martifers Posted July 9, 2009 Share Posted July 9, 2009 Trying to get my first 90 through it's first MOT. It failed :-(! Rear discs and pads shot, so before the test I replaced pads with new and discs with others from an axle that is on my Lighweight overland project that has been sitting in the garage a few yrs; however, they were not getting a high enough brake reading so failed the MOT. The discs which I put on did have a fare bit of surface rust, although a had hoped this would be cleared during bedding in, it was not! Have sinse deglaized disc with wire brush, now lovely and shiney, and rebled but the rear's are still not locking at all, not even on grass! The fronts work extremely well. I was wondering if it could be a faulty pressure reducing valve? Is there a simple way to diagnose this? Or can anyone suggest any other reason why the rear callipers are not producing enough pressure? Really need to get this sorted tomorrow if I have any chance of getting it MOT'd and taxed before a GLASS trip to the Cotswolds on Sunday. Any ideas, much appreciated :-) Quote Link to comment Share on other sites More sharing options...
western Posted July 9, 2009 Share Posted July 9, 2009 take the PRV out & bridge the space with a short section of brake pipe correctly fitted. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted July 9, 2009 Share Posted July 9, 2009 Do that as a test to see if the prv is working ok. I wouldn't remove it permanently - it's an important part of the braking system. Les. Quote Link to comment Share on other sites More sharing options...
martifers Posted July 9, 2009 Author Share Posted July 9, 2009 Cheers guys, I think that may be the next step if the brake test tomorrow morning also comes back as a failure. Although I am slighlty confused as to why the prv is used in 90's but not 110's? If it is there to balance breaking and to reduce the rear brake bias for more control breaking, surely its effect would be more noticable in a longer wheelbase vehicle, am I missing something? Does it work on an inertia basis or are the rear callipers working at a lower constant pressure and will always produce a lower brake effeciency than the front? What sort of difference should i expect between the 4 pot vented fronts and the 2 pot standard rears on my 90 with the prv valve? Even with the a reduced pressure i still would have thought the rears should lock up! Is this not the case? Quote Link to comment Share on other sites More sharing options...
Les Henson Posted July 10, 2009 Share Posted July 10, 2009 Rear drum braked 110's had a prv. How is the MOT tester checking your brakes? Les. Quote Link to comment Share on other sites More sharing options...
white90 Posted July 10, 2009 Share Posted July 10, 2009 My 90 suffered this on the brake rollers the tyres giving too much grip pumped them up a fair bit and it passed (just)better to get him to use a deccelerometer and road test the brakes Quote Link to comment Share on other sites More sharing options...
martifers Posted July 10, 2009 Author Share Posted July 10, 2009 110's did? oh, not according to my 300tdi defender workshop manual, odd. As for test method, he is using a rolling road / rollers and i'm on 235.85 insa turbo special treks, will double check tyres pressures and increase to help, worth a try! He is a Landrover fan so will chat to him before hand. The road test would be the best thing, then he could see how well it really stops, even if the rears are a bit weak! Cheers or the suggestions guys, will let you know how this morning goes. Quote Link to comment Share on other sites More sharing options...
bishbosh Posted July 10, 2009 Share Posted July 10, 2009 How many miles have you done on the new pad / disc combo? It will take a while for the pads to bed into the discs. Until they have you won't get good braking effort. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted July 10, 2009 Share Posted July 10, 2009 Shouldn't be testing it on a rolling road. Recommended method for the MOT is Taplow meter - naughty tester! Les. Quote Link to comment Share on other sites More sharing options...
western Posted July 10, 2009 Share Posted July 10, 2009 Shouldn't be testing it on a rolling road. Recommended method for the MOT is Taplow meter - naughty tester!Les. don't start that thread again, Quote Link to comment Share on other sites More sharing options...
martifers Posted July 11, 2009 Author Share Posted July 11, 2009 It passed, but only just!! :-) Still don't think it is correct though, but will wait a few miles. Have done about 60 miles bishbosh including a trip to see Ian at IRB developments this morning, a very positive visit, found out a fair few things about the TD5 that had previously been fitted, and looking forward to some tuning later in summer once the funds allow. As for the brakes, could it be that the prv valve is stuck 'on' or in the reduce position? Will have to do some more investigations and bridging as has been suggested. Although need to get our SII Lightweight back on the road first and mothers Polo, garage is a bit full at present! :-) MOT wise, he did have a decelerometer that he was going to use if we still had problems but he let the brakes pass. The rears originally tested a 200 lbs, on retest 350, in comparison to fronts which registered at near 1000 lbs! so quite a big difference there!! What difference would you expect between 4 pot vented fronts and 2 pot plain rears? Quote Link to comment Share on other sites More sharing options...
Les Henson Posted July 11, 2009 Share Posted July 11, 2009 I would expect 350 max on rear drum brakes. Les Quote Link to comment Share on other sites More sharing options...
alfaman Posted July 11, 2009 Share Posted July 11, 2009 Hi, I've got a similarly related problem, but the opposite way round. It's not failed the MOT test though, but it almost caught me out once. Whilst driving in the wet I notice it most,I can lock the rear wheels up, not so easy in the dry, but I can do it. A change of the rear shoes hasn't cured it. Front pads have more than half of the meat on em. Too hard pads? Sticky Callipers? Faulty PRV? Any ideas? Cheers, Keith. Quote Link to comment Share on other sites More sharing options...
martifers Posted July 12, 2009 Author Share Posted July 12, 2009 350 on rear drums... Les, i'm running discs all round.. :-( lol. Well atleast they are on par... :-s. Alfaman, it sounds like your prv is not doing what it says on the tin. Have you got a friendly garage who can check front and rear on rollers? What pads are you using? Have you checked that the pistons move sufficiantly on the front callipers? Like the guys suggested to me above, which i will do before replacing the prv, is bridge the pipes, negating the prv. In your case if it is faulty, then I would have thought there would be no change in your braking sinse it sounds like the prv is not reducing the rear pressure at the moment. Just out of interest what are they like braking in reverse, with weight transfer to the rear? Quote Link to comment Share on other sites More sharing options...
alfaman Posted July 12, 2009 Share Posted July 12, 2009 Have you got a friendly garage who can check front and rear on rollers? Nope, my car was tested the last time on rollers, the MOT tester wasn't alarmed with the readings. Sorry don't know what they were. Made him jump a bit when it came to the hadbrake test - got one of those X-Brake jobbies. What pads are you using? As far as I can remember, I got them from Craddocks and they were in a Mintex box. Have you checked that the pistons move sufficiantly on the front callipers? Aside from taking them off and stripping them down, they stop the front wheels when jacked up and tested. Like the guys suggested to me above, which i will do before replacing the prv, is bridge the pipes, negating the prv. In your case if it is faulty, then I would have thought there would be no change in your braking sinse it sounds like the prv is not reducing the rear pressure at the moment. I'll give it a go. Just out of interest what are they like braking in reverse, with weight transfer to the rear? To be honest, don't know. I'll give it a try later. I'll try the tests with and without the PRV. Thanks. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.