I was annoyed with myself for letting air into the brake system. So last night I set to work straight away to fix this. I also think I might know what has happened. The brake fluid reservoir on the W123 is divided into two parts. When you fill it only one half fills, the rear one, till it overflows into the second one, the front half.
This is in case there is a leak in the system, only half the system will drain. A very simple and prudent design. The problem on the Mercedes reservoir is that you really need to fill the reservoir to almost the top before the fluid will actually overflow.
As you can see in the previous images, my pneumatic bleeder comes with a simple auto-fluid filler bottle. It is just a bottle with a small valve and a small opening at the bottom. You insert it into the brake fluid reservoir and open the valve. It is just a small opening so as long as it is underneath the fluid level of the reservoir no fluid will drain from the bottle into the reservoir. But as you put vacuum onto the brake line, fluid is drawn through the master reservoir and the lines, meaning the fluid level in the reservoir drops and the auto filler bottle neck pops out of the receding fluid and starts replenishing until its below the reservoir level again.
I think the auto-fluid filler bottle was inserted to deeply, meaning it started replenishing just as the fluid in the reservoir was about to spill from the rear into the front. So the front half of the reservoir was not filling properly. With hind sight an easy adjustment of the auto-fluid filler bottle.
Anyway, just to finish the job quickly I decided to use my other brake fluid bleed system. The Easy Bleed.
Here you see the filler bottle. Hooked up to the reservoir. Before filling it with new brake fluid it is always a good idea just to pressurise the system and see what happens first. Make sure the various connections are leak proof.
The first time I used it on the W123 many, many years ago I did not. What I had not realised is that the hydraulic system for the clutch is fed with a simple hose from the brake fluid reservoir. There were no clamps on the hoses. So the hose popped off and sprayed brake fluid anywhere. Remember you are putting pressure on something that is supposed to operate under atmospheric pressure normally
The Easy Bleed is a DIY bleeder set to be used on the road. So it is pressurised by using the spare wheel. You do need to make sure that the tire pressure is wel below 1.5 bar.
Once you pressure test the system I use a large syringe to draw out most of the old fluid from the reservoir. Fill up the Easy Bleed bottle, pressurise the system and dive under the car, same sequence as before opening the bleed nipples one by one.
I catch the old brake fluid in a simple glass jar. I use a valve of one of my bicycle tires to ensure no air can enter back into the system. Very simple, very effective.
Any fluid left in the Easy Bleed bottle is uncontaminated and I pour it back in the original container for re-use. I write the date of opening on the bottle. After half a year or so, I do not use it anymore. The problem with brake fluid being it attracts moisture. So once you have broken the seal on a brake fluid canister use it or loose it. But I figure a couple of months should be alright.
Lastly, as this is a pressurised way of bleeding the system, the brake fluid reservoir fills to the brim. So when you are done, you need to extract some fluid as it will be filled well above the max level.
This system works really well. Obviously, it is depending on having a spare tyre. My experience is that with the tyre pressure reduced to 1.5 bar that is usually enough to push two fillings of the Easy Bleed bottle into the system, which should be enough.
I also quickly bled the clutch hydraulics as well.
Happy to report that the brake pedal is again working normally!
I also took my bicycle wheel to a bicycle repair shop. As I was expecting the hub is really damaged beyond repair. Can not get a new wheel. The combination of a three speed and drum brakes is very rare. Nobody seems to use that anymore.
It would also cost a lot, at least Euro 150 for a complete new set. This is an old bicycle. I like it and I like to keep it running mainly for sentimental reason. When we moved back from the UK to the Netherlands in 1986 my dad bought me this bicycle as a welcome back home present.
I am going to try and make an improvised repair with a simple roller bearing. Which means I need to fabricate some sort of bushing to hold it in place. I know how to do that, but I do not have a lathe or mini mill. Time to get me one, but I might try a mate of mine first.
Jeroen