On or around Mon, 13 Jun 2005 16:10:23 +0100, Marc Draper enlightened us thusly:
aye. Discounting the possibility that something was on the verge of failing anyway, I spose, and the act of braking with the transmission brake overloaded something already-weak in the transmission. But that's a very long shot.
On or around Tue, 14 Jun 2005 00:12:45 -0000, "Alan Morris" enlightened us thusly:
was this the incident on the road?
If so, then the CV joint was worn/damaged beforehand, very probably. Front brake test doesn't load the CV joints. If the diff lock had been engaged in the centre diff, then the brake tester would have immediately showed this. Could have damaged the diff or the difflock, but not likely the CV joint, IMHO. The CV joints are pretty tough.
I'd not actually rule out the possibility that the CV joint was damaged, but it is, IMHO, extremely unlikely. Nor would damage to the centre diff or difflock affect the CV joint.
The only brake test that can damage things in the rear half of the transmission is the handbrake, which is of course a drum on the gearbox. Thus the REAR half of the transmission is put under (possibly excessive) load by hauling on the handbrake. Front brakes, however, work on the wheels and put no load on the transmission, UNLESS the centre diff was locked, which there would be no need to do. Still, I doubt if such loads would damage a CV joint unless it was already weak, more likely to damage the centre diff or the difflock.
CV joints in "straight" position are pretty strong.
Normally when the vehicle is placed in the rollers both rollers a run together to straighten up the vehicle if the diff lock had been in and the hand brake applied then yes the dials would have shot up or if the roller not being run locks (some do to help you get out) again this would have had the same effect But as SimonJ said it would have shown itself imediately the rollers had started turning The question is who put the diff lock in? A chap tried this on me because he had a faulty rear brake that wouldn't show itself on a tapley (decelerometer) test but did on the rollers
Or there is a pressure limiting valve on the rear brakes
The wheels are not driven by the engine during the brake test !
The front axle should be a lot higher in reading than the rear !
If the centre diff was engaged then the front wheels would either not turn because the hand brake was on or it would just pop out of the rollers because the rears would turn as the fronts were driven by the rollers.
I find it very hard to believe that the rolling road can but the transmission under more load than the car can itself when under general usage especially a Discovery. The CVJ are hugely strong.
The reason your tyre was flat spotted is because your CJV locked up other wise the other one would have had a flat spot too !
If the bushes have play in them then they need changing
I do think your failure was more bad luck than MOT damage.
To make a comment as you did regarding the death of his son was unnecessary on a public forum !
The vehicle handbrake is for holding the vehicle when parked, but it is also an Emergency Brake. As such, it needs to be tested to prove it is capable of bringing the vehicle to a halt when required.
The transmission handbrake can be tested on rolling roads. There is a procedure outlined in the MOT Inspection manual to perform this test.
Both rollers must be run together. The handbrake must be pulled up very s-l-o-w-l-y while holding the release trigger in. The tester will know what readings to expect to see, and as soon as these readings are attained, then the brake should be released.
The readings are 16% for dual circuit brakes, and 25% for single circuit. Using a vehicle of 2000kg as an example, this equates to:
16% = 320kgf (or 160kgf per rear wheel) 25% = 500kgf (or 250kgf per rear wheel)MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.