ChrisC Posted June 11, 2017 Share Posted June 11, 2017 Hi AllI am looking for some pointers in trying to track down a very loud resonance at 2500 rpm. It seems to come from under the dash behind the speedo, but obviously noise travels. It's present stationary and moving, in any gear. It's very pronounced, and can be clearly heard over 37db ear plugs. It's really is spoiling the pleasure of driving the car, it's like having a rev limiter, because I don't want to go over the resonance point, and hate it as decelerating back through it. So far I have checked:All the instruments, and the brackets holding themThe wiper tube, fixings and plates.Bonnet and nose, happens with them off the car.Gearbox touching the Chassis, there is a gap (not much, but a gap)Column clears the exhaust, and the exhaust is not touching anything.Touching the dash, outer column, steering lock, knee pads, coil cover, windscreen, heater, battery, airbox, ECU, side skins, fuse cover, all to no effect. Basically, if I could touch it when the engine is running I have, yet the resonance exists.So, where next to look?Chris. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 11, 2017 Member Share Posted June 11, 2017 Basically, if I could touch it when the engine is running I have, yet the resonance exists.I'm not sure if it adds anything at that frequency to touching but how about trying a stethoscope?Jonathan Link to comment Share on other sites More sharing options...
ChrisC Posted June 11, 2017 Author Share Posted June 11, 2017 Would a stethoscope help? The noise / vibration I am looking for is louder than the exhaust at 2500 rpm. I thought a stethoscope amplifies the sound, won't that blow my ears off? Link to comment Share on other sites More sharing options...
TomB Posted June 12, 2017 Share Posted June 12, 2017 I have something similar when setting off from a standstill, it seems worse with some steering applied. It is incredibly annoying and I cant seem to find the answer. I did find the large FIA key resister was flapping around making a knocking sound. The list above is helpful Ill continue searching. Link to comment Share on other sites More sharing options...
AdamQ Posted June 12, 2017 Share Posted June 12, 2017 I'm sure I've read somewhere on here that a loose spark plug can make a fair old din, though I'd have thought that would be independent of RPM. Still, FWIW ...Good luck with tracking it down ... Link to comment Share on other sites More sharing options...
ChrisC Posted June 12, 2017 Author Share Posted June 12, 2017 Hi Tom No FIA switch on mine :-( but thanks anyway.As for yours, there is a small unused mounting tang inside the pedal box, at the front of the box, directly in line with the steering column as it passes through. Mine touched the column and had to be bent out the way during IVA, I wonder if yours is touching at some steering angles. Chris. Link to comment Share on other sites More sharing options...
ChrisC Posted June 12, 2017 Author Share Posted June 12, 2017 Thanks Adam, I will check the plugs and snug. Link to comment Share on other sites More sharing options...
TomB Posted June 12, 2017 Share Posted June 12, 2017 Thanks will have a look. I was wondering whether Id lost a plastic sleeve from one of the steering column bushes, but there is no play at either end of the steering column as its passes through the dash, so don't think its that. Link to comment Share on other sites More sharing options...
Jim 123 Posted June 12, 2017 Share Posted June 12, 2017 Maybe try putting a slice of rubber/cardboard in/to the small gap between the gearbox and chassis to see if the gearbox is touching with the engine revving Link to comment Share on other sites More sharing options...
ChrisC Posted June 12, 2017 Author Share Posted June 12, 2017 Hi Jim. That has been my prime focus all weekend. Initially the gap was smaller, I have doubled the gap to about 5mm but this made no difference to the resonance. I didn't test with something between the gap, so that's another thing on my check list. Link to comment Share on other sites More sharing options...
John Vine Posted June 12, 2017 Share Posted June 12, 2017 A few thoughts: Engine mount(s) allowing metal-to-metal contact with chassis Gearbox mount (ditto) Silencer mounting Pedal box and internals Scuttle panelJV Link to comment Share on other sites More sharing options...
ChrisC Posted June 12, 2017 Author Share Posted June 12, 2017 Engine/Gearbox and Silencer mounts are all standard, how do you mean allowing metal to metal contact? It does have the wider gearbox tunnel for the Mazda box, but being a 6sp the gearbox mount is the standard type 9 mount, all be it on a removable mounting plate as per Mazda install. The chassis is almost vibration free apart from 2500 rpm, where all hell breaks losses. Pedal box lid removed and the resonance still happens, also happens if brake and clutch pedal are pressed. Scuttle panel. I will check. Link to comment Share on other sites More sharing options...
MADMALC Posted June 12, 2017 Share Posted June 12, 2017 Check that the steering column is not touching or too close to the engine at the lower end. Have you tried holding the lower shaft to see if you can alter the sound. Link to comment Share on other sites More sharing options...
ChrisC Posted June 12, 2017 Author Share Posted June 12, 2017 Been trying to alter the sound for days :-( Steering column checked, no vibration upper or lower, and well clear of primaries. Link to comment Share on other sites More sharing options...
ScottR400D Posted June 12, 2017 Share Posted June 12, 2017 Have you fitted the knee trim panels? When mine were fitted the RH one touched the OBD plug and made a real din. Bending it away sorted it. Link to comment Share on other sites More sharing options...
ChrisC Posted June 12, 2017 Author Share Posted June 12, 2017 They are fitted, and the noise does seem to come from the RH side. OBD plug / knee trim contact on the list to check. Link to comment Share on other sites More sharing options...
TomB Posted June 12, 2017 Share Posted June 12, 2017 Im going to check windscreen mounts/ fasteners, FIA key, steering column tube, pedal box & contents, ECU & fuse box mounting, wiper spindles, knee trim panels, instrument mountings. Fingers crossed Ill find something only finger tight that cure it! Link to comment Share on other sites More sharing options...
malcolm1sim Posted June 12, 2017 Share Posted June 12, 2017 Idea from a numptysit in car and create noise. Have someone go round the car filming, phone should do. Stay about 1 foot off ground and similar away from car. Go all round and over in hoops again about foot apart.watch and listen to film carefully. You may able to narrow down an area by the changes in sound. Good luck. Link to comment Share on other sites More sharing options...
Jim 123 Posted June 12, 2017 Share Posted June 12, 2017 I believe there is an internal shaft inside the wiper tube. Maybe try holding the revs to produce the resonance and see if anything changes with the wipers operating? Link to comment Share on other sites More sharing options...
John Vine Posted June 12, 2017 Share Posted June 12, 2017 ...how do you mean allowing metal to metal contact?Are the rubber sections in good nick, or have they deteriorated or broken up?JV Link to comment Share on other sites More sharing options...
Shaky Posted June 12, 2017 Share Posted June 12, 2017 I had exactly the same, just at the revs the car sat at on the motorway. Seemed to be under the dash. It was something you say you addressed so might not help but here goes. It turned out on my car to be the spring clamp for the bonnet. At just the right revs it vibrated against the bonnet, what a noise. Even made a noise with bonnet off but at different frequency etc. Just happened to touch it during one investigation. A plastic tube expanded in hot water and fitted over the spring took it away. Hope that helps. Link to comment Share on other sites More sharing options...
ChrisC Posted June 13, 2017 Author Share Posted June 13, 2017 Thanks for all the suggestions, all are food for thought, and I will be checking all of them. If I get no luck its time for a video. JV - The all mounts are under 800 miles old, with no signs of wear, that said it does not exclude manufacturing faults. Link to comment Share on other sites More sharing options...
Jim 123 Posted June 13, 2017 Share Posted June 13, 2017 Chris, I can't locate the thread but there was a posting on here about 6 months ago which a vibration on a new build turned that out to be a dodgy engine mount. Thr original culprit was thought to be the gearbox touching chassis. Link to comment Share on other sites More sharing options...
ChrisC Posted June 13, 2017 Author Share Posted June 13, 2017 That was Marcus's 420R. I sort of ruled that out because he described the chassis having a constant vibration, mine is resonance only at a specific rpm. Link to comment Share on other sites More sharing options...
Pawson6844 Posted June 14, 2017 Share Posted June 14, 2017 I have a very similar fault to this. Just started on a road trip this weekend to Wales. Can hear a vibration behind the dash over the exhaust at 70mph. Will go through this thread and check as I go. Very annoying Link to comment Share on other sites More sharing options...
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