MOT test of R75 Front suspension lower wishbone rear bushes - MG-Rover.org Forums
 
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post #1 of 5 (permalink) Old 28-02-2017, 20:32 Thread Starter
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Exclamation MOT test of R75 Front suspension lower wishbone rear bushes

Hi Folks, I have a 2004 R75 Mk11 with 83K miles and I took it for MOT test last week. It failed on front lower arm rear bushes deteriorated allowing excessive play. I checked them out myself and they looked like new. I tried a length of wood between the arm and the body in front of the bush and there was very little movement with hand force. I also tried a 1m bar into the wheel to move the suspension (with the car raised on a jack under the centre engine lift point) with the wheels just about to lift off and the only movement discernible was the alloy wheel starting to flex. Same both sides. The bushes are (or were before the brutality of the MOT test) fully attached between inside and outside and very little visible cracking. I spoke to the garage and the workshop supervisor said he would get another technician to check it and show me the problem. They showed me the vehicle on a ramp on a test pit but what they did horrified me. They turned on an automatic wheel play detector that seemed to try and pull the wheels apart and ram them together again rapidly. The suspension was going in and out like a fiddlers elbow between maximum and minimum travel and the ends of the lower arm were being wanged about. I thought they were going to rip the bearings off the car. My understanding is that the MOT test should use gentle force but this machine seemed to be set to destruction testing. Does anyone know how such machines should be used and is such a test expected in an MOT? Having seen the bushes again there appears to be the start of some tearing and I am not surprised if this is what they are subjecting them to. The bushes seem to be designed to have some movement but I would have thought that if they are rapidly twisted, pushed and pulled between their extremes, they won't last long. Is there anyone here who does MOT tests and is familiar with these machines, that can comment please? Are they normally that violent and can the speed and range of movement be adjusted? They agreed to just issue an observation rather than a fail but I am worried that having gone through this aggressive test they will now be compromised.
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post #2 of 5 (permalink) Old 01-03-2017, 10:30
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The suspension testing machine is standard these days. It may appear excessively harsh, but no more so than when the car hits a pothole at speed. I replicates the real life stresses far better than manually rocking the wheels or levering the ball joints with a screwdriver. If you can see signs of cracking in the rubber bush, it needs replacing. The age is irrelevant I'm afraid. Only fit OEM quality rubber bushes.

TC
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post #3 of 5 (permalink) Old 01-03-2017, 19:05 Thread Starter
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Thanks for your thoughts TC.
I am thinking of putting some string in a loop round the arm by the bush and behind the mounting, so that it allows the arm to move about 1/4 inch, which appears to be the intended movement. I can then drive the car for a while and see if the string breaks. If it does then clearly the arm is moving more than the free movement of the string. This will prove if the arm is moving about under normal driving conditions.
It seems to me that the automated test is much more arduous than a manual one and in the future I shall stick to a smaller garage for my MOT that does not have an automated test facility, in order for the car to not be stress tested.
I try to avoid holes and ramps in the road or drive slowly over them.
Having had this experience I think back to when I had a Hillman Avenger many years ago. It failed its first MOT test due to loose tie bars. These were mounted onto the front cross-member with a foam bush. I changed both for new Hillman ones and both were flat as pancakes within about three months! Certainly would not have passed retest even with new ones on one of these automated tests.
Cando
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post #4 of 5 (permalink) Old 01-03-2017, 19:28
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These testers have been used on HGV tests for many years and as said above, they simulate "real" forces. I have recently replaced my wishbone bushes (which also "looked" OK) and there was a massive difference between new and old. The old ones were full of micro splits, which, during disassembly ended up shearing. The old bushes had allowed the metal parts of the bush to rub together under load. My car is an 05 reg and has only covered 66k miles. I have also had to replace the lower engine mount, which was also full of micro tears. It seems that these rubber bushes deteriorate over time, aswell as mileage.
Mike
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post #5 of 5 (permalink) Old 01-03-2017, 20:18
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We use the single tester lanes now, you just put car on plates, push the button, look at the bushes etc job done. There's no human interaction on how much the plates move or anything. MOT's are slowly getting harder thats why older cars are getting more difficult to get though. How much play which is acceptable is still of course down to the tester
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