My truck is due for its first mot under my ownership in a few weeks time. For some reason the idea of the VC being a problem when testing the brakes entered my mind. Is there a special procedure for testing the brakes that I should warn the dude about. Over hear we have to bring into a DVLA MOT center ( not the dodgy back street garages like in england!) I should mention that my cause for concern is that when they put the front or rear wheels on the rollers will it pull out or damage anything in the transmission?
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VC at MOT test.
- Thread starter IRLGW
- Start date
This one has been done to death in the past. My local place where I have been going for 30 years, puts it on rollers and does the test in seconds. There no real danger of damage - hell it's nothing like what it gets when I am off road. They know what the truck is and they can see if the brakes work or not.
But they should use a decelerometer and drive up and down outside in a more scientific way. Do I know my truck is safe and legal, yes I do. That's about as much as I need to know. But is it the correct procedure, no it is not. Is it going to damage it doing this once a year, no.
Chris
But they should use a decelerometer and drive up and down outside in a more scientific way. Do I know my truck is safe and legal, yes I do. That's about as much as I need to know. But is it the correct procedure, no it is not. Is it going to damage it doing this once a year, no.
Chris
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It's always nice to be able to second an opinon and put someones mind at rest. I had my MOT done yesterday and was reminded of how the brake test is done. The engine was not driving the tranny and the rollers were turning very slowly. I can confirm there is no chance at all that the VC or any other part of the tranny can be damaged. Not even the synchro 
.
Frank
.Frank
Good Job. I was thinking that it might send drive to the front wheels and cause it to jump out of the rollers or something. I can't say I notice the difference the vc makes when in low grip situations. I certainly have to bring on the cdl much sooner than I would have done in my landrover say.
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They do have to rev it up a bit to make it drive out of the rollers but nothing like enough to engage the VC let alone break it. You could ask them to use the centre diflock to make it a million percent sure. Chris?
Frank
Frank
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Cptsideways
Well-Known Member
A tight CV will result in it popping off the rollers 
I don't know if there is any variability in the VC's of these old buses but mine most certainly gives a goodly amount of drive to the front. I know 'cos I drove it around the village with no front prop and the diff unlocked. It was only a really steep bit that brought me to a halt. When I am off road, I sometimes stick the locker in just to save the VC doing its nut. In my mind this makes sense. I dont' want to overheat it and put all that heat into the tranny which is not going to get much cooling at 1/2 mph as I plug around. Much of the time I don't need it in, it goes fine.
Chris
Chris
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REMEMBER !!
Only use the difflock to get the car out of the rollers then disengage it and make sure it is disengaged otherwise testing the brakes will end up with a brocken tranny or MOT station.
As Chris says ther is plenty of drive to get off the rollers so perhaps not use the difflock.
Frank
Only use the difflock to get the car out of the rollers then disengage it and make sure it is disengaged otherwise testing the brakes will end up with a brocken tranny or MOT station.
As Chris says ther is plenty of drive to get off the rollers so perhaps not use the difflock.
Frank
Actually driving on and off the rollers with all the lockers disengaged of course is and interesting test of the VC. With the rear wheels in the rollers, the only grip you have really is with the front. If they pull you out then your VC is doing a good job. I think that they have a way of locking the rollers though to get single axle drives off. Usually it involves a few revs though. I would like to see a Landrover do this - not bashing the Oval, just interesting to see what happens with a completely open diff. By rights the back wheels should just drive the rollers and the vehicle remain static. Mine is actually due and I shall ask them specifically to try to drive out with front wheels only. I may video it.
Chris
Chris
I think that I covered that Toby by saying that they have to give it some revs to overcome the rollers. If they tried that on tick over, they'd not get out, I'm pretty sure. The rollers spin like a freespool on a winch, but there is a point at which they can't be driven any faster by the tyres and that's the point that you pop out. I shall ask them to pull forwards slowly and see if it climbs out using front wheel drive.
This way, you seem we learn stuff. Stuff is good.
C
This way, you seem we learn stuff. Stuff is good.
C
Red Oktober
Well-Known Member
umm ....when i had the mot done on our 80 ... they didn't put it on the rollers to test the brakes, ... they just hammered it down the industrial estate road and jumped on the brake peddle to see if it stopped in a sensible distance. ...which it did.
was that the wrong way to do it then ??
was that the wrong way to do it then ??
just been going over some of the comments again but not sure we are all on the same concept! My concern was that if the rear wheels are in the rollers and the front are not....then will spinning the back wheels on the rollers send power to the front wheels via the VC causing it to pull fwd? Then if this was to happen and the dude was to apply the brakes would that then damage anything?
Does it make more sense to test a VC equipped truck with the transfer box in neutral?
I think it will drive off the rollers ok when finished.
Does it make more sense to test a VC equipped truck with the transfer box in neutral?
I think it will drive off the rollers ok when finished.
Dude - chill, no. It doesn't happen. Anyway, they are testing the brakes , where's it going to go? They don't spin it up to 70 mph and drop the clutch. If it DID pop up out of the rollers (which it won't) it's not in gear so it's not going anywhere.
C
C
Towpack
Well-Known Member
Yes. This test will tell you (or the tester) nothing about brake balance. You could have one wheel at 100%, another at 60%, etc, etc, but you'll still stop in a 'sensible distance'. A belt and braces approach to brake testing IMO.
