I did a very foolish thing and tipped some power steering fluid into the brake fluid reservoir. Just a few cc's before I realised that I was pouring out of the wrong bottle.
I immediately syphoned out the reservoir, and flushed the system through with fresh fluid.
Unfortunately it seems sufficient ps fluid remained in the reservoir to contaminate the lines, and a leak has developed under the ABS control unit. I need to fill the reservoir with about 1/2 an inch of brake fluid every 100 miles. If I keep my foot on the brake pedal, it goes all soft and needs filling up faster.
I think fluid may also be leaking out around the brake pistons down at the wheels, but that will (should) be relatively straightforward.
I am taking the car in to the dealer in a couple of days for an appraisal and quote, and expect he will say this will cost $2,000 upwards in parts alone. On a 10 year-old car, this doesn't make a lot of sense.
Since I'm reasonably handy with a spanner, I wonder is it a straightforward job to replace the unit with a reconditioned or junkyard unit? I believe these can be bought for quite a reasonable cost.
Does anyone know of any problems which might arise? Is there a need to recalibrate the unit after fitting? Is there going to be any incompatability problem with the ecu? Would it be wise to change the brake fluid reservoir at the same time?
All advice gratefully received.
The car, by the way, is an Australian (Euro)-spec m.y. 2000 A4 1.8T quattro manual without traction control or stability control and the part number of the Bosch control unit is 8EO 614 111 A. The Bentley manual suggests replacement is simple enough, although the US-spec unit illustrated is different from mine which has all six brake lines on top.
I believe that you wouldn't have any recalibration problems if you use the original electronic/solenoid assembly. The brake pedal sinking under foot pressure would usually be the master cylinder leaking, unless the ABS unit leak is really that bad. It is probably a good idea to flush out the lines, though I'm not sure that plain brake fluid dissolves mineral oil. I'm also surprised that oil would have such an effect on the rubber seals. To do a really complete job, you might have to disconnect all the brake lines at the calipers, and with the ABS unit removed, flush the lines with industrial-grade isopropryl alcohol, then blow them out. The calipers may need to be dissembled and washed, including the reservoir.
Thank you for this useful advice. The leak is definitely coming from the ABS unit as there is a small pool on the garage floor directly under it (and there is no corresponding pool inside the car under the master cylinder!)
It seems the leak may have been happening before I tipped in the hydraulic fluid as it would otherwise presumably have affected the m/cylinder as well as the caliper seals. The dealer told me failure of the pump seals on the ABS module is not unknown, and looking back the car had just been serviced so the m/cylinder should not have needed topping up.
Other posts suggest that the electronics on some Bosch units will need recoding (through VCDS), but the Ross-Tech list of part numbers suggests mine is a simple swap-over.
Luck has been with me on this one as ECS happens to have this part on sale at $249 (regular price over $1100), and the Australian dollar being very strong at the moment against the greenback it's as cheap as it could be. I think I'll order a second one as a backup...
Your comment that maybe the leaking was prior to the addition of a small amount of hydralic oil makes sense to me, in fact I think my first suggestion of flushing with alcohol may be overdoing it. I'd still give a couple of thourough changes of brake fluid, go through a liter or so. I searched for anything on the effect of brake fluid mixed with mineral oil, but no luck. I think you'lll be fine with your current plan.