I’ve bled brakes many ways over the years.   The traditional two person method of pumping the pedal; various one man systems such as vacuum pumps or valves.    So far I had found the vacuum pump system the best.  However I had ruined two vacuum pumps by getting brake fluid in them.    The Motive Power Bleeder looked promising.

At first, it looked like it was going to be much harder than the videos suggested.  I couldn’t get the system to hold pressure.   There was a hissing sound, and it appeared that it was coming from the cap.   I tried to bleed the brakes anyway, and got one wheel done before fluid started gushing out of the reservoir.

Turns out the little rubber grommets above the fluid level sensor had gotten hard and were letting fluid through.   They were still available and quite cheap.   The reservoirs were also still available, an updated version without the grommets.  I got both, as I didn’t want to find the grommets didn’t fix the problem and have to wait another couple of weeks to get the reservoir.   Also in my mind was having a spare reservoir on hand given how little interest Mercedes-Benz has these days on suppling youngtimer parts. The picture above shows the reservoir with the grommets removed, and below shows with the new ones installed.

Once I had the leak fixed, Bleeding W126 brakes with the Motive Power bleeder was a cinch.   It took longer to get the car up in the air and take the wheels off.

I needn’t have put that old tee shirt around the reservoir to catch any overflow, as the new grommets did their job.   There was enough vacuum to do all four wheels.   This may not be the case if starting from scratch, as I had done one wheel last time.

Instead of buying the motive catch cans, I used an old coke bottle with a hole drilled in the lid.   It worked quite well. I drilled hole in an oval shape so it held the hose but let air get into the bottle.

Due to COVID lockdown, I didn’t get a chance to test drive the car.  The pedal felt firm so I am confident that all is well.    I also noticed that I have a miss matched set of wheels on the car, so I want to change some of the tyres so I have a set that match on this car and a set that match as my spare set.

Now I have the Motive power bleeder, I will probably do regular fluid flushes myself.  I don’t think I’ll be that keen to take on the replacement of the hoses though.

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I recently had the hoses changed on my 560SEC.   I was originally planning to do this job myself, but when I inspected the hoses under the car it seemed apparent they had not been changed since the car was imported from the UK in 2005.   After seeing this, I decided no to tackle this job myself and I’m glad I didn’t as the old hoses put up a good fight.    I figured since the 300SE was an Australian delivered car, the job would be much easier.

W126 brake hose replacement requires different hoses depending on the model.   Based on my 86 300SE and 87 560SEC and SEL, these were the required hoses.

300SE

Front: 129 428 00 35

Rear: 126 428 03 35

560SEL/SEC

Front: 129 428 00 35

Rear: 126 428 01 35

I haven’t looked but I suspect the rear hose difference on the 560 models is due to the anti-squat suspension geometry.    I found that the attachments to the caliper were easy to remove, but I was only able to get one of the connections to the brake hard lines off easily.   Even after letting the other ones repeatedly soak in penetrating oil, they still wouldn’t move.   I was using the correct flare nut spanners but I still couldn’t get them to budge.

In the end I had a mechanic from up the road help me and we only got them off with vice grips.   This is not ideal, but the only way to get them off.    Cutting open the old hoses didn’t show any restrictions, but they were very hard and were starting to get some minor cracking on the outside.    I think next time I will not tackle W126 brake hose replacement myself and just send the car into a mechanic.

With the new hoses installed, the next step was to bleed the brakes.   I had bought a new vacuum bleeder a few months ago and this would have been its first use.

The power bleeder is quite easy to use, however I ran into another problem.   I couldn’t get my system to hold pressure.  At first I thought it was just a minor leak from the cap.   It turns out the rubber grommets on top of the housing for the fluid level were leaking quite badly and fluid poured out when I tried to bleed the brakes.    I’ve ordered a new set of grommets but also a new fluid reservoir in case there are more leaks.

As so many W126 parts are going NLA as Mercedes-Benz loses interest in the model, it will be good to have one on the shelf even if I don’t use it today.   The new housing is an upgraded part and it looks like it doesn’t need the rubber grommets.

In the short time I used the bleeder before I noticed the leak, I found it quite easy to use – the best system for bleeding brakes I’ve used so far.  I am confident it will be quite a simple job once I get the parts in I need.

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