuild, so I would assume that I checked/replaced the washers.

I will have to investigate further, although I really must fix the fuel pump.
Dave O'Neill 2

I had a similar clonk and by a process of elimination started off by replacing worn anti-roll bar bushes and mountings. While I was about it, like Steven, I thought by chance it might be springs so decided to swap them over as drivers side was slightly lower. On one side easy as recently replaced fulcrum pin came out with ease from poly bush sleeve. On other side pin ( 2yr old?) had seized in sleeve, so I undid shocker. However, I noticed a bit of play in lower trunnion so I think I'll need to replace lower bush. It'd be great if, like Paul, I could get away with bolt, sleeve and thrust washers as I bet that bush will be a pain to remove in-situ.
Peter Allen

Steven - maybe terminology, to me the A-arms are in the lower part of the suspension, carry the spring pan, and go between the bottom of the cross-member and the lower trunnion. The damper - often referred to a 'shock absorber' - has the arms going to the upper trunnion that rest on the rebound rubbers when the car is jacked up and the suspension hangs down. You have to lift these just off the rubbers to take all the force of the spring pushing down, or you won't get the lower pivot bolt out - or if you force it out it will release the tension in the spring pretty violently.
paulh4

Just a thought.......Wire wheels???
Colin Parkinson

Could be centre-lock hubs, but that is more likely at the rear as the forces there are continually being reversed with acceleration and braking.

At the front the forces are only ever in on direction, except when braking in reverse, which by comparison should be pretty minimal.
paulh4

This thread was discussed between 31/08/2018 and 01/09/2018

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