Front brake caliper thread repair

Andy Davis

2010 ST1300. Took the brakes off the forks to change the front tire. Stripped (just barely) the mounting bolt threads on the right side (which are 8 x 1.25 mm)...disaster! Okay, what should I do:

Helicoil? Do you suppose I can safely do this in place (caliper hanging by its hoses)?

Loctite Form-A-Thread the threads in place. Tempting, but these bolts are supposed to be tightened to 23 ft-lbf?

Drill and retap to 10 mm (bad idea)?

Disassemble the brake and buy a brand new bracket subassembly?

I'm hoping people will say, "yeah, Loctite!"
 
Not so very far from here, I started a post with a similar scenario, but in the back of the bike.
I would suggest trying a thread chaser first - not a tap / die - to see if you can reform the threads. You said "barely" stripped.
Problem I found in my town was finding a single size I needed. The sets I've found online are about $100 or so, and the ones available at tool stores or auto parts chains are for O2 sensors or spark plugs, both too large for our needs.
 
Andy Davis said:
Stripped (just barely) the mounting bolt threads on the right side
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Just to be clear ... "right" side, being the right when sitting on the bike?
Andy Davis said:
Helicoil? Do you suppose I can safely do this in place (caliper hanging by its hoses)?
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I might consider a helicoil.

BTW, I never let the calipers "hang by the hoses" ... I use bungee cords to hold the calipers.
Andy Davis said:
Drill and retap to 10 mm (bad idea)?
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Yea, not a good idea, because the caliper bolt hole will also need to be drilled larger
Andy Davis said:
Disassemble the brake and buy a brand new bracket subassembly?
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Ummm. Bracket subassembly? Have I forgotten already and need to go check my bike? The caliper bolts to a fixed bracket on the fork (correct?).

I need to go check my bike, but one other thought would be to drill the bracket hole all the way through, then buy a longer 8x1.25 bolt plus a locking nut.

However, I'm still leaning to helicol.
 
Longer bolt and nylock nut on backside if you have the room. That would be just as strong as the OEM solution. Helicoil could be done in place. Drilling the hole oversized, the drill will track straight following the existing hole. Holding things steady might require a helper, or clamping the part to a support board or other bike part.

RT
 
I had a similar event on my 94- I got a longer bolt of the same thread pitch and it worked perfectly (40 mm), plus it had the serrated flange to bite into the metal of the caliper just a bit- wasn’t too long out the back side of the caliper either.

I didn’t have room on the back for a nut, but it wasn’t required anyway.

This type of bolt:
 
It's your brakes for heaven's sake. Is there any system more critical? No helicoil or thread repair that requires removing any of the fork leg lug.

I would consider using a longer bolt and a locking nut on the inside if the nut clears the spinning wheel but I wouldn't drill out or remove what threads are left in the fork leg. Clean up the hole with a thread chaser and just thread the longer bolt out the other side of the lug - or insert the longer bolt from the inside so the nut is outboard. I wouldn't want to drill out the fork leg lug's threads and end up with one iota of play in that threaded lug. If I was you after buying a torque wrench I would start looking for a good used right hand fork leg to fix it right.
 
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I agree entirely the sentiment behind Dave's post. This isn't a place to be messing around with Heath Robinson repairs. (Who is Robinson, anyway ??)

The thread is in the bracket, not in the fork leg - but I still would not want to drill out the fork leg lug to accomodate a larger diameter bolt. Ditto the caliper bracket, for a new thread or a hexicoil insert.
I don't think that there is enough space for a bolt head or a nut on the lower mounting hole. The upper mounting hole clears the brake disk/rotor but does not have enough clearance for a bolt head or a nut head to fit. The curvature of the bracket casting adjacent to the hole will prevent it from seating properly.

Compared to a life - any life, not just your own - a brand new bracket is peanuts.

Or buy a good second hand one - but beware of getting one with accident damage. As I mentioned earlier, note that the pre-2008 versions are different from 2008 models and later. The bolt holes align OK with the forks, but the calipers mounts (and the ABS sensor mount) are all different.

It sounds a bit over the top to buy new ? Well I had to in the last few months. My right hand cliper bleed thread hole was damaged. I could not risk the bleed valve from seating incorrectly and slowly leaking fluid. Safety demanded a replacement. I found a pristine 2nd hand one for less than the cost of two tanks of fuel.

You say yours is a 2010 model ? But check the actual model year of your bike - not the date of first registration. It's on the label under the seat, and is represented by the 10th character of the VIN stamped on the right hand side of the headstock. The letter code is A for 2010, but I am unsure how the USA system of the vehicle code on the label works. It is different in the UK from what I see on the Ron Ayers site.

As a quick check - the pre 2008 models have a recessed allen key socket at the end of the pad pin, fitted with a rubber bung. From 2008 they have a protruding hexagon bolt head that requires a spanner or socket. But these can be retro fitted with a slight modification, so it isn't a foolproof method of recognising the model year.


Andy Davis said:
Disassemble the brake and buy a brand new bracket subassembly?
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No need to disassemble the brake caliper on the right hand side. Just remove the pads, undo the bolts (you already have) and slide the caliper off the bracket. If you have ABS, you'll need to unbolt the sensor. You may need to fit a boot, a slider and a pad retaining clip from the old bracket, and grease the sliders with silicone or rubber grease. And there is possibly a cable retaining clip - I can't remember for certain. The caliper will then slide on to the new bracket.

This is unlike the left hand side which has the SMC plumbed into the brake lines. The right hand bracket is not affected at all by the brake's plumbing.
 
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If you're going to try a longer bolt/nut fix, you might swing by Bowlin to see if they have what you need. I don't know that they have everything, but boy, they have a lot of fasteners. It's kinda between Sprouts and Whole Foods. https://www.bowlinbolts.com/
 
The hyperbole is hysterical. It's an 8mm bolt, torqued to 23ft/lbs. How strong, exactly, do you all think that is? How weak is a correctly installed Helicoil? I'll give you a hint: It is The equivalent strength of the original fastener. The only possible problem would be if the hole in question was to close to an edge, or resulted in too thin a wall on a casting. But an 8mm bolt at 23ft/lbs is laughably low clamping force. You do understand that they are approved for use in aircraft? This isn't a space shuttle motor mount...

RT
 
I admit that I relied on memory at first in regards to what part of the caliper / fork leg assembly was threaded. I pulled out the SM last night to look at it where the threads in question are actually located. I was thinking the lug on the fork leg was threaded instead of the caliper bracket but It doesn't change my opinion that I would not use a thread repair insert in this application. It's not the clamping force that loosens the caliper retaining bolts, its the shearing force applied to the bolt and the vibrations from the brake pads against the disk under braking that are transmitted to the bolt, all in repeated heat/cool cycles. There is a reason Honda recommends replacing the caliper bolts and the disk bolts every time they are removed. They are under great stress in a critical system.

A thread repair requires removing some metal and enlarging the hole in the bracket thus weakening it. It may not crack when the present doting owner owns the bike but what about the next owner that might ride the bike a lot more aggressively than the present owner?

The bracket is even easier to replace than a fork leg and I would only use a longer bolt as a temporary repair. It's only my opinion and worth what you paid for it. :)
 
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dduelin said:
There is a reason Honda recommends replacing the caliper bolts and the disk bolts every time they are removed. They are under great stress in a critical system.
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Just curious about this claim, the 1100 service manual says nothing about replacing the caliper bolts upon removal, do they recommend it for the 1300?
 
dwalby said:
Just curious about this claim, the 1100 service manual says nothing about replacing the caliper bolts upon removal, do they recommend it for the 1300?
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Yes, they are single use ALOC fasteners but I would apply removable thread locker for security and reuse them once or twice before replacement with new ones.
 
Thanks for the help. I helicoiled them. I found some specs on the Loctite fix a thread stuff and the allowable torque was only about 5 ft-lbf for that size bolt. I couldn't find any allowable torques for helicoil, so I did a test on a piece of aluminum bar stock and could tighten it to >> 23 ft-lbf. As RWThomas noted it is an approved repair for aircraft.
 
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