Indiana_Jones Posted May 8, 2020 Share Posted May 8, 2020 Hi all, Just thought I might pick some brains here, currently trying to sort out the brakes on the XJ40, which the VCM is telling me has low pressure and the pedal does sink down a bit. I've rebuilt the master cylinder (which the bore of looked to be in fairly good nick to me) as well as replaced the front flexi-lines. I've bled the brakes a couple of times, using the 2 man method, but for some reason, I still getting the low pressure. I've given the pedal on over night a whirl, but no joy. Given that I'm getting low pressure at the start and not after multiple applications of the brake, I would imagine that the funky hydraulic booster system (with the accumulator etc) isn't causing the issue. Any other ideas? Cheers Quote Link to comment Share on other sites More sharing options...
Ranter Posted May 11, 2020 Share Posted May 11, 2020 Assuming the two man method is the British car method, pedal down close bleeder, pedal up open again? I think some models had some tie up with the ride height hydraulics? Cannot remember, another thing although unlikely is if there is adjustment possible on the pedal that someone has fucked with. I admit I've given up a few times on some British stuff years ago and had them vacuum bleed at local specialist. 1 Quote Link to comment Share on other sites More sharing options...
Taistorm Posted May 11, 2020 Share Posted May 11, 2020 Another thing to try is bleeding it across all the fittings in between the master and the brakes. Might be an airlock somewhere else that isn't bleeding right through. 1 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted May 11, 2020 Share Posted May 11, 2020 I've had good.results by bleeding with a syringe to suck the juice through. Also with a rebuild master make sure you get all the air out of the master cylinder 1 Quote Link to comment Share on other sites More sharing options...
Indiana_Jones Posted May 11, 2020 Author Share Posted May 11, 2020 Thanks for the input chaps. Yeah the method being done is where one person is at the brakes, the second person pumps up the brakes, holds the pressure. Then the person at the brakes opens the nipple, with the second person holding the pedal down. The first person closes the nipple off and then the second person removes the pressure on the pedal. I did give the MC a bleed before I proceeded onto the main system, but I'll double check. Also I saw Dicksmith had a vacuum bleeder on special, looked like a cheapie job, but given the price it might be worth a punt. Taistorm, yeah that's something else that had come into my mind, like the ABS system, but can't for the life of me figure out how one would bleed that (not in my workshop manual). Quote Link to comment Share on other sites More sharing options...
CarolsHusband Posted May 11, 2020 Share Posted May 11, 2020 Not wanting to be a smart arse or anything but I've always bled brakes on my own using a rubber tube, blocked at one end with a slit cut in the side. Just keep pumping away at the pedal keeping an eye on the reservoir, it's always seemed to work for me. If I need to come up with a theory why it works I'd probably say you're forcing the air out, not trying to trick it out ? I can't imagine I've just been jammy over the years. /two penneth... 3 Quote Link to comment Share on other sites More sharing options...
Bling Posted May 11, 2020 Share Posted May 11, 2020 1 hour ago, Indiana_Jones said: Also I saw Dicksmith had a vacuum bleeder on special, looked like a cheapie job, but given the price it might be worth a punt. Dicksmith one is probably the same as ones from aliexpress? Which was the same ones resold on trademe, which could be cheaper, worth a look. I got one from Ali like this: https://www.trademe.co.nz/motors/car-parts-accessories/tools-repair-kits/other/listing-2613493571.htm?rsqid=954ab67877364b37be4e457500fcd1d6-001 (requires air compressor) Haven't used it on brakes yet but it worked really well for draining my power steering! I very rarely find someone willing to pump the pedal so just run some pipe into a bottle and open the bleed screw a little bit. Seems to work, once there is some fluid in the bottle, air can't get back up the hose if it's submerged. 1 1 Quote Link to comment Share on other sites More sharing options...
chris r Posted May 11, 2020 Share Posted May 11, 2020 i've got one of those vacuum bleeders and they are a bit shit. I've never had success vacuum bleeding brakes with them. works mint for clutches though I got one of these and it works real good for one man bleeding brakes 2 1 Quote Link to comment Share on other sites More sharing options...
CarolsHusband Posted May 11, 2020 Share Posted May 11, 2020 Ooh, that's the fancy version of what I use 2 Quote Link to comment Share on other sites More sharing options...
sr2 Posted May 12, 2020 Share Posted May 12, 2020 22 hours ago, Indiana_Jones said: Thanks for the input chaps. Yeah the method being done is where one person is at the brakes, the second person pumps up the brakes, holds the pressure. Then the person at the brakes opens the nipple, with the second person holding the pedal down. The first person closes the nipple off and then the second person removes the pressure on the pedal. I did give the MC a bleed before I proceeded onto the main system, but I'll double check. Also I saw Dicksmith had a vacuum bleeder on special, looked like a cheapie job, but given the price it might be worth a punt. Taistorm, yeah that's something else that had come into my mind, like the ABS system, but can't for the life of me figure out how one would bleed that (not in my workshop manual). The bleeding process you're describing is called 'surge bleeding'. It has it's uses but is prone to aerate the fluid, particularly if there is a considerable amount of air in the system (e.g. after replacing a major component) and far more likely to occur in an ABS system (there are a lot of small valves/orifices in there). Aerated brake fluid has had air dissolved in it under pressure (as opposed to air bubbles) and is your 'bleeding enemy' (apologies for the bad pun!). I'm in favor of a more gentle approach; release the bleed nipple with the pedal in the rest position (i.e. compensation port uncovered), have the 2nd man (or the Mrs) smoothly push the pedal to the floor, tighten the bleed nipple, release the pedal and allow to rest for a few seconds - repeat until fluid is clear of bubbles. The air should come out in bubbles, if the fluid looks frothy of milky you're aerating it and things will only get worse. Never re-use fluid when bleeding even if it is new and clean, always allow it to rest for a few days - it takes quite some time for the dissolved air to separate. I'm by no means an XJ40 expert (years since I've worked on one) but don't get sidetracked by the hydraulic booster, it only provides mechanical assistance to the pedal and is not connected to the hydraulics in the braking system. In essence it does the same job as a vacuum suspended mastervac. Hope this helps. 4 1 Quote Link to comment Share on other sites More sharing options...
Indiana_Jones Posted May 12, 2020 Author Share Posted May 12, 2020 Thanks for that sr2, appreciated, will give that method a go the next time I get a chance. Also glad to hear that it should be separate to the booster system, as you do see mention of it, but by my logic that shouldn't be so. Quote Link to comment Share on other sites More sharing options...
sr2 Posted May 12, 2020 Share Posted May 12, 2020 Just now, Indiana_Jones said: Thanks for that sr2, appreciated, will give that method a go the next time I get a chance. Also glad to hear that it should be separate to the booster system, as you do see mention of it, but by my logic that shouldn't be so. The modern 'Mastervac' style of booster (the XJ40 Hydraulic system is just a weird , overly complicated version of the same principal) is deliberately designed to be separate from the brake systems hydraulics to avoid complete loss of brakes in the event of booster failure. Its predecessor the 'Hydrovac' is easiest described as a 'hydraulic amplifier' that was plumbed in series with the master-cylinder, in the event of its failure (which wasn't unheard of) the result was a complete loss of brakes. 1 Quote Link to comment Share on other sites More sharing options...
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