drilling bridge on seat stays for internal nutted brakes

[mikeg]

Hi all,

Fitting Dual Pivot internal nutted brake calipers to an early 80's Tange DB steel frame in place of the old single pivot standard nut caliper.

I need to drill out the forward part part of the bridge out to take the internal nut. I don't have a right angle drill attachment, and the ones I have looked at (Bunnings and Supercheap Auto) are a liitle big to get into the space between the seat tube and the seat stays.

Any alternatives or recommendations to enlarge the hole in the bridge, but keeping the original diameter for the caliper bolt on the caliper side of the bridge?

Mike

[ggundersen]

just drill right through from the back

[GaryF]

I have no real clues besides an air driven angle headed drill. Sometimes these are quite compact.

Of course you would need a compressor, hose and angle drill and probably shorten the drill bit on a grinder - but who has that equipment and the angle drill would probably be too big to fit in the space anyway.

sorry,

Gary.

[ggundersen]

<<but keeping the original diameter for the caliper bolt on the caliper side of the bridge? >>

Why?
If you just drill a hole the dia of the smallest part of the internal bolt. Then the problem is solved because there is a little increase in dia at the end of the nut. And you have a washer on the other side to hold the caliper steady.
There is no sideways movement possible.
Have done it myself many times.

[mikeg]

The diameter of the hole already in the bridge is of size of the calliper bolt. The internal nut is approx. 2 mm greater than the bolt diameter.

If drilled right through then there would be about 5-7 mm of bolt, closest to the calliper floating in an oversized drilled hole.

Would not this then present a problem?

Correction: the nut is a recessed nut, used wrong terminology



Mike

Edit: terminology correction

[Mulger bill]

Never thought of this job before.
Would a Dremel do the job from the back of the frame? Nifty units them.

Shaun

[ggundersen]

okay maybe I'm not so good at explaining myself
maybe a picture would be easier
drill the hole the size of the smallest diameter of the nut.




ps your lbs has recessed nuts in different lengths

[MichaelB]

Did that very thing this weekend (drilling the side from the fwd part of frame).

Dodgy angles, but a special tool that I had did the job.

The other thing that you ideally need is the up shaped washer so that the nut sits properly on the round tube (as in my frame).

It depends on the bridge style that you have.

May need a longer nut for the front of mine, so will check with the LBS.

[mikeg]

Dodgy angles, but a special tool that I had did the job.

What tool is that?

The other thing that you ideally need is the up shaped washer so that the nut sits properly on the round tube (as in my frame).

I do have the curved washer/spacer for the nut side

It depends on the bridge style that you have.

the bidge style is round with circular flat plate fixed to the bridge to take the caliper



Mike

[MichaelB]

The tool is a Sheet Metal Step Drill - bloody brilliant.

The bridge on my bike is a plain tube both sides, hence I need one more of those special washers.

Here is the rear of mine




You can see where I need the extra washer

[mikeg]

The tool is a Sheet Metal Step Drill - bloody brilliant.

The bridge on my bike is a plain tube both sides, hence I need one more of those special washers.

Here is the rear of mine




You can see where I need the extra washer

I think your brake blocks are installed upside down

As I understand, the wings on the blocks are guides to help guide the wheel between the blocks when installing the wheel.


UPDATE:

1. Bought some drill bits and a right angle drill adapter

2. The space between the rear bridge and seat tube was the same as that needed by the RA adapter.

3. The RA adapter came with a keyless chuck. I have a 9V Makita Cordless drill wth a smaller length keyed chuck. Swapped chucks - gave me nearly a cm of clearance to be able drill.

4. Selected a 9/32 bit I had a resharpened after breaking the tip off earlier while progressively drilling out the back of the front fork without being held properly in a vice or similar.

5. Took to the selected drill bit and broke it to reduce its length to about 25 mm.

6. Tackled the task to drill the brake bridge out to take the diameter of the recessed nut. Expected that the bridge was not solid but a bridge contained sleeve within it, and was of about 8 mm OD. This was based on some old TANGE frame component sheets of similar date dug up on the web.

7. Drilling all but removed all of the sleeve, but the rearward facing disc on the bridge remained it's original ID.

8. Shaped aluminium washer/spacer for nut side of bridge drilled to fit recessed nut.

9. Rear brake caliper now mounted on rear brake bridge.

Mike

[MichaelB]

I think your brake blocks are installed upside down

As I understand, the wings on the blocks are guides to help guide the wheel between the blocks when installing the wheel.
Mike

Yep, twas only there for the pics.

Thanks for tellning me what the "wings" were for, was wondering.

Got my required washer from the shop, so all is good.

Glad to hear that your's worked out in the end.