Myles Posted May 13, 2005 Share Posted May 13, 2005 I'm upgrading to HiSpec 4-pots at the front this w/e - and taking the opportunity to install flexi lines at the rear to make bleeding and maintenance easier - and (some say) get more even brake wear on the rear pads. Anyway, I've been at it for the last two evenings and have some issues/questions: i) The front discs are new and were sourced from HiSpec - I noticed (by chance - I had the old calipers still dangling from their hoses) that the LH one has some run-out (I think the term is). The caliper was lightly touching the surface of the disc - and as I checked the bearings for stiffness, I noticed that the caliper left the surface of the disc in one area (noticed by dint of the scraping sound coming in and out...). I took the disc off, removed it from the hub, checked that the hub-face was clean and reassembled - same result. It looks like the variation is something like 2-thou (I think -I'd need to check my feeler gauges again) - it's certainly not visible to the naked eye (unless you've got a soon-to-be-redundant) caliper hanging against it. Should I carry on with the installation, or cry fowl (). To be honest, I can't tell if the problem is with the disc or hub or whatever. Vinnie (on Cam7) has suggested that if I noticed it with a dangly caliper, the runout is probably worse than I measured - and I really ought to get it measured properly and then source another disc. I've not really got time for that though... 😳 ☹️ ☹️ Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
stevefoster Posted May 13, 2005 Share Posted May 13, 2005 Hmm, Well, max disc run out quoted on my Passat is 0.05mm (vented disc) = 0.001968504 inch. On our Citroen ZX it's 0.2mm (solid disc) = 0.007874016 inch (seems too high). On a Ford Capri 1969 to 1974 it's quoted as 0.0035 inch (Solid disc). So from that I conclude vented discs seem to have less allowable run out. I'd call Hi-spec and query it. Are you sure the disks were bolted up with the mating faces nice and clean? Also do you have a dial gauge to measure it with. If not a good opportunity to invest... Hants (North) and Berkshire Area club site here My racing info site here Link to comment Share on other sites More sharing options...
Myles Posted May 14, 2005 Author Share Posted May 14, 2005 I'm going to pull the disc off (again) and triple-check it. I've not got a dial-gauge... and yes, now might be a good time to get one as it's a faff to borrow a set every time I time the cams. Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Myles Posted May 14, 2005 Author Share Posted May 14, 2005 Right, well, I spent a fair bit of time investigating today - no dial-gauge though... To cut a long-story short, I put the old disc back on and checked that... ...it exhibited worse runout than the new one *AND* the runout was in exactly the same place... So, I'm reasonably confident that; i) The new discs will be no worse than the old and ii) (part of) The problem lies somewhere in the hub or bearings (unlikely**) I'd say bearings are unlikely - because they went back in randomly - and so it would have to be a hell of a coincidence for it all to line up again. The hubs are alloy - I'm assuming this is standard and is *not* the lightweight option - I'm guessing it's quite expensive to replace for little gain??? Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
stevefoster Posted May 15, 2005 Share Posted May 15, 2005 It sounds like machine tolerance in the face of the hub or bearing surfaces. If both are near max tolerance you are unlucky and they add up. his happened to me with De dion tube end and ear = too much -ve camber. The alloy hubs are the lightweight versions. The SLR/R400 racers went to all steel = very heavy, as they crash the curbs so hard the alloy ones were at risk of failing. They get pad knock off on most fast curbs You could split the disc and put just the hub on and measure the run out of the mating face with that dial gauge you have promised yourself That way you would know it was the hub. Hants (North) and Berkshire Area club site here My racing info site here Link to comment Share on other sites More sharing options...
Myles Posted May 15, 2005 Author Share Posted May 15, 2005 I always seem to end up doing most jobs three or more times - it does give me the advantage that I end up working about as quickly as a WRC mechanic... I can't be ar7ed to split them again. I'm not about to replace the hubs - and I haven't got time before I need the car on the road anyway. If I do end up with problems (and I'll be doing 1000-1500 miles within the week), I'll get that gauge... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
oldbutnotslow Posted May 16, 2005 Share Posted May 16, 2005 Hi Myles, I had run out problems on a new set of standard discs that I fitted prior to my upgrade. I found that there were a couple of contributory factors, 1, the large mounting holes in the discs were slightly smaller than the original set and therefore sat slightly tighter to the hub bearing. 2. one of the 4 mounting flanges on the hub was slightly proud ( I established this using engineers blue and a DTI) Cure: - I increased the chamfer on the large mounting hole to allow greater clearance I used a fine oilstone and very thin oil (wd40) and honed the offending mounting flange. They are fine now. Regards Grant Black and stone chip. here Link to comment Share on other sites More sharing options...
Myles Posted May 16, 2005 Author Share Posted May 16, 2005 Hmm - *might* be worth me having a go at the main hole then - but I've no E-blue to check the rest of it. Gives me something to think about anyway... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
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