Hi 2003 T4 Transporter 2.5 @ 220,000kms here. I have developed a loud hissing noise in the cabin over the last couple of journeys which goes completely when I apply the brakes but returns once off the brakes? It sounds like a leaking air hose. No loss of braking effect or any obvious cause or leak. Noise is less obvious inside the engine bay. Anyone had this or any thoughts as to what it may be? Thanks in advance, love this van.
							
						
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Strange brake hissing noise!?
				
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Hi there,
It is possibly a brake booster leak possibly in the brake booster diaphragm somewhere where it meets the brake lever through the firewall. Or somewhere along the brake booster vaccum line to the brake booster. Check booster hose has not popped off or split. Also check there is no brake fluid loss with a leaking master cylinder.
Regards,
Scott
 
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