Souster Posted December 29, 2014 Share Posted December 29, 2014 Hi all Ive carried out a lot of work on my 1995 300tdi defender braking system as some of you may know. And its hugely improved from when i purchased it. It actually stops now haha. 6-7months ago i replaced the calipers all round and new mintex discs and pads on the rear. Couple of months ago changed the flexis hose for braided. And then a few weeks ago, replaced front discs and pads, and rebuilt the master cylinder. The reason for rebuilding the master cylinder, was because the brake pedal felt poor and spongy. Anyway, the brakes seem a big improvement, however i cant work out why the rear discs are not being cleared of their rust. The pads are lightly skimming the disc, and clearing the surface rust, but not properly sweeping the disc and polishing it as they should, as good working brakes do (like the fronts do infact). Theyve only been on six months, so arent heavily corroded, i just notice they are starting to Pitt. The reason i replaced them was because they were excessively rusty on the rear. Not due to being worn. This led me to replace the calipers. Has anyone got any ideas please? Could i have messed up the master cylinder rebuild? Thanks in advance Quote Link to comment Share on other sites More sharing options...
Puffernutter Posted December 29, 2014 Share Posted December 29, 2014 I don't know about rear discs, but certainly on my Defender that had rear drums, the wear was very marginal as all the braking is done by the front discs. When you brake the weight is thrown forwards and taken off the rear wheels, they are braked lightly, otherwise they will be likely to lock up. I'm sure my 1990 Defender had a balance (weight-load) valve? (or I could be getting confused with my LDV Convoy). I sold the Defender a year or so ago, so I can't check. Not sure if that helps.... Cheers Peter Quote Link to comment Share on other sites More sharing options...
ballcock Posted December 29, 2014 Share Posted December 29, 2014 It sounds as if they are not activating fully, try jacking the rear then see if the wheels will turn with light brake pressure. could be the dual circuit is not working properly. Quote Link to comment Share on other sites More sharing options...
Souster Posted December 29, 2014 Author Share Posted December 29, 2014 Thanks guys! The fronts seem to be working well, and the brakes are pretty good. The back are just starting to develop pitting. Which suprised me considering the whole system is new. I'll try your suggestions though. Quote Link to comment Share on other sites More sharing options...
Puffernutter Posted December 30, 2014 Share Posted December 30, 2014 It looks like there is a pressure reducing valve to the rear brakes. Could that be throttling the pressure too much? Cheers Peter Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 It looks like there is a pressure reducing valve to the rear brakes. Could that be throttling the pressure too much? Cheers Peter Cheers Peter The vehicle is totally unloaded most the time, but so is a friends of the same model and the discs are well polished. You guys dont think i could have made a mistake with the master cylinder then? Brakes feel decent really Quote Link to comment Share on other sites More sharing options...
Team Idris Posted December 30, 2014 Share Posted December 30, 2014 This is coming up regular now, by the standards of weird faults. I think it's a flow issue against the pressure-reducing-valve. It isn't allowing enough flow to overcome the springy-ness of the seals. And I believe the fix is to remove the calliper and push the pistons out a little with the pedal and re-fit, so the pads are already touching. Or use a brake clamp to hold fluid in the calliper like; Push down pedal, lock off rubber hose, release pedal, press pedal again, let more oil through, until the seals are fully out. But maybe the valve is duff? I had them on Deutz and I have one on the van. They seem okay. I guess it could be duel circuitproblem, but I thought oil went to the back axel from both sides, and only from the good side if the other half blows out? It's a shuttle valve thing on some vehicles. Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 Thankyou for the reply. Thats interesting! You guys dont think i could have messed up the master cylinder rebuild then? Im sure the discs were being cleaned slightly better before, but not what they should be. The pedal feels better than it ever has done after all the work ive done though, and the brakes are pretty decent. When i bought the vehicle, the MOT advisory was due to corroded rear discs. I fear i may have messed up the master cylinder rebuild, all though pedal feels good. Any thoughts? Quote Link to comment Share on other sites More sharing options...
Les Henson Posted December 30, 2014 Share Posted December 30, 2014 The seals in the master cylinder MUST go in the right way round and there is one for the front, and one for the rear brakes. If the rear brake seal is the wrong way round, then you may not notice it on the pedal, as most brake effect is on the front. Les. Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 The seals in the master cylinder MUST go in the right way round and there is one for the front, and one for the rear brakes. If the rear brake seal is the wrong way round, then you may not notice it on the pedal, as most brake effect is on the front. Les. Thanks Les. Do you think its most likely that then? Could it be anything else? Quote Link to comment Share on other sites More sharing options...
Les Henson Posted December 30, 2014 Share Posted December 30, 2014 Could be the valve not working properly. Older ones could be dismantled, cleaned, and reassembled, but I'm not sure about later ones. Either way - they will have to be taken apart I think. Les. Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 Could be the valve not working properly. Older ones could be dismantled, cleaned, and reassembled, but I'm not sure about later ones. Either way - they will have to be taken apart I think. Les. Thankyou Les, Is there anyway i can check which one it could be? The vehicle is unloaded most the time, not sure if that makes a difference. I have tried to brake hard to get the discs to clean up, but with no luck. Im going to get an assistant to press the pedal to see if i can see the pistons moving in the rear calipers later. So its either poor master, or faulty bias valve do you think? Could poor servo assistance cause it? Mind you brakes feel decent to be honest Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 Here's a picture of the one disc Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 The pictures of the discs the lines arent scoring, they just havent been cleaned well enough. The black spots are the beginning of rust and pitting. Th fronts are perfect, cleaning perfectly. I had an assistance press the brake pedal and i check the rear calipers. The pads were moving, but there wasnt much difference between engine on and off. They havent got far to move though with new discs and pads. Thankyou all Quote Link to comment Share on other sites More sharing options...
eds Posted December 30, 2014 Share Posted December 30, 2014 if you are really worried why not put it on an mot rolling road? Briefly! Quote Link to comment Share on other sites More sharing options...
bushwhacker Posted December 30, 2014 Share Posted December 30, 2014 Hi Those discs don't look that bad . The only way to get the rear brakes to work harder would be to put a loaded trailer on, drive and do some hard braking. Take it to your local mot place and stick it on the rollers that'll let you know how good or bad the rear brakes are. Good luck. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted December 30, 2014 Share Posted December 30, 2014 Turn the pads back to front and go for a drive -clean and de-lipped discs for sure Quote Link to comment Share on other sites More sharing options...
Souster Posted December 30, 2014 Author Share Posted December 30, 2014 Hi Those discs don't look that bad . The only way to get the rear brakes to work harder would be to put a loaded trailer on, drive and do some hard braking. Take it to your local mot place and stick it on the rollers that'll let you know how good or bad the rear brakes are. Good luck. They arent absolutley terrible. But the pictures make them look a lot better than they are. Another year on those discs and i dont think they would be in a very good state at all. Thats what bothers me really. Thankyou all Quote Link to comment Share on other sites More sharing options...
Nigelw Posted December 31, 2014 Share Posted December 31, 2014 I go with Bowie on the loaded trailer idea, unbraked makes them work harder Part from the obvious thing of getting brake force tested on the MOT rollers all you can do is to start swapping parts out, can get expensive though. Quote Link to comment Share on other sites More sharing options...
steve b Posted December 31, 2014 Share Posted December 31, 2014 another vote for a brake roller test , it will show you exactly whats happening cheers Steveb Quote Link to comment Share on other sites More sharing options...
Souster Posted January 1, 2015 Author Share Posted January 1, 2015 Thanks guys. I appreciate that getting the rear brakes tested will help me see figures of brake efficiency, however it still won't tell me why my rear discs are rusty compared to similar vehicles the same age. Other than that test, could anyone help me with my next stages of what to do? *take no notice? *should I be re bleeding? *should I be replacing the Master cylinder? *replacing the bias valve? *master and bias valve? Sorry to make it long winded, I haven't got the money to swap any old part with not knowing it maybe the culprit. Thank you all for your help! Much appreciated 1 Quote Link to comment Share on other sites More sharing options...
qwakers Posted January 1, 2015 Share Posted January 1, 2015 however it still won't tell me why my rear discs are rusty compared to similar vehicles the same age. yes it will it will tell you if there is a problem and what the most likely cause is.... Quote Link to comment Share on other sites More sharing options...
bushwhacker Posted January 1, 2015 Share Posted January 1, 2015 I can sympathise with you on money front. I would swop the pads from p/s to d/s and inner and outer every week or so and see how it goes from there. I put a rear td5 disc axle in my 110 and to be honest yours looks a whole lot better than mine which mot'd with no problems. Quote Link to comment Share on other sites More sharing options...
Souster Posted January 1, 2015 Author Share Posted January 1, 2015 yes it will it will tell you if there is a problem and what the most likely cause is.... I see your point. But I can tell there's a problem by just looking at them. And how will it tell the most likely cause? Quote Link to comment Share on other sites More sharing options...
qwakers Posted January 1, 2015 Share Posted January 1, 2015 if you get pulses in the readings it can indicate disk or caliper issues, if you get a very low reading that improves over time that could be a bias valve issue if you get one wheel much better than the other that reverses sides on retest that could again be bias issues. the list goes on but a experienced tester can tell you what's most likely wrong just by looking at the results. Quote Link to comment Share on other sites More sharing options...
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