Lambretta rear brakes weak

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colin
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Lambretta rear brakes weak

Postby colin » Tue Sep 11, 2012 10:50 am

Cleaned hub (with brake cleaner), buffed a little rust off hub braking surface with very fine sandpaper, brand new quality cable. When braking with the rear, didn't grab well (kind of like a P-series front brake, maybe worse).

Got new pads, re-cleaned hub, greased pivot point, etc, no change, still just kind of slides even when jamming on the rear brake.

Doesn't wobble or anything to suggest it's warped or otherwise broken...

WTF?
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Serendipity
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Re: Lambretta rear brakes weak

Postby Serendipity » Tue Sep 11, 2012 11:17 am

Mine was pretty bad too - changed the pads etc...Then Greg at MC really cranked that cable extra tight and it works fine now. That said, I don't know how a P brake feels, so maybe its not as good.
~Jennifer

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Zeets
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Re: Lambretta rear brakes weak

Postby Zeets » Tue Sep 11, 2012 11:43 am

Odd, the rear brake on my Lammy was ...sufficient... (compared to putting your feet down and dragging your heels)

I'd tighten the cable until the rear wheel binds, back off the adjustment until it's spinning but there is still some amount of light scuffing occurring, take it out, zing it up to 40 or so, jump on the rear brake as hard as you can and repeat that 5 or 6 times to bed the brakes in. Then when the brake is cold, adjust it up until the point when it's barely scuffing again and start riding it.

Sounds like you may be running out of travel on the brake cam too, possibly, although with new shoes, that's probably not likely. Did you mark the position of the brake arm on the cam before you disassembled it? If you were one or two splines off from the proper position, it could make a huge difference as well.

Or, you could try this
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70' Vespa Sprint (2009 LML power)
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Zeets
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Re: Lambretta rear brakes weak

Postby Zeets » Tue Sep 11, 2012 11:52 am

Also, there is a slight possibility you have a cracked drum, but it's unlikely.

if you had one that was cracked radially, you may not necessarily feel it, bu the drum would expand with the brake pressure. You can go to an autoparts store or here to buy a Magnaflux penetrant/developer kit to inspect for cracks.

Also, check your pedal mount, if it was damaged or loose, you pedal could be moving with the brake force and never really applying the brakes.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
2008 Suzuki DRZ-400SM (thumper)

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colin
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Re: Lambretta rear brakes weak

Postby colin » Tue Sep 11, 2012 12:06 pm

When disassembled, I checked the travel and lever is clearly doing it's job. Also definitely have cable tight enough and brake is definitely engaging (and engaging early). It's not a matter of the pedal going down and there not being resistance or contact, it's a matter of there being plenty of resistance and contact and it not seeming to do much.

As for comparison, the S2 rear brake is solid and feels "right" (same as it was on the P-series and much like the VBB), so I know what is should feel like.

I sure as hell hope it isn't a cracked hub, that would.... suck.
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normratscoots
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Re: Lambretta rear brakes weak

Postby normratscoots » Tue Sep 11, 2012 12:16 pm

When you light-sanded your hubs, did you scuff them sufficiently? Rhetorical question; I don't know what sufficiently is. Still, something to think about. I don't recall what grit I used the last time I serviced my P200's rear brakes, but I do recall sanding a second time -- more roughly than I thought I would -- and that making a difference.
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colin
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Re: Lambretta rear brakes weak

Postby colin » Tue Sep 11, 2012 1:10 pm

I can try that. The sanding I did was very light, just to take off the light rust. If I smoothed it out too much with that then this is a far more temperamental system than I would have thought!

I'll try that, and google for details... but if anyone has gone from non-grabbing to good brakes by scuffing their hub surface, I'd love to hear what exactly they used and how they did it.
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Zeets
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Re: Lambretta rear brakes weak

Postby Zeets » Tue Sep 11, 2012 1:14 pm

If it seems like everything is working, find a spot with plenty of runout and go out and bed the brakes in.

Totally different situation, but on my mountain bikes, when I replace the brake pads, I have about 20-30 hard lever grabs before the brakes actually will develop feel and stop. That's on a hydro-caliper with sintered metallic brake pads and a clean stainless rotor. I realize I'm only trying to stop ~260 lbs total, but if your pads are new, your drum is old and has some grooving it could take an afternoon to properly bed them.
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porter
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Re: Lambretta rear brakes weak

Postby porter » Tue Sep 11, 2012 3:09 pm

Colin,
I have the exact same issue with my S3 brakes. Seems like there are plenty of folks out there with the same complaint.
Because some owners say that there brakes are fine, or even great, its truly an intermittant thing. If I go about tightening mine any more, I get a drag spot when I roll it forward. Still, I have little to no grab on the pads. Its wierd.

After searching around, I found a fix. Its called Jockeys Boxenstop rear brake thingy.
The problem with the brakes is that some of the castings from the factory are slight off, which does not allow the brakes to align for full concentric contact. This thingy has ovalized holes for the pivot points, and you set it up once, and then tighten down after pulling the brakes, it self aligns.
http://www.jockeys-boxenstop.de/shop/en/lambretta/lambretta-serie-3-dl-gp/rear-brake-jockey-s-boxenstop-series-1-3-dl-gp.html

I put a post up on LCUSA, asking about the brake issue, and Mark from Jet200 chimed in and said that he had already had plans to stock this product, and he is awaiting them to arrive from europe. I'll be buying it.

If scuffing up your pads doesn't do the trick for you, I'll be testing these out when I can get my hands on them.

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colin
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Re: Lambretta rear brakes weak

Postby colin » Tue Sep 11, 2012 4:59 pm

Ha, I saw that post this morning or last night when I was looking into the issue and such. I'm going to try scuffing the rotor/surface a bit and do the "setting in" trick Adam is suggesting. If both of those work, I'll just take it easy on the downhills that are in my very near future :D
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tony
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Re: Lambretta rear brakes weak

Postby tony » Tue Sep 11, 2012 8:05 pm

Using the brakes won't help you win the Corsa.
2011 CORSA BIke! ct90.tumblr.com

dirtyhandslopez
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Re: Lambretta rear brakes weak

Postby dirtyhandslopez » Wed Sep 12, 2012 2:44 am

The problem you are describng Porter is usually only on Indian casings, not Jet casings.

Colin, you may have a quality cable, but if it is too long, it will flex, making the brake feel spongy, which is what it sounds like you are describing. No amount of brake cleaing will fix it, you have to get the length right on.
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