charlie_pank Posted January 5, 2003 Share Posted January 5, 2003 Kermit's driver's-side front brake is juddering at very low speed at a specific pedal pressure. As we slow down beyond that speed there is a persistent, repetitive squeak that slows down as the speed is reduced. I thought it might be a stone stuck somewhere, but reversing and braking normally fixes that and it hasn't made a difference this time. I'm going to take the wheel off, and probably the disk and the caliper too, is there any advice about this procedure (and reassembling) that anyone can offer before I start, so that I don't fall into any of the traps that other people have? Thanks Charlie The plan is: there is no plan Kermit the frog Link to comment Share on other sites More sharing options...
F355GTS Posted January 5, 2003 Share Posted January 5, 2003 Charlie Other than a disk the only thing I have had which gave a similar symptom was a loose caliper Mark Edited by - F355GTS on 5 Jan 2003 16:19:40 Link to comment Share on other sites More sharing options...
alicat Posted January 5, 2003 Share Posted January 5, 2003 Had a similar problem some years ago on a vehicle - turned out to be wheel bearing adjustment ❗ Alicat Link to comment Share on other sites More sharing options...
charlie_pank Posted January 5, 2003 Author Share Posted January 5, 2003 Thanks for the suggestions, I'm expecting a loose caliper or warped disk. Is there anything special I need to know about the process of removing the disk from the caliper or the caliper from the upright (and the reassembly process)?. -eg. Do I need some pipe grips to squeeze the piston back into the caliper before I can fit it back around the disk, or is this a no-no, in which case what's the better way of doing it? The plan is: there is no plan Kermit the frog Link to comment Share on other sites More sharing options...
Blatman Posted January 5, 2003 Share Posted January 5, 2003 I'm with Alicat. Reversing mayhave the effect of "re-setting" the bearing temporarilly. If it was something fixed, like a disc or caliper, reversing wouldn't affect it, IMO. Link to comment Share on other sites More sharing options...
charlie_pank Posted January 5, 2003 Author Share Posted January 5, 2003 If it is wheel "bearing adjustment", what should I do with it? I'm not very experienced with wheel bearings. BTW, the brake seemed to be actually juddering on and off - the wheel would lock and skid, then release, then lock and skid etc...(a bit like ABS!)-all at about 3 mph, it was fine when braking harder and at higher speed, does this affect your opinion about it being the bearing? Thanks Charlie The plan is: there is no plan Kermit the frog Edited by - charlie_pank on 5 Jan 2003 20:08:41 Link to comment Share on other sites More sharing options...
StewartG Posted January 5, 2003 Share Posted January 5, 2003 This is by no means an uncommon fault. I spent ages trying to cure it, tried new discs, checked caliper bolts, changed the pads and adjusted the wheel bearings. All seems to temporarily alleviate the problem but it's still there and I've given up worrying about it. By the way the longest lasting treatment was de-glazing the discs and pads or changing them. Link to comment Share on other sites More sharing options...
alicat Posted January 5, 2003 Share Posted January 5, 2003 Charlie Not had the pleasure of the wheel bearings on a Se7en. But there are several ways of adjusting them, the bearing in question was adjusted by tightening, then backing off to achive a degree of float, I remeber it well as I had to make a bracket to fix a dial gauge to. Other bearings are just torqued up. Alicat Link to comment Share on other sites More sharing options...
Swiss_Tony Posted January 5, 2003 Share Posted January 5, 2003 Before doing anything it would be worth checking the steering and suspension/bearings for excessive play.Also check the caliper fixings etc. Do you have access to a dial gauge?You can check the disk run out to see if thats it. By the way there should be a small amount. If not as Stewart says try de-glazing the front discs and pads. This can often cause similar problems. Have a good look at the discs and pads to see if there are any signs of excessive heat or contamination. Good luck James Su77on Se7ens Link to comment Share on other sites More sharing options...
Asklepios Posted January 5, 2003 Share Posted January 5, 2003 Charlie, Do a search on the forum ,on warped disc,or even just disc. There was a good reference on the subject about 8 months ago. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 6, 2003 Share Posted January 6, 2003 the front bearings is done up tightish and then backed off until the hole for the split pin lines up with a castlelation. There are two holes I think so you end up with a position every 12th of a turn. The disk should then spin pretty freely. Try giving the wheel a good tug and see if you get any mechanical movement in there (it will squrim on the tyre and rack as well but these should feel pretty different) HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
allegro Posted January 6, 2003 Share Posted January 6, 2003 I have a very convinsing document detailing what causes this and how to prevent it. I printed it from a posting on this site, so a good look in the archives will be worth doing. But apparently it is caused by invisible to the naked eye cementite deposits unevenly deposited on the disc by maintaining pressure on hot brakes while stationery. A method of removing these is scrubbing the friction surfaces thoroughly with garnet paper. Do not use regular sand paper or emery cloth as the aluminium oxide abrasive material will permeate the cast iron surface and make it worse. It is posible that if the condition has just started then simply fitting a good 'semi metalic' pad and using them hard after bedding may remove the deposits. If they have excessive deposits, then remove the discs and have them blanchard ground. They will then need proper bedding in. I have the same problem, but have not been agrevated by it enough to fix it. Please post how you get on. Andy Mac C7 GON 😬 Team Langoustine. Hard Core Prawn here 😬 Link to comment Share on other sites More sharing options...
Dave L. Posted January 6, 2003 Share Posted January 6, 2003 Thanks for the tip Allegro - I have this problem, but like you have not been too concerned about it. But I was sure it had to be something to do with variable friction around the disc, 'cos warped discs just give you a pulsing feeling through the brake pedals and I definitely don't get that. The braking force doesn't seem to vary much with a warped disc either. I also considered wheel bearings, but just couldn't figure out logically how they could give this effect. That's your company car !?! Link to comment Share on other sites More sharing options...
StewartG Posted January 6, 2003 Share Posted January 6, 2003 Allegro, you may be onto something there. I do have a habit of resting my foot on the brakes at traffic lights etc. This may well explain why no matter what I do to cure the problem it always comes back after a short while. I'm going to try cleaning up the discs and pads again and use the handbrake. Link to comment Share on other sites More sharing options...
StewartG Posted January 13, 2003 Share Posted January 13, 2003 Try www.procutinternational.com saw them at the show and their sales pitch sounded convincing. Link to comment Share on other sites More sharing options...
StewartG Posted January 13, 2003 Share Posted January 13, 2003 The web-site doesn't seem that informative but basically what this is all about is a machine that skims the discs on the car. Mine run out slightly but so do the wheels leading me to suspect that the disc bearing face is not perpendicular to the axis of rotation. Skimming the discs on the car should sort this and I'm led to believe costs about £30. Link to comment Share on other sites More sharing options...
Luke Beaumont Posted January 13, 2003 Share Posted January 13, 2003 Saw that, neat idea. I've just fixed a similar problem on mine the hard way. I think the hub must have been machined slightly off centre, allowing me to measure two of the disc mounting lugs high, two low. My dear old Dad had some 0.002" shim brass, so I cut a couple of washers from that to place between the disc and the low lugs, and voila, disc runout down to 1.5 thou from 10. Link to comment Share on other sites More sharing options...
charlie_pank Posted January 13, 2003 Author Share Posted January 13, 2003 Update: Put Kermit up on axle stands and gave wheel a good tug/shake - nothing amiss there Took wheel off and had a look at disc - there were a couple of ugly looking marks and it seemed more difficult to turn through the caliper in some places than others Got some garnet paper from a model shop (tried Halfrauds and a couple of independent motor factors to no avail). Gave the whole disc a good rub down, paying particular attention to the nasty marks Put wheel back on, found that spinning it still offered more resistance through the caliper than in others Went for quick blat to find I'm back to the normal squeak from both front brakes when cold, but no juddering, so I think it's worked ok. I'm keeping the garnet paper for the next time it happens though, as I have a harness and a glove-box mounted handbrake I HAVE to hold the brakes on sometimes! BTW what is "run out" on the disc? Thanks for all your help C Charlie'n'Kermit The plan is: there is no plan Link to comment Share on other sites More sharing options...
allegro Posted March 20, 2003 Share Posted March 20, 2003 Update My disc wobble annoyed me for the last time. So wheels off and gave the discs a good scrubbing with Garnet paper. I spent 30mins on each disc. I now have NO 'wobble' or uneven brake friction on during brakeing. Easy fix. Andy Mac C7 GON 😬 Team Langoustine. Hard Core Prawn here 😬 Edited by - ALLEGRO on 20 Mar 2003 10:59:07 Link to comment Share on other sites More sharing options...
R2D2 Posted March 20, 2003 Share Posted March 20, 2003 To measure disc run out you will need a DTI and a stand with a magnetic base. You need to measure the change in the position of the face of the disc perpendicular to the disc pad as you rotate the wheel. I would suggest measuring in radially at about mid-pad position. This measurement will measure run outof the disc/hub assembly so you need to be sure that the wheel bearings are correctly adjusted. If the run out is more than 0.2mm and you are confident that the disk is the cause of the problem you need to either machine or change the discs. Before you machine the discs you need to measure the thickness with a micrometer. make sure that you don't machine the discs to less than their minimum thickness or they could fail during very heavy braking. Depending on the type of disks you have fitted will help you to decide what to do next. Standard solid discs are only about a tenner each and it just isn't woth messing about. Vented discs are much more expensive but have quite a limited machining allowance before the have to be replaced. Both the measurements and the work involved is quite straightforward. Some times limited amounts of judder can be caused by glazing which is easier to remove and a way to avoid this is to pre-fade new brake pads as soon as they are fitted. Link to comment Share on other sites More sharing options...
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