I have done a few thousand miles in the Luego since it past SVA. in 2008 I noticed last summer that the rear brake discs were a little rusty but didn't think to much of it.

Recently I changed the brake fluid and used an easy bleed system that runs off the spare tyre pressure to do it. There were no obvious signs of any problems.

Today, during the MOT I realised that the back brake light is not working as well.

The balence bar appears to be working as it should. There are no leaks in the system.

So I think it might be the master cylinder. Is there a way to service them if this is the case? If it is not the master cylinder then any suggestions welcome the cause of the problem?

Cheers
Steve

On your pedal box do you have washers each side of the brake pedal?

On mine i bent one of the push rods going into the mc

Are your calipers mounted so that the bleed nipples are at the top? It might be worth slackening the handbrake cable right off so the caliper lever is fully returned then unbolt the caliper without disconnecting the cable or brake hose and wind the piston out slightly to take up any clearance between the pads and the disc. Do not wind out too far so as to cause the brake to bind, refit the caliper and then give the foot brake a few pumps before adjusting the hand brake. Chances are the caliper auto adjusting mechanism isn't working

Just to clarify, it failed the MOT due to having no braking effort on the rear?

Do you have any brake pipes which run under the chassis and may have been crushed?

I take it you have a hydraulic switch which is operated from the rear circuit?

Regards
Davie

I maybe wrong but I think master cylinders are duel action. ie if the rear developes a fault a ballbearing moves across in the mastercylinder and only allows braking on the front. If you bled them maybe the mastercylinder has gone into fault mode. Maybe there is something in the Haynes manual or try bleeding again with someone sitting in the car, get them to hold down the brake and then release the bleed nipple under pressure then bleed in the normal way. Be sure to get a nice tight fitting bleed tube and mind your eyes. Barry

Just to clarify, the brake light switch operates from the rear circuit and is located towards the front of the transmission tunnel. As it is not working I am convinced that the problem lies between that and the pedal. The balance bar set-up appears to be operating correctly and certainly doesn't look like it has changed since the SVA test but I will definitely check the mc rod for its operation. Does this shed any light on the matter?

Is your rear master cylinder fully returning after being pressed?
If not then you will not get any fluid movement on subsequent presses.
At a guess you have the pushrods to the cylinders not at the correct length.
I'd dis assemble the pedal and push the rear master seperately to check it

Most likely cause is you haven't set the balance bar mechanism up correctly.

(1) Make sure you have enough side clearance between the trunnions and the tube welded to the pedal that houses the spherical bearing --- the balance bar needs some free angular movement to work.
(2) Check the push rods are not screwed out ---- the master cylinder pistons need to be able to come full back to the rest position.
(3) Bleed the rear circuit for just a couple of pumps of the pedal using the old fashioned method --- systems with Girling master cylinders are easy to bleed.
Eezibleeds are great devices but if using one you need to pump the pedal a couple of times during bleeding to prime and clear air out the master cylinder.

(4) If Sierra or VW style callipers check the handbrake cable is not too tight and "choking" the self-adjusters.
Slacken the cable right off, and with the handbrake off pump the pedal.

(5) If none of the above check the pads are stuck in the calliper.


Other points
(I) Brake light switch should be worked by the front brake system --- an obscure but sensible bit of the law that is often not known about even by vehicle inspectors and traffic police.

(II) If to get a brake balance you have to set the balance bar more than a few turn off centre you should consider changing the bore of one of the master cylinders to bring closer to the centre.

(III) Brake balance bars systems really aren't a great idea for anything other than serious track use, for road use a tandem duel circuit cylinder (Fiat or Fiesta) is a much better idea.




[Edited on 2/4/10 by britishtrident]

If your rear calipers are mounted like the Indy you need to take them off to bleed them as the bleed nipple will be at the bottom NOT a the top, and no amount of bleeding will clear an air pocket from the caliper also worth noting the brake switch needs to be pointing downwards otherwise youwill get an air bubble in the switch part which will prevent it from operating properly

tony