Rear Brake Lock-up - very scary!

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Horny675
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Rear Brake Lock-up - very scary!

Post by Horny675 »

After a 1200km ride through Australia's SW, I was returning home along a relatively busy freeway at about 100km on my beloved Xtra Raptor. All of a sudden I lost power - it felt just like an engine seizure. I pulled in the clutch, but this did not stop the back wheel from locking up solid! I pulled over to the hard shoulder training the back wheel in a 100m long skid! Very Scary!.

The bike was locked solid and would not move, even in neutral of with the clutch pulled in. So I called the RAC and got the bike carried home - only about 15km away. On the way home I googled second hand engines!

Right said Fred - Have a cup tea! After team I went to retrieve the bike from the bottom of my steep driveway, wondering how I was going to get it up to my garage at the top!

However, the bike had now cooled and it started and drove normally with no ill effects!

I was then trying to work out why pulling in the clutch had no effect and, furthermore, why the bike would not move an inch - even if the gearbox had seized it should have moved a bit due to the slack in the chain.

I then noticed the rear brake disc! There was evidence that the brake pads had SEIZED TO THE DISC!

This is strange - because I cannot remember ever using the back brake in my 12 years of Raptor ownership (or on any other bike for that matter).

Whilst it is possible that I was resting my foot on the brake peddle, I don't think this was the case. I am an experienced rider and this has never happened before.

So I have now worked out what probably happened. I recently lowered the footrests and set the brake pedal down lower. I think the issue was that the stroke on the brake master cylinder had consequently been reduced so as the piston was not retracting far enough to open the "compensation" port to the reservoir. Hence the fluid in the caliber was effectively "locked in". I may have used the back brake a bit just before the incident during a bit of lane splitting in heavy traffic. This caused the back brake to heat up and also heat the fluid in the calliper. As I continued to drive, the brake heated more and more, heating the fluid, which expanded and increased the pressure on the rear brake, thereby increasing the braking and friction. Eventually the brake pads seized to the disc and locked the back wheel.

Tell tale signs were lots of brake dust on the back wheel (never seen that before) , severe scoring on the disc and a mark showing where the brake pads had welded themselves to the disc!.

So beware it doesn't happen to you because it is very dangerous! Glad to report the beloved Raptor is OK though - and doesn't need a new engine!
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shebee
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Re: Rear Brake Lock-up - very scary!

Post by shebee »

Eeek :shock: , glad you are ok!
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nickst4
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Re: Rear Brake Lock-up - very scary!

Post by nickst4 »

Oh wow; that could have been terminal for you and the bike! Fascinating account though, and well done for tracing the cause of the problem so analytically. Hopefully the brake disc isn't damaged much and even the pads might be salvageable too.

Ride safe!

Nick, in sunny GB
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Crap Tartan
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Re: Rear Brake Lock-up - very scary!

Post by Crap Tartan »

Had something similar happen years ago on mine but wasn’t too dramatic luckily enough.
Anyway, it was my MC that was goosed so replaced it and all fine ever since.
I did strip the calliper and replace all seals as it had been heated a lot and put in new pads as Excess heat isn’t good for the pad material.
Make sure pedal is adjusted properly too
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Widetrak
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Re: Rear Brake Lock-up - very scary!

Post by Widetrak »

Never used back brake?😳Glad you’re 👍
andybaggies
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Re: Rear Brake Lock-up - very scary!

Post by andybaggies »

Yep, happened to me also and was caused by winter crud in the master cylinder.

In my case the line & caliper actually burst into flames... :shock:
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Craigfell
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Re: Rear Brake Lock-up - very scary!

Post by Craigfell »

Holy shit :shock:

I'd be putting the lottery on.
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Trevor68
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Re: Rear Brake Lock-up - very scary!

Post by Trevor68 »

Did you need the seat removal tool?! :P
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Horny675
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Re: Rear Brake Lock-up - very scary!

Post by Horny675 »

I realise now that pulling in the clutch actually caused the wheel to lock - it was only the engine keeping the wheel turning! Sort of counter intuitive in the heat of the moment.

And yes, I tend not to use the rear brake much. 90% of the stopping power is from the front anyway.
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Re: Rear Brake Lock-up - very scary!

Post by nickst4 »

Hi Horny,

In case my PM didn't reach you, can you expand on the footrest-lowering effort that indirectly led to your exciting lock-up? I've found some affordable adaptors on ebay that are sold for Hondas and await the maker's comments regarding the size. Plus or minus wouldn't be a problem for me, and I'm keen to try something like that on the 1K.

Cheers,

Nick
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