Holding a caliper

[grim_d]

I have a couple of rear brembo calipers from my legacy that need their mounting holes repaired, both have 1 snapped stud and 1 hole with the threads pulled out.

Whilst I'm waiting on the helicoil kit arriving I'm after a little advice on holding the thing to drill the stud out, I'm happy enough to do the damaged holes freehand but I'd like to be spot on with drilling the old studs out so I'd like to use my milling machine.

How on earth do I hold this thing steady to drill them out? There isn't a flat surface on it anywhere apart from where I want to drill. In an ideal world I'd split it in half and clamp it down but I really don't want to do that.

I'll admit I haven't really had any time to attempt to find a solution so I'm cheating a bit by asking ahead of time.

Whilst I'm at it, what's the best way to making sure I'm right in the middle of the stud for drilling? There might be enough sticking out to edge find it but I wonder if there's a better way? There a tiny bit of wiggle room on the mounting lugs but the closer to original the better.

Thanks in advance!

 

[Robotstar5]

Probably one for @doubleboost

 

[Pete.]

A number of things you can do:

• The busted stud is sticking proud. Put a larger nut over the exposed thread and fill with mig weld. Let it cool a bit and you can turn the nut to un-screw the stud.
• You can split the calipers by removing the four through-bolts. Then you can put the half piece flat on your mill bed and clamp it down there.
• If you're worried about the bolts snapping when you split the calipers, you could cantilever a heavy block of steel over two packing blocks and then clamp the middle flat area down onto the cantilevered piece.

 

[grim_d]

A number of things you can do:

• The busted stud is sticking proud. Put a larger nut over the exposed thread and fill with mig weld. Let it cool a bit and you can turn the nut to un-screw the stud.
• You can split the calipers by removing the four through-bolts. Then you can put the half piece flat on your mill bed and clamp it down there.
• If you're worried about the bolts snapping when you split the calipers, you could cantilever a heavy block of steel over two packing blocks and then clamp the middle flat area down onto the cantilevered piece.

I didn't consider attempting to remove the old studs because it's so stuck, immediately thinking of drilling it out. it's stuck in place because the aluminium threads have galled onto the bolt and it's ripped the threads off and jammed so ferociously half way out that the bolt sheared. A heat cycle from welding might help free that though.

I don't want to split the calipers, it could easily create more problems than it solves and I don't have any new seals either.

Yes I considered some sort of arrangement passing through the middle, I suppose using a cantilever and clamping it down so the face is resting on to a peice of wood to reduce flex would work, good idea.

 

[Ashley Burton]

I would probably go for the welded nut approach. Works a dream when I've done it in the past!

 

[grim_d]

I'll definitely give it a go in the first instance, nothing to lose. Can't believe I didn't consider it, done it loads in the past as well!

I hope the heat doesnt damage the paint too much.

 

[mr haynes]

Don't split the calipers, you'll end up with 4 more sheared bolts.
I've always had to drill them out of ally calipers, bloody nightmare!
Bimetallic corrosion pretty much guaranteed with dry steel bolts

 

[grim_d]

Don't split the calipers, you'll end up with 4 more sheared bolts.
I've always had to drill them out of ally calipers, bloody nightmare!
Bimetallic corrosion pretty much guaranteed with dry steel bolts

Yep, for the sake of a bit of anti seize compound as well.

I've no Intention of trying to split them. I'll have them rebuild and painted at some point and then it can be someone else's problem.

Have you tried the welded nut in this scenario? It's basically like trying to force an unthreaded shank through a threaded hole but if it holds I might be able to burst it through.

 

[Seadog]

Repair the stripped thread. Make up a fixture with two holes at the correct distance/diameter. Centre the fixture on the broken stud hole. Bolt the caliper to it using the repaired thread. Drill out the broken stud to major diameter and then Helicoil that one too.

 

[garethp]

Is the flat area around the pistons machined or just as cast flat? Can't tell from the photos.

 

[grim_d]

I think it's flat, there might be a raised portion around the piston where the dust boot locates I wouldn't want to clamp on top of the dust boot.

 

[gaz_moose]

if your going for the weld a nut on method wind it wout when its still glow red hot.

if drilling it out I would clamp it to a big angle plate through where the disc goes so the outside of the caliper is against the angle plate.

id drill it under size then use a milling bit and mill the remains out till you can just pull the threads out.

 

[RichardM]

Looks like you only have two faces which are machined and those have the snapped / stripped studs in them. I'd make two hollow spacers up to go between the machined face and the mill table, the brake fluid in-feed needs to point to the table, maybe worth putting an old banjo bolt in to give a three legged support. Bolt through the stripped one to the table, clamp the other so you can drill then drill the snapped stud out, helicoil or make new studs up and tap while clamped up. This will ensure you keep the correct alignment. Probably best to get a long centre drill to start the hole.

 

[dobbslc]

Not sure if this'll help as I split the caliper.

e

 

[addjunkie]

The faces on the inside either side of the pistons are flat. Can you not clamp it through there, and support ends to stop wobbble accordingly.

Or a piece of square stock, in there the pads go, right through and clamp at either end

 

[grim_d]

if your going for the weld a nut on method wind it wout when its still glow red hot.

if drilling it out I would clamp it to a big angle plate through where the disc goes so the outside of the caliper is against the angle plate.

id drill it under size then use a milling bit and mill the remains out till you can just pull the threads out.

Sadly I don't own an angle plate. It's getting a helicoil in it anyway so no need to be too careful getting the stud out.

Looks like you only have two faces which are machined and those have the snapped / stripped studs in them. I'd make two hollow spacers up to go between the machined face and the mill table, the brake fluid in-feed needs to point to the table, maybe worth putting an old banjo bolt in to give a three legged support. Bolt through the stripped one to the table, clamp the other so you can drill then drill the snapped stud out, helicoil or make new studs up and tap while clamped up. This will ensure you keep the correct alignment. Probably best to get a long centre drill to start the hole.

Yep it's getting helicoils, this seems a good idea But I don't know if I've enough clearance for the chuck etc with it that way round.

The faces on the inside either side of the pistons are flat. Can you not clamp it through there, and support ends to stop wobbble accordingly.

Or a piece of square stock, in there the pads go, right through and clamp at either end

Yes this would work, the biggest challenge with this is avoiding chewing up the visible part of the caliper whilst maintaining rigidity.

Some good ideas here guys to get my brain in gear.

 

[mr haynes]

Yep, for the sake of a bit of anti seize compound as well.

I've no Intention of trying to split them. I'll have them rebuild and painted at some point and then it can be someone else's problem.

Have you tried the welded nut in this scenario? It's basically like trying to force an unthreaded shank through a threaded hole but if it holds I might be able to burst it through.

I've always found end up snapping off again. Gave up that option and now just drill out or throw away the bloody things! Some instances been cheaper to get new ones than time spent messing about

 

[grim_d]

I've always found end up snapping off again. Gave up that option and now just drill out or throw away the bloody things! Some instances been cheaper to get new ones than time spent messing about

These Subaru brembos seem to go for crazy money, I guess all the WRX lads want them.

A couple of helicoil kits (I've a front caliper to repair too) and a set of bolts is just shy of £100 so they are worth repairing and I get a couple of helicoil kits for the tool collection.

 

[doubleboost]

Probably one for @doubleboost

Weld nuts on is the first thing i would try
To hold it you could but a large block in the caliper then blow the pistons out with air pressure
That would give you a mounting point
Once the old bolts are out i would just use the "eye ball" method and free hand the helicoil tap

 

[garethp]

I think it's flat, there might be a raised portion around the piston where the dust boot locates I wouldn't want to clamp on top of the dust boot.

I was thinking a flat bar with a hole cut to clear the the piston and seal, then you can clamp the caliper to the bar and some how clamp that to the mill table. 1-2-3 blocks? This relies on the flat area being square to piston bore.

Doubleboost's idea for air would also work with plenty of clamping pressure - don't put your fingers near the pistons when you turn the air on, I was overthinking it and trying to figure out using hydraulics to push the pistons out - and gave up.