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Impreza's and brake testing.....The definitive answer....

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Old 28 August 2014, 11:41 AM
  #61  
Carnut
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Originally Posted by hodgy0_2
not if is an open diff - try it, jack the front wheel(or rear) up and try and turn the wheel

if you can (which on most Scooby's you will) - then you have an open diff - all torque is going to that wheel - whether by your own efforts or the engines
)
I thought that it works the opposite way, if a wheel loses grip (or in the air) then the power goes to the other wheels.

I await to be corrected.
Old 28 August 2014, 12:22 PM
  #62  
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Originally Posted by chris j t
I thought that it works the opposite way, if a wheel loses grip (or in the air) then the power goes to the other wheels.

I await to be corrected.
it only works like that if there is some form of "limited slip" between the spinning wheel and the wheels with "grip" - irrespective of whether you have 2/4/6/8 wheel drive

as I said in an earlier post, in reality the issue is with the amount of "slip" allowed in the drivetrain

open diffs allow 100% slip - that is why you will be able to turn the wheel that is in the air - all power/torque will go to the spinning wheel
Old 28 August 2014, 01:07 PM
  #63  
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Originally Posted by G27
I asked my MoT man about this yesterday, prior to seeing this thread, and for 4WD he uses the decelerometer.

They only test 2WD cars on the rollers, and one time a Golf 4Motion was tested on there it damaged the grip coating on the rollers, not the car.
There's a first.
Hope the garage didn't try to make a claim off the owner
Old 28 August 2014, 01:12 PM
  #64  
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Originally Posted by hodgy0_2
it only works like that if there is some form of "limited slip" between the spinning wheel and the wheels with "grip" - irrespective of whether you have 2/4/6/8 wheel drive

as I said in an earlier post, in reality the issue is with the amount of "slip" allowed in the drivetrain

open diffs allow 100% slip - that is why you will be able to turn the wheel that is in the air - all power/torque will go to the spinning wheel
Ok, understood now.
Old 28 August 2014, 05:57 PM
  #65  
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This is where it gets really confusing. Which Imprezas have fully open diffs?
Old 29 August 2014, 12:25 AM
  #66  
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Originally Posted by terzoscooby
This is where it gets really confusing. Which Imprezas have fully open diffs?
Exactly the central point !

Hodgy0_2 has said how to find out what sort of diff a car has.
Anyone can carry out that test.

But would you really want to?
  • If it is locked you'd HAVE to find a garage that knows and uses a decelerometer;
  • If it isn't you've still spent time and effort testing it.
The guaranteed way to save that effort is just to go to a garage that knows and uses a decelerometer.

One call to an MoT station:

"Hello, MoT's R Us"
"Hi, I've got a Subaru. Do you use a decelerometer to test cars?"
  • "Yes we do (if it's 4 or AWD)"
    "Fine - can I book mine in please"
  • "Pardon?"
    "Sorry - wrong number".
Old 29 August 2014, 09:15 AM
  #67  
G27
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Why not simply insist on decelerometer for all Impreza?
Old 29 August 2014, 12:15 PM
  #68  
hodgy0_2
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funnily enough I have spoken to two MOT testers (one who's opinion I value extremely highly)

and they both said they would not put on rollers, not so much for the technical reasons - but simply as people have said for commercial and risk mitigation reasons

VOSA clearly states MOT tester are liable
Old 07 September 2014, 08:45 PM
  #69  
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Ahhh,but what if the test station had a plate brake tester as opposed to a tap meter......
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