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MG MGA - Brake Pressure Slow Release
| My car annual road test today revealed a slow release of brake pressure, something I had been suspecting for a while. When the car was up on jacks I had noticed a significant tightness when rotating the wheels after releasing the brakes (disc brakes). After about 5 to 10 minutes the wheels would spin quite happily. I assume it is partial blockage by the MC brake piston of the fluid return hole. This is despite shaving 10 thou off the piston 12 years ago. I spoke to Bob West this afternoon and he was of the same opinion, stating that the increased swelling of the seals with silicon fluid has probably negated my earlier engineering modification. He said that he normally takes 25 thou off the 'older' MC pistons, rather than my meagre 10 thou. He also said that the problem appears to have been rectified by the manufacturer in recent years. Before I savage the piston in my lathe in the morning for that extra 15 thou anyone want to comment? Steve PS. Maybe a free running set of wheels will improve my MPG - averaging 22.98 since 2005. |
| Steve Gyles |
| I forgot to ask, can anyone quote me the original piston length please - just a double check that I don't go mad on my lathe and that it was only 10 thou I took off all those 12 years ago. Steve |
| Steve Gyles |
| How old are the brake flex lines. They do break down internally and cause those very symptoms. Sandy |
| SANDY SANDERS |
| Sandy. I have those in mind as well. One thing at a time then I will know the cause. I have a lathe, so checking and altering the length is a freebie. If that does nor cure it, then it's the brake pipes. Steve |
| Steve Gyles |
| I would suggest you look through my previous thread where I had the same issue....and it was discussed at length. Probably the hoses collapsing like in mine? Why not rebuild the MC with new seals? |
| Gonzalo Ramos |
| Sandy, Gonzalo et al The seals are original old stock and were replaced about 6 months ago. I previously replaced them about 18 months ago. I have had long running doubts about the integrity of my hydraulic system and have had the MC apart 3 or 4 times over the last year or so. Anyway, phase one completed and shortened the piston by a total of 0.025". The original length of these pistons is 2.0001". I am glad I did it. I found the small cup washer at the end of the brake cylinder had unseated itself (not for the first time) and I guess that could be indicative of failure of the line pressure to release. I also found that the clutch piston seal had unseated itself - rather odd. I have decided to bite the bullet on this one while I have the MC drained and replace all three flexible hoses. I am happy to concede that the pipes may well be the cause since I have been suffering brake squeal from the front left when I apply the brakes. This could have been caused by the collapse of the pipe on that side, holding the pressure on and causing the pads to become'polished' when not braking. All brake pads and rear linings were replaced about 6 months ago. I will let you know the result when the new pipes arrive tomorrow and I have them fitted. Steve |
| Steve Gyles |
| Steve - Sounds to me that you have once and for all shown that silicone fluid does not belong in there, or at least the kind you are using. Seals unseating themselves is unheard of, and can only mean they are swelling and/or going soft, not what you really want. Not in your new hoses either! Might be a nice thing to tell people exactly what fluid you are using. And if you get good seals and fluid that doesn't swell them, you will find that your piston mods have added useless free movement before the brakes come on. FRM |
| Fletcher R Millmore |
| I don't understand how the piston seal can come unseated - those things are hard to put on at the best of times, and when the piston is surrounded by its cylinder, I don't see how there can be enough space to roll it off again, especially if it has allegedly swelled. I suspect they are either wrong (in the correct NOS box). I would also suggest that using NOS seals that may be 30 years old may not be the best idea either. To NOS design but brand spanking new is what I fitted last time, and I have had no trouble at all with them. |
| dominic clancy |
| FRM You wont get me on that one. I swear by silicon fluid. No way would I ever go back to mineral fluids. I can only assume it was my error in assembly of the clutch seal. The brake seal was firmly in place. Never had any problems with the seals that I can blame on silicon fluid. I will attempt to dissect the old flexible pipes tomorrow to see if there was any problem with them. My Silicon fluid is made in the USA, so I could always blame you guys! It is Automec SBF Dot 5. Cheers Steve |
| Steve Gyles |
| Dominic I misunderstood what Bob West meant when he said NOS. I just phoned to clarify. What he meant was New British made to the original design (made by AP Caparo), rather than Chinese imports. Steve |
| Steve Gyles |
| Where does the "swelling" of seals comment on silicon fluid come from? An old wives tale? Check the science DOT 3-4 swells seals. Not swelling seals is one of DOT 5 advantages. Seals don't "unseat" themselves. That is a description of improper assembly. The incorrect seal instalation is your problem, been there done that. First time I used DOT 5 20+ years ago I had the same problem. Fought that for quite a while. Finally pulled out the seals and found one folded over. Silicon is not as "slippery" as dot 4. This makes it a bit harder to get the seals in right. Sit it on end and use a lot of fluid to put it together. |
| R J Brown |
| I have seen a report where the US military changed to DOT 5 (silicone) some years back but that they also allow mixing of silicone and glycol ester type fluids (DOT 4 & 5) if the need arises - apparently there are no ill effects! Maybe you could use DOT 4 to fit the seals then fill the system with DOT 5! By the way it is silicone brake fluid not silicon - silicones are polymers of elemental silicon (Si) - a silvery hard metalloid (sorry for being pedantic). Mike |
| Mike Ellsmore |
| I don't know, I go out of my way to use some sort of universal English, usually shortening spellings as is the US way, and on this occasion you keep the 'e'. lol On the subject of seal swelling, I have never been a believer in it, but was just reporting 3rd party comments. Steve |
| Steve Gyles |
| Mixing fluid is a NO NO. On my bottle it reccomends flushing entire system and replacing all seals and boots if your system has DOT 3-4 in it. My bottle is spelled with the "e" Silicone. Don't trust my spelling if it weren't for spell check we might not be able to communicate. |
| R J Brown |
| Steve I just had Brown & Gammons fit a new master cylinder and braided steel hoses - The Brakes are perfect now very firm pedal and no leaks.Ready for our 1800 mile round trip to the Western Isles next week. Paul |
| P D Camp |
| Update. New flexible brake pipes fitted, in addition to the piston shortening modification. Result: No change. Still running with brakes partially on - probably been like this for years. Got home, jacked up the front (not with a Shelley Jack) and it took both hands to rotate the wheels. Released a brake nipple and they ran free. Repeated trial and released other side nipple, same result. Deduction: It's an MC problem. Tried poking a wire down the pressure relief hole and it fouled with the primary seal. Operating the piston on the bench, sometimes the hole was almost totally blocked, other times almost clear, but bear in mind that the hole is only slightly larger than 0.5mm diameter so the tolerance are very tight. Seems I have 3 options: 1. Replace the MC. 2. Shorten the piston by say another 10 thou. 3. Enlargen the hole to a decent size. I wonder if I had a Friday afternoon MC and the hole was drill out of tolerance? If you look at the holes (there are 4 - 2 each for the brakes and clutch), the pressure release hole (nearest the bulkhead) has a 3mm pilot hole to a depth of 4.5mm, then the relief hole within it through to the cylinder of about 0.5 to 1 mm diameter. Any thoughts? Steve |
| Steve Gyles |
| Is the spring too soft? Not pushing the piston forward? The piston size and hole size have been as they are for 50 years. Stretch the spring and make sure it returns the piston forward. |
| R J Brown |
| Thanks RJ. Not thought of that one. Steve |
| Steve Gyles |
| I assume that you have the required amount of clearance for your master cylinder push rods so that the piston can move all the way forward? I seem to remember someone shimming the retainer plate out by adding another gasket that had the center trimmed out. That would allow the piston to move forward by the amount equal to the gasket thickness. |
| Ed Bell |
| Ed Since you mention it, I seem to recall the original gasket on mine had cylinder size cut-outs - could be mistaken, memory not as good as it was. The current one does not! Hmmm...Same deal as skimming a bit more off the piston front face. Oh yes, push rods correctly adjusted. Steve |
| Steve Gyles |
| Steve, if you can bear to take the brake cylinder apart again may I suggest that you reassemble it but this time without the one way valve. This will show if the valve is at fault by retaining too much pressure. Please don't think that I am suggesting you do not replace the valve permanently but it may serve to isolate the problem. |
| J H Cole |
| John It's no hassle taking the MC out. In fact it's on the bench as I type. 3rd time out in 2 days It's only a 15 minute job. My gut feeling is that it is the pressure relief hole in the casting remaining covered, so even without that slow release on-way valve there would still be too much residual line pressure in the system. I will investigate/sort today and report back. Steve |
| Steve Gyles |
| Steve, I have used the extra gasket approach with the circular hole on the brake side opened out to 1 inch dia. I used a pair of dividers and patiently kept spinning them around until they cut a near perfect circle. I then cut the gasket at the top of each hole and slipped it over the push rods having first unscrewed the plate and let the pistons come back against the rods but not out of the cylinders. The cut gasket still performs perfectly well since its not credibly that cuts at the top would be detrimental. Result -no difference to the brake binding so this is why I suspect the one way valve although I have not checked as you suggest the pressure relief hole. I'm told its possible to take a mirror and see if the hole is clear in situ or even probe with some fuse wire. |
| J H Cole |
| John I thought I discovered the problem. On the bench the piston was sticking occasionally about 1/8" inch from the front plate. Honed it out slightly. Had everything working great on the bench. Put it all back and it made no difference. Needs 2 hands to rotate the wheels after brake release. Does not roll on a slight incline. I am told MGB calipers retain a fair bit of residual contact/pressure with this is silly. Discs very very hot after just a 5 minute drive with not much braking. Had enough of it. I have had issues with this MC since new 12 years ago. Not messing around with the braking system any more. It has to be right every time. Ordered a new one. Steve |
| Steve Gyles |
| Steve, understand your sentiments entirely, but it would have been nice to have got to the bottom of it. When you get the new MC it might be worth comparing side by side on the bench the new and old piston assembly and see if you can spot any differences possibly with a micrometer. One suggestion before fully connecting up the new MC is to fill it with silicone and work the pistons up and down with a rod until they move freely rather than installing it straight away. This is because, as has been said before, silicone is less slippery. I installed my new MC straight away and found the pistons stuck a little as you have said with your old one. |
| J H Cole |
| As J H Cole advised: Last week I installed the MC in the coupe. Prior to install I used low (15psi) air pressure to assist the return spring on the bench. Push in blow back, push in blow back about 20 times to insure full return and smooth action. I did stretch both return springs prior to install. Could help, can't hurt. I then used low pressure held by an assistant into the MC top to bleed systems. We used a rubber tipped air nozzle large enough to seal around the cap opening. We filled the MC between each wheels bleed. |
| R J Brown |
| Thanks John and RJ. Before I gave up I did stretch the spring a tadge. Both springs were the same length prior to that. I worked the piston probably many more times than 20 on the bench and I was entirely happy with its movement by the time I reinstalled. I am guessing that the problem lies with the end cup, but I cannot be certain. It could still be the piston sticking. Who knows? If my brake squeal has been a consequence of this problem then I have been running with it since 2004 during which time I have replaced all the seals 3 times to my memory and had the MC apart at least 6 times, may be more. I had a chat with James at Bob West's and it seems my problem is not that uncommon with some of the MCs supplied about 12 years ago. Anyway, even if I had persisted with investigation and rectification I could not be sure in my own mind that it would not recur, so I have bitten the bullet. Time to replace. Cheers Steve |
| Steve Gyles |
| It exactly this type of experience that stands behind my attitude to brake issues. Don't refurbish, just replace, and always use new. The only exception is the periodic replacement of the MC seals when they wear out, and that is because having used Si fluid since it was new, the bores are absolutely perfect. The rest of the cylinders are relatively cheap, so it's more cost effective to replace them than fix them - especially if you are paying for the labour to do the job rather than doing it yourself. |
| dominic clancy |
| I used the extra gasket method and it worked fine. And I'm using silicone fluid. |
| H L Davy |
| New MC fitted. The difference is amazing. Pressure releases perfectly. Wheels spinning so freely. Has not been like this in years. I had been assuming that the remaining back pressure I was experiencing in the MGB calipers was standard. Not so, I can now spin the wheels with one finger instead of both hands. Prior to fitting, I inspected the innards to confirm that I had my my old MC assembled correctly, which it was. On the bench, the new MC operated so smoothly in comparison to the old; and that is not down to anything to do with the so called swollen seals argument etc. I can readily recall what the old MC felt like after fitting new seals and there is simply no comparison with how the new one feels in the same state. I am coming to the conclusion that the old MC was simply poorly made - a piece of junk. However, the bores look fine so it is all bit of a mystery. Maybe the cylinders have been under bored. I will measure them shortly. What is the correct diameter? - I should have measured the new one before I installed it. My next fuel top up will be interesting. I think this problem has been causing a significant drop in MPG. Steve |
| Steve Gyles |
| The bores in my old MC are 0.863in diameter. Am I right in saying that the bores are quoted at 7/8" (0.875")? If so, that could well be the problem; under size by 12 thou. Steve |
| Steve Gyles |
| Good news about your brakes Steve, but if you don't mind me harping on about the old MC, if the pistons/seals were too tight in their bores and therefore slow in returning back under the spring pressure would you not have sensed this on the brake pedal as slack in the rods when you reapplied the brakes a second time immediately after braking? |
| J H Cole |
| John No, never felt a thing. Seemed just the same then as it does now with new MC. The only thing I have noticed today is how much more free running it feels. It even rolls on slight inclines which it has not done before. Makes me wonder how I ever got it up to 100mph. Must try it again sometime! Steve |
| Steve Gyles |
| I have been chatting with Bob West about my problem. Seems that Lockheed made small batches of MCs back in the 1990s. Some batches seem to have been okay, others not. He has had endless numbers of customers with similar symptoms to myself. Seems my thoughts about under size bores may have some founding. Bob was surprised I managed to get the seals into the cylinder - yes it was a hard push. The MC production was bought out by AP Caparo and decent production runs to high specs are now made. I can vouch for that. My new MC is by that manufacturer and is superb. Steve |
| Steve Gyles |
| Steve, I bought a new MC for my car a couple of weeks ago (my old MC was beyond honing as it had some really deep pits), it too was an AP manufactured one, I got it from the MGOC. Both pedals feel much nicer and really positive and the brakes go off immediatly and completely (drums). |
| Lindsay Sampford |
| Better not follow you too closely this weekend Lyndsay if your brakes are so much improved!! ( Thinking about it I think maybe I ought to put my bumpers back on just in case!) Steve, to improve my cars braking, I have been thinking about modifying my new giant plastic cooling fan so that I can reverse the blades whilst braking. This would provide me with BAe Harrier-like vectored thrust similar to the reverse thrust that airliners use to slow them down. It could also be used to blow away unwanted obstructions from in front of the car that I would otherwise crash into! ( eg. Lyndsays car, radar speed cameras, traffic wardens etc etc ) Colyn |
| Colyn Firth |
| Didn't say the brakes were improved Colyn, just feel nicer! See you in Chollerford, hopefully. |
| Lindsay Sampford |
| Nobody has come back and confirmed the correct diameter of the MC Cylinders, so I am assuming that mine was under bored. I have had my lateral thinking hat on overnight and have come up with the following theory based on based the number of Lockheed under bored MCs in circulation: When drivers like myself finally investigate their braking problems or their cars fail MOTs, investigation finally zeros in to the MC. Dismantling the MC, the mechanic finds the sticky/tight pistons, but wonders why. He then notes that silicone fluid is in use (as is the case of countless classic car owners who cherish their paintwork) and makes the assumption that the fluid has caused seal swelling and stiction. And so the old wives tale starts! I suggest we have been looking at the wrong cause all these years. It is undersized bores due to poor manufacturing tolerances in some MC batches and not swelling of seals. It has always intrigued me why some people have never had any problem with silicone during, say, 25 years of use, whilst others will categorically disagree, quoting braking problems similar to what I have been experiencing. Food for thought. Steve |
| Steve Gyles |
| In the interest of science, and despite being sick for a month, needing to leave on a 12 hour drive in a couple of hours, and at 3AM, I just went out and took apart a known undisturbed since 1980 Magnette cylinder. This is essentially the same and uses the same kit as the MGA one. The pistons are .872 where not worn, and the bores are .875 likewise. This is in keeping with references I came across recently that said clearance should be .002 - .005 max on a new master cylinder. I find this whole thing incredible at best. I couldn't believe you actually could get the .875 seals in a bore of .863, but I do believe you. Must have been right sticky, and anybody who thinks that you should have to stretch return springs ought to stretch their mind instead. You nay be partially correct on the seal vs. size point, but I don't think that is the full story. There have been, on these boards (maybe the MGB one), recently, statements of new servos coming with stickers that say warranty is invalid if used with silicone fluids, and it's not the first time I've heard what sound like manufacturer's statements to that effect. The manufacturers are presumably actually doing testing to ensure that their products do not fail, especially on life critical components. Fluid standards are minimums, are not checked by anybody, but only "self certified" by the producers. Seal materials vary widely, and are similarly "certified"; I know for certain of at least three visibly different seal materials. I have personally done swell tests on different "complying" fluids. and found that some destroy at least older Girling/Dunlop seals and hoses. I have not done any tests on silicone fluid. Anybody who wants to talk "science" should get a copy of a Parker O-ring/seal catalogue and look up the tables of seal material vs fluid compatibility and swell. I can only imagine the same "polymer engineers" compounding brake parts as have been doing all the other rubber stuff that falls apart on the shelf these days. Once you figure it out, and determine what your seals really are made of, and what your fluid really is, then you might be able to figure out what might work. I have wanted to believe the silicone superiority since the stuff was invented, but there are just too many stories of trouble, and Castrol GTLMA works fine for me. I wasn't happy when Castrol Crimson went away either, but it has worked out. You almost have to know exactly what brands work together, and pray they don't change anything! FRM |
| Fletcher R Millmore |
| Interesting stuff FRM. I am not going to talk the chemistry bit. I can only talk with some degree of certainty on the measurements I have have taken on my bores. Thanks for confirming the 0.875". I have now done dozens of re-measurements of my bores. I appear to have a small error with the calibration of the internal caliper posts of my digital external/internal vernier caliper. Using a different external micrometer on the piston I get the 0.872" you describe. But this is then the same (+ 0.0015" ish) as the bore when I put the micrometer on the internal caliper posts. I definitely do not get anything near the 0.875" quoted. The piston is an interference fit, something close to a normal piston with rings in a bore). It was only when testing alongside the new MC that I realised how easily the piston should move. Anyway, with a slightly undersize bore it certainly accounts for my very stiff piston action and distortion (flattening and elongating) of the seals such that the pressure relief hole was covered and/or the piston was having trouble returning to its normal at rest position . Steve |
| Steve Gyles |
| Steve - Suggest you get your measuring tools sorted, it will make your life easier. It all makes a bit more sense now, since at .863 bore it would mean that the piston also had to be well under normal size. That in turn would point to a design change, the sort of thing that does sometimes happen, with great annoyance created. (some rebuilders overbore cylinders and fit OS seals - real pit of snakes there!) If the piston were actually an interference fit, it would never move at all. So, the piston must be essentially identical in size to the bore, like within .0001 or less. The piston should fall freely through the bore without seals etc, and it would at a true .0001 clearance. Quite possibly this cylinder missed the final hone to size step, which would also mean the bore finish was way too rough when new. That would seriously aggravate seal friction and wear first time round, maybe adding to reports of trouble with some of these. All this is certainly enough to account for your problem. Look at it this way: a trip to a decent shop and a few passes by a good hone and presto - a brand new spec cylinder! Since you have a lathe and like to play, make an expanding copper lap and resize/finish the bore yourself, but get the measurement problem worked out first. Shoot for .8740/.8745, ie within .002/.003 over piston size. I make plug gauges for such critical size holes, as the definitive and easy low dollar approach to accuracy. I have on occasion fitted a 1" diameter steel plug in a cast iron blind hole such that it took 24 hours to fall down 1/2" when supported only by the air in the hole, all parts clean and dry; with oil on it you could not make the plug stay in the hole - perfect air spring. This may be my last communication, as my daughter is going to kill me for being about a half day late fetching her from school - and she's not getting fed anymore there! FRM |
| Fletcher R Millmore |
| I normally agree with you Steve, but not this time! I used to be a great advocate for silicone fluid but, largely for the reasons you have enumerated, I no longer use it. I submitted a critique about it (and the problems that I had) some time ago which was greeted with howls of derision (mainly from dyed-in-the-wool advocates in the USA)! The main point is that for some years now master and slave cylinders in OZ have been resleeved with stainless steel (thus the pitting problem is more or less overcome) and I stuff a (hidden) rag under the master cylinder in my MGA's to avoid damaged paintwork (ie I attend to the master cylinder as soon as I see weeping). Thus the "benefits" of silicone fluid really no longer apply! |
| Barry Bahnisch |
| Barry, no problems. Unwittingly I seem to have started the great debate off again! See how I get on with the new MC and silicone fluid. Braking system is spot on now, so only time will tell. I hope that I can come back in 25 years and still say the same. As I said in previous posts nothing ever changed with the old MC even with brand new seals. It just never worked right. I have difficulty aligning the problem to anything whatsoever to do with silicone fluid. I have also been having a look at the calibration of my internal calipers. I seems to be more a case of my measuring technique at fault rather than instrument error. I was not resting the instrument squarely on the MC machined front plate face whilst taking the internal readings. I was just holding it freehand. Lesson learned, I am not a trained engineer, just picking it up by trial and error as I go along. The accurate readings I now have are 0.8725 to 0.873; so on the extreme lower tolerance limit that FRM describes and is probably down to the finishing of the bores. Sometime I will get round to a bit of honing etc. In the meantime I'll enjoy the good braking I now have. Steve |
| Steve Gyles |
| Hello all, "Johnny-come-lately" here. A week ago I was about to say something while Steve G was making some progress with his investigation. Then he ordered a new MC without notice, so I thought I'd wait for the report after installation. Report is good, so it figures the problem was in the old MC. Sorry I didn't jump up in time to say how to fix it without buying a new one. One issue is the Workshop Manual description of how the MC works. It mentions 8-psi residual pressure in the lines, which could indeed keep the brake pads in contact with the rotors. Unfortunately the WSM stops short and doesn't mention that the 8-psi is supposed to be temporary and fleeting within a few seconds of brake release. Steve's problem is (was) that his old MC was not properly releasing the intended short term residual pressure. For a description of how all this works, and how to solve the problem, see a new web page here: http://mgaguru.com/mgtech/brakes/bt101a.htm The short answer for solution of the problem is, drill a single small hole in the metal Valve Body for the Inlet/Outlet Control Valve (errantly called Non-return Valve). This hole should not be needed, but it is an easy solution for the defective control valve. Without having the suspect parts in hand I can't say why the old valve is defective. Since Steve's problem has persisted for years, and was not cured by installation of a new packing kit, I recon it must be something amiss in design of the old Valve Body. I have always been a little disappointed that the little metal Valve Body is never included in a replacement packing kit, but I guess the original is supposed to be good, and you should never lose it. |
| Barney Gaylord |
| Thanks Barney, interesting stuff. I wondered whether that non return valve was being too efficient. I had devil of a job seating that rubber cup washer into its holder. You may recall that I once reported that I found it unseated and twisted 90 degrees. Currently it is so tight in I don't think I could get it out without damaging it. I am still of the opinion that the piston was not sliding freely and sticking short of its rest position, masking the drilled oil return hole. If I lived closer, I would send it all to you to have a look. Cheers Steve |
| Steve Gyles |
| Steve, That's one of the problems I had. I machined some off the front of the master cylinder piston but other problems arose. |
| Barry Bahnisch |
| Disassembled my MC today and measured the piston: dia 0.872", length 1.977" MC bore 0.875" ish -difficult to measure since I did this with the MC in situ. I think this is as one might expect without any inconsistencies except for the length that in the original pistons is 2.001" My MC was bought new from Brown & Gammons about 7 years ago. The piston is not shiny like originals but has that dark blue colour to it and the machining is a little 'sharper'. It seems that in my case the piston was already reduced in length by 24 thou. The piston with seals moved freely in the bore despite its close fit. I then followed Barney's suggestions as above and drilled a 1/32" hole in the valve body to miss the cup and washer. After my first test drive with liberal use of brakes I jacked the car up and found no binding at all - I could spin the wheels with one hand - first time ever! Its early days yet and I will report any adverse symptoms if they arise but I'm not expecting any. The thing is that a 1/32" hole is extremely small and equalizing pressure will still take a few seconds after brake application so there's no sudden change. I'm sure that some will shake their heads over all this as tampering with the brakes but the logic is sound and the brake pressure stroke and hence braking ability is unaffected. It is also an entirely reversible operation. |
| J H Cole |
| Barry and John Did not know you also had problems. Welcome to the club! We should compare data on our MCs to see if there is a link. Mine has Lockheed 7/8 38183G on one side and Q89 on other. I don't know if this means anything, but it's a start. My new one is made by AP Caparo and the casting has Lockheed replaced by AP. Can't see the other data, it's masked by the bracket. Cheers Steve |
| Steve Gyles |
| Steve, yes I've had brake binding for a long time but not as bad as yours sounded and I just lived with it but when these recent discussions came up I decided to try and cure it. After talking with Barney he made the point that the 8 psi retained pressure was not meant to be permanent so I followed his suggested remedy. I will see if I can get the part numbers off my MC but do not want to undo it again. This last exercise took me about 3 hours- can you really do it in 15 mins? |
| J H Cole |
| I played around with the redundant MC this morning, pushing the piston in and out. 50% of the time it was pulling up about 1/4" short of the front plate... Took it all apart again. Lubricated all the moving parts with 3-in-1 oil (light general purpose oil). Put it all together and the MC worked a dream. Slight delay in the suction through the NRV as published, but all was spot on. Makes you wonder about the lubricating properties of silicone fluid...................... Steve |
| Steve Gyles |
But Steve....You state the new one is doing just fine using silicone fluid, right? Maybe it has more to do with a possible difference in the chemical composition of the new vs. old seals? (Ignoring the obvious dimensional differences for the moment). |
| JM Morris |
| Silicone fluid is not as "slippery" as conventional (vegetable?) fluid. Some years ago, when a staunch advocate for silicone, I had my nephew's TC master cylinder sleeved and replaced the hydraulics with silicone fluid, however the brake pedal would not return. Bugger! From memory I must have removed the m/c again (!) and probably polished the bore (sleeves were still brass then, I think) and after that all was well! I have heard (recently I think) of stretching the return spring (assume that TC's have one) to overcome this problem. Not something that I would readily do. |
| Barry Bahnisch |
| It may be that the slightly undersize bore on my MC, combined with the apparent less slippery properties of silicone fluid has been the cause of my problem. I guess all works well with silicone when the bores are the 'correct' size for the seals, as is the case on my new MC. Never had to use my handbrake so much! Rarely had to use it when stopped at traffic lights etc. Now, the car has a mind of its own and seems to wander off by itself even on flat ground! Steve |
| Steve Gyles |
| Steve, I know that I will sound like a "smart alec" but in my previuos thread about silcone brake fluid I made the point that it is no longer sold in Australia although it is still available if especially ordered. The city's largest brake specialist firm could not remember when it was last asked for. |
| Barry Bahnisch |
| Barry Despite its apparent limited slipperiness, I am grateful that it has saved my paint work over the years. On one occasion I forgot to remove the pressure source from my Eezibleed before I detached the cap from the MC. The result was hydraulic fluid absolutely everywhere, including all over me. If I had been using ordinary fluid I would be needing a respray by now. That brings me to another question: Is it just cellulose paint that the mineral fluid attacks or will it do 2-pack as well? Steve |
| Steve Gyles |
| Some years ago, on the night before one our Club's first concours d'elegance events, a member with an outstanding TF spilt brake fluid over the car and they spent the night repairing the paintwork-- it was pristine again by the morning start! A true hero and he still has the car although regrettably he has not driven it for some years. I dare say that brake fluid (ie other than silicone!) probably also damages two-pack paint--I would be interested in any responses! |
| Barry Bahnisch |
| Just refuelled for the first time since sorting the slow release brakes by fitting the new MC. I have just been doing local short trips, much the same as before. MPG has improved 2mpg. At the current price of fuel the MC should pay for itself before too long! Steve |
| Steve Gyles |
This thread was discussed between 04/05/2010 and 30/05/2010
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