Mushy brakes, rear part of reservoir empty... (85 300D) - Page 2 - PeachParts Mercedes-Benz Forum

barry123400 · #16 12-28-2011, 12:54 PM

If there is evidence the vacuum seal grommet or o ring between the booster and the master cylinder is wet. Then the seal in the rear of the master cylinder has failed.

It has been so long since I rebuilt one of these master cylinders I cannot remember if there is a separate last seal or the seal is dependant on the condition of the rear piston seal and bore. I suspect it is the latter. Either way the missing fluid should turn up in the brake booster.

Thats if the vacuum seal between the master cylinder and booster is wet. .Loosen the master and have a look. Wet in there means at this point a replacement master cylinder. You do want that fluid cleaned out of the booster for sure as well. One usual type of failure to be expected with master cylinders.

vstech · #17 12-28-2011, 07:55 PM

Quote:

Originally Posted by barry123400

If there is evidence the vacuum seal grommet or o ring between the booster and the master cylinder is wet. Then the seal in the rear of the master cylinder has failed.

It has been so long since I rebuilt one of these master cylinders I cannot remember if there is a separate last seal or the seal is dependant on the condition of the rear piston seal and bore. I suspect it is the latter. Either way the missing fluid should turn up in the brake booster.

Thats if the vacuum seal between the master cylinder and booster is wet. .Loosen the master and have a look. Wet in there means at this point a replacement master cylinder. You do want that fluid cleaned out of the booster for sure as well. One usual type of failure to be expected with master cylinders.

... then again, if the reservoir grommet has failed, fluid will be all over the MC, the booster, the car in general...
it' best to clean it all up, pull the reservoir, pull the MC and look for signs of fluid in the booster, and check the condition of the MC o-ring...

MS Fowler · #18 12-29-2011, 08:41 AM

Its the BRAKE system, for goodness sake. Not a place to worry about saving a buck or two. You really need good brakes--that are not optional.
Empty MC means something is leaking. If there is not a puddle under the car, then keep looking. Brake fluid does not evaporate ( under normal circumstances)--it went somewhere. Rear compartment of the MC means front brakes, right? Look for leaks around the front of the car. If nothing is obvious, then suspect the fluid is leaking out the brake pushrod area, and likely into the booster, or running down the firewall.
The point is--brake leaks are something that deserves immediate and full attention--its not like " can I adjust my ALDA for more power". Its more like, will I die , or will I kill someone else, when I push the brake and nothing happens. Brakes are redundant--there is a backup--but in your case the backup is gone. Your system needs attention, now.
Please keep us informed, and tell us what was leaking.

t walgamuth · #19 12-29-2011, 08:56 AM

Quote:

Originally Posted by LandYaghtLover

I dont think you got the little joke there. No need to throw insults.

x2.... the fellow is trying only to help you figure out the problem.

wildest · #20 12-29-2011, 10:26 AM

I had the same thing happen on my '85 which was fixed with a pair of reservoir gaskets, but since your's got soft, I'd suspect that there is air in a line, and with that much pedal movement, there's a possibility of master cylinder damage. Which leads to a more comprehensive brake system check.

whunter · #21 12-30-2011, 06:13 AM

Quote:

Originally Posted by frankengrant

Today I took the ole Benz for a ride for the first time in a few weeks and noticed the brakes were very mushy. I pulled over and the rear part of the reservoir, closest to the brake booster, was empty. The grommet at the bottom of the reservoir going into the master cylinder (right?) was a bit wet.

I refilled the brake reservoir and went for a drive, its a bit better but not all the way, I will bleed it this weekend.

Other than replacing that gasket, what else should I do?

Anyone who has replaced that gasket have a few tips for me?

Thanks!

Here are the parts you need.

Grommet, Brake Fluid Reservoir to Brake Master Cylinder (12 mm I.D) (2 Per Car)
MB# 000 431 09 50
ATE Brake Reservoir Grommet,W0133-1643032 - PeachParts

.

Skippy · #22 12-30-2011, 06:21 AM

Quote:

Originally Posted by whunter

Here are the parts you need.

Grommet, Brake Fluid Reservoir to Brake Master Cylinder (12 mm I.D) (2 Per Car)
MB# 000 431 09 50
ATE Brake Reservoir Grommet,W0133-1643032 - PeachParts

.

I just did mine. Five minute job. I didn't even need to bleed the brakes afterward.

frankengrant · #23 02-20-2012, 10:08 PM

Doing this on Friday, have a rebuilt MC on hand. I filled the reservoir with brake fluid and have driven it a few times, no problems.

There is a whining sound from the brakes, which stops as soon as I push the brake pedal, even slightly.

Exactly what this guy reported:

bad master cylinder or calipers 84 300d?

I'll update this when I finish, thanks for the help.

frankengrant · #24 02-22-2012, 01:08 PM

So I opened the box for the MC, and it came with two nuts and one oring. Are there any other parts that I need to do this job? I read some thing about a donut shaped gasket but I may be mistaken...part number?

whunter · #25 02-23-2012, 12:05 AM

Quote:

Originally Posted by frankengrant

So I opened the box for the MC, and it came with two nuts and one oring. Are there any other parts that I need to do this job? I read some thing about a donut shaped gasket but I may be mistaken...part number?

That should be all you need.

.

frankengrant · #26 02-23-2012, 11:46 PM

Well I pulled the MC today, the brake booster was about 3/8ths full of brake fluid. I suctioned it all out, and it nearly filled a 32oz water bottle.

One question, there is a piston (appears to be) in the middle of the brake booster, it wiggles a little bit, I twisted it to try and tighten it, nothing happened. I'm pointing to it in the pic attached. What is that? Should it be tight, or should it wiggle a little?

I am going to install and bleed the new MC tomorrow, I will report back tomorrow night.

whunter · #27 02-23-2012, 11:51 PM

Quote:

Originally Posted by frankengrant

Well I pulled the MC today, the brake booster was about 3/8ths full of brake fluid. I suctioned it all out, and it nearly filled a 32oz water bottle.

One question, there is a piston (appears to be) in the middle of the brake booster, it wiggles a little bit, I twisted it to try and tighten it, nothing happened. I'm pointing to it in the pic attached. What is that? Should it be tight, or should it wiggle a little?

I am going to install and bleed the new MC tomorrow, I will report back tomorrow night.

It should be fine as is.

That is the push rod that actuates the master cylinder plunger.

.

frankengrant · #28 02-24-2012, 05:56 PM

Finished this morning.

Hooked the MC right up and bled it in place after reading a few thread where people had success with this method. Started at the rear right, and worked my way toward the MC. Had it bled completely in two bottles of DOT 4 which was two trips around the car. Bled it with the partner method, haha my pumper was an olympic class marathon runner

. Pedal feels good and firm, the car drives like new, almost. The car is no longer pulling to the right, and there isn't any rapid deceleration upon release of the throttle like there was previously.

One negative thing I am noticing is that when I roll to a stop, when I am going less than 5mph and begin to release the pedal so that my car doesnt jerk, the brakes sound a little clunky in the front, like they are slipping on the caliper instead of sliding slowly like they should.

Any ideas?