Richard_420R Posted March 7, 2022 Share Posted March 7, 2022 Hi all,During track day at Blyton yesterday, I was getting some grauncy noises under hard left cornering - I didn't get it unless flat out in the dry as seems only to happen at grip limit. No such noise when turning right. Ideas and should I be worried about it? Not super loud but it is audible on my gopro vid I did when I'm not on the throttle.Car is 2.5yr old on 4k miles with LSD ... is this a sign the diff needs servicing soon?Richard. Link to comment Share on other sites More sharing options...
timb2117 Posted March 7, 2022 Share Posted March 7, 2022 Only guessing - rear wheel bearings maybe? definitely wouldn't harm to freshen up the diff oil. Link to comment Share on other sites More sharing options...
Wrightpayne Posted March 7, 2022 Share Posted March 7, 2022 I'd check for touch points between the transmission and chassis. If clearance is tight / not centred, slacken off the engine mount through bolts and transmission mount bolts and ease the gearbox over. Link to comment Share on other sites More sharing options...
ScottR400D Posted March 7, 2022 Share Posted March 7, 2022 I'd be checking the diff first. Link to comment Share on other sites More sharing options...
Beagler Posted March 7, 2022 Share Posted March 7, 2022 Check left drive shaft joints. Link to comment Share on other sites More sharing options...
ChrisC Posted March 7, 2022 Share Posted March 7, 2022 I think I would start with a spanner check of everything. It could be as simple as the wheel touching the dedion tube (13" have a habit of doing that), or your exhaust hasn't been dragging on the ground. A preload check on the diff might give you a clue, but be careful of your equipments ability to compare clockwise and anti clockwise readings. This might lead you to a wrong conclusion (don't ask me how I know) The problem with noise, it's very difficult to diagnose. Link to comment Share on other sites More sharing options...
Richard_420R Posted March 7, 2022 Author Share Posted March 7, 2022 Thanks all - much appreciated - will investigate some more!! Link to comment Share on other sites More sharing options...
7 wonders of the world Posted March 7, 2022 Share Posted March 7, 2022 look for witness marks in the above mentioned places, also check rear dampers as the springs can deform and bulge under compression and rub on the damper body, A frame front mounts and to the Dedion too.Look at the handbrake cable routing too Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted March 8, 2022 Share Posted March 8, 2022 Also check the deDion to A-frame bush, it can be easily torn with spirited use, allowing too much lateral movement of the axle relative to the body with consequential noises when metal to metal contact is made. Link to comment Share on other sites More sharing options...
Richard_420R Posted March 10, 2022 Author Share Posted March 10, 2022 Thanks - will try and take a look this weekend. Link to comment Share on other sites More sharing options...
Richard_420R Posted March 11, 2022 Author Share Posted March 11, 2022 I did a quick check of the rear left and there is a lot of grease/oil on the inside of the wheel rim and on the ARB and lower suspension parts. Can't see an obvious source and will get a better look with the wheel off later on but any tips on where to look to diagnose?R. Link to comment Share on other sites More sharing options...
AG2728 Posted March 11, 2022 Share Posted March 11, 2022 Check the outer CV boot. On my 420R the LH ARB drop link was fouling the CV boot under compression and I lost all the grease. Had to replace the split boot and stiffen the ARB up one hole to allow enough clearance. Link to comment Share on other sites More sharing options...
gaxor Posted March 11, 2022 Share Posted March 11, 2022 I know when I used to race we would occasionally get tyres catching the wheel arches under heavy load. Could be any of the reasons previously mentioned, but a tell tail sign will be black tyre marks on the underside of the car Link to comment Share on other sites More sharing options...
Richard_420R Posted March 16, 2022 Author Share Posted March 16, 2022 Hi AG2728, this looks like what has happened to me. I've just softened the ARB to the last hole and this is the first trackday following that change. Seems a bit rubbish that we can't use that setting but I suspec I will reset to the previous setting as a precaution given there is no other reason I can think of why this has happened.Richard. Link to comment Share on other sites More sharing options...
AG2728 Posted March 16, 2022 Share Posted March 16, 2022 Hi RichardYes, on full soft the LH drop link was impacing the outer CV joint. I now run one hole off full soft.See here - https://www.caterhamlotus7.club/forum/techtalk/more-driveshaft-woesregardsAndy Link to comment Share on other sites More sharing options...
Richard_420R Posted March 19, 2022 Author Share Posted March 19, 2022 Thanks Andy. Turn7 have had a good look at it and looks like exactly the same issue - although they think extending the drop link will allow running in softer setting whilst maintaining enough clearance. Changing CV boot and extending drop-link is the plan.Richard. Link to comment Share on other sites More sharing options...
AG2728 Posted March 19, 2022 Share Posted March 19, 2022 Hi RichardGlad you got to the bottom of it.I did try to run the existing drop link as long as it could go. (too long really, with only a few threads left) and it would still kiss the CV joint over some curbs. A modified, longer drop link may do the job though, if that's what Turn 7 are suggesting.FWIW, suprisingly I found that running one hole off full soft was hardly noticeable for me. It is after all, a really weedy ARB. On this setting I also found it preferable to run my rear tyre pressures a couple of PSI lower. Just an opinion. Works for me.RegardsAndy Link to comment Share on other sites More sharing options...
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