steve-d

Well I obtained this gorgious frame and lots of super go-fast goodies. Frame is fantastic and I'll post pics when it is done.

Problem. It has a braise-on front derailleur mount and it causes the derailleur to be placed MUCH too high.
This is my first frame with a braise-on derailleur mount and I now HATE braise-ons!!! Forever!!!

I have the FD set to the lowest point of the braise-on slot and the gap between the derailleur and the large chainring is huge!

I know it is best to have about the thickness of a dime or less between the FD and the large chainring. This gap is about .4 inches or 9mm. It is real sloppy in the shifting and tends to throw the chain off the crankset when going from inner to outer. I'm currently running a 53-39 with a new chain.

It is a top notch race frame and I suspect it may have been designed for a time trial effort of some sort with a HUGE big gear of about a 58 (if Campy made such an animal). I say that because the frame is so well constructed in every way, it would not be likely the framebuilder made a 'mistake' in placing the braise-on so high.

Any suggestions short of having a local framebuilder remove the seat tube, put a new one in the frame, take it to a painter and then build it up all over again?



Steve

jds108

buy a sram red front - it has two mounting holes. I had to do that when I went from std to compact crank.

timkstl

yes, but will the sram front work with whatever shifting system he has?

bite the bullet, get it put on correctly. you'll be thankful later.

DannoXYZ 

If the braze-on is really a brazed-on bracket, then it's a simple matter to unbraze it, lower 10mm and re-braze it back on. Would take me about 15-minutes maximum. You'd need to repaint the seat-tube again.

What I've seen some people do without resorting to such drastic, but proper measures, is to carefully cut and grind off the braze-on bracket. Clean up the area with touch-up paint and use a clamp-on bracket or a clamp-on derailleur.

jtarver

Solid^
Another option is just to go with a human sized chainring and a clamp on mounted below the existing braze on.

operator

Or how about just buying a band on braze on adapter and running that = $5 fix.

kycycler

I see 2 possibilities. First what kind of frame material? Was the frame manufactured incorrectly?

HillRider

Those things are to let you use a "braze-on" style fd on a frame without the braze-on fitting. They basically turn it into a clamp-on fd.

To use it on a frame with the braze-on fitting already there you need to remove the fitting or have enough seat tube exposed under it to fit the clamp.

Also, some frames with non-round seat tubes can't take a clamp of any kind.

steve-d

Hi all and thank you very much for the replies.

First, it is a Reynolds 753 R tube set. The seat tube is a 'standard' size of 28.6mm and I'm sure it is paper thin and not forgiving to much abuse.

Further, as I understand the Reynolds tubing, it is very sensitive to heat and heating the seat tube excessively to install and then to remove the braise-on will weaken it measurably.

The shift system is a Campy friction seven speed, 12-26 rear and a 53-39 front, Super Record derailleurs and a C Record crankset. It originally came with C Record derailleurs, but they couldn't handle the 26 rear cog my legs demand. The Super Record rear is now just fine.

I looked at the option of installing a clamp-on adapter below the braise-on. But there isn't enough room to allow the derailleur assembly to fit below the exiting braise-on as it won't clear the chainring.

In a similar fashion, I tried to fit a tradional clamp-on front derailleur, but it too wouldn't clear the front chainring.

I'm getting closer to accepting the need to either have a frame builder install a new seat tube w/o a braise-on adapter or get a new style Compact crankset. Possibly, that would then allow me to use a tighter rear freewheel and then use the C Record derailleurs.

If any other ideas come to mind, please don't hesitate to let me know.

best
Steve

steve-d

As far as the frame builder making a mistake, I just think it was originally intended the way it was made. The quality of the overall frame set indicates it was designed that way. Possibly for time trial events with a huge chainring? Possibly a 58? I'm not really up on that sort of thing.

HillRider

753 is a heat treated verision of Reynolds 531 and is more heat-sensitive but is not that difficult to work with if the builder knows what he is doing. Generally it is silver brazed (BTW it's brazed, not braised. Braising is what you do to food) as that can be done at lower temperature.

A competent frame builder could remove the fd mounting tab with no danger to the seat tube and you could then use a clamp-on adapter or a clamp-on fd and position it anywhaer you need to.

The tubing is certainly plenty strong enough to handle the clamping force of a clamp-on adapter or fd. Weaker and thinner tubing than 735 uses them all the time.

jtarver

I guess you could fab or have someone fab an "extension". Basically another FD Braze on bolted to the existing one. I would think you'd need two bolts to prevent it trying to twist and I'm not sure if having it mounted a bit forward would affect the function. If you have a local framebuilder maybe he would give you one to try. Just grind off the mounting tab and mount it like you would FD. Kind of far fetched but might be worth a try.

steve-d

Thanks for the insight on the 753. I'll give a frame builder a call to see if it can be removed. If so, it'd be a great and perfect fix.

Thanks for the 'Z' modification too! I'll have to resist using cooking terms in the bicycle world!

nitropowered

Its a 15 min job to remove the tab, clean up the area and re-braze the tab.

You'll still have to repaint it though.

steve-d

I'll have it removed and then go primal: Clamp-on.

Here is a pic or two. If you can enlarge it, you'll be able to see the gap.


Best
Steve

HillRider

Yeah, except I have the builder remove the tab, clean up the area and stop right there. Another braze-on tab is likely to be in the wrong place sometime in the future. Repaint the area and buy an adapter clamp that will let you put the fd anywhere it's needed.

Except for non-round tubes where you have no choice, I've never seen the advantage of a braze-on fd mounting tab.

norwood

To me the key question here is, does it actually shift or not? True the gap may be a bit larger than normal but it doesn't appear to be all that bad. Not as bad as you described. I've seen worse that still worked. Did someone give you a load of #@*& about too large of a gap? Seems you may be going to a lot of trouble for a minor issue. Maybe try a different model/brand of front derailleur? Let shifting performance be the guide, not how it looks.

steve-d

I measured the gap as described.

It does shift the chain off the large chainring.
Tried the C Record and Super Record f. derailleur.


Don't know what else to relate as to the problem I have.

Steve

jtarver

Any chance you could grind the slot in the hanger down a mm or two. I know they can be quite thin at the bottom, but it looks as if that would put you into a functional range.

steve-d

Hi jtaver,

I looked at lengthening the slot downward. Unfortunately, it wouldn't gain much. I'm going to discuss it with John Holland, frame builder as to a solution. Whether it is total removal or grinding it off, I don't know. I'll keep everyone up to date as to what he suggests.

Thanks very much for all comments. They were very helpful and I thank all for the time in writing.

Steve

DannoXYZ 

Reynolds 753 isn't some super-magical material, I've done plenty of bikes with it and it just requires more careful attention to heat. I actually find it quicker to work with since it needs less heat to get it up to operating temp.

And the only loads you have to worry on the seat-tube is lateral wobble from pedaling forces. Much, much lower than the forces faced by the seat/chain-stays or the down-tube. Unbrazing & rebrazing that tab won't hurt a thing, especially if silver is used.

All of the broken seat-tubes I've seen were fatigue-failures at the stress-riser caused by the transition from thin-tubing to thick lugs. Tapering the lugs to reduce the step would help relieve this stress tremendously.

JohnDThompson 

I would never put a FD braze-on on a 753 frame. We had a customer insist on one, so we put it on and sure enough, a couple months later the chain jammed and the seat tube was destroyed.

The problem with 753 is that the heat treatment makes the tubing quite brittle. It does not deform easily and tends to fail by cracking. The FD mount is on the thinnest section of tubing and thus is particularly vulnerable to this.

Reynolds initially advised against any braze-ons on 753 frames and only reluctantly accepted top tube cable guides and down tube shift lever bosses. I've seen 753 frames fail at the lever bosses after frontal impacts as well.

For the OP, I would strongly advise against un-brazing the mount. Carefully grind it off and use a clamp-on FD.

N.B. I have experience brazing many 753 frames from my work at Trek back in the 80s.

HillRider

Did the metallurgy of 753 contribute to this failure or was the chain jamming severe enough to have badly damaged any seat tube no matter what material it was made of. I'm not sure if this was a metallurgy failure or a geometry (the tab's location) failure.

deweyhtucker

Leave the Frame alone!!!!!!!!!!! Redo the bracket on the FD.

HillRider

And how do you propose that be done?