Master Cylinder and Brake Bleeing - first time - PeachParts Mercedes-Benz Forum

1981_300sd · #1 11-12-2007, 08:47 AM

Hello all,

This weekend I replaced the master cylinder and bled the brakes on my 240d.

Being the fact that this is my first time doing this, the fact that the brakes are very important, and that I am paranoid, I wanted to check here to make sure I did everything correctly.

I bench bled the MC per instructions found here, then I bled the brakes with this crappy 1 person auto bleeder that I wish I never bought. Did in the order of right rear, left rear, front right, left right. Of course left the resivor cap open and refilled when starting to get low.

The car appears to brake just as good as it ever has, except I am just concerned that I may have left air bubbles or something in the lines. No reason in particular, im just wondering what the symptoms would be if I did have air in them?

The one other thing that I was a little concerned with is on my test drive I got the car up to 45 mph, braked hard to squeal the tires just a little, and the only one that sounded like it "squealed" was the front left.

The brake pedal is firm, and like I said I do not notice any difference in braking at slow speeds. I am just concerned that they may be able to do a better job for that time when I need to slam my brakes on the freeway to avoid an accident.

Thanks.

Whiskeydan · #2 11-12-2007, 08:54 AM

A firm pedal should indicate little or no air left in the lines.
If the pedal is firm(er) after a few pumps, there's more bleeding to be done.

Your car is likely due for new rubber brake lines. Most of them this old are needing attention.

spugeddy · #3 11-12-2007, 12:21 PM

I would second that if you had a spongy feel, or occassional soft, you have air in lines....

If you are that worried, I would re-bleed the lines with a two person system. One person pushes the brake pedal while the other opens and closes the bleeder screws.

You may be talking about $10 worth of brake fluid, and maybe 20 minutes total time......

CarreraDan · #4 11-12-2007, 05:46 PM

You might also consider ordering a Motive Power Bleeder as it makes bleeding the brakes a joy. I rebuilt my front calipers today and bled the system in under five minutes--petal is rock hard. If you don't have a helper to pump the petal for you this is the way to go. It seriously takes longer to take the wheels off with air tools than it does for me to bleed my brakes. I second the recommendation on new rubber lines as they are well past their intended life if they are original.

toomany MBZ · #5 11-12-2007, 06:23 PM

Quote:

Originally Posted by CarreraDan

You might also consider ordering a Motive Power Bleeder as it makes bleeding the brakes a joy. I rebuilt my front calipers today and bled the system in under five minutes--petal is rock hard. If you don't have a helper to pump the petal for you this is the way to go. It seriously takes longer to take the wheels off with air tools than it does for me to bleed my brakes. I second the recommendation on new rubber lines as they are well past their intended life if they are original.

Ditto.
A brake squeal is unrelated to fluid, check rotor and pads thickness.

spugeddy · #6 11-13-2007, 12:58 PM

I bled with the wheels still on the car. I took the first one off, and realized we didn't need to do it on the other 3.

300SDog · #7 11-13-2007, 03:35 PM

Yep, they tell ye to work from furthest to nearest in bleeding operation. Personally I recommend starting with front calipres and flushing the reservoir and master cyl with fresh DOT 4 fluid first. Then bleed rear brakes until fresh clean fluid flows through em. Otherwise you'll be pumping until Christmas trying to purge old master cyl and reservoir fluid through rear brakes.

1981_300sd · #8 11-26-2007, 03:02 PM

Hey I know this post is a little old, but wanted to say thanks for the info! I have had problems and was not able to get on the internet recently.

toomany MBZ · #9 11-26-2007, 06:55 PM

How are your brakes?

mobetta · #10 11-26-2007, 11:05 PM

heres my homemade power bleeder. I use a 100 psi gauge, as it also fits the wifes volvo w/ abs(30psi). the benz bleeds fine at 10 psi.

unlike a "real" powerbleeder, you do need to remove this and fill the reservior to keep it from going dry. but it was almost free for me to make.

dont over-pressurize your system and blow out your reservior.

bolzano · #11 01-29-2008, 02:03 PM

Quote:

You might also consider ordering a Motive Power Bleeder

Which bleeder do you have? I have the Motive Power universal model bought for not MB cars. The cap for the car's reservoir bends and does not seal well. Works very poorly on my non MB cars or not at all. Have not tried it on my 300sd.

vstech · #12 01-29-2008, 02:49 PM

Quote:

Originally Posted by mobetta

heres my homemade power bleeder. I use a 100 psi gauge, as it also fits the wifes volvo w/ abs(30psi). the benz bleeds fine at 10 psi.

unlike a "real" powerbleeder, you do need to remove this and fill the reservior to keep it from going dry. but it was almost free for me to make.

dont over-pressurize your system and blow out your reservior.

hmm, I would modify that by taking out the schrader valve, and putting in a hose barb connector there, then hook up to a plastic garden sprayer full of brake fluid. works great!

tobybul · #13 10-07-2008, 10:23 PM

where did you get the cap?

vstech · #14 10-08-2008, 08:53 AM

the cap is a standard GM cap available for 3.00 at any parts store in the "help" section.

tobybul · #15 10-08-2008, 12:07 PM

How did you adapt the brass fitting to the plastic cap? I realize you drill the hole and so on but the pic looks like it has more plastic material on top. Is that like JB Weld stuff?