96 bighorn brakes problem

[fabio86]

Hi everybody, I am fixing bits and pieces on my 96 bighorn xs plaisir for the next wof, I am trying to figure out a brake problem that is making me go mad. Brakes work ok, maybe a bit weak, but every time I step hard on the pedal I can hear a loud high pitch whistling noise coming from where the brake booster is. Also when I push on the brake pedal to change automatic trans from park to gear or reverse, I can hear a whistle, usually only right after starting the car in the morning. It sounds like a vacuum leak to me but vacuum lines between alternator, vacuum tank and brake booster seem ok. I have found somewhere on the internet that replacing a faulty booster vacuum valve can fix this whistling sound. Problem is I cannot find the valve. On the manual it says that it should be inside the pipe between the brake booster and the tank, I have removed that hose and also the one between the alternator and vacuum tank but couldn't find the valve anywhere. Does anybody have any idea where that valve could be? Could it be missing? Also does anybody have any idea on how to fix that whistle? Thanks for your help!!

[geeves]

both my wagons do this from time to time. The wizard has been doing it for years. I also keep meaning to ask about it.

[fabio86]

Sounds like a common problem, would be interesting to know if anybody got the same problem fixed. Could my car somehow just be missing the return valve? Maybe it was replaced with a regular hose by previous owner... all that the repair manual says is that it should be inside the hose... the manual also says that if the valve lets air trough both ways it needs replacing. Does anybody know where else it could be? Thanks

[fabio86]

Also would my car fail the wof because of that whistling noise? How do they actually check the brakes? Thanks again

[geeves]

Mine does it the first couple of times the brakes are used and it happens more if the car has sat a few days. A sticky non return valve could easily be the cause but its inside the booster. My wizard did also suffer no brake assist for up to 5 minutes after starting which was fixed by fitting a non return valve out of a petrol car at the wreckers in the vac line.

[isuzurob]

the diaphams in the boosters split causing hissing and bad brakes, ive replaced a few in ubs55 bighorns

[fabio86]

Thanks geeves and isuzurob, I will try to replace the booster and non return valve and see if it fixes the problem. Cheers