Front Drum Lockup When Wet?

[gocytocis]

I’ve never ridden my Airhead in the rain before but I recently got caught in a downpour & waited it out in a cafe while the bike spent 2 hours outside getting soaked.

When it was time to carry on, I found the front brake had become VERY grabby, like binary. It locked right up at the first stop sign & remained unusable for the rest of the ride. I got home using only the rear brake & I haven’t had the guts to go for another ride since.

A quick Google search gave me several references to abrupt braking when cold/wet. Anyone on here have experience with this phenomenon? Any fixes?

[Kurt in S.A.]

Duane mentions grabby (and squealing) brakes at the bottom of this page:

https://w6rec.com/5-front-drum-brake-ad ... nd-repair/

Kurt in S.A.

[gocytocis]

Duane mentions grabby (and squealing) brakes...

Thanks for the link. In it, Duane writes, "The /5 double leading front drum brake is a superb brake... It is, however, sensitive to humidity. The first few uses on a damp morning can easily lock up the wheel. Solution: warm it up by gingerly using it in the first block of riding...Alternate solution; move to the desert." A humorous but disappointing answer.

I've found plenty of on-line references to the general problem of wet drum brakes locking up (especially with rear drum brakes on pick-ups), but the most convincing solutions are all similar to Duane's above-noted recommendations. Unfortunately moving to the desert isn't an option for me, & gentle initial application of the brake has its own risks due to the totally binary braking progression I experienced.

If this is simply an inherent quirk of drum brakes, I guess I'll need to:
a) ensure I never ride my /5 in the rain ever again,
b) abstain from using the front brake in the wet altogether, or
c) finally get around to doing a front disk conversion.

[gocytocis]

Update: after spending the night in a warm & dry garage, I can confirm that the braking action has returned to normal.

I find this very odd, especially since I’ve had vehicles with drum brakes before & never encountered anything remotely close to this issue before.

Perhaps our pads are composed of organics & ‘swell up’ when damp?

[Kurt in S.A.]

Not sure...if they swelled a lot, they would fill up the gap to the drum which wouldn't be good. Do you know if the shoe material is OEM? Maybe something aftermarket has been used. Or maybe the shoes don't arc enough to match the drum. Is there a good chamfer on the leading/trailing edges of the material to help with mating to the drum?

Kurt in S.A.

[gocytocis]

Do you know if the shoe material is OEM?...Or maybe the shoes don't arc enough to match the drum. Is there a good chamfer on the leading/trailing edges of the material to help with mating to the drum?

I've never replaced the shoes myself but they have the BMW emblem cast into them so I assume they're OEM. There was still plenty of pad material, with good chamfers & consistent arcing matched to the drum last time I had the front wheel off several hundred kilometers ago.

The brake cable was replaced earlier this year, so I know it's fine. I also lightly greased all internal pivots, shafts & bearing points inside the brake at the same time.

I performed Duane's troubleshooting routine described in the link you provided & found nothing improper.

Now that it's dried, the brake appears to be operating normally again, so I guess I'll just continue riding as before, but I'll be extra cautious about keeping out of the rain.

[gspd]

" It locked right up at the first stop sign & remained unusable for the rest of the ride."

I grew up with drums, the most memorable ones being the huge ones on my 72 laverda sf750.
I've owned and ridden many other drum brake bikes before and after that, and although they are rarely (never?) as predictable and efficient as most disc brakes, I've never encountered any that were "unusable". Maybe you can describe exactly what you meant by "unusable".
When this happened, was you wheel rotating freely or was the wheel staying locked with the brake lever released?
For sure drum brakes can be grabby on the first few stops, especially if there is a fine coating of oxidation (rust) on the friction surface of the drum (this can appear in a just few hours of being parked in the rain or just from washing the bike with a hose and letting it dry). Also, a cold tire on cold wet pavement is very easy to lock up, especially during the first few stops regardless of the type of brakes you have. I'm assuming you have a good front tire so the tire itself is not to blame for the lockup.

Maybe you should have just tried to ease the front brake on and off at cruising speeds a few times, with just a finger or two, to warm it up and then progressively adding more force as your confidence builds?


me at 18

PS: Duane's article is spot on . +1

[gocytocis]

I grew up with drums, the most memorable ones being the huge ones on my 72 laverda sf750.

That old Laverda of yours was already 20 years old by the time I started riding, but I remember drooling over SFs & 3Cs as a new rider, sad that I was unable to afford one at the time. As my first bike I picked up a 1979 Yamaha XS650 instead. It had a rear drum which was never problematic, in wet weather or otherwise.

I've never encountered any that were "unusable". Maybe you can describe exactly what you meant by "unusable".

Up until this point in my riding career, I’d honestly never encountered “unusable” brakes either. In this case however, the brake ceased to have any progression whatsoever. It simply became an on-off, device, causing the front wheel to abruptly cease rotating, & the tire to skid, even with the slightest feathering of the lever. The brake would release alright, but any subsequent attempts to use the front brake had the same results, so I simply quit using it for the rest of the way home.

Maybe you should have just tried to ease the front brake on and off at cruising speeds a few times, with just a finger or two, to warm it up and then progressively adding more force as your confidence builds?

I habitually brake with only 2 fingers anyway, & I was being extra cautious on the wet roads too, so I’m confident that over-application of the brake was not the issue. The temperature was a cool 10C (50F) but I’ve certainly ridden in much colder temperatures without issue. I was concerned that applying the brake in this condition at speed would have disastrous results so I didn’t even try. I was frankly more interested in just getting home in one piece at this point.

I'm assuming you have a good front tire so the tire itself is not to blame for the lockup.

Front tire is so new that it still has whiskers on it!

PS: Duane's article is spot on . +1

Agreed!

[Wobbly]

The "lock up" is caused by the friction material used by BMW. All you need to do is order a third party set of replacement brake shoes, like EBC or Emgo.

[gocytocis]

The "lock up" is caused by the friction material used by BMW. All you need to do is order a third party set of replacement brake shoes, like EBC or Emgo.

THAT’S something that makes sense to me. I’ll put it on my list of winter tasks. Thanks!

Apparently (so Google tells me) Ford Ranger pick-ups with rear drums notoriously suffered the same problem & when a recall was finally issued, the fix turned out to be different brake pads.

QUESTION: Am I looking for replacement shoes with sintered or organic pads? Seems to me that organic pads would be more permeable to water & therefore more likely to lock-up when wet...