upper fulcrum pin shearing ?

[lightning]

I mentioned to a well respected MG and classic car restorer that I was about to replace the front suspension bushes with polyurethane ones and was most surprised when he said that on three previous occasions he had to replace the top fulcrum pin that had sheared. It was thought that this was caused by the poly bushes (used in each case) being too stiff and putting too much stress on the pin.
Has anyone had a similar experience ?

[Ian F]

Never experienced that, or ever heard of it previously.
I am still using the original upper fulcrum pins, and I am sure they are very robust - I can't really see them shearing?
Of course, if these original pins have been replaced by aftermarket items, then the material used may be of poor quality, unlike the originals.

Would be interested to hear of anyone elses experience here?

Ian F

[Trouble Monkey]

I fitted blue poly bushes a few years ago and kept the original fulcrum pins. I've not had any issues with them. I recently had them all apart too to fit new stub axles and couldn't see any unusual wear or damage to the fulcrum pins.

[Ian F]

Just another thought on this: if the MG is being used for racing or other Motorsport, and has stiffer dampers etc. then some failures of suspension components may occur due to the excessive forces applied.
I used a TR2 in speed events some years ago with generally beefed up suspension. I had a failure of a front wheel hub. The hub cracked all around the central portion (containing the bearing) and I lost the wheel, the front brake drum,and the outer part of the hub which remained bolted to the other lost components. Fortunately I was coming back down a hill climb course at a leisurely pace, not going up at speed!
I would think that such failures on a road car would be quite uncommon.
So, if using an MG in Motorsport an annual stripdown of suspension and crack testing would always be the norm.

Ian F

[Peter Cresswell]

I have never experienced any problems with this on an MGB (I've had 3) but did on an MGA and a TD both of which use threaded trunnions top and bottom. The threads wear and eventually the kingpin pulls out (a la Morris 1000)!
As far as the extra loading goes from uprating the suspension using thicker anti roll bars, polybushes and heavier rated spring and dampers, I'm not convinced that would exceed the material limits the components are made from. What can be a problem is the use of the poor quality 'F' quality nuts and bolts supplied in the workshop packs bought at show to hold everything together. The bolts should be 'T' quality and tightened to recommended torque figures. And never ever use Stainless Steel nuts and bolts!
The biggest load on suspension comes from tyre grip and although road tyres are not a problem, competition and racing tyres offer so much more grip and therefore loading on the suspension components that frequent inspection and replacement is essential. When I was racing my MG TC the wheels were 72 spoke AC Cobra wheels (6in x 15in) instead of 48 spoke 19in x 3in. Tyres were Dunlop CR65 5.50 x 15. Nobody thought about the loading these tyres were putting on the suspension components until Dave Clewley was approached by a Warwick University student who was researching stub axle strength. Using several strain gauge sensors fitted to a pair of stub axles and a multi-channel recorder the loading was measured over a few laps of Silverstone. The results showed that Copse was the worst corner as the speeds through it were the highest (it was flat out!) and on every lap the stub axles stretched and never returned to normal. In other words the elastic limit had been exceeded! Initially this explained why we always had to tighten the front wheel bearing (the ball races had been replaced by roller bearings) but after this we always had the stub axles x-rayed once a year and used dye penetrant crack testing after every race. The problem was, new stub axles were not available at the time so we were always having to fit the least cracked ones!

[Ian F]

Thanks for that Peter, interesting and entertaining!!

Ian F

[lightning]

Thanks to all of you for your very informative replies, I will pass this info on to the restorer, it should regain his confidence, he has two GTs, a C and a V8.