Brake concern
QI did some routine maintenance on my 2004 VW LT35 LWB high-roof 2.5 109bhp. I undertook a simple disc and pad change on the rear axle. After completing this, I checked the brake fluid for moisture level. The tester showed a small degree of degradation so decided to renew it.
Of course, the bleed screw was totally seized on both the nearside front and offside rear calipers. So, I replaced them with reconditioned items. I pressure bled the system at about 10psi. Made completely sure all air was out and new fresh fluid was coming through.
Got in the cab and the brake pedal went straight to the floor with no resistance at all. Sought a bit of advice and was told it’s probably the master cylinder.
Ordered a new one – it arrived – and I bench bled it, then fitted. Made sure any air was bled from each caliper again. Still no pedal. Bought a guaranteed second-hand master cylinder. Did the same thing and no difference. Changed the ABS pump, no difference. Changed the servo, no difference. Bought the other two calipers, no difference. Tried the traditional ‘two-man’ method of bleeding, no difference.
I bought a new load compensating unit, bled that – no difference. I’m at my wits end and ready to scrap it, but I want to have one last go at sorting it.
It just doesn’t make sense, so can you offer some advice please?
Roger Pool
AI will first say that I know how frustrating brake problems such as this can be. You would expect the process to go quite smoothly and then without warning you are faced with an unexplainable fault. I would also warn that new parts are not infallible and although thankfully not an everyday occurrence, I am still aware of many hours wasted in the workshop due to a new part which has just been fitted!
There are a set number of checks you can follow which may hopefully get you back on track. The first would be to check the mechanical linkage at the top of the pedal, ensuring that it is pushing onto the servo and consequently pushing into the master cylinder is fine. By removing the master cylinder (the brake pipes can stay attached) and having an assistant push down on the brake pedal you can confirm its operation. This may sound a bit obvious, but sometimes the simple things can be overlooked.
Once you are happy that the master cylinder is being operated it can then be refitted, clamp off all four brake hoses and then re-check the pedal. If you then have a brake pedal with a modicum of resistance, the clamps should be removed one at a time to discover what corner of the vehicle the problem is with.
If this does help to determine that one particular corner is the cause of the problem, with the other three hoses remaining clamped, you should attempt to bleed the troublesome caliper.
If no particular corner appears to make any difference to the sinking feel of the brake pedal, then a similar process should be followed by removing one clamp, attempting to bleed that caliper and when a sufficient amount of fluid has been bled-out, then the clamp should be refitted and you should move to another caliper.
With only one caliper/hose allowing fluid through this will give a greater pressure to each circuit and to each individual caliper. It should also be considered that a faulty brake hose can allow air to enter the system without displaying any signs of leakage.
If you still have no brake pedal you may wish to invest in a vacuum brake bleeder. I have often found that sucking the fluid through can achieve results where other methods have failed. This unit http://bit.ly/cm3dbbk is £36 and well worth the money if it does the job.