21BK40

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.

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 !!

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

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 ?

Hmm, great idea, thank's Clive

Hey both, drifting snow eh ! - kind of reinforces my recent decision to buy a nice SUMB, I figured it was a wothwhile purchase compared with potenrial loss of earnings (I'm a contractor so no work - no pay !!) Going to Bristol next w/e to have a look at it. It will take the pressure off having to rush to get the Pig done if I have something else to take to shows in the meantime. Back to brakes... yes nice & firm now but the stopping power doesn't seem up to par, I'm going to jack up each corner to see if everything is as it should be when the brakes are applied, I might have a siezed wheel cylinder or two or maybe just needs adjustment - too cold down here as well today so it will have to wait. I bought some "vintage" wiper blade from a site on e-bay (poss the same one you bought your cylinder from as I saw one on there as well), they duly arrived this week. They were for a much larger windscreen and the metal backing strips are slightly larger dimensions but I managed to cut them down to Pig size and re-attach the old clips - great job.

Hi all, Just an update on my Pig brakes - still no fluid lost after a week so I must have cured the leaks with the master cylinder refurb kit. I put my NOS clyinder on test by filling it with DOT 4 and leaving the plastic thread protectors in place to test the reaction of the rubber to the fluid. No problems so far, I'll leave for another week to see if there is any apparent change :-D

Ah, all very interesting, thank's guys - just for the record I have always used Dot 4 on my Pig. I put my refurbished Master cylinder back on today & spent an hour bleeding the Servo & wheel cylinders - wasn't overly impressed by the results, although I'm not losing fluid any more the brake efficiency didn't seem up to par. I will go round the adjusters and re-bleed next w/e to see if I can improve things.

Ah, ok, thank's Clive, is the earlier spec "orange" fluid a mineral fluid (although I know they were generally green in colour) and is the OX-8 compatible with Dot 3 - what do you use in your Pig ?

The new one shown in your photo looks just like the one I bought recently. With regard to the correct fluid for the Pig, maybe Clive can advise what it says in the Maintainance schedule, unfortunately it's the one thing I dont have a copy of. I did re-read Clive's guide on lubricants and fluids and noted that he referenced a possible suitable pig brake fluid as being; OX-8 H-542 TS 10 145 SAE J 1703 Apr. 1968. Brake fluid for certain hydraulic clutches & most automotive braking systems fitted with cups & seals made from natural rubber & styrene butadiene. From what I have read, this seems to equate to DOT3, maybe someone in the know could comment

This for example is a particularly interesting statement from a Jaguar forum explaining why they wouldn't use silicone fluids... "Seal compatibility is another potential problem. Glycol fluid is designed to swell the rubber seals in various cylinders to a controlled degree. They wouldn't work otherwise. Silicone, however, must rely on additives to swell the seals. The additives work fine with current-technology rubber, but the older seals found in many British applications don't fare so well, often softening and swelling too much."

Hmm, I have just done some reading on t'internet about fluid compatibility, it's a bit of a minefield and well worth reading the various articles as it gives a lot of insight into the different Dot types and chemical makeups and possible consequences of using incorrect fluids.

Ha ! yes I'm sure I'm going to get a similar result - fixing one knackered part just puts more strain on the nearly knackered parts ! I have some new hoses and wheel cylinders at the ready. Back to brake fluids - how have they changed since the 50's,- if the emphasis is on using the correct fluid, is the "correct" fluid still available to suit older seal materials ? If so, I'm guessing you can use the newer seals with both older and newer spec fluids but not vice versa. .......Anyone know enough to explain ?

Fair play, since I paid £90 for mine at what I thought was a bargain price, the only other price guide I had was that quoted by that "certain other supplier", if they are available for £50-£60 then I'm with you all the way, go for them all day long. I'll be a bit more picky in future when I see an apparent bargain to pass on - to be honest, I hadn't needed one until recently and was just glad to find one at all and didn't mind paying £90 as opposed to £250 !! Re- the top plate arrangement for the Ferret, I would think that the plates are all the same and that the extended filler screws in, in place of the plain plug and ditto for the Pig's drilled & tapped plug type fitting. I think I would take on board the comments about the suitability of the rubber parts provided with modern brake fluid & swap them out with a more recent refurb kit just to be sure,total brake failure can be so inconvenient :cool2: