Souster Posted July 15, 2014 Share Posted July 15, 2014 Hi there. Parked my 300tdi 90 on a slope this morning next to a wall. Started the engine, released the handrake with my foot on the foot brake and allmost rolled into the wall. There was no servo assistance what so ever. The servo assistance comes back after about 10 seconds after the engine is started, which i know isnt right. And then the brakes work fine. How do i test which component is at fault? Could it be the servo, or the vacuum pump? As added note, when washing down the engine bay yesterday, once the engine was turned off, i noticed a hissing noise from round the servo area, wasnt sure if it was the servo or vacuum pump though. Any help would be great, abit scared of driving it now incase of failure of the brakes. Cheers Quote Link to comment Share on other sites More sharing options...
Jim1 Posted July 15, 2014 Share Posted July 15, 2014 I've been told put foot on brake and start the engine the foot brake should go down this confirms servo is fine. Have to admit this was fine on mine so changed the vacuum pump still has hissing noise but now servo suspect? ( my vacuum pump was leaking oil which is why I changed it) Quote Link to comment Share on other sites More sharing options...
oneandtwo Posted July 15, 2014 Share Posted July 15, 2014 Open the bonnet and inspect the brake servo - the 300tdi/td5 servo seems to crack around the curve of the servo near the right hand mounting bolt. I have had three do this now. The crack can be hard to see as they are only hairline cracks but if you run the engine and rub some spot around the area you will see the spit get sucked into the crack. Quote Link to comment Share on other sites More sharing options...
Souster Posted July 15, 2014 Author Share Posted July 15, 2014 Yeah i allways do that test. But how can you tell if its the servo or the vacuum pump? I pulled the pipe off the servo from the vacuum pump and it is sucking air. Im not sure how much its supposed to be though? I then plugged the pipe back i to the servo, and had no servo assistance for about 15 seconds. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted July 15, 2014 Share Posted July 15, 2014 As mentioned in post #3: the "tin can" part of the servo fatigue-cracks round where the master-cylinder bolts on - allowing air to leak in. Depending on the size of the leak this can either delay, or prevent altogether, the vacuum-pump getting the servo up to full 'suck'. When the engine stops, so does the vacuum-pump - and then after a time (depending on size of leak) the vacuum will all have been dissipated. It then takes a while after restarting the engine for the pump to suck out this leaked air and give you proper servo-operation. I think you need a new servo. A temporary fix can sometimes be made by removing the master-cylinder and sticking a piece of duct-tape over the servo to cover the crack, the m/cyl hole and its bolts, then using a sharp knife to cut out the holes before refitting the m/cyl. Quote Link to comment Share on other sites More sharing options...
Souster Posted July 15, 2014 Author Share Posted July 15, 2014 Cheers guys I'll give your suggestions ago. So its very unlikely the vacuum pump is at fault? Theres no way they can work hit and miss? It does seem to be oily under the pump, infact i think it maybe leaking. But its deffo sucking from the pipe. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted July 15, 2014 Share Posted July 15, 2014 Again. Post 3. The servo cracks easily near the master cylinder. You might need a torch to see the crack. As mine will soon need changing. Will an early Range Rover Classic or a Discovery servo fit ? Thoughts ? Quote Link to comment Share on other sites More sharing options...
oneandtwo Posted July 15, 2014 Share Posted July 15, 2014 Earlier servos and disco ones don't fit - new correct Trw ones are only £60 or so. For reference, I actually have a 1998 110 with a cracked servo here awaiting me scrapping it. Quote Link to comment Share on other sites More sharing options...
Souster Posted July 15, 2014 Author Share Posted July 15, 2014 Cheers guys. Ive had a good look, but cant see any cracks, allthough there is abit of rust around the bolts for the master cylinder. I spose this would explain the hissing noise after i washed down the engine bay and turned the engine off!? Quote Link to comment Share on other sites More sharing options...
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