jeffrey taylor Posted June 8, 2020 Share Posted June 8, 2020 evening , newby ,so bear with me please .took the top off the brake master cylinder and got wifey to push the brake pedal down and come of it as you would normally , and the fluid nearly jumped out of the reservoir ! . faulty master ? . also read on the forum to check the servo , stop the engine , and leave for 1/2 hr. then pull the one way valve out , where you should hear a hiss as the air enters/ escapes the servo ? no hiss ! one way valve is new and working o.k. also , foot on brake and start motor , the pedal drops about an inch . faulty servo ? also tested the vacuum pump , which showed .85 bar .so o.k.? must add all the above components are orig. on a 196.800 mile motor .front/rear calipers and discs replaced (front ventilated ) about 12 months ago . any ideas ? Jethro . Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted June 8, 2020 Share Posted June 8, 2020 So, your brakes don't work ? Mo Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 8, 2020 Author Share Posted June 8, 2020 mo, sorry about that ,brake pedal feels good, but when braking from about 50-60 mph. ,it"s the last 10 yards or so that I start to pray , but the pedal stays up pretty well . its just that I get brake fade . Quote Link to comment Share on other sites More sharing options...
Mutley Posted June 9, 2020 Share Posted June 9, 2020 Have you bled the brake system all round, checked for leaks and probably a daft question, when you put vented disc on the front did you replace the calipers for vented brakes disc? And...…. WHAT THE HELL ARE YA DOING GETTING UP TO 60MPH IN A DEFENDER!?!?!?! Quote Link to comment Share on other sites More sharing options...
Pawl12 Posted June 9, 2020 Share Posted June 9, 2020 If its just a small jet of fluid rising in the reservoir at the very initial movement of the brake pedal, its probably OK. The reservoir has an open connection to the mastercylinder pressure circuits while the brakes are off. The first couple of mm of brake pedal movement seals the opening. If you tap the pedal quickly, some fluid in the mastercylinder gets pushed through the connection to the reservoir quickly & can appear as a visble jet of fluid, before the mastercylinder seals off & displaces fluid into the main brake system. Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 9, 2020 Author Share Posted June 9, 2020 mutley, brakes bled o.k. no leaks , and I don"t think solid disc calipers will fit , being too narrow ? and she will just touch 80 mph on the flat with a fair wind and if you push hard on the windscreen .mods, stainless sports down-pipe ,tho" it looks the same as orig. one ,no middle box , and standard rear box, until I find some thing with-out a bog "u" bend in it! , foam air filter, which get"s washed in soapy water and rinsed every oil change "5000 miles" , and an air scoop fitted to the wing intake from bolt on bits from Bolton , which does seem to make a difference .and on 235x85 16 cooper at/3 tyres .never changed the speedo drive , so my speed , according to my sat. nav. is spot-on pawl 12, fluid jumps about 30mm , so might change master cylinder ? and servo if not holding vacuum? Jethro Quote Link to comment Share on other sites More sharing options...
Snagger Posted June 9, 2020 Share Posted June 9, 2020 The fluid does travel back to the reservoir as you release the pedal, but it’s more a pressure than fluid transfer operation.tion, so the surge should be small. It sounds like you has a large surge, and the one part of the system that is eleastic enough to cause that is the flexible hoses. That would also explain the poor pressure despite a decent feel and thorough bleeding - a hose (or more) is inflating, sapping hydraulic fluid and applied pressure, reducing braking, and when you release the pedal, the inflated hose shrinks back and sends a larger than normal fluid transfer back to the reservoir. Goodridge make very nice stainless braided hoses that give far better braking than new standard hoses, so they’re worth considering. Just be aware that you mustn’t use clamps on braided hoses, so fluid loss whenever you remove a calliper is a problem unless you make up caps to screw onto the pipe or hose unions. Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 9, 2020 Author Share Posted June 9, 2020 snagger, have already fitted what you suggested . and as you say, it" as you come off the pedal that the fluid surges . Jethro Quote Link to comment Share on other sites More sharing options...
Maverik Posted June 10, 2020 Share Posted June 10, 2020 I'm not sure you've got any problems with the brake master cylinder - I've had fluid come back out the reservoir while bleeding with some over energetic pedal pushing. You say your pedal is hard but its not stopping, this sounds more like a servo problem? - are you getting the servo assist when breaking? How you can check this is put your foot on the brake pedal and start the engine, the pedal should then go to the floor a little bit further. Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 10, 2020 Author Share Posted June 10, 2020 maverick, the brake fluid only shoots out of the master cylinder when you come off the brake pedal in the same way you would if you were driving ,it jumps up about 30 mm. brake pedal does drop about an inch with your foot on the pedal and start the engine . new one way valve in servo, and checked vacuum , and showing .85 bar on (new) gauge, but if I stop engine with foot off brake ,and leave for 20 min. and pull the one way valve out ,there"s no sound of air entering/leaving the servo. so not holding vacuum pressure ? it"s only when I stop from , say, 50mph or so that I have trouble stopping in the last 10yards or so , slower speeds ,10/15 mph seem o.k. all new brake calipers, discs , ventilated on the front ,copper pipes , and stainless flexibles ,ferodo pads all round , Jethro Quote Link to comment Share on other sites More sharing options...
Snagger Posted June 10, 2020 Share Posted June 10, 2020 You could have a leaky servo. Check around the master cylinder mounting for cracks, and have someone pump the pedal and look for flex of the front of the servo - they’re prone to cracking on the front face. Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 10, 2020 Author Share Posted June 10, 2020 thanks snagger , i didn"t realise you needed somebody to pump the pedal to see if it leaked . will go and check know . Jethro Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 10, 2020 Author Share Posted June 10, 2020 snagger, just checked servo , and there MIGHT be a very small crack/split next to the master cylinder bolt nearest the wing, about 25mm long. started engine and got wifey to pump brake pedal, and could JUST about see the servo flex their . also could feel some sort of movement inside . I also started engine, turned it of, and pulled one way valve out, just to be sure there was vacuum. did the same again and left it for 5 min. ,pulled valve out ,no vacuum. would you say there should be still some vacuum after 5 min. ? Jethro. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted June 10, 2020 Share Posted June 10, 2020 (edited) also check the servo mounting nuts.Where the servo bolts to the master cylinder. The 110 servo is known for splitting there Edited June 10, 2020 by mmgemini Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 11, 2020 Author Share Posted June 11, 2020 mmgemini ,checked mounting nuts ,every thing looks o.k. thanks, Jethro . Quote Link to comment Share on other sites More sharing options...
Snagger Posted June 11, 2020 Share Posted June 11, 2020 Any crack in the servo, which would start as hairline until it gets worn by rubbing or corrodes, would kill the vacuum. Worse, it allows the master to move away from the pedal box as you apply the pedal, negating some of the input. If the crack is allowed to grow enough, the master cylinder will break away from the servo and the pedal mechanism, giving complete brake failure. Inspect it closely, and if it is cracked, replace the servo as a matter of urgency. The old servos that are deeper but have smaller diameters, as used on non-ABS Discovery’s and RRCs are much more robust, give better feel and I understand them to be a simple swap, but double check they fit as I have never done the swap myself. Quote Link to comment Share on other sites More sharing options...
Maverik Posted June 11, 2020 Share Posted June 11, 2020 19 hours ago, jeffrey taylor said: you say there should be still some vacuum after 5 min. ? Jethro. Yes - I've got to my truck days after last use and there is still a vacuum in the servo. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted June 11, 2020 Share Posted June 11, 2020 5 hours ago, jeffrey taylor said: mmgemini ,checked mounting nuts ,every thing looks o.k. thanks, Jethro . Did you check for very fine almost un noticable cracks in the servo around those mountings . You may need a very bright light to see them Quote Link to comment Share on other sites More sharing options...
jeffrey taylor Posted June 11, 2020 Author Share Posted June 11, 2020 MMGEMINI, HAVE DONE EVERY THING YOU HADE SAID, SO I AM GOING TO CHANGE THE SERVO X MASTER CYLINDER , JUST TO BE ON THE SAFE SIDE ,AS IT LOOKS AS THO" IT IS AT LEAST LOOKING LIKE A SERVO PROBLEM . THANK YOU ALL FOR YOUR INPUT ,VERY GRATEFUL FOR YOUR HELP . Jethro 1 Quote Link to comment Share on other sites More sharing options...
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