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Car Forum / Audi Cars / November 2007hydraulic system problem
Hi all, car is a 1994 UK coupe 2.6 auto, 115k miles. A year ago, I made the mistake of putting brake fluid in the power steering fluid reservoir, I realised the next day and drained the fluid, replacing it with regular red steering fluid - another big mistake. 2 weeks later the car dumped all of it's fluid, and my garage diagnosed failure of the power steering pump. They replaced it, and since then the car's been fine, but the brake light flashes for up to a minute on a cold start. On a warm start it doesn't flash. Also the steering occasionally creaks. A couple of months ago the car was MOT'd, and the rear brake pads changed, no other problems reported, and this is a reputable garage, I trust them. Another point is that I've researched this, & tried the brake 'bomb' test - switching the engine off, and pumping the brake pedal - it takes over 40 pumps to go hard. Any ideas what's causing the flashing light? Many thanks, J. > Hi all, car is a 1994 UK coupe 2.6 auto, 115k miles. > A year ago, I made the mistake of putting brake fluid in the power [quoted text clipped - 15 lines] > > This may be entirely too obvious. Have you checked your brake fluid level? Not familiar with your particular model but could it be a failing component of the ABS system? > Any ideas what's causing the flashing light? Not offhand. Lift the front, start the engine, and turn the steering lock-to-lock half a dozen times. >the brake light flashes for up to >a minute on a cold start. On a warm start it doesn't flash. [snip] >Another point is that I've researched this, & tried the brake 'bomb' >test - switching the engine off, and pumping the brake pedal - it >takes over 40 pumps to go hard. I am not sure about your model, but on the earlier models, the warning light can have three possible causes: 1: Low brake fluid level. 2: Low hydraulic oil level. 3: Low hydraulic pressure. I'd say your bomb is slowly leaking. Try the bomb test before you start the engine after a night's rest.  SignatureRoRo > >the brake light flashes for up to > >a minute on a cold start. On a warm start it doesn't flash. [quoted text clipped - 14 lines] > -- > RoRo Hi Robert, I tried the test this morning, after leaving the car over night, and the brakes were hard straight away (before starting the engine) - does this indicate the bomb is leaking? There's no loss of fluid, the level has been fine for ages. Many thanks, Jamie >I tried the test this morning, after leaving the car over night, and >the brakes were hard straight away (before starting the engine) - does >this indicate the bomb is leaking? There's no loss of fluid, the level >has been fine for ages. Leaking may not be the correct word, but yes, it confirms my suspicion: Fluid is slowly seeping back into the reservoir. Notice how the fluid level is a little higher after the pressure has had time to seep out. Note that the car I used to have is not the same as yours, so what I say might be completely irrelevant: I can think of two possible causes. One is the pump. I that case, however, you'd have to have two check valves fail in a similar manner, i.e. both having a slow leak. I don't think that is likely. The other possible problem is that the brake booster (the one that the brake pedal activates) has a slow leak so that the pressure from the bomb slowly seeps through the valve and into the return line to the reservoir. To test: Disconnect the brake booster return line from the reservoir and place a jug under the open end, so that you catch any fluid that comes out. Start the engine and let the bomb charge. Don't touch the brake pedal while the return line is disconnected, or you'll make a mess. Stop the engine, note the reservoir fluid level, and leave overnight. In the morning, if there is fluid in the jug and the reservoir level is unchanged, the booster is bad. If the jug is empty and the reservoir level has increased, the pump is bad. If you have other hydraulic components, such as suspension, they can also be the cause of the problem. SignatureRoRo > >I tried the test this morning, after leaving the car over night, and > >the brakes were hard straight away (before starting the engine) - does [quoted text clipped - 33 lines] > -- > RoRo Thanks very much for your help, much appreciated. Is the booster the same thing as the bomb? J. >Is the booster the >same thing as the bomb? No. The booster is the hydraulic actuator that sits between the brake pedal and the master cylinder. It looks a lot like the master cylinder, and is bolted directly to it. The booster has two hydraulic lines connected to it: One is the high pressure from the bomb, and the other is the return to the reservoir. Do NOT disconnect the high pressure line unless you are absolutely sure the bomb is discharged, because the pressure in that line is very high. SignatureRoRo |
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