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MG MGB Technical - Rounded caliper bolt

I just purchased a 1974 mgb roadster in really great condition. However, the second owner of most of its life passed away 4 years ago. So, it sat in the garage for four years without being driven or moved.The left front caliper locks up. When I went to remove the top caliper mounting bolt I found it was rounded. The lock metal was driven off so it was not the problem. I have put penetrating foam spray, heated the bolt and the part it runs through.I've even tried vise grips and that only made the head rounder. Nothing has worked. If I drill the head off the bolt the caliper will still not be able to be removed. I need to get this caliper off to replace it. I would prefer to not damage the caliper so I can trade it in on core for the new one. I was able to get the pistons to move, but when I apply the brake it locks up again. Any ideas or solutions from someone who has gone through this is really appreciated. George
GH Higginson

If you do drill the head off, could you separate the two halves of the caliper to remove it? I can't remember without looking. Or, as you can get the other bolt out, can you swing the caliper out far enough to clear the disc?

Another possible cause of it locking could be the flexible hose collapsing and restricting the fluid from returning.
Dave O'Neill 2

George - Disk brakes depend on the run out of the disk to push the pads out after releasing the brakes. Chances are that rolling the car out of the garage will disengage the pads. At that point, I would suggest taking the car to a brake shop and let them get the rounded bolt out (drilling the bolt will be an exercise in frustration since the bolts that hold the calipers are hardened bolts that will just dull any drill bit you use. Cheers - Dave
DW DuBois

I've not had this problem myself, but it may be worth trying one of these - Gator Grip ETC-125 11-32mm Multi-function Hand Tools Universal Repair Tools These universal sockets are really useful when you are stuck trying to get a rounded nut or bolt undone.

Andy Robinson

George. Have you tried using a 5/8 single hexagon socket as opposed to a 5/8" bi hexagon, next thing to try is tapping on a 19/32" or a 15mm single hexagon socket, first ensuring the lock tab is right out the way, and the socket is right home and square, also use a long bar, one of these methods usually works,99% of the time
Andy Tilney

or try these...

best of....
M McAndrew

The final solution for such things is usually to find a nut of the next size up, drill out the centre of it and then plug weld it through the hole onto the remains of the stud.

p.s. Always use 6 point sockets for dismantling anything that looks even slightly iffy to avoid ending up in this situation again.


Can you not get stiltsons (monkey wrench) on to it. I've always found that if you can get them on they always bite and either it will undo or twist off.
Paul Hollingworth

Flank drive sockets are good on nuts which have "lost" their corners.
Allan Reeling

This thread was discussed between 27/07/2017 and 01/08/2017

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