Need help tonight!! Working on brakes - PeachParts Mercedes-Benz Forum

spugeddy · #1 03-17-2007, 08:40 PM

Need help tonight.. WOrking on brakes tomorrow.

Can someone please tell me about the "bleed screws" on my 85 300cd

Are they on the top of the brake caliper, or are they part of the rubber brake hose. I see a connection at the caliper with the hose and a nut?? and I see another above that about 9 inches, going back towards the master cylinder, and then on the caliper I see a bolt sticking out that is threaded into the caliper. Is that option 2 to bleed,

Can someone describe, or provide pictures the best was to gravity bleed this.

I have been searching and reading post for 2 weeks , but it is still not clear.

I am going to do the go to the farthest wheel, one at a time method, but not sure how to open bleed screws, or where they are.

Any input tonight would be great.

vito · #2 03-17-2007, 08:47 PM

Quote:

Originally Posted by spugeddy

Any input tonight would be great.

I will preface this by saying that I have yet to do this on a MB (just got mine in Jan).

But in the past I have done many a disc brake jobs without bleeding at all. If you can get the caliper to compress, then I would just skip the bleed. Once again I dont know if MB's differ in any way to my old Caddilac, but I changed those front pads multiple times without bleeding at all. For whatever it's worth.

cavaliers16 · #3 03-17-2007, 08:48 PM

Do you see the brass looking thing on the caliper on the left? It is near the top, has a circular opening on top, and a hex fitting near the base. It is right above that black bolt. They are supposed to be covered with a small rubber piece, but often that piece falls off. Use some PB blaster on the screw for a day or two before you try to turn it- I broke one of my bleeder screws and ended up getting a new caliper

. Even if you don't have to buy a new one, you will have to drill out the old hole and thread a new fitting.

Be sure to keep refilling the reservoir when you bleed the brakes. There are two compartments to the reservoir (front and back) to prevent total brake failure in case of a leak. One compartment can run dry and it will look as though the reservoir is full.

Edit- here is the bleeding order:
Right Rear, Left Rear, Right Front, Left Front

spugeddy · #4 03-17-2007, 09:36 PM

I expected to see a rubber cover.. mine seems to have a (plastic bolt looking part) with a larger head and a stem in this apparent same location.

psfred · #5 03-17-2007, 10:00 PM

There should be a plastic cover over the fitting. There are only the brake hose, the bleed fitting, and the mounting bolts on the inside of the caliper.

If you have not done so in the last two years, you should change the brake fluid as well.

Peter

spugeddy · #6 03-17-2007, 10:01 PM

do you get a wrench on the hex head and loosen it all the way out of the caliper... or do you just loosen it and the brake fluid starts to flow...

cavaliers16 · #7 03-17-2007, 10:04 PM

Just loosen it a few turns, attach a section of hose to the bleeder, put the other end of the hose in a container, and pump the brake pedal. Clear hose is the best because you can see the air bubbles in the lines. Stop bleeding when there are no air bubbles. Just remember: keep checking the reservoir so you don't have to bleed the whole thing again. Tighten the bleeder when you are done with that wheel.

psfred · #8 03-17-2007, 10:11 PM

You really need to have two people -- open the valve, press down on the brake pedal and hold it, then close the valve, then let the pedal up. Otherwise, you are likely to pull air in.

I use a MitiVac with the brake fluid reservoir. It leaks air around the threads on the bleeder, but you can tell the difference between them and an air bubble in the caliper, and it's then a one man job.

For the rear brakes, you MUST make sure there is plenty of fluid in the reservoir. The rear chamber can be hard to see, and it will run dry if you don't overflow the front one.

Peter

Brian Carlton · #9 03-17-2007, 10:16 PM

Quote:

Originally Posted by cavaliers16

Just loosen it a few turns, attach a section of hose to the bleeder, put the other end of the hose in a container, and pump the brake pedal. Clear hose is the best because you can see the air bubbles in the lines. Stop bleeding when there are no air bubbles. Just remember: keep checking the reservoir so you don't have to bleed the whole thing again. Tighten the bleeder when you are done with that wheel.

Agreed. This method works perfectly fine.........and is excellent if you're not married.

tobybul · #10 03-17-2007, 10:50 PM

Make sure you DO NOT overtighten the bleed screw!! They are a softer metal and you will easily strip the screw threads.

There are many articles on how to bleed brakes. Here are some:

http://www.stoptech.com/tech_info/wp_howto_bleedbrakes.shtml
http://www.aa1car.com/library/2003/bf90347.htm
http://www.answers.com/topic/brake-bleeding

No need to use Mityvac. But you will need another person to be in the car to pump the brakes.

If you are replacing pads, have a C-clamp on hand. They are great for pressing back the caliper piston. Make sure the C-clamp is large enough for this application. Don't bother with the "special tool" for this. They don't seem to hold up.

pawoSD · #11 03-18-2007, 03:56 AM

I can honestly say that after doing MB brakes a number of times, never have I had to bleed the brakes while changing the brake rotors or pads....the only time I bleed them is if I change a rubber or metal line, and once every two years for the fluid renewal. My fluid renewal is coming up in less than a month, spring maintenance time!

tobybul · #12 03-18-2007, 08:22 AM

Quote:

Originally Posted by pawoSD

I can honestly say that after doing MB brakes a number of times, never have I had to bleed the brakes while changing the brake rotors or pads....the only time I bleed them is if I change a rubber or metal line, and once every two years for the fluid renewal. My fluid renewal is coming up in less than a month, spring maintenance time!

pawoSD, where do you get your 5w40 syn oil?

spugeddy · #13 03-18-2007, 09:47 PM

All done, turns out I didn't have the ATE calipers... the bleed screw was on the inside... anyway two hours later we had the new master on and the brakes bled....thanks for all your help.

pawoSD · #14 03-18-2007, 10:07 PM

?? The ATE and bendix calipers both have the bleed screw in the same place, they are just different sizes....9mm and 11mm or something. One of the calipers on the '83 is bendix...all our others are ATE.