Asciidv Posted March 28, 2015 Share Posted March 28, 2015 I have a mid-50's Dennis fitted with a Rolls B80 engine with a vacuum hydraulic Clayton Dewandre servo. I am in the process of bringing this back to life after it has stood for 8 years. I had to fit new brake hoses and brake cylinder repair kits but I have been puzzled how one week the brake fluid reservoir can be full only to find it empty the next time I looked, but with no trace of fluid on the floor. I have kept refilling and then bleeding the system without understanding what the true cause is. Today I think I have found the cause. It appears that the fluid is being sucked into the engine and burnt in the engine via the Clayton Dewandre servo. With the engine running and the fluid reservoir empty I can put brake fluid into the reservoir and hear and immediate change in engine note with black oily smoke coming out of the exhaust. Looking at the servo diagram it seems a very tortuous route for the brake fluid to reach the vacuum pipe. The seals on the master cylinder would have to be worn and the vacuum diaphragm on the servo piston would have to leaking too. Has anyone ever experienced this before, or can offer me any other explanation of how the brake fluid can just vanish. Over the past few months I have been through quite a few litres! Any suggestions gratefully received, Thanks, Barry. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted March 28, 2015 Share Posted March 28, 2015 I have a mid-50's Dennis fitted with a Rolls B80 engine with a vacuum hydraulic Clayton Dewandre servo. I am in the process of bringing this back to life after it has stood for 8 years. I had to fit new brake hoses and brake cylinder repair kits but I have been puzzled how one week the brake fluid reservoir can be full only to find it empty the next time I looked, but with no trace of fluid on the floor. I have kept refilling and then bleeding the system without understanding what the true cause is. Today I think I have found the cause. It appears that the fluid is being sucked into the engine and burnt in the engine via the Clayton Dewandre servo. With the engine running and the fluid reservoir empty I can put brake fluid into the reservoir and hear and immediate change in engine note with black oily smoke coming out of the exhaust. Looking at the servo diagram it seems a very tortuous route for the brake fluid to reach the vacuum pipe. The seals on the master cylinder would have to be worn and the vacuum diaphragm on the servo piston would have to leaking too. Has anyone ever experienced this before, or can offer me any other explanation of how the brake fluid can just vanish. Over the past few months I have been through quite a few litres! Any suggestions gratefully received, Thanks, Barry. Hi Barry, I have come across this before with those Clayton servos. There is usually a drain on the casing, a small pressed steel plate with a rubber flap, but it might be bunged up with dirt. Any leak has to come from the open end of the master cylinder, due to wear or rust damage in cylinder or worn seals. The fluid can be drawn past the leather piston seal on the servo and back to the engine. There might be a screwed plug in the bottom of the casing so remove that and see what comes out. Richard Quote Link to comment Share on other sites More sharing options...
Asciidv Posted March 29, 2015 Author Share Posted March 29, 2015 Richard, Thank you for your reply. It is re-assuring that someone has come across this problem before. I looked at the bottom of the servo today and you can see quite clearly where brake fluid has leaked out of the bottom section of the servo. I'll take off the servo next weekend, but in the meantime can anyone suggest where I should go to for a rebuild kit. Although there are some on ebay only the kit number is given and not the servo to which they are applicable. I rebuilt the Solex carburettor for the B80 engine and it didn't seem right to put a sparkling carburettor on a dirty engine so it was given a clean and re-paint too. Although I say it myself, I do think it looks very smart! Barry. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted March 29, 2015 Share Posted March 29, 2015 Hi Barry, It will not be the servo seals at fault, this is the master cylinder that is leaking, go to Past Parts Ltd at Bury St.Edmunds. I have been dealing with them for 20 years. If the master cylinder has any corrosion or rust spots in the bore, they can sleeve it with stainless steel, and supply seal kits. Richard Quote Link to comment Share on other sites More sharing options...
Asciidv Posted April 4, 2015 Author Share Posted April 4, 2015 This weekend the servo came off and this short video tells all! [video=youtube_share;mhgh0vyJF8A] Barry. Quote Link to comment Share on other sites More sharing options...
Asciidv Posted April 5, 2015 Author Share Posted April 5, 2015 When the piston came out of the vacuum housing, the damage caused by the brake fluid being in the chamber could be seen. It appears that some of the brake fluid had dried out to hard crystalline 'lumps' and these 'lumps' dragging past the seal had damaged the lip of the seal. The leather seal is backed by a spring steel disk with curved 'fingers' which help to keep the seal in contract with the vacuum housing. The seal is a simple leather disk of 4mm thickness. I intend to make a new one and wet mold the leather into the basic shape. Has anyone made such seals before and can you offer any advice? Thanks, Barry. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 5, 2015 Share Posted April 5, 2015 The seal is a simple leather disk of 4mm thickness. I intend to make a new one and wet mold the leather into the basic shape. Has anyone made such seals before and can you offer any advice? Hi Barry, I have made and fitted a number of leather piston seals for Clayton servos on Austins and Bedfords. First you need some good quality leather of the correct thickness. The type I have done have a single hole in the centre, unlike yours, but should still be a simple task. Once cut, fix it to the piston, then soak it in water for a period, next step is to push it into the bore and leave to dry out. If yours is a steel bore, it will be a good idea to oil or grease the cylinder to stop rusting. Once leather is dry, remove piston and take off leather seal and soak it in oil, then it is ready to reassemble. Not sure on your type, but the ones I have rebuilt before have an oiler to lubricate the seal periodically. regards, Richard Quote Link to comment Share on other sites More sharing options...
Tony B Posted April 5, 2015 Share Posted April 5, 2015 Just to clarify Richard. When you say soak the seal in oil. Do you mean leather oil, Neatsfoot (Cowsfoot) oil? Go see your local saddler, they will have something suitable and can advise on stretching and fitting. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 5, 2015 Share Posted April 5, 2015 Just to clarify Richard. When you say soak the seal in oil. Do you mean leather oil, Neatsfoot (Cowsfoot) oil? Go see your local saddler, they will have something suitable and can advise on stretching and fitting. Tony, Not neatsfoot. In this case, you use engine oil as it has to lubricate the seal as it slides up and down the cylinder. There is a oiling point to regularly inject it as well. I have done this many times and never had any problems. Quote Link to comment Share on other sites More sharing options...
Tony B Posted April 6, 2015 Share Posted April 6, 2015 Normally mineral and oil and leather don't mix! :-D Though soaking it in cheap vegtable cooking oil would lubricate it, and make it more resitant to mineral oil rotting. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 6, 2015 Share Posted April 6, 2015 Normally mineral and oil and leather don't mix! :-D Though soaking it in cheap vegtable cooking oil would lubricate it, and make it more resitant to mineral oil rotting. Tony, try thinking outside the box ........ many oil seals still being used are leather. This is how they were in the CD servos, the oil is a lubricant as well as a sealer, not a preservative like neatsfoot. Quote Link to comment Share on other sites More sharing options...
Asciidv Posted April 6, 2015 Author Share Posted April 6, 2015 My plan was to use neatsfoot oil to keep the leather supple and durable and then red rubber grease for the lubrication. This was prompted by seeing Clayton Dewandre rebuild kits on ebay which included a tube of 'special' grease. However if engine oil has proved successful in the past as Richard has described then this is perhaps the approach that I should take. My vacuum tank is 7" in diameter and is a deep drawn aluminium cylinder. There is no auxiliary port for lubrication injection. Barry Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 6, 2015 Share Posted April 6, 2015 My plan was to use neatsfoot oil to keep the leather supple and durable and then red rubber grease for the lubrication. This was prompted by seeing Clayton Dewandre rebuild kits on ebay which included a tube of 'special' grease. However if engine oil has proved successful in the past as Richard has described then this is perhaps the approach that I should take. My vacuum tank is 7" in diameter and is a deep drawn aluminium cylinder. There is no auxiliary port for lubrication injection. Barry Hi Barry, I was not sure if there was an external lubricator on your servo as the casing is different. On the all alloy one-piece housing there is a fitting that allows drops of thin hydraulic oil, but with modern engine oils being thinner that 1940's I use that. The rebuild instruction say to soak the leather seal in this oil. There is a drain plug to drain off any excess, on the alloy servos, likely to be on yours as well. regards, Richard Quote Link to comment Share on other sites More sharing options...
Tony B Posted April 6, 2015 Share Posted April 6, 2015 The Red Rubber Grease sounds very like Coachaline. :-D Very useful stuff to preserve and lubricate leather and metal fittings on canvas and vehicles. Richard remeber my knowledge of leather is stuck on the back of horse! Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 6, 2015 Share Posted April 6, 2015 Richard remeber my knowledge of leather is stuck on the back of horse! Tony, my knowledge of leather is using it in mechanical engineering ..... two different things ! You need to enter the 21st Century and ditch the horse Quote Link to comment Share on other sites More sharing options...
Tony B Posted April 7, 2015 Share Posted April 7, 2015 (edited) Ah but if your 21st century is in the ditch. The horse will still be going! :cool2: Any way, horse hair is used to make gaskets for cryogenic work. The use of carbon fibre to rebuild tendons was a technique pionnered in horses, and you still measure your mechanics,in Horse Power. Edited April 7, 2015 by Tony B Quote Link to comment Share on other sites More sharing options...
Asciidv Posted April 7, 2015 Author Share Posted April 7, 2015 This is the vacuum tank in which the piston operates. This machine had stood unused for almost 8 years and quite possibly brake fluid had sat in the bottom of the tank for all of this period which has resulted in corrosion of the aluminium. I hope that this will not result in a significant loss of vacuum although once the brakes are activated the piston moves further down the tank where there is no corrosion. I suppose my main concern is that the engine could be sucking air in and weakening off the mixture to the B80. I wonder if this is a valid concern when you compare the possible size of the air leak here compared to the big open hole on the Solex? Barry. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 7, 2015 Share Posted April 7, 2015 I suppose my main concern is that the engine could be sucking air in and weakening off the mixture to the B80. I wonder if this is a valid concern when you compare the possible size of the air leak here compared to the big open hole on the Solex? Barry. Hi Barry, The engine would only draw air from that chamber when the brake was applied. There is a little valve that opens as clearance is taken up when pedal is depressed. What you could do is fill the corroded area with something like Belzona and polish off so it fills in the pits. Quote Link to comment Share on other sites More sharing options...
Asciidv Posted April 9, 2015 Author Share Posted April 9, 2015 Tonight I made the vacuum piston seal. As I wanted more than one, I first milled a template. I used this to drill the leather (3mm thick from ebay). I then bolted through the template and leather onto a bed plate. I then profiled the inner and outer diameters ..and within a few minutes I had a lifetime supply of 7" CD vacuum piston seals. Here is one fitted to the piston assembly. It has already been soaked in water ready for fitting to the vacuum cylinder. After an hour in the cylinder it came out looking like this, exactly as it should. It is now being left to dry out and despite Richard saying any old oil will do, I am first going to give it a good soaking in Neatsfoot oil. After it is all assembled I am going to test out the unit before fitting. I hope a 'Henry' type vacuum cleaner is going to give enough suck to prove the correct operation. Barry. Quote Link to comment Share on other sites More sharing options...
Tony B Posted April 9, 2015 Share Posted April 9, 2015 Ordinary cooking vegtable oil would work as well Barry. I'd lather the thing with Cocohline, the red grease you described. That dosent dry out preserves metal and lubrictes. Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted April 9, 2015 Share Posted April 9, 2015 After an hour in the cylinder it came out looking like this, exactly as it should. It is now being left to dry out and despite Richard saying any old oil will do, I am first going to give it a good soaking in Neatsfoot oil. Good work, Barry! Actually the workshop manuals say use a light oil mineral oil such as hydraulic oil. cheers Richard (the Equine orientated member on this thread will still bang on about neatsfoot and saddles :yawn:) Quote Link to comment Share on other sites More sharing options...
Tony B Posted April 10, 2015 Share Posted April 10, 2015 good work, barry! Actually the workshop manuals say use a light oil mineral oil such as hydraulic oil. Cheers richard (the equine orientated member on this thread will still bang on about neatsfoot and saddles :yawn:) neigh! Quote Link to comment Share on other sites More sharing options...
radiomike7 Posted April 1, 2019 Share Posted April 1, 2019 Henry will not be too impressed as he relies on the airflow to cool the motor. Quote Link to comment Share on other sites More sharing options...
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