solid brakes

[leslie1961]

Hi everyone,hope someone can help.I have a 1991 transit luton,ice cream van,converted from petrol to diesel.When i started the van this afternoon i noticed as i pressed the accelerator their was a high pitched whirling noise that rose and fell as i increased or dropped the presure on the pedal,then the brakes became almost solid and usless.Any thoughts would be great as i cant afford to take it to a garage at the moment.

[madmark]

sounds like your servo is gone!

[leslie1961]

Thanks for the prompt reply,i dont like the look of that sad smily thingy,how much would this cost me to fix,thanks in advance.les

[Vee4]

You may have sorted this out by now but one thought: how long ago was the conversion? The diesel engine will have a vacuum pump, probably on the back of the alternator. If the conversion is untidy, there could be a vacuum leak if the hose is joined or bodged, and that would cause the whistling noise and lack of servo assistance.

[leslie1961]

Thanks for the the reply Vee,the conversion took place years ago,to put you in the picture,im a complete novice when it comes to repairs and can no longer afford to keep shelling out for a mechanic.So im going to have a go myself,I suppose the best way would be to get hold of a manual.But i need to know what is causing the problem or im wasting my time,ive looked on a parts site and second hand servos are 40 to 50 quid which i can stretch to.
Is the repair an easy one?
Thanks in advance les.

[Vee4]

I guess this is the manual you need, indispensable for the DIYer:

http://www.haynes.co.uk/webapp/wcs/stor ... &langId=-1

There are some checks you can do to see if the servo is working normally, described in the manual. If the engine has been running, there should be a vacuum 'stored' in the servo diaphragm chamber so if you stop the engine and listen carefully, you can press the brake pedal and you should hear a hiss or some evidence of air movement each time from the pedal area. After 3 or 4 presses, the stored vacuum will be exhausted. If you then rest your foot on the pedal and start the engine, the newly-created vacuum should pull the pedal down noticeably. This is the response of a normal unit.

The servo is a mechanical amplifier, using the relatively low pressure differential across the large area of the diaphragm to produce a much higher pressure in the relatively small bore of the master cylinder. Here is a link to some good drawings of a basic system:

http://www.autoshop101.com/forms/brake05.pdf

Give yourself an A* if you answer all the questions!

If you think the servo is not working as it should be, and you have eliminated other possible problems (e.g. is the vacuum pump working?), then madmark is right. I used to buy service kits for my old vans, with the seals, valves, etc., but these days I'd be inclined to replace the whole thing.

[leslie1961]

Cheers V,very helpful i will let you know how i go on,ill tackle this at the weekend.Again cheers mate.

[jezwild2001]

I've had this on my 2.5 di smiley. It was the vacuum pump on the back of the alternator dying. The whirring noise was probably the vanes inside it breaking up, And a lack of vacuum pressure will give you a hard peddle and useless brakes.

[Vee4]

As jezwild2001 says, and I stated in the above posts, you should check the vacuum pump before getting involved with the servo. Disconnect the hose and see if it sucks air in while the engine is running - make sure you don't Hoover the engine compartment though! Hold a flat piece of wood or metal over the end of the hose to assess the vacuum.

[leslie1961]

Cheers guys,yep it was the vacuum pump.Not to much trouble to fix..even for me.
Many thanks.Les.