I’ve been meaning to change the brake hoses on the 300SE for a while. I have no history for the car, so I don’t know how old they are. As I also wanted to change the brake fluid, I thought it made sense to do both jobs at the same time. I had noticed a slight pull to one side on hard breaking. It may not have anything to do with the hoses, but they are a good place to start. Brake fluid really should be changed ever two years. Most people don’t do it that frequently, but regular changes are still important. Probably even more important on cars that don’t see much use.
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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