Author Topic: Laughably flexible front end (Read 2622 times)

rogerzilla · « **on:** 02 June, 2018, 04:58:15 pm »

I can't ride out of the saddle on the Holdsworth because the front brake rubs really, really badly. It even rubs with the brake's QR open. Hub skewer is tight and it's now a one-piece Campag Record l/f hub, which should be pretty stiff. Front wheel is a x2 (slightly stiffer than x3) 32 spoker on a Velocity Deep V rim. I know these are stiffest in the wrong direction but they're not exactly light or flimsy.

I'm going to have to swap out the fork for a cheap s/h steel one to see if it makes any difference. I can't try a different wheel in the Holdsworth fork as the fork ends are 5/16" but if a substitute fork doesn't solve it I can swap out the wheel on that. Both fork blades are intact and if the steerer was cracked, I'd probably be in a ditch by now. Any other ideas?

Brucey · « **Reply #1 on:** 02 June, 2018, 05:36:29 pm »

Q; if the fork is to take a 5/16" axle, how on earth did you get a QR campag hub into it?

cheers

rogerzilla · « **Reply #2 on:** 02 June, 2018, 05:39:06 pm »

Took the axle out and filed flats on it. SOP if you don't want to file a vintage fork (axles are just spare parts).

Brucey · « **Reply #3 on:** 02 June, 2018, 05:55:20 pm »

daft question; you are sure that the flats are long enough and/or that the QR isn't bearing down on the springs or something instead of the (presumably skinny) dropouts?

That will tend to make the whole assemblage somewhat floppy...

BTW many common wheels used maillard/Normandy hubs with non-QR axles, that were 5/16" sized. It shouldn't be too difficult to rustle up one of those and try it out.

cheers

rogerzilla · « **Reply #4 on:** 02 June, 2018, 06:20:28 pm »

It's not the hub, as I've already swapped a bolt-on BHC Airlite for this one, thinking the 3-piece Airlite might have had movement between the barrel and flanges.

Edit: I popped the front wheel in another bike and it wasn't noticeably flexy, which points at the fork. Going to swap that out for a cheap s/h one (found one of the right steerer length) and see if that cures it. If it does, there's either something wrong with the Holdsworth fork, like a crack, or it is just badly designed. Brakes had much less mechanical advantage and a greater clearance in t'olden days, but I'm talking about half an inch of flex here.

Brucey · « **Reply #5 on:** 03 June, 2018, 11:30:57 am »

if it is the fork, I think it is very likely to be cracked somewhere. Either that, or it is built in unfeasibly light gauge tubing.

cheers

rogerzilla · « **Reply #6 on:** 03 June, 2018, 06:15:04 pm »

What's the stuff you paint on to reveal cracks? Blades look fine, steerer is a bit manky where it meets the crown (see photo) but, if the steerer was cracked, would that make the rim flex relative to the crown?

20180603_180727 by rogerzilla, on Flickr

mzjo · « **Reply #7 on:** 03 June, 2018, 07:02:39 pm »

Go into a welding equipment shop or a general industrial suppliers and ask for crack finder. There are usually three aerosols in the complete kit but a lot of people don't bother about the first one which is a cleaning/buffing solution ( which may be a mistake). The second one is the penetration stage and the third the developer to show you where the crack is. Follow the instructions on the tin AFAICR

Brucey · « **Reply #8 on:** 03 June, 2018, 07:21:19 pm »

look up 'dye penetrant testing' if you need more info.

FWIW I'd check the fork very carefully of course. However I have never heard of a wheel move that much unless

a) the fork is on the verge of complete failure or
b) the wheel isn't fastened into the frame properly.

Changing the wheel into other forks proves little regarding the fit of the wheel; the dropouts need only be a fraction a mm thicker and (say) a QR hub will hold perfectly well, where it won't in the subject fork perhaps. A common fault is that the QR tightens onto the dropout at one end, but the load is taken by the axle (often via the spring) at the other, resulting in a wheel that feels tight, but can move around.

The flaw in the forks (if there is one) is most likely to be in the crown or the top of the fork blades, from a stress viewpoint. (The steerer could be on the verge of failure and the brakes wouldn't rub, BTW.) Another rare fault is that the dropout brazing fails and the dropout itself becomes able to slide in and out of the slot in the end of the fork blade.

cheers

Paul · « **Reply #9 on:** 04 June, 2018, 01:08:38 pm »

If

Quote from: rogerzilla on 02 June, 2018, 04:58:15 pm

... the front brake rubs really, really badly. It even rubs with the brake's QR open.

I would be looking at the fork below the brake caliper mounting bolt. That's not to say that there isn't anything going on at the crown/steerer join, but that (it seems more logical to me that) the problem would be lower down.

andrew_s · « **Reply #10 on:** 05 June, 2018, 01:53:44 pm »

Quote from: Brucey on 03 June, 2018, 07:21:19 pm

Another rare fault is that the dropout brazing fails and the dropout itself becomes able to slide in and out of the slot in the end of the fork blade.

Surprising as it may seem, it's possible to ride around for a fair while like that.
I only discovered it when I went to straighten up the handlebars with the wheel between my knees, and the other dropout came out too.
You can also ride quite a while with an almost broken fork blade. A friend brought a pair of forks in to the pub one time with a spiral crack about 85% of the way round one blade, starting from an old tyre rub point. You could waggle the end of the blade a good couple of inches with your little finger.

I'd have the wheel out, and give the fork blades a good hard push/pull, individually.

rogerzilla · « **Reply #11 on:** 19 August, 2018, 05:40:08 pm »

I swapped out the fork for a fairly nasty s/h one, sold to me as 531 but a tad heavy. It appears to have cured the flex, altjough I won't really know until I honk it up a steep hill.

If this is a fix, I'l get the fork resprayed to match the frame;the lugs aren't a terrible match. I could have a new fork built but it's expensive and just might be as bad as the original.

rogerzilla · « **Reply #12 on:** 21 August, 2018, 07:51:38 pm »

It is indeed fixed. Took it up some utter bastard hills tonight and there was no brake rub at all. I conclude that Sandy Holdsworth didn't build a great racing fork.

Brucey · « **Reply #13 on:** 21 August, 2018, 08:18:16 pm »

how heavy is the old one? BITD 531 tubing was made in a very large variety of different gauges, (plus they can be trimmed to give a very different flex too) and your frame could have been built for someone of very slight build.

'Old' pattern 531 blades had a narrower oval and were laterally less stiff too.

Note also that if it really flexes as much as you say it might be cracked or damaged, and something else (like the QR not tightening properly because the dropouts are very skinny) has not exactly been ruled out either. I've lost count of the number of times I have had to delete the springs or shorten an axle because of this.

To conclude what you have is not really justified IMHO.

cheers

rogerzilla · « **Reply #14 on:** 21 August, 2018, 08:47:09 pm »

QR was fitted without springs, made no difference. Previously used a bolt-on hub (which was a genuine 5/16" axle) and that was just as bad.

Can't see a crack in the blades, and I've had it on the bench and flexed it in all directions. It's just noodly.

LittleWheelsandBig · « **Reply #15 on:** 21 August, 2018, 08:48:45 pm »

Assuming no cracks, I'd suspect somewhat less than ideal braze penetration.

rogerzilla · « **Reply #16 on:** 21 August, 2018, 09:09:46 pm »

Could be. Has to be the blades if it is that as the steerer can't cause brake rub. Maybe the blades were filed to get them into a tight crown, which is a real no-no.

Brucey · « **Reply #17 on:** 21 August, 2018, 09:10:42 pm »

have you weighed them?

mrcharly-YHT · « **Reply #18 on:** 23 August, 2018, 08:05:19 am »

I have very flexy forks on my mercian and the brakes don't rub - the flex is just fore and aft.

could it be that your wheel isn't seating fully into the dropouts? Or that the dropouts aren't parallel, resulting in different fork lengths? That could result in the wheel moving under load.

Wobbly John · « **Reply #19 on:** 23 August, 2018, 08:40:21 am »

I would expect fork flex that causes brake rub to be problems around the drop-out end.

Having had forks fracture at the crown,and going approx 30 metres on my shoulder/side of head ( tweed jacket saved most abrasions, but couldn't prevent the fractured colarbone), I would recommend anybody experiencing fork flex or juddering front brakes, to check the joints of the fork crown if it is brazed.