ChrisC Posted August 22, 2013 Share Posted August 22, 2013 Hi All Had a little problem this weekend with my A-Frame. It snapped 😳 I got a small knocking noise after a trackday, which sounded like loose handbrake cables when braking on the way home, took the car out last weekend for a gentle drive (had my 9 year old daughter in the car) where the noise much worse very quickly. When home rocking the car with the handbrake on, there was a snap, and the left hand mount of the a-frame parted company Photo I had to wait a bit for Caterham to have them in stock, before i took it apart, where I found the wrong bolt fitted to the right hand side of the car. According to the manual a M12 x 100 bolt should be used on the a-Frame to chassis fitting, but on the Right hand side I had a M12 x 120 bolt and this meant there was some play in the A-Frame to chassis fitting on the side that did not snap. So my question. 1, Where should that M12x120 bolt have been used? I feel the need to check where that bolt should have been used. 2, Do you think the wrong bolt on the RHS, allowing play in the a-frame to chassis fitting on the RHS would explain the snapping of the a-frame on the LHS. Hope you can help Chris. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 22, 2013 Member Share Posted August 22, 2013 It says that I have to be signed in to see that photo. Jonathan Link to comment Share on other sites More sharing options...
ChrisC Posted August 22, 2013 Author Share Posted August 22, 2013 Humm - let me check Link to comment Share on other sites More sharing options...
ChrisC Posted August 22, 2013 Author Share Posted August 22, 2013 Sorted Link to comment Share on other sites More sharing options...
Mankee Posted August 22, 2013 Share Posted August 22, 2013 Might the longer bolt on the driver's side be for a side impact bar? I have one on my car but I have no idea how much longer (if at all) the bolt is compared to the passenger side. Link to comment Share on other sites More sharing options...
garybee Posted August 22, 2013 Share Posted August 22, 2013 Unless I've misunderstood you I think you're concern about the bolt you've fitted to the RHS of the A-Frame is entirely unfounded. So long as the bolt is long enough, any spare length is just sat in free space. In which case it doesn't matter if it's a foot too long, it has no impact on the joint. Is it possible that you torqued the bolts up with the car still on axle stands? If this is the case then the bush/A-frame will be heavily stressed with the car on the ground. This could conceivably lead to failure at that point. Can't help with where the bolt should have been though. Are Caterhams really so well supplied that there is a bolt for every purpose and they are all the correct length, no spares etc? Edited by - garybee on 22 Aug 2013 21:38:14 Link to comment Share on other sites More sharing options...
Grubbster Posted August 22, 2013 Share Posted August 22, 2013 I can't see why a longer bolt would make any difference to the play (wouldn't it just mean more thread poking out of the nut?). There shouldn't be any play anyway, the A-Frame needs to be centred in the cassis using shims - I do know of a couple of people who didn't put any shims in which meant they damaged the A-Frame as they tightened the bolts 😔 Link to comment Share on other sites More sharing options...
Z3MCJez Posted August 22, 2013 Share Posted August 22, 2013 A-frames snapping there is relatively common on race cars. The longer bolt is likely to have been as a result of the fitment of a side-impact bar on the drivers side, as mentioned above. As Steve said, there shouldn't have been play - just a longer end to the bolt. My guess is that you have an ex-Academy car - so a Roadsport 125 of some vintage? Jez Link to comment Share on other sites More sharing options...
ChrisC Posted August 22, 2013 Author Share Posted August 22, 2013 Mankee - thats a distinct possibility. The car was ex-Academy, and would have had the side protection, so I assume this is why the longer bolt was fitted. It was lose and someone had tired to pack the 120 bolt with lots of washers. Grubbster - The a-frame was packed, poorly on the side with the long bolt garybee - This is a distinct possibility, the bolts where way to tight, had to dig out an extension handle to undo the broken side and the de dion tube fitting, but is this enough to snap the a-frame ? Link to comment Share on other sites More sharing options...
ChrisC Posted August 22, 2013 Author Share Posted August 22, 2013 Z3MCJez - ex-Academy, Yes spot on Link to comment Share on other sites More sharing options...
ChrisC Posted August 22, 2013 Author Share Posted August 22, 2013 So it looks like case closed, typical race car damage, and the long bolt was because it used to have side impact protection. I feel better about replacing it and sleeping easy not worrying why I had a longer bolt, and that a shorter bolt has not been fitted in the wrong place . Thanks Link to comment Share on other sites More sharing options...
garybee Posted August 22, 2013 Share Posted August 22, 2013 Ah, I think I understand what's going on on the RHS. Does the bolt have a long plain (unthreaded) portion and the washers were an attempt to stop the nut/bolt becoming 'threadbound' (nut tightening against end of thread before joint is tightened)? Link to comment Share on other sites More sharing options...
ChrisC Posted August 22, 2013 Author Share Posted August 22, 2013 Quoting garybee: Ah, I think I understand what's going on on the RHS. Does the bolt have a long plain (unthreaded) portion and the washers were an attempt to stop the nut/bolt becoming 'threadbound' (nut tightening against end of thread before joint is tightened)? Yep nut was hitting the end of the thread before tightening, and the person that put it back without the side protection packed it with loads of washers. This is all going to be replaced, because I purchased a all new fixings/washers and packing washers. Link to comment Share on other sites More sharing options...
garybee Posted August 22, 2013 Share Posted August 22, 2013 Gotcha' I would say that the slightly loose joint could well be the reason why the RHS didn't fail. So long as you torque up the fittings for the replacement with the car on the ground you should have nothing to worry about then. Link to comment Share on other sites More sharing options...
Z3MCJez Posted August 22, 2013 Share Posted August 22, 2013 I understand the washer packing point now too. The chance of an A-frame failing on both sides at the same time through fatigue is nil, though. It will go at the weaker point. As that gets even weaker it won't load the over weak point. A bit like pulling a cracker - someone always gets the middle bit. Jez Link to comment Share on other sites More sharing options...
simonpa Posted August 23, 2013 Share Posted August 23, 2013 Overtightened bolts should not have affected this failure, as the tourque should all be applied to the centre tube in the bush, leaving the outer tube free to flex via the rubber sandwiched in between. Overtorquing the bolts could weaken the bolt/nut through stretching/thread deformation, so always a good idea to replace suspension fixings. When you put the new tube on, follow the manual regarding spacer washers to centralise the dedion and make sure the large penny-washers have the chamfer towards the bush to reduce the chance of the washer fouling the outer tube of the bush and preventing the arm moving. In practice, it's not normally possible to 'lock' the bush as the inner tube is slightly longer than the outer. However, it would theoretically be possible to lock the bush if washers were used with larger internal diameter than the smaller tube on the bush, so locking the outer against the washer/chassis. I've never seen this happen tho'. Do make sure you follow the manual and support the car on the dedion, so the A-frame (and other suspension) bolts are done up with the bushes in an un-stressed state. AFAIUI, A-frames tend to fail on the nearside in race/ex-race cars due riding the kerbs excessively, or from impacts. Link to comment Share on other sites More sharing options...
Z3MCJez Posted August 23, 2013 Share Posted August 23, 2013 Quoting simonpa: AFAIUI, A-frames tend to fail on the nearside in race/ex-race cars due riding the kerbs excessively, or from impacts. They do tend to fail on the nearside - I'd not really thought about why the nearside rather than the offside, given the offside carries more of the driver weight. But fatigue from kerb riding is clearly a big point. Is it possible to ride the kerbs excessively in a race car? 😬 Jez, broken A-frame at Oulton Link to comment Share on other sites More sharing options...
Birkin S3 ZA. Posted August 23, 2013 Share Posted August 23, 2013 Throw the bonded bushes away as far as you can. and fit some nylon bushes or bearings. I have seen a few fail due to not enough flex on the bushes causing the end of the A arm to flex and fracture. I am busy making a new set for my car with 2" longer arms, using needle roller bearings, 26mm od 16mm wide 20mm id needs two to replace one bush. One inner hardened bush 35mm long 20mm od 1/2" id and two nylon washers 32mm od 20mm id and 1 to 1.5mm thick to space and keep the grease in and muck out. The best thing is the difference it makes to the ride Link to comment Share on other sites More sharing options...
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