Hi ,i have simular simtoms to ketts ,failed test three times now [costing a fortune] .I have gone through braking system time after time ,already changed brake linings ,re-sealed wheel cylinders and changed master cylinder although only second hand one ,pressure bled system ,put extra weight in back but still cannot get rear brake lockout. Any ideas would much appreciate.
P/S , Has gone to commercial garrage now ,seems like they are running out of suggestions?

paul, February 2010

Hi I had the same problem changed and checked allsorts and still failed the mot then found the answer and that was to burn the rear brakes by driving along and applying the secondry brake so making the engine pull I did about three mile doing this and it cured it and then passed the test. gone are the days when a good driver is a light braker you must keep doing heavy braking to keep it good mine has been good for 12 months no problem

Laurence Cope, August 2015

Did you ever resolve your issue as I have the same problem with Leyland Roadrunner 1986?

BellaUK, February 2015

air pressure maybe master cylinder faulty

acrrecovery, September 2010

Hi K ,thanks to your help ,i have seen movement on lsv ,i also went down the route of putting a pressure gauge to rear and front brake lines ,i did get different pressure readings ,front about 30 psi rear barely 20psi,would this still indicate master cylinder problem,should they be equal.Is it possible the air servo behind master cylinder weak? PAUL..

paul, March 2010

have you checked load sensing valve ? when brake pedal is depressed you should see movement on lsv if not it could be siezed /faulty

k, February 2010