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  #1  
Old 10-16-2013, 01:46 PM
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85 300D vs Brakes, Car 0 - Brakes 3

Recently dicided that I was going to try my luck at another diesel mercedes, even thoght the last episode didn't work out too well. I bought a non runner, got it going and all seemed well until I noticed that the booster was leaking fluid into the cab, giving me poor stopping power. I went out to the parts store and picked up a new master cylinder and boosting, got them all installed and called it good. Seemed like everything was fixed, no more leaksand better brakes.

I drove it to work the next morning and the brakes locked up and I had a rock hard pedal. I left the car and got a ride to work, then when I got off (7 hours later) picked up some vacuum parts that I had ordered a couple days before (noticing the JB Weld "fixes" the previous owner had done) and went to check on it. The pedal had normal play to it again and thinking it was just a vacuum issue went about fixing what I could. Shortly after the brakes siezed again on the way home.

The front passanger is the hotest, followed closely by the driver. The rears feel equal and about ~1/3 the heat of the fronts.

While I had bench bled the MC I had not had a helper to bleed the actual lines and then forgot about it when there was somebody around to help. So I bled the lines yesterday, there was definite air that was bled out. Thinking I solved it, tried a a short drive that had some heavy braking, they seized in short order.

I have one more larger vacuum leak on the line that comes off the booster (part ordered, just waiting) that is jerry rigged the best I can for the moment, but this leak was there with the old MC and booster with no locking of the brakes.

I have to wait for aprox 20 minutes to get slight pedal travel back and closer to 45-60 for full use again.

Any ideas???

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  #2  
Old 10-16-2013, 01:52 PM
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It's not vacuum and it's not air. It's either bad calipers that are sticking or a bad line that is not releasing pressure. You could probably tell by opening the brake bleeders when it's seized and seeing if you get a strong squirt of fluid out of the system. If so, it's still pressurized.
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  #3  
Old 10-16-2013, 01:55 PM
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x2 to kerry.

how long was it sitting? sounds like stuck pistons in the bores or delaminating rubber brake line holding the pistons closed.

I have the same problem with a car that was running fine with good brakes and sat for a year being occasionally driven. calipers seized up.


verify the master is the correct one for the car and the correct pushrod after seeing if there is pressure at the calipers still.
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  #4  
Old 10-16-2013, 11:19 PM
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I will check for pressure. I don't really think that it is a bad caliper being that I made the exact same drive plus a little more before I swapped out the MC and booster with no sticking issues what so ever.

Could it be with be with no vacuum the pedal can not recover to the neutral point?
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  #5  
Old 10-17-2013, 07:01 AM
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The pedal will recover with or without vacuum. It's either sticking calipers, internally swollen lines, or both. If it were me I would just go ahead and replace calipers and lines, and probably do rotors while I was at it.
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  #6  
Old 10-17-2013, 07:42 AM
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If the Caliper Pistons are stuck all on their own when you Jack the Car up and open the Bleed Screw they are still going to drag more than they should.

I have never had any Problems with any Brake Booster on any of the Cars I have owned so I cannot tell you if the Rebuilt Power Brake Booster itself could be the cause.

On mine the Master Cylinder Push Rod is part of the Master Cylinder and is not adjustable.
If you loosen one of the Master Cylinder Lines at the Master Cylinder and fluid spurts out there it possible there is some issue in the Master Cylinder that is not allowing the Pressure to bleed out. There is passages for that inside the Master Cylinder.
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Old 10-17-2013, 07:57 AM
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This is what is in the Motor Manual Auto Trouble Shooter under Bendix Diaphragm Power Brakes.
Brakes grab; Control Valve sticking or defective (that is inside of the Brake Booster), reaction Diaphragm leaking, worn or distorted lever plates, bind in the linkages. I assume the last 2 have to so with the Brake Pedal and their apparatus.

No or slow release; Pushrod adjustment incorrect, linkages binding, return Spring defective.

On mine when I brake it seems like the Push Rod is a little Short (no adjustment on mine) as if feels like I have some Pedal travel before the brakes engage; more Pedal Travel than I have on other Vehicles.
If on yours your Pedal Travel seems to have no play at all as the brakes are applied it may be the Push rod is slightly too long.
It might be you could tell for sure by making a temp thick Paper Gasket between the Master Cylinder and the Brake Booster do increase the clearance of the Push Rod.

Of course if for some reason you Rod is adjustable; adjust it.

This is sort of a Generic Car problem troubleshooting site
http://www.aa1car.com/library.htm

Car Repair Alphabetical index
AA1Car Alphabetical Index of Automotive Articles
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Last edited by Diesel911; 10-17-2013 at 08:18 AM.
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  #8  
Old 10-17-2013, 08:02 AM
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I agree, air could not be the culprit. lack of vacuum could easily cause a rock hard pedal, but not a locked caliper. I think you have several problems, and I'd start with the MC.
swap another MC in there. personally, I'd get one from Pelican and be sure it's a good rebuild, or new.
then after it's bled, and installed, I'd either trace out the vacuum or bypass everything but the booster line. Just pull off the small lines, and plug them, so only the booster gets vacuum.
report back.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Last edited by vstech; 10-17-2013 at 08:25 AM.
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  #9  
Old 10-17-2013, 08:10 AM
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Your new master cyl could also be defective. Something to try... when the brakes lock up, loosen the line at the master cyl and see if fluid sprays out.

With a car of this age, the rubber lines should be replaced, but I had a similar issue with a pickup and it turned out to be the master cylinder.
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  #10  
Old 10-17-2013, 08:29 AM
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1985 Mercedes-Benz 300D Sedan - Brake Hydraulics - Page 2
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #11  
Old 10-17-2013, 09:27 AM
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What brand MC did you get? If A1-Cardone, it is garbage (frequently). I talked to the manager at AutoZoo. They have a huge percentage of Cardone returns.

Cardone is the cheapest thing on the block. One time I bought a remanned steering rack for my Datsun Z for less than the inner tie rod would cost.
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  #12  
Old 10-17-2013, 10:11 AM
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Quote:
Originally Posted by southofantarctica View Post
I will check for pressure. I don't really think that it is a bad caliper being that I made the exact same drive plus a little more before I swapped out the MC and booster with no sticking issues what so ever.

Could it be with be with no vacuum the pedal can not recover to the neutral point?
Your description strongly suggests either a sticking piston in the caliper or a bad rubber brake line. I would lean to the brake line; there are many stores about brake lines causing exactly this behavior. The rubber brake lines break-down on the inside first and can easily create a one-way valve situation; brake fluid can be pressed toward the caliper but cannot flow back because of one-way restrictions inside the brake line.

Of course, a caliper with a slightly rusted piston bore can do exactly the same thing. And on cars where the brake fluid is not regularly flushed, this type of rusting is not unusual.
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  #13  
Old 10-17-2013, 09:17 PM
vstech's Avatar
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Quote:
Originally Posted by mikeyfev1 View Post
Your description strongly suggests either a sticking piston in the caliper or a bad rubber brake line. I would lean to the brake line; there are many stores about brake lines causing exactly this behavior. The rubber brake lines break-down on the inside first and can easily create a one-way valve situation; brake fluid can be pressed toward the caliper but cannot flow back because of one-way restrictions inside the brake line.

Of course, a caliper with a slightly rusted piston bore can do exactly the same thing. And on cars where the brake fluid is not regularly flushed, this type of rusting is not unusual.
except the behavior only started AFTER he changed the MC...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #14  
Old 10-17-2013, 09:31 PM
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My vote would be MC or booster. See if there's any adjustmet at the brake pedal-to-pushrod bolt. Some cars have an eccentric there.
I had a W115 220 years ago where the brakes would gradually loose boost and at the same time, gradually lock as the car warmed up and under-hood temperature increased.. I initially solved the locking by drilling the pushrod bore in the MC very slightly deeper. But the boost failure was only eventually cured by replacemnt with a salvage-yard power-brake unit.

Happy Motoring, Mark
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  #15  
Old 11-01-2013, 01:09 PM
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Ended up getting the problem shorted out, I'm claiming bad booster. After reading up on brake issues in general, it sounded like my mc wasn't bleeding off pressure. Took everything off, used my warranty and got a new one. The replacement had an adjustment bolt on it, backed it off a could of turns and slapped it in. So far so good, have close to 100 miles on it and no issues.

Thanks for all the help!

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