Changing Brake Fluid
 

Could someone please outline the correct proceedure for changing the brake fluid in my 300D?

Pretty straight forward. Start by siphoning off most of the fluid in the resevoir, then top it off with fresh fluid. Then bleed the brakes by either the pressure bleed or the old fashioned two person method. Start at the right rear, then left rear, right front and left front in that order. Bleed them until fresh, clean fluid is coming out, I think the book calls for something like 80ml of fluid bled at each caliper.

Be sure not to spill any fluid on the paint.

Mike Tangas is the right way. After doing it the correct way, I got to thinking that periodic replacement of the reservoir may do the job, it took 4-5 times every week and guess what.....the fluid started to clear all the way down to the calipers....not a 100% purity but then it is so time/cost-effective that I had made it a yearly practice after winter (the thing is hygroscopic so I figure when the old and new mixed if further clears it) It has been seven years with my 91 300E and 911SC and its so clear all this time. I figure every other week would work better(4 cycles while you have the hood open for other stuff). However, nothing beats the right way, as for me I'm sticking to my method. Same with the power steering fluid.......so clean.....so easy, and keep that fluid away from the paint please...Later.

Adam:

I read a while ago that replacing the fluid in the reservoir twice a year is all that is necessarily to keep the brake fluid in the entire system fresh.

Yes, the fluid does not circulate as engine oil, but apparently there is enough diffusion and fluid motion through braking for the new and old fluids to mix. Then if one replaces frequently enough (twice a year), the fluid remains fresh.

My previous post does not read right: it is a reservoir volume per week during 4 weeks per year (more/less if you want to be cleaner) My experience then seems to be that the accumulation rate of contaminants is more than offset by this renewal method.

I don't know guys, that sounds like changing your underwear one tread at a time. You'll always have stanky drawers. :)

I guess the point here is to maintain the cleanness of the fluid once it is clean.

Once the fluid is fresh, change more frequently than recommended, i.e., twice a year rather than every two years so the contaminants and water cannot reach damaging levels.

So one changes half the underwear every 6 hours instead of the whole underwear every 24 hours. That way the underwear stays clean.:D

This periodic replacement is so easy and painless that for me it just makes sense and it seems to be working. With the time and effort saved I get to do other maintenance chores. A small pump with long wires makes this work a 3 minute affair every time. Later.

Surgical Hose
 

What a gret idea replacing the break fluid. You could use a foot long piece of sugical tubing over the bleeder screw to catch in a jar, this will keep bf off the floor and easy to dispose of.

Whether I'm pressure bleeding or using the two person method, all my fluid is collected in a jug. I have clear tubing with a rubber boot that fits snugly on the bleeder screw. First I crack the screw to get it loose, then gently tighten, attach the hose and start bleeding by opening/closing the screw using a 9mm box wrench. Then clear tubing allows you to see when the clean fluid is coming through the lines.

I guess it doesn't hurt to siphon and replace the fluid in the reservoir, but most of the problems result from the gook that collects in the calipers. This gook is not going to rise up through the lines and abs valving and make it to the reservoir. Even if you replaced the reservoir fluid EVERY week, you will still need to occasionally(annually) follow Mikes instructions and bleed the entire brake system.

Good luck,

Thanks for all the info. Where is the pressure bleeder screw and how does this all take place.

i want to try speedbleeders. anyone have any comments on those? i am going to do the fluid as soon as it is warm enough. tis the season for brake fluid replacement...

I bought the german auto products power bleeder that you hook to the resovoir and pump up so all you must do is open the bleeder screws at the wheels and wait until it runs clean. I usually change brake fluid with every set of pads, and its never that dirty. I only use Castrol GT-LMA dot-4 brake fluid.

Power bleeding is the way to go. Do a search on "pressure bleeder" and you'll find Donald's instructions on how to build your own "el cheapo" pressure bleeder. I just built mine last week and I made a few modifications. I'll report on it's performance after I put it through the paces...