ATE T50 brake booster
My restored ATE T50 brake booster
The brake booster has been gone through by me before, during the end of the eighties when I did the whole brake system and changed to silicone fluid. At that time I didn't find new rubber, diaphragms etc at a reasonable price. Since it worked as it should I only checked and cleaned everything thoroughly before re-assembly. The paint on the slave cylinder in the first picture below is from that time. I didn't spend time to find the dark blue - actually shifting in violet - color that it had. But I can still remember it. Well, more of that later and let's proceed to what I did this time (do also see Mercedes-Benz Ponton Page's booster article).
The first picture below, shows you the booster in its "original" shape, when I started this restoration. The second and third picture show one way - probably a rude one - to remove the large piston; squeeze it with the help of a vice so that you can remove the rivet that holds it in place. From that point and onward it's very simple and it won't take you many minutes until you have everything in front of you which you can see in pictures four, five and six. The vacuum can was polished on the inside (underway in the seventh picture below, the markings are not wear, it's buffing paste).
When restoring the can I did a stupid mistake. I sandblasted the outside surface. Tried to polish it but gave up and hoped that the surface would look like new after the metal finishing, in this case white cadmium. I don't remember, but I assume that I wanted to do too many parts/items with a far too short schedule. A couple of micro millimeters of white cadmium don't hide anything, which I already new from earlier mistakes. Anyway, the can came back and looked quite awful, with the marks of the sandblasting still visible. I didn't want to polish it again and have it re-finished since I'm a little bit too scared of hydrogen embrittleness caused by the electroplating. So, in my next life I'll try to find a new can, restore it to perfection and put it into the car. Meanwhile I put a couple of layers of car wax on it in order to make the small "pits" in it more easy to clean (last picture above). On the other hand, the can won't be easy to see under the hood.
Click the picture to download in PDF-format, "Power Brake T50 for passenger cars, Construction, operation, installation and maintenance, 1 Edition 1956", © ATE (file is 10MB!)
Next step was to get the cover back in shape which you can follow in the gallery below. First I covered all holes and threads, glass beaded it and then had it tumbled at Trumlingsaktiebolaget. The first photo shows you the result - perfect!
All parts were ordered from Will Samples. I could have bought most of the parts new in Europe too but not all of them and then from 2-3 different suppliers incl Mercedes-Benz. But ordering everything from Will was much more simple, probably cheaper and above all, I could send him my questions and got answers within a couple of hours! That is more than invaluable. First I didn't really know who he was but looking through some old american Mercedes-Benz articles I found out that he's been in the business for quite some time. And the quality of the parts were - of course - very high!
Mercedes-Benz ATE T50 brake booster, reproduced 2006, © Daimler AG
Then we came to the piston with its leather sleeve. If the leather sleeve is in good condition there's no reason to replace it. Just clean it up and oil it. They are more or less indestructible. As said above, during my previous booster "restoration" I dismantled and cleaned all parts including the leather (see pictures three and four below). This time I only spent half an hour on cleaning the leather with Acetone and then soaking it with oil. Some sources have told me to use Calipsol on the leather and then fill the can with castor oil. However, the original ATE T50 manual says "mineral oil with viscosity 5-6 Engler at 20 degrees Celsius".
The product support at Shell told me that today you measure it in centistoke (cSt or mm2/sec) at 40 degrees Celsius. This conversion gives you ISO VG 15. Shell had two suitable products which could stand cold weather, Clavus 15 and Tellus T15. The previous is a pure mineral oil without any additives. It's however some sort of cooling compressor oil and can be hard to find, especially in my quantities. Tellus T15 is a thin, hydraulic oil with no additives that could spoil your leather sleeve (at least not according to Shell). So I spent some days tracking these oils down and ended with 2 liters (!) of Tellus T15 from SGA in Stockholm. They've dealt with Shell oils for a looong time and confirmed that either of the oils would work and Tellus T15 they had in stock.
Click the picture to download in PDF-format, "Reparatur-Anleiting für Bremsgeräte T50, T50/10, T50/12, T50/14 und T50/20", © ATE (file is 5MB and it can also be noted that some pages at the end are missing, been trying to get a complete one but have failed so far)
T15 has a "pour point" of -42C. The "pour point" of a liquid is the temperature at which it becomes semi solid and loses its flow characteristics. You can compare that with e.g. some stories on the internet with bikers who had standard mineral brake fluid oil and whose brakes stopped working around 0C. No, I don't plan to drive while it is -42C but at least I want to be able to take the car out on a nice, sunny winter day with -10 to -20C. Those days can be fantastic!
The last five pictures show a replacement I did 2017 when I reviewed the 2003-restoration. I wanted to check the leather sleeve before proceeding with assembling the brake system. It looked as new but I wasn't comfortable with the "rope" I had used and which you can see in the third picture. Instead I went to a shop for old brass lamps. They had cotton wicks in 8, 10 and 12mm diameter. Since the slot for the wick is 8x8mm I went for the 10mm wick. Not cheap to buy 60cm but it fitted perfectly and absorbed the mineral oil beautifully. The wick is approx 49cm in length.
Note the last two pictures showing how to assemble the packing ring in the bottom of the slot for the wick.
And now to the color of the slave cylinder. From my memory as well as some input from Will I found a color that is almost perfect - Auto K Multona's #0800. On the picture the color looks a little bit too light blue and glossy. Reality is better but yes, it ought to be more lilac in its tone and a little bit more semi-gloss. It's very close to a NOS slave cylinder a friend of mine had. Right now I think it's enough. In my next life though...
Explosion drawing of ATE T50 brake booster for Mercedes-Benz series W105, W120, W121, W180*, W188, W198* and O319* (*depending on the Vehicle Identification No.), © Daimler AG
The rest of the gallery below shows you something that I'm quite proud of - the end result.
Even though it worked like it should when I dismantled it and I'm 100% sure everything is assembled correctly I wanted to have it pressure tested. So I went to a very reputable and old brake shop in Stockholm who has helped me before. We first had a long conversation about old Mercedes-Benz in general and what I'm doing with my 219. Then I showed them the booster and asked them to test it. They refused to do it, it was too nice looking and they didn't want to have on their responsibility to damage the like-new-finish! Their comment was "If it looks like that on the outside and you've accomplished the same on the inside and it worked as it should before the restoration there's no reason to test it" plus "The functionality is so simple so you can/will test it as well during the first drive. If it doesn't work you'll notice but you can still brake without it". My father's comment was the same so I skip it (any comments from you, dear reader?). It's partly flattering but partly annoying not to have it tested, I've restored fully functional parts before with a bad result...
During 2017 I started to go through the brake system parts before their assembly. I didn’t feel comfortable without testing the brake booster. I went back to the same company that earlier, as mentioned above, didn’t want to test the booster, Bil & Industribromsar in Bromma. They didn’t remember me and that they already had turned me down. After some persuasion efforts from my side they said yes to do it. They had been asked by other clients and they had most of the equipment but didn’t knew how to perform it. Since I had the ATE-instructions we decided to do this in cooperation. It took some time before they had time for the tests and unfortunately, the tests rather quickly showed that I had a leakage in the valve housing on the upper part of the ATE T50’s front plate. It turned out that I had two small scratches in the seat against which the small valve disc of the atmosphere poppet seals. Strangely enough the three pins that limits the outward going movement of the large valve disc was worn down (5th picture). The large valve disc’s bushing had also left small markings in the valve housing (6th picture). I decided not to care about these two things. The new bushing had a slightly different size so according to my measurements the new bushing would not come in contact with the housing. Beside of a small, easily fixed leakage in the small control valve piston (7th picture) behind the diaphragm in the same vacuum valve housing, the hydraulics was without any leakage.
Main problem, finding a new poppet
To remedy that, i.e. grind the seat carefully (maybe 1/10 mm to get it levelled and tight), I needed to remove the poppet. Removing the poppet meant destroying it. Where could I find a new one? I took contact with several companies in Europe and USA but no-one had a replacement poppet, only complete, used valve housings, often for ridiculous amounts of money, even for dull looking or painted housings. Had they tested them? “No, but we can promise it’s tight”. What is “tight” if it hasn’t been tested? This valve is impossible to get 100% tight, it is a matter of how small an amount of vacuum that slips out during a certain amount of time. This amount is specified in the ATE-instructions. If you haven’t tested it, can you say it is “tight”??? According to me you cannot.
Teaching board DBL 205 Brake booster ATE T50, © Daimler AG
I didn’t want to spend money on something used and untested for my brakes. I would also have had to glass bead and tumble the used housing to get the same luster/finish as the other parts of my ATE T50 unit. With some further googling I found a replacement poppet made by an Argentinian company, but I didn’t feel confident with the looks of it and I also heard that some have had problems with it. If this is correct I don’t know, it’s up to you to check it yourself, I didn’t want to take that chance either. Finally, it turned out that Werner Karasch had one poppet to sell, the last from a batch of parts they had bought from a, to me unknown, company. My Indian friend, Mr Tagore, who also had bought one from Karasch, recommended it. From the pictures I got from Mr Tagore and Karasch I could see it looked very well manufactured. Could it be some left-overs from Mercedes-Benz’ reproduction of the ATE T50 booster around 2006? It took some time before the shipment from Karasch was complete (…) but it was worth the waiting, the items were perfect. The old poppet’s valve discs were connected with a flexible wire as can be seen in the 5th picture in the gallery below. The new poppet came with a flexible shaft, a very nice solution.
I spent some time measuring and understanding the poppet and its function/movement. I was rather sure the replacement parts, together with my assembly, wouldn’t be 100% like the original so I wanted to understand how that would affect the function of the small control valve piston, the diaphragm and the atmosphere poppet itself since I would level the seat. I only had one try when assembling it and didn’t want to make mistakes.
In the gallery below you first see a drawing of the parts of the poppets. Second drawing shows the position of the atmosphere poppet depending on if the brakes are engaged or not. As you can see the horizontal movement of the poppet is only 1,5-2,0 mm! Much less than I thought. You could of course extend the shaft and thereby also extending the movement. I don't know why that would be beneficial though. When the small valve disc leaves the seats the vacuum will be release even with a 2 mm gap. Due to different reasons it is not possible to extend the shaft more than 3-4 mm. The two last pictures show the snap ring and the piston stop washer (that picture is of another booster, not mine) as well as the control valve in its fitting.
First the valve seat was carefully leveled with a soft Dremel emery polishing wheel (#425) set up in a bench drill to get it even and straight. The first picture in the gallery below shows the result. The second activity was to secure the large valve disc, the one that rests against the diaphragm, to its bushing. Instead of having a tool manufactured, I decided to use what I had at home. The homemade tool consists of the following parts (from the right to the left in the 2nd picture below): - a washer to center the pin in at the bottom, the wide part, of the socket - a pin to center the bushing and with a carefully measured length in order to get the bushing into the correct height in the socket - a socket to hold the bushing and to act as a counter hold - the bushing - the valve disc - and finally, a small socket with which a flange is pressed out on top of the valve disc The 6th picture shows the complete “package” that I carefully put into a vice which I used as a press. The 7th picture shows the original flange and the 8th picture shows the final result (this picture is a detail from a picture of the completely assembled poppet so you can also see the press marks for securing the bushing to the shaft).
Then I turned to figure out how I should secure the valve discs and their bushings against the shaft. It took some time and testing. In the first picture in the gallery below you can see how the three indentations looked like originally. I tried to find a tool or suitable pliers for pressing this but didn’t succeed. I could have had a tool manufactured but that turned out to be too expensive. One of my bright ideas was to create a tool with the help of a drill chuck (2nd and 3rd picture). Unfortunately, I couldn’t create enough pressing power in its jaws in order to secure the bushings to the shaft. Maybe it had been possible if I have had access to a lathe chuck. I finally settled for using a die stock handle. That gave me the possibility to press from all three directions, with enough power, and also performing this work inside the valve housing which is necessary for the large valve disc. One problem was however that the threads in the handle weren’t tight and hard enough, so one screw got tilted. The result maybe doesn’t look 100% nice but it definitely holds the parts together with the sealing surfaces in parallel. The atmosphere poppet is now “tight”. The result is shown in the two last pictures.
The hose connector
The valve chamber, in the valve housing, is connected to the cylinder chamber, the chamber behind the large power piston, via a tube with 10mm outer diameter. The tube actually consists of two parts, the long one that is welded onto the can and the shorter one, screwed on top of the valve housing. Those tubes are connected with a hose connector made of rubber. It turned out that my old connector wasn’t tight, I lost vacuum there as well. Finding hoses that look like the original, thick walls and hence a large outside diameter, was impossible. I found decent looking hoses with inner diameter 9 and 10 mm but those were not tight enough either. Going for a hose with 8 mm inner diameter would have given me a hose with a far too small outer diameter to look good. One alternative would of course be to seal my old hose in some way (e.g. with some suitable type of tape or thread glue) but instead I ordered a NOS hose. It turned out that its inner diameter was only 8 mm. I pain in the b-tt to push onto the tube but the result was 100% tight.
Completing the test equipment
During our first test, the one that revealed that my atmosphere poppet seat had scratches, we only had one vacuum manometer. Due to this we couldn’t measure the vacuum difference between the cylinder chamber, the chamber behind the large power piston, and the vacuum check valve at the bottom of the front plate. That vacuum manometer’s wide scale range also made it difficult to measure the low vacuum that is being measured. Hence, I ordered a specially made, new vacuum manometer from Svenska Manometerfabriken with a 0 to -10PSI scale range and double/differential gauges.
A new double gauges vacuum manometer
Unfortunately I write about this second test over a year after it was performed so my memory fails me regarding the details. Briefly it can be said that nothing goes without a problem in this restoration business, the brake shop rather quickly dropped the new manometer on a steel table so it went back to Svenska Manometerfabriken for repair and a check. After that the brake shop lent me their equipment so that I could continue the work at my pace in my hobby room. The new tests didn't work out well. It turned out that the new, now repaired and "checked" manometer was leaking (see first picture below). I did a solder repair myself but the gauges didn't move as they should so it went back to Svenska Manometerfabriken again. They finally fixed the manometer and also provided (sold) me with special hoses that would fit the brake booster better than the homemade I had been using so far.
The second test thereafter went perfect. Maybe the picture of my home-made test bed in the gallery below don't give a professional impression but it worked as it should and helped me to, together with the manual, reveal a lot of small leakages here and there in the assembled unit and finally prove that the ATE T50 unit met - and actually exceeded - all specifications. For the first time in my life, I could hear the sound of the flowing air when I "stood on the brakes". I have never heard that before, only heard of it. So, I can make the conclusion that the brake booster has never worked as it should as long as I have been driving it. Now it does!
Manufacture atmosphere poppets?
I have enough drawings and knowledge of the poppet today in order to be able to have it manufactured myself. The start-up cost is however high for the manufacturing of a high-quality poppet. If you’re interested, let me know and I’ll put you up on a “waiting list”