M.O.T.Disco Fail.

Hi my 200 tdi has just failed the m.o.t it passed every thing except the rear brakes,they are only 47% when they should be a minimum 50%. I have put new pads on, cleaned the the callipers, no jammed pistons, in and out freely, anyone have any ideas. Possible pressure regulator according to the tester. GEOFFO.

May be wrong.... but I believe the pressure regulator part of your brake system is taken care of by the master cylinder so thats where your problem lies.

There are two types of braking circuits primary and secondary and it dependes on the year of your disco what happens in relation to what brake is operated and from what circuit, this info is explaned in detail in the repair manuals

Or it could be a small blockage in the pipe/s for the rear brakes (doubtfull) u would bleed the rear brakes first.

U should aim for a lot higher than 50%, discos a not the best stoppers even when new.

Regards

Just a thought , when did you last change the brake fluid ? it does degrade over time and often gets overlooked , not sure but it might make the difference you need .

geoffo said:

Hi my 200 tdi has just failed the m.o.t it passed every thing except the rear brakes,they are only 47% when they should be a minimum 50%. I have put new pads on, cleaned the the callipers, no jammed pistons, in and out freely, anyone have any ideas. Possible pressure regulator according to the tester. GEOFFO.

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Mine 300 failed on rear brakes last test, just changing the pads sorted it.

Once spoke to a bloke that did a braking mod on the 200 master cylinder, reckoned afterwards that he could stop on a six pence!! Can't remember what it was though! Soz!

Changed the fluid last year,the system is the type that has the diagonally opposite wheels working if one fails,it does have a pressure regulator under the mastercylinder

geoffo said:

Changed the fluid last year,the system is the type that has the diagonally opposite wheels working if one fails,it does have a pressure regulator under the mastercylinder

Click to expand...

So it does, Pressure control release valve-brake NTC6868L

Also in my book early models have one piston only in each of the front calipers on the primary circuit and the remaining pair of pistons in the front calipers with the rear on the secondary circuit (just like the 3.5 RRC)

On later models the primary circuit operates the rear and the secondary operates the front.

So is there is now a third braking system available.

Thanks for the links I will try the pressure regulator it sounds like its the problem, I will see how much I am going to parted from,I cannot grumble it has sailed through for the last six years.

Ok I guess I must be lucky mine ge tested with a road test and visual examination

How were the brakes tested on the road or on a four wheel roller setup?

On a four wheel rolling set up,its the only thing I cannot check,it stops on a sixpence,even the tester said the front wheels looked up on test.