21BK40 Posted September 25, 2011 Share Posted September 25, 2011 (edited) Oops - wrong category !! Hi y'all, I bought a SUMB a year or so ago but haven't been able to enjoy it due to problems with the brakes. It's a problem inherited from the previous owner who assured me that the brakes were in good order (yeah right!!). As some of you may know, the SUMB uses an Air over Hydraulic system employing a French made Bendix Air Pack (not dissimilar to the one used on the Stalwart as it happens), this if fed compressed air via an engine driven compressor and storage tanks. The system provides hydraulic non-assisted braking in an emergency & since I have to virtually stand on the pedal to get it to brake, I suspect that the Air Pack isn't doing it's job at all. I even fitted a take out Air Pack from RR Services but the problem persisted. Given that RR or myself have not been able to find a source of sevice parts for the Air Pack, I was wondering what the chances were of converting it to a Pig/Ferret like remote servo system since these are available. (Leads me to wonder why the SUMB used the Air Pack system in the first place - is there a lack of available manifold vacuum with the old V8 flathead or some related problem ?) Has anyone else out there fitted alternate brake actuation systems to a SUMB ? Edited September 25, 2011 by 21BK40 wrong category Quote Link to comment Share on other sites More sharing options...
g0ozs Posted September 26, 2011 Share Posted September 26, 2011 Hi I have a SUMB with the original air over oil system working and the brakes apply viciously when the air assist is activated so it isn't a design fault. A couple of checks I would suggest based on how mine behaves are: 1) the pressure gauge should reach 9 or 10 and the warning light go out after about a minute from starting the engine 2) the air cylinders should hold pressure up to 8-9 on the gauge after a week or more 3) if there is pressure you should hear a loud hiss for 8 to 10 presses of the brake after the engine is stopped 4) there are pressure valves under each cylinder which should operate after the engine has been running for a few minutes and if you disturb the pin sticking out of the bottom air should be released even after weeks As far as I can recall at this time in the morning away from the manuals the air supply is from a belt driven compressor so if none of the above is true I'd look either for insufficient belt tension or a faulty compressor - it should be possible to put a pressure gauge on the output given some rubber hose and jubilee clips as final proof one way or the other ... If the air pressure is good then it's likely the air operated cylinder not working - what should happen is that the hydraulic cylinder works alone until it travels around 1/3 of the way under manual pressure then opens an air valve to trigger the air operated cylinder at the back of the air pack which pushes it the rest of the way. Dismantling and cleaning all of the assembly at the back of the air pack would be a first suggestion in that case. You can find the full service manual MAT4155 on line as individual jpeg scans of pages with a little help from google and http://www.tm-ww2.com sold me a PDF version last year As to why air over oil seemed a good idea at the time rather than vacuum assist or full air brakes I am not sure - no doubt people who were involved in motor vehicles in the late 50s can comment ... Hope this helps Iain Quote Link to comment Share on other sites More sharing options...
g0ozs Posted September 26, 2011 Share Posted September 26, 2011 An afterthought on air over oil vs. Vacuum is that the air system can store enough pressure for several applications of the brakes for an extended period even with the engine off - I wonder if that's why it was used ? Iain Quote Link to comment Share on other sites More sharing options...
21BK40 Posted September 26, 2011 Author Share Posted September 26, 2011 Hi Iain, Thank's for your thoughts - the system seems to operate correctly in all other ways (building up pressure from cold, red light going out, pressure release as pressure exceeds max allowed etc.) The problem I have is that on the first push on the the brake pedal, it feels fairly progressive but very solid (it needs a fair bit of foot pressure to fully depress), on every subsequent stroke, the pedal is almost impossible to press and hence takes an age to get to the point where the brakes start to apply - obviously not good. Having replaced the Air Pack for a take out (with no improvement),I stripped the Air Pack and found that the seal on the hydraulic piston controlling the air valve was leaking & thus was probably not operating the air valve. I suspect that all other take out Air Packs will have similarly old seals and will start to leak after limited use. I have challenged a brake specialist to try to match the seal (and the one on the slave piston)to a current type...I'll let you know how I get on. On another note (since you are an owner), despite a carb change and an electronic ignition upgrade, I can't seem to get any power out of the engine, having checked most things through (and replacing the accelerator pump with one from a UNIMOG kit) I'm wondering if it could be a head gasket problem or similar - any thoughts. (I have timed the ign as per the EMER). Regards Quote Link to comment Share on other sites More sharing options...
g0ozs Posted September 26, 2011 Share Posted September 26, 2011 Hi It sounds like I should get a seal in anticipation of future failure if you find a source - I can also inquire in France (a ham radio friend there holds a stock of parts from when he used one). I have similar engine issues - it splutters when picking up speed after changing from 3rd to 4th or going up hill so i dont think I'm getting 110hp - the oil breather pipe blows a bit so I suspect a gasket is failing on 1 or 2 cylinders - I have got a spare set of gaskets but it isn't yet bad enough to want to dismantle without access to a covered workshop unless desperate. I will likely do a compression test to prove it first and wait on a good forecast next summer ... The gaskets came from ass.service.national on e-Bay in France who ships some items to UK. Regards Iain Quote Link to comment Share on other sites More sharing options...
21BK40 Posted September 26, 2011 Author Share Posted September 26, 2011 Hi Iain, At last!! .. a positive update on the brake seals I'm glad to report. I spoke to a UK seal manufacturer today who say they do a lot of one-off's and small batches. For a small seal such as the ones we require, they were talking about £7.50 each with a 7 to 10 day turnaround. These are made to order and they prefer to have the assembly as well as the old seal to which the seal is fitted to determine the proper sizing - sounds as though they know what they are doing ! The plan is to send them the key bits of the Air-Pack, a master cylinder and a wheel cylinder to see what they come up with. If they mange the whole package, I'll fit and test whatever they can manage and pass on my findings to the forum. As for the engine, I do have a gasket set thank's and am thinking more and more about popping the heads off to see what condition everything is in. I too did a compression test but it wasn't very conclusive although there were some inconsistencies between cylinders - I have since bought a Gunsons exhaust analyser which I may use just to check the carb settings before lifting the heads but the more I think about it, the more I think it's lack of cylinder pressure for whatever reason. Watch this space !! Quote Link to comment Share on other sites More sharing options...
g0ozs Posted September 27, 2011 Share Posted September 27, 2011 Hi I'd be happy to buy a 2nd set of the seals for the air and wheel cylinders for stock - please PM me so we can arrange payment and delivery Regards Iain Quote Link to comment Share on other sites More sharing options...
21BK40 Posted September 27, 2011 Author Share Posted September 27, 2011 (edited) Hi Iain, This is all looking very promising - I did have an interesting conversation with the manufacturer about materials, they offer EPDM as standard and I questioned the compatibility of this with Mineral and DOT grade fluids. What he seems to be saying is that EPDM is compatible for use with mineral or DOT grade (see update below) fluids but you need to be careful about how you apply them. You can for example replace just the master cylinder seal or the Air-Pack seals (or both) but you shouldn't do only one wheel cylinder on an axle to avoid potentially unequal braking forces due to the better sealing qualities etc. of the new seal vs the old one. I'm still awaiting his confirmations on the compatibility issue but that seems to be the flavour of it at the moment. If he can supply all the seals, the plan is to change them all for EPDM and use Dot 4 fluid to avoid any uncertainty, I have to admit that without checking the EMER, I'm not sure what the SUMB used (Mineral or DOT). (The SUMB EMER refers to an American spec for the brake fluid which relates to "non-petroleum based" fluids so I guess that means that the SUMB uses DOT type fluid and not mineral). Important update on the above for anyone following this thread - I am now informed that EPDM is not the best choice for Mineral oil based Brake fluid....so its EPDM for all DOT type fluids and NBR for Mineral types as advised by the seal manufacturer. Edited September 28, 2011 by 21BK40 Further information rec'd Quote Link to comment Share on other sites More sharing options...
MUDMAX Posted October 15, 2017 Share Posted October 15, 2017 I'm keen to know the outcome of the air pack seals UK manufacturer special order.... Was it successful? My SUMB has exactly the same symptoms as described by 21BK40. All looks good on the air pressure but brake pedal needs a hell of a heavy boot with no apparent air assistance kicking in. I haven't yet checked if the air pack is getting the necessary hydraulic "signal" via the master cylinder, but I suspect that the air pack isn't operating properly and it is either 'sticky' and needs cleaning out or needs new seals. If you are still out there 21BK40, how did your story finish? MUDMAX Mike Quote Link to comment Share on other sites More sharing options...
Slimjim176 Posted September 8, 2018 Share Posted September 8, 2018 I'm also interested as my air pac is in a poor state and requires a complete overhaul (or replacement with an equivalent) Thanks, Adam Quote Link to comment Share on other sites More sharing options...
rdg Posted May 19, 2019 Share Posted May 19, 2019 Hi I have the same problem whats the seal manufactures name and contact number I am not pop eye and stoping is a bit hairy sometimes Quote Link to comment Share on other sites More sharing options...
Slimjim176 Posted November 3, 2019 Share Posted November 3, 2019 On 5/20/2019 at 12:38 AM, rdg said: Hi I have the same problem whats the seal manufactures name and contact number I am not pop eye and stoping is a bit hairy sometimes Nelson Hydraulics can supply the wheel cylinder seals, but I haven't tried to source any air pak seals Quote Link to comment Share on other sites More sharing options...
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