bahf Posted May 20, 2018 Share Posted May 20, 2018 Does anyone know what size the rear disc bolts are - the ones that fix the disc to the hub. My manual says they are 3/8" UNF but I'm not convinced. The reason is that being Sierra units, I would expect them to be metric BUT a standard M10 does NOT fit. Might they be M10 x 1mm pitch?I have tried 3/8" but they're just a bit tight, which may be due to the hubs having threadlock applied previously.Thanks in advance.Brian Link to comment Share on other sites More sharing options...
CharlesElliott Posted May 20, 2018 Share Posted May 20, 2018 The calipers may be from a Sierra but the brake discs are from a Triumph Spitfire, same as the fronts. Link to comment Share on other sites More sharing options...
bahf Posted May 20, 2018 Author Share Posted May 20, 2018 it's the hub that has the female thread into which the bolts screw and I believe this to be a Ford Sierra part. I'm pretty certain it's 3/8" UNF, which may surprise some people as it's a Ford part, but someone out there may have better information. maybe it's not a Ford part?? Link to comment Share on other sites More sharing options...
Wrightpayne Posted May 21, 2018 Share Posted May 21, 2018 These have thinned down heads. I believe Roger Swift (ECR) has used allen cap head bolts successfully. Ian Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 21, 2018 Member Share Posted May 21, 2018 They're not in Shaun's bolt list and I can't find a definitive answer in the archives, other than to ask Redline.Jonathan Link to comment Share on other sites More sharing options...
ECR Posted May 21, 2018 Share Posted May 21, 2018 If I have Ian, please remind me when..... It sounds like the sort of thing i'd try but I certainly can't remember doing it Link to comment Share on other sites More sharing options...
Wrightpayne Posted May 21, 2018 Share Posted May 21, 2018 It was prob 10 years ago - I’ll see if I can find the post!Ian Link to comment Share on other sites More sharing options...
ncm Posted May 21, 2018 Share Posted May 21, 2018 https://www.lotus7.club/forum/techtalk/rear-brake-discs-de-dion-axle-and-standard-sierra-calipers last discussed in January. Correct bolts are 79085 . Cheers, Brian. Link to comment Share on other sites More sharing options...
bahf Posted May 21, 2018 Author Share Posted May 21, 2018 That makes sense - thinned down head similar to seat belt bolts and most probably 3/8" UNF. Additionally, the nice man from Caterham confirmed this morning that they were 3/8" UNF.The reason the heads are thinned is that the steel Sierra hub will contact standard head bolts, hence the suggestion that socket head bolts may work. They don't work on mine BUT they are very close, so I will either "fettle" the socket head diameter or the hub OD.The tight fit when I first tried the 3/8" must be due to residual loctite - I have re-tapped most of the threads but I have a really tight one where I would like to "dissolve" the residual loctite - has anyone got any "good recipes" for dissolving loctite?Cheers Brian Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 21, 2018 Member Share Posted May 21, 2018 interesting question.I don't know the chemistry of any of the types of Loctite, but I'd suggest gentle heat or petrol or acetone followed by the tap.Try a test piece first and keep acetone off plastics, finished surfaces etc.(Many proprietary brake and clutch cleaners contain acetone.)Jonathan Link to comment Share on other sites More sharing options...
bahf Posted May 21, 2018 Author Share Posted May 21, 2018 Be careful readers - the KEY word in the previous post is ...... "or" !!!! Link to comment Share on other sites More sharing options...
SM25T Posted May 21, 2018 Share Posted May 21, 2018 Try a hot air gun and re-tap it while hot and soft. Link to comment Share on other sites More sharing options...
Paul Deslandes Posted May 21, 2018 Share Posted May 21, 2018 A lot of sockets have a radiused face so they don't engage fully onto a thinned down bolt head. This can cause them to slip so if possible either turn or file the socket face so that it's flat to allow the maximum engagement with the hex.Paul Link to comment Share on other sites More sharing options...
rhauri Posted May 24, 2018 Share Posted May 24, 2018 I can confirm the correct bolt is '79085' and changed them earlier this year when changing rear discs.A few LADS top tips helped me out: Lay your wheel on the floor (face down, maybe on top of cardboard to protect the finish) and put the hub/brake disc into it. I put a couple of the lug nuts on too, finger tight Buy a spare socket (can't remember the size off the top of my head, will check when I get home if no one else comments) and grind/flatten it down so the tapered end is gone - should give more purchase on the shallow bolt head Kneel on the tyre to keep everything steady To undo the bolts, use a breaker bar, go slow, and ensure you put downward pressure on the socket end (last thing you want is for the socket to slip and round off the bolt head)That should be enough to overcome the thread-lock (it was for me, I didn't use any form of heat. That said, heat should weaken the thread-lock so not a bad idea at all).I'm sure you've probably already read this on other threads and I may have even repeated what others have already said! Hope it helps anyway. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 24, 2018 Member Share Posted May 24, 2018 ± Penetrating fluid before removal?Jonathan Link to comment Share on other sites More sharing options...
SM25T Posted May 24, 2018 Share Posted May 24, 2018 Think I remember it is 9/16" AF ... Not sure if a 14mm would fit on. Best to use a hexagonal rather than 20 point socket too. I applied a lot of heat from a hot air gun to the hub to soften the loctite. That helped. As above ... wheel face down on the ground ... hub studs into their holes and a long long breaker bar. Kneel on wheel and heave. Leverage is your friend. Link to comment Share on other sites More sharing options...
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