I have an '88 240 with some very black brake fluid and a brake failure light that lights, dimly, every so often. The car is new to me and I am looking to do the wrenching in the best way I can. So, should I rebuild the master cylinder? Do I buy a kit? What about brake lines? Are there other things to replace/renew that I might not expect?

This forum was of great help with my rear shocks. Input is much appreciated.

Kirk

'88 240 - 170K miles

/// Black brake fluid is a sympton of Dot3 contamination. There is a chemical reaction between Girling rubber brake seals and American Dot3 brake fluid. Check your calipers and see if they are Girling. The Girling logo is a capital "G". The cross member is a human forearm and the fist is gripping the rear curve of the "G". On front four piston calipers it is located between (above) the two input lines. This is a problem only with Girling parts. ATE or Bendix are not affected. Hoses not manufactured by Girling are not affected. Other washers such as in the combination box may be affected.

There have been ATE master cylinders for about $55 recently available. If you determine that you have this contamination problem flush the system or drain it before you start replacing parts. Do not allow any of the old fluid in the new parts. Stick to high grade Dot 4 and use "Approved by Girling" if available. Castrol GT LMA Dot 4 is what I use.

Kirk:

I agree with Paul, flush the system and then reassess your situation. If you don't already have one, get a pressure bleeder to help you with the job. The Motive Products pressure bleeder (www.motiveproducts.com) is a favorite of mine, best $40 I've ever spent on a tool. I like Castrol LMA brake fluid, too. And, if the bleeder screws on the calipers haven't been opened in awhile (from the condition of your fluid, I'd say maybe never!), best to spray some penetrant (PBlaster) on them a day or two before you try to open them up. If you do end up having a problem with your M/C, I see new ones on eBay from time to time going for around $40 or so.

I would give the brake system a good flush with up to 3 quarts of DOT-4 fluid. (I use Castrol LMA)

Why suspect the master cylinder? The light?...more than likely this is you distribution block sensor....follow the brake lines down from the MC and see this little beauty....the light will come on when there is a pressure imbalance. Is it leaking? Flush first to see what happens.

I wouldn't rebuild a MC, they aren't that expensive.

Check the brake lines for wear, bulging. Look for leaks, dead crumbly cylinder piston boots, pad wear, rotor scoring...