Yes that seems to be he case, I'm fairly good at mechanics but never had a retest fail again
Rear wheel balance has become a major test issue recently , i had my first mot fail due to it . I think it has always been an issue , but recent developments in technology has mean't its easier to test individual wheels . Basically the machine deems one wheel will lock before the other , and could lead to the vehicle pulling to the strong side . The aim here is to get both wheels locking at the same time .
Now before you start anything , securely chock both rear wheels , and put the vehicle in gear . You will find at this point , it's an advantage to slacken the wheel nuts on both rear wheels , but you already know this don't you , then jack the rear of the van up enough to remove both wheels . Release the hand brake fully , and once your happy the vehicle is secure , you can now remove the wheels . Next slide under the van , and fully release the handbrake adjusting nut . Brake adjustment can be a pain with this in tension (please don't ask me how i know this) , plus the cable may not centralise which of course will add to the imbalance .
Okay , so i'm gonna stick my neck out here and say the main problem wheel , will be the one where you replaced the wheel cylinder . You probably had to fiddle with the adjuster to get the hub back on , and never readjusted after you had . If you had , the chances are you wouldn't be asking the question !
Right , so taking the hub off , you will see the shoes set in the vertical orientation with the , in your case , replaced wheel cylinder at the top yeah . At the bottom you will have a post that the shoes sit in held in place by a long spring . Yes i know there are clips that hold these in place as well , but lets just ignore them for the present okay .
So at the top , just below the wheel cylinder you should see a strange piston like arm , along with another spring . That cylinder should look something like this ;
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Okay so it won't let me upload an image , so we will have to go this way .
This is the self adjusting mechanism , and the bit you need to adjust ! . Now it maybe better if you take the hub off and take a look at this thing , even check that it will adjust . My guess is it will , and probably the bit you upset to replace the hub . The cog to the right of the image is the actual adjuster part , it turns on a threaded shaft so should turn freely . The two metal plates you can see in the picture are a lock which will only allow the cog to turn in one direction to prevent it unadjusting , so you will need to gently prise these out to unlock the the cog to turn it back . Notice as the cog is turned the two forks extend or retract . Mine were very stiff so i replaced them , but then i replaced a good 90% of the rear braking system as well , so don't be too surprised . Yes i had a failed wheel cylinder as well , found it while replacing , would you believe , the wheel bearings .
Now the next bit is really fiddly , so prepare yourself . To adjust you need to slip a tool through one of the wheel stud holes in the hub and turn this cog to achieve the adjustment . I used a small hooked tool , so you will need to find something similar . A second tool i would strongly suggest you source , is a fish scale . This is how i balance the braking effect , and i used something similar to this :
I've had them for years , and proved it ideal for the job . You won't get a perfect balance , but it will be within the 10% required to pass the test . I think my first attempt was something close on 94% , leaving a 6% unbalance . My last test value was a 2% unbalance , at 98% .
So now replace the hub , and line up one of the wheel stud holes over the adjuster cog . This will be a faff , but you must be able to turn the cog inside with the hub in place . To help , you should be able hear a click as the lock engages the new indent on the cog . The correct way to do this job , is to lock the hub , then slacken the adjuster off , so the wheel turns with just light binding . With this set up i do it the other way , adjusting up , instead of down . Totally down to the lock , it really is a faff to release the lock plate . Once you have the wheel lightly binding , place a wheel stud in a lower hole on the hub . Hook the fish scale on to the stud and and tension until the wheel just begins to turn . Now repeat the process on the other side , until you have the same value , and your wheels will now balance . But here we have a problem , you will have to make the call as to when the adjustment is right . Too little , and you will have weak brakes , too much and they will be deemed as binding , also an mot issue . Personally i allow the brake to bind a little , the run to the test centre beds the shoes . When your happy replace the wheel , and retest with the fish scales .
Now you can readjust the hand brake cable , set the lever to the fourth notch , and tighten the adjuster till both fully wheels lock up .
