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  #1  
Old 12-31-2022, 05:43 PM
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w124 abs pump funny business

I have been going through the brakes fixing sliders, calipers, master cylinder, etc on my 90 300d. Now I have a strange symptom: Very firm pedal and almost no braking. I am only getting braking on one wheel, front left. I checked at the abs pump and fluid is getting there no problem...but nothing for the output to front right (and probably also rear). I don't think it is a bleeding issue because no matter how hard you push on the pedal nothing comes out the far side of the Abs pump.
Anyone seen this before?
I read a thread of someone fixing it by tapping with a hammer...but I'm thinking of getting a used one from eBay.
Do I really need a power bleeder once I install the new one?
thanks,
James

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  #2  
Old 12-31-2022, 10:16 PM
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How bad was the old fluid?

Did it work ok before this work?

Tap on with a hammer? Do it at your own risk, I'd try it but be reasonable with the force, if it works afterward I'd change the ABS assembly.

Pressure bleeder? It is a lot better, I use a Motive brand.

Is there a bleeder screw.under the black plastic cover on the ABS? Some have it.

Good luck!!!
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  #3  
Old 01-01-2023, 09:06 AM
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The brakes were not very good when I got the car a year ago but they did work a little. Then the pedal started going to the floor from time to time but when backed off and reapplied held fine. So I replaced MC and booster (which was full of fluid).
The old fluid was pretty bad to front right, since the bleeder was broken off. The PO had bled the rest of the system fairly recently. I bled it by opening up the brake line coming in and it was dirty. Yesterday I put on a new caliper...but the abs pump is locking up and not giving it fluid. I thought about the hammer trick...but I don't like the idea of this happening again, so I ordered another one. I'll report back once I put it in. I think my pump is the one without the bleeder since it is a non ASR.
The good thing about this is that I have gone through all 4 brakes checking everything out, and solved some other issues. It did take a while for me to figure it out since I have never seen anything like this before.
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Old 01-01-2023, 11:09 AM
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May want to check the ABS pump relays.

Here's a good tutorial

https://www.pelicanparts.com/techarticles/Mercedes-W124/65-BRAKES-ABS_Relay_and_Pump_Replacement/65-BRAKES-ABS_Relay_and_Pump_Replacement.htm
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Old 01-02-2023, 09:08 AM
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I will have a couple of spare relays on the new pump, so I will try that before I swap it in.
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  #6  
Old 01-05-2023, 08:33 AM
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I didn't try the relays, but swapped pumps and appears to have solved the problem. I now have a full flow of fluid to right front wheel. I still need to bleed the other 3 wheels and test drive, but I have a firm pedal now. I would have thought that when the internals fail on these pumps that they would have been designed to allow brake fluid to be pushed through them...but in this case 3 out of 4 wheels could get no fluid.

If anyone is bleeding brakes and pedal is hard and no fluid to a wheel, check the abs pump.
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Old 01-05-2023, 04:41 PM
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Thanks, learned something.
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Old 01-07-2023, 02:28 AM
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What do you mean "the pedal started going to the floor from time to time???"

Quote:
Originally Posted by jdulle View Post
The brakes were not very good when I got the car a year ago but they did work a little. Then the pedal started going to the floor from time to time but when backed off and reapplied held fine. So I replaced MC and booster (which was full of fluid).
The old fluid was pretty bad to front right, since the bleeder was broken off. The PO had bled the rest of the system fairly recently. I bled it by opening up the brake line coming in and it was dirty. Yesterday I put on a new caliper...but the abs pump is locking up and not giving it fluid. I thought about the hammer trick...but I don't like the idea of this happening again, so I ordered another one. I'll report back once I put it in. I think my pump is the one without the bleeder since it is a non ASR.
The good thing about this is that I have gone through all 4 brakes checking everything out, and solved some other issues. It did take a while for me to figure it out since I have never seen anything like this before.
Wait a minute, man. What do you mean the brakes weren't that good but they worked a little???? And that the pedal started to go to the floor from time to time??? You're driving a 3,500 pound car around. They'll put you in jail for about 12 years if you hit and kill someone because you're driving a car with bad brakes. If you don't know what you're doing with the brakes....have it towed to a brake shop. Please.
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Old 01-07-2023, 09:46 AM
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I bought the car as a car that needed repair. When I first got the car the brakes worked, but felt like they needed going through. When it did the pedal to the floor thing, a second pump restored the brakes to normal...but I then parked it until I replaced the master cylinder and brake booster. From there I realized that there were additional problems, which I have now solved. Don't worry, this is not my daily driver, and won't be until the brakes are great.
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  #10  
Old 01-07-2023, 09:50 AM
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Most of my driving in this car has been at 10mph going between two farm properties, but I am planning on driving it on the road soon.
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  #11  
Old 01-07-2023, 05:14 PM
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So I finished bleeding the brakes and they work great. Solved all my issues.

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