I have a 1997 landrover disco 1, 4.0L V8, 4x4, manual.

I had a small brake fluid leak, turns out it was the pressure combination valve(proportioning valve), and I was negligent, so I just kept on topping up the fluid every week or so.
After a while, I noticed that it had stopped leaking and the fluid in the reservoir had began to become discolored. A couple weeks after, I completely lost brakes. So I took it in, and the contaminated
brake fluid had knocked out the master cylinder. (according to the mechanic, it was contaminated with power steering fluid) To my knowledge, I had never made the mistake to put power steering fluid in the brake reservoir.
Anyways, I swapped out the pressure combination valve and the master cylinder, we bled the system, and all was well with the brakes, no leaks and excellent braking(rear and front).
A couple weeks later, I began to notice the discoloration in the fluid reservoir again, I went for a long drive and on my way back, I lost brakes completely again.(I'm assuming that the master cylinder's seals are gone again).

So what is causing the contamination of the brake fluid? I haven't topped up fluids since the last bleeding and there is no signs of leakage anywhere.

 

I’m failing to understand how power steering fluid could possibly get into the brake system, or how the mechanic knew it was PS fluid. Power steering and ACE share a reservoir but I can’t think of anything they share with the brake system. There are others who know a lot more about this system and may chime in.

 

Update, I just noticed that DOT3 brake fluid was being used, instead of the recommended DOT4.

And I inspected the brake fluid yesterday and it was light tint green.

 

DOT 4 is the recommended fluid, but it’s very compatible with DOT 3. I doubt that that’s your issue. Does this confirm that it’s not mixing with power steering fluid?

 

First, there is no way that the power steering fluid and brake fluid mixed. Any contamination would have been from someone who adding power steering fluid into the brake lines. But, that may not even be the problem because both of these types of fluids are hydraulic fluids and work under some form of pressure.
If you have already replaced your master cylinder then, I wonder how that could continue being the problem. Instead, I would want to know about the brake lines and the calipers. The calipers have dust covers on the tops of them to prevent dust and other particles from getting in. But, they are rubber rings. They get brittle and crack after time - especially with an '97 Disco (I have a '98 and completely rebuilt the entire brake system). I would start there and work backwards. If the calipers are not leaking, how about the brake lines themselves, or the metal, more static lines from the master cylinder to the brake lines? Check everything. If you have contamination, it could be coming from somewhere else. None of these things are difficult, just time consuming. But, in order to get the calipers out, should you go that direction, you will want to use a pressure hose to push the individual pistons out. You can get a complete rebuild kit on this for about $140.00 with new pistons & rings.

 

Thanks for the comments guys, very helpful.

Again, I have no visible leaks, however I do believe that my rubber seals need to be swapped, and that probably is the cause for the moisture in the system.

Some history about my disco, only recently have my brakes been in top condition, for the first time ever actually (I've had bad brakes for as long as I could remember).

But this new saga started with the leak from the proportioning valve (which stopped by itself, why?). I then began to experience contamination, and then subsequent complete brake failure (the reservoir was still filled with contaminated brake fluid). I then replaced the proportioning valve and the master cylinder, had trouble bleeding the system initially, but then got it done. My brakes were then in top condition, so good that my rear pads had to be changed, due to them finally being fully engaged.

I drove only short distances for a while, had no issues at all, I only experienced complete failure again after a 50 mile drive, with some speeding and hard braking. (I had to drive back home with no brakes, but she's a manual, so I was fine.)

So now, I'm waiting to receive my new master cylinder from the states, hopefully I can also swap out all my rubber seals as well.

 

I would flush and bleed the entire system and then fill it with clean Dot 4. I did this on my 98 after replacing the master, all four calipers, and the flex lines. A power bleeder is very helpful for this.

Cheers

Phil

 

Update.

Swapped out master cylinder, caliper seals, and bled the entire system. Brakes working 100% again, thanks for all the advice guys! I'll keep you all updated.

I also did an oil change and swapped out my tire rod ends. But I soon encountered a problem shortly after! :/

I literally had just left the garage, stopped at a store to get some celebratory beers, and upon returning to the vehicle, spin but no start. I did some quick troubleshooting, and I realized that the pump wasn't coming on.
I currently have an old disco fuel pump on that I got from a scrap yard (had to adapt it, because my housing is original and does not have the same connectors). So I am moving again, however this old pump is constantly whining.

Any fuel pump recs?

 

I tried the inexpensive way of replacing the fuel pump. I bought one off of eBay for all of about $50.00. It was not the correct one. Wasn't even tall enough. You have to spend the money to get the correct one. The ones listed on eBay are generic and not accurate to the vehicle.

 

On my D2 I got the Bosch from Rock Auto. It wasn’t expensive and has been perfect for 2+ years now.