Car Mechanics (UK)

Brake bleeding

- Stephen Gum­m­er­sall Iceland · Austria · Belgium

I have a one-man Gun­son brake bleeder that con­nects onto the tyre and pres­surises the brake fluid to bleed the brakes. It does an OK job, but have you any idea why, on two oc­ca­sions, when I re­leased the pres­sure pipe from the tyre, the bleeder sucked the re­main­ing fluid from the reser­voir bot­tle up the pipe and re­leased it ev­ery­where? I had to get a basin of soapy water to wash the fluid off the tyre and un­der the bon­net to pre­vent last­ing dam­age. I had the same Gun­son bleeder back in the 1990s and it never gave trou­ble, apart from get­ting worn out, which is why I bought this re­place­ment.

The pipe which con­nects to the spare tyre should only go into the cap of the bleeder bot­tle and the pipe to the reser­voir should go to the base of the bot­tle. The rec­om­mended pres­sure to use for bleeding is 20psi. Un­less the bleeder bot­tle was par­tic­u­larly full or the spare wheel was at too high a pres­sure, I can see no rea­son why the fluid would push back into the pres­sure hose and out of the valve at­tach­ment.

As brake fluid can­not com­press, the only com­pressed pres­sure should be the air in the sys­tem. The only sce­nario I can think of where this might hap­pen would be if there was still air in the brake sys­tem which was then com­pressed. When the pres­sure was re­leased that air would force the brake fluid back out and into the bot­tle. But even this should not push the fluid up out of the top of the cap and through the tube which con­nects to the spare wheel.

It is worth not­ing that many space­saver spare wheels do run at a far higher pres­sure and, if using the Gun­son bleeder with one of these, the pres­sure should be dropped sig­nif­i­cantly.

 ??  ?? The Gun­son brake bleeder which uses the pres­sure from the spare tyre to aid bleeding.
The Gun­son brake bleeder which uses the pres­sure from the spare tyre to aid bleeding.
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