98 Mercedes SLK230 Front Brake Pad Replaced - No Brake Pressure after start but resumed in seconds

I DIY replaced my front brake pad. After that, I found there is barely any brake pressure when I start the car. But after a few seconds, when I press the pedal again, the pressure comes back. Then, it brakes like normal. I park my car on drive way so I can tell the same thing happen everyday when I start the car.

The only thing was - I forgot to open the brake fluid reservoir cap and suck out some excessive brake fluid. When I pushed the calliper piston, excessive fluid leaked out. Does it matter?

I did not bleed the brake line.

Anybody experienced something similar?

That’s normal.

When the pads are replaced the caliper pistons have to be pressed back into the calipers. Then when calipers/pads are installed, there’s a gap between the pads and the rotors. So the brake pedal has to be depressed a few times to push the pistons out so the brake pads are positioned closer to the rotors. Once that occurs the brakes function normally

I pump on the brake pedal before I start the engine to make sure there’s a firm brake pedal.


Please clarify, does this soft brake pedal still happen every day?

Thanks. I did push on the pedal several times after I started the car right after I installed the pads.
The problem is I don’t have / have little pressure every morning when I start the car since the replacement. As I park my car on drive way, when I put the car to “D” gear with the brake pedal push, the car still move down slowly for a few feet. After a few seconds or when I release the pedal and push it again, the pressure comes back and I can drive and brake normal. But it is scary when I start the car every morning…if I have to park my car on a slope and start the car later.

“…the car still move down slowly for a few feet.”

When this happens, how far down is the brake pedal (how close to the floor)?

Yes…it still happens every day when I start the car.
When it happens, it is somewhat close to the floor. I can not tell it is time as “several seconds” after that matter, or when I release the pedal and reapply it matter. After that, brake pressure resume.

Let’s try this, next time BEFORE you start the car, gently push the brake pedal and see how far down it goes. What I’m getting at, is if you can get the pedal to go to the floor, it’s usually a master cylinder problem. (How pushing fluid back through the master cylinder when the wheel pistons were pushed in would cause a problem, I don’t know.)

I feel this is problem that requires a real brake repair shop and soon. Until then I hope you set the parking brake until you know that you have brakes.

Some brake systems have a mechanical means to retract the pads slightly so they don’t drag and reduce fuel mileage…Maybe when you replaced the pads (you should have opened the bleeders to give the fluid someplace to go other than forcing it back into the already full master cylinder) maybe the hardware was not installed correctly and the springs/clips are retracting the caliper piston far more than required…I would inspect the pads carefully to be sure everything is assembled correctly…

When I replace brake pads I open the brake bleeder before I expand the piston enough to get the old one out and fit the new pad in. Then I re-tighten the bleeder. I want the extra brake fluid to just flow out the bleeder, and not back up into the master cylinder. On some brake systems this is highly recommended (or mandatory) as reverse fluid flow can damage other components in the system. Especially true if equipped with ABS. And once everything is back together I always bleed the calipers in both wheels afterward.

I think your best and safest bet is to take it to a mechanic for an appraisal of what is wrong. Once you find out what it is, you may decide to fix it yourself. If you want to skip the mechanic, probably what I’d do first is to give both calipers a good bleeding and see if that improves things.

Hi insightful,

I followed your suggestion to push the brake pedal BEFORE I start the car…here was what happened…

My car is parked on a slight gradient driveway with the car pointing downwards. BEFORE I started the car, I push on the brake pedal… it was only about an inch was it became firm. Then, I started the car while keeping my foot on the brake pedal, the pedal went down slightly…less than an inch and firm. When I shifted the gear from PARK to DRIVE, the car start to move down slowly while I maintain my foot on the brake pedal. This time I attempt to make a firmer push on the pedal. No effect. I let the car move slowly with my foot on the pedal to see if “Time” is a factor. The answer was no. I released the brake pedal and then I pushed it again. The braking effect came back like normal… so it seems I have to release the brake pedal and give it a second push to get brake effect right after I started the car.

After I arrived at my office, I found a quiet and a slightly sloped parking space. I stopped the car. Wait for some seconds and started the car with exactly the same steps. I got brake effect immediately after the car without the need to release the brake pedal and give it a second push.

I think one of your calipers may be sticking causing the lessened effect when cold.

First, on modern braking systems, you should open the bleeder to expel excess brake fluid when retracting the piston. It serves to reduce the propensity for pushing debris backwards through critical areas like seals and ABS components. Then only retract the piston far enough to fit the new pads over the rotor or you risk pushing the piston seal through a historical crud line that builds up over time. This can damage the piston seal.

Secondly, you should never need to add fluid in between service intervals. This is a good way to see if your pads are worn to the point of needing replacement by looking at the fluid level. If you need to add fluid, you have a leak that needs to be addressed separately.

Third, it is probably too late now but you really need to clean up spilled brake fluid immediately. It is one of the best known paint removers.

Fourth, when you go to set the pads after the re-installation, use very short strokes of the brake pedal. Under no circumstances should you purposely press the pedal to the floor. This can result in a similar scenario in the master cylinder as the caliper piston when pushed too far back.

Lastly, did you grease the sliders to ensure the caliper is sliding properly?

When you pushed the caliper piston back in, it sounds like you did not open the bleed valve on the caliper, thus you damaged your ABS. Now you need to go to a good brake repair shop or the dealer and open your wallet wide. Sorry.

@wongro, your test, up until putting it into drive, was “normal.” I have to agree with others who concluded that your ABS actuator was damaged by forcing fluid backwards through it, possibly from dirty fluid contaminating the works.

You might get lucky and a “power flush” by a reputable mechanic will fix it.

The fact that your car will roll after being parked over-night even though you have pressure on the brake pedal means there is something seriously wrong with your brakes…When you forced the fluid from the caliper back into the master-cylinder, that may have damaged other components in the brake system, the ABS or the master-cylinder…I would have a Benz specialist check out the entire brake system…

I bleeded RR, RL, FR, FL on Saturday and tested it no problem!.. Let the car cool down till Sunday morning and retest (as…when I usually have this problem). The problem goes away!

What would be the best explanation?

I would say you “undid” what you “did” by pushing the fluid back through the ABS actuator. Moved contamination? Moved valve(s)? Can’t say.

Maybe he just had a bubble in the caliper or two calipers? He got some braking from the ones that had no bubbles, and pumped up the others each start. When he bled them again the problem was fixed.