Bowie69 Posted January 15, 2015 Share Posted January 15, 2015 Maybe it's the driving style.....? Quote Link to comment Share on other sites More sharing options...
Souster Posted January 15, 2015 Author Share Posted January 15, 2015 Maybe it's the driving style.....? Deffo not the driving style. I've tried everything from smooth and no braking. Gradual, or slamming them on at last minute. All leave the same results Quote Link to comment Share on other sites More sharing options...
Boydie Posted January 16, 2015 Share Posted January 16, 2015 I still think the problem is in the rear calliper's, that's assuming that the pressure limiting valve is okay. With any hydraulic system the fluid will always flow to the furthest point before pressure increases, therefore it will begin to apply pressure to the outer brake piston before the inner, ergo it may well be that you are achieving the required degree of brake force without the inner piston being required to apply the same degree of force, but this is doubtful as the calliper is designed to "float" on it's locating pins to ensure that the pressure is equal and . Land Rover specifically state not to separate the two calliper halves, and if you have not done this before I would recommend that you practice on an old unit first. When I've done this in the past I've found that there is a small "O" ring sealing the fluid ports between the two halves, this is made from unobtainium, so treat it with great care. Some callipers have two ports, other makes have one port and then there is the port leading to the bleed nipple. After cleaning out the fluid ports (I found one partially blocked with 15 year old crud from the brake system, this crud will always over time progress to the rear callipers being the furthest point in the hydraulic system). Smear some extra fine grade lapping paste to one of the faces of the two halves rub them together to ensure that the two are perfectly mated and that you have removed any sealing compound that may have been used during factory assembly, remove the paste by washing the two halves in degreaser, blow dry to remove all traces of the paste and refit the "O" ring and re-assemble,( it's a lot easier to re-fit the pistons and seals at this point with the two halves separated and before you fit the "O" or "O" rings) and remember when re-fitting the pistons and seals lubricate them with clean brake fluid) - a tiny amount of Rolls Royce gasket liquid can be applied to the mating surfaces around the "O" ring but this should not be normally necessary. No torque figures are available for the bolts connecting the two halves so bloody tight is the only advice - but use a torque wrench so that they are taken up equally and to the same figure. Connect the re-assembled calliper to the brake line and using a block of wood between the two pistons have a assistant apply the brake hard and look for any leaks. If there are none, re-fit to the disc, finally make sure that the calliper, "floats" so that even wear is applied to both pads. Quote Link to comment Share on other sites More sharing options...
Boydie Posted January 16, 2015 Share Posted January 16, 2015 just looking at the previous photos it would seem that the rear callipers are solid to the axle this being the case the "float" will be by the two pistons. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 16, 2015 Author Share Posted January 16, 2015 Cheers boydie. Yeah they are fixed calipers so no sliders. I'm nearly 100% certain there is no muck in the fluid ways and have successfull experience with rebuilding the land rover brake calipers. My next job is to get the wheel off and inspect what's happening with the pistons. Failing that is going to have a new bias valve or vacuum pump I think? Just don't know which one? Can anyone help me decide? I'm going to book it in at a land rover specialist next week I think. Not totally convinced it's not crappy discs tho Quote Link to comment Share on other sites More sharing options...
Tanuki Posted January 16, 2015 Share Posted January 16, 2015 Maybe it's the driving style.....? Try a few weeks of "drive it like you stole it". I don't think a set of discs/pads on my TD5 90 have ever lasted more than 15,000 miles. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 16, 2015 Author Share Posted January 16, 2015 Try a few weeks of "drive it like you stole it". I don't think a set of discs/pads on my TD5 90 have ever lasted more than 15,000 miles. I've tried that mate with no luck. I'll have no tyres left haha. Is that your rear pads only lasting 15k too, if so then there's Deffo an issue with mine. As I think these would last a life time Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted January 16, 2015 Share Posted January 16, 2015 OK, I've avoided posting this because I have no hard evidence -pun intended, but read on... the theory goes: Rust, is a harder material than the surrounding steel, so... once you let a set of discs get rusty the softer metal will wear away around the rust a tiny bit, but ultimately, the rust will hold the pad off the disc, reducing contact area. As the contact area is not as it should be, the 'good', but thinner, surface of the disc starts to corrode, as it is not longer being cleaned by the pads. This 'spreads' the rust over the rest of the disc slowly due to the lack of cleaning, until the whole disc is black/brown and your braking efficiency has taken a nose dive. I was told this by an MOT tester many, many moons ago, albeit in a simplified form that I have expanded a little on, but it does make sense in a number of ways. Broadly though, if you let your discs get rusty, they will never be the same again. Quote Link to comment Share on other sites More sharing options...
Boydie Posted January 16, 2015 Share Posted January 16, 2015 What Bowie has said has a degree of truth to it, rust being an oxidised form of the base metal however .......... lets apply some progressive thinking here. It will not be the discs, one side of the disc is not going to have a softer material and be more rust prone than the other and when you think about it the outer surface is more likely to get rusty as its exposed to rain more than the inner face, by the same reason, going through mud and crud, the inner face is more likely to have longer contamination unless you are fastidious and give the underside a good pressure clean after every outing, I do this after every bush trip but then I'm an anally retentive old fart, retired and have very little else to do until my next desert trip. Its not going to be the vacuum pump, or the servo unit for the simple reason if either was defective you would certainly know it as you would need to apply huge peddle pressure to stop the vehicle. You are getting hydraulic pressure to the rear brakes (even if it is just the outer pads)and they are not locking up under heavy braking so scratch the pressure limiting valve, it's working okay. Ergo it has to be the calliper / pistons. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted January 17, 2015 Share Posted January 17, 2015 Not sure I made the point clear enough..... once a disc has had some significant rust (other than surface rust, i.e. some pitting) on it, then it is likely to hold onto that rust for the rest of its life, no matter how you drive it. A cure is to stick it on a lathe and face it off, or replace. Or use my tongue-in-cheek reply earlier and put the pad in backwards for a hundred miles or so ( NO THIS IS NOT RECOMMENDED!) If the LR had been 'driven like it was stolen' the whole time, and not left to attract any rust for a period of time, then it just wouldn't happen. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 17, 2015 Author Share Posted January 17, 2015 Thank you boydie and bowie for your replies. That's interesting what you say about the discs and I totally agree. I've got a day off today so I'm going to get the rear wheels off and inspect the calipers to see what the score is. The vehicle is a truck cab with no cover on the back, I'm not sure if that would be why the discs are rusting a bit easier on the inside. But the vehicle is only left for a maximum of a week or two at most, surely that's not enough for it to ruin the rear discs. If that was the case then cars round the country would constantly need new discs. The outside of the discs nearest the wheels are better. Not perfect but acceptable. Still showing early signs of pitting. I'll report back with my findings later and hopefully get to the bottom of it. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted January 17, 2015 Share Posted January 17, 2015 Indeed, a couple of weeks is not likely to pit them enough, was more thinking a 2-3 months, or less if off-roaded. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 17, 2015 Author Share Posted January 17, 2015 Right guys. Whipped the wheels off earlier and took the pads out. Got an assistant to press the pedal while I inspected the pistons. Both pistons came out freely with no issues at all. No restrictions or sticking of any sort. What I did notice when looking at the pads is that the one side where the disc is poor, the pad doesn't look like it has been used (see link for photo) where as the good side of the disc that pad is shiny and used. http://s905.photobucket.com/user/souster4/media/Mobile%20Uploads/20150117_124733.jpg.html?sort=3&o=0 On further inspection it appears the discs are covered in black spots similar to wager marks on a car. Except you can't feel them. so maybe they are crappy discs and pads. But other than that I'm absolutely clueless now. What do you guys think? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted January 17, 2015 Share Posted January 17, 2015 Black spots is old rust. Quote Link to comment Share on other sites More sharing options...
Boydie Posted January 17, 2015 Share Posted January 17, 2015 Obviously one pad is not applying any pressure, and this can be a problem with fixed callipers as against "floating" my guess would be that these are the inners - the outer pads being the furthest from the master cylinder and therefore subjected to greater hydraulic force. Get the discs skimmed to remove any rust / grooves (but not less than the machining limit) and see how it goes, if you continue to have poor pressure application on the inner face brae pad then replace or overhaul the two rear callipers. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 17, 2015 Author Share Posted January 17, 2015 Obviously one pad is not applying any pressure, and this can be a problem with fixed callipers as against "floating" my guess would be that these are the inners - the outer pads being the furthest from the master cylinder and therefore subjected to greater hydraulic force. Get the discs skimmed to remove any rust / grooves (but not less than the machining limit) and see how it goes, if you continue to have poor pressure application on the inner face brae pad then replace or overhaul the two rear callipers. Cheers boydie. Any ideas where to get them machined? Also you don't think it could be faulty calipers do you? Poor fluid ways. Other than the fluid ways the pistons are like new. So a rebuild Deffo wouldn't make any difference. Replacement may do. People not think it could be the bias valve then? As I say there was less pressure when bleeding for the rear calipers than the front. About half the pressure in fact Quote Link to comment Share on other sites More sharing options...
qwakers Posted January 17, 2015 Share Posted January 17, 2015 it could be the bias valve. certainly cheaper to replace than the calipers and i wouldn't bother machining the disks. Quote Link to comment Share on other sites More sharing options...
ballcock Posted January 17, 2015 Share Posted January 17, 2015 You say your pistons move freely, are the pads a tight fit? it could be with lower rear pressure the internal pads are jamming in the calliper and and allowing all the pressure to press the outer pad. I often find I have to file at least the paint off the pad edge and a little copper grease to get pads moving freely. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 17, 2015 Author Share Posted January 17, 2015 You say your pistons move freely, are the pads a tight fit? it could be with lower rear pressure the internal pads are jamming in the calliper and and allowing all the pressure to press the outer pad. I often find I have to file at least the paint off the pad edge and a little copper grease to get pads moving freely.That's something I haven't checked I must admit. Worth a look I suppose. I'm starting to doubt the bearmach rear calipers now to be honest. The front are OEM and are braking as good as a brand new one. Should there be less pressure at the rear when bleeding? Quote Link to comment Share on other sites More sharing options...
Boydie Posted January 18, 2015 Share Posted January 18, 2015 No, with the bleed valve open the rate of the fluid expressed should be the same as the front brake pads because there is no build up of pressure in the rear brake system, so look at your bias/pressure limiting valve. It looks as if the limiting valve is not opening fully, you can either get an overhaul kit or buy a replacement unit, if you're not sure of how to set it up buy a new one. Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted January 18, 2015 Share Posted January 18, 2015 My discs are scored to hell as well, though fairly rust free. I find the inboard pads wear away after only a few months (5,000 miles or so) in the winter, and the resulting metal-on-metal is what had knackered my discs. New ones are on the cards, but to me this means the inner pads have plenty of pressure on them to wear out first - even though in my case it is accelerated by the wet gravel roads and the lack of disc shields. Quote Link to comment Share on other sites More sharing options...
Boydie Posted January 19, 2015 Share Posted January 19, 2015 Odd, yours (Retroanaconda) are wearing on the inner face of the disc, Souster's are wearing on the outer - maybe you two should get together and swap components, that way you should have at least one disc wearing evenly Quote Link to comment Share on other sites More sharing options...
Souster Posted January 19, 2015 Author Share Posted January 19, 2015 Thanks guys and retroanaconda for the picture. It seems most people's rear discs work just as good as the fronts. Been as the brake fluid flow is about half that of the fronts there must be some restriction. So I think I'll get someone to replace the proportioning valve Quote Link to comment Share on other sites More sharing options...
Souster Posted January 21, 2015 Author Share Posted January 21, 2015 I'm ordering a new brake proportion valve tonight and having it fitted next week. Do you guys think I'm doing the right thing to solve this problem? There's only that valve or the vacuum pump left Quote Link to comment Share on other sites More sharing options...
Lewis Posted January 21, 2015 Share Posted January 21, 2015 It's not the vacuum pump Personally I wouldn't bother at all chasing the problem Quote Link to comment Share on other sites More sharing options...
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